{{Short description|Non-native organism causing damage to an established environment}} {{Good article}} {{Use mdy dates|date=February 2020}} [[File:Beaver dam in Tierra del Fuego.jpg|thumb|North American beaver (''Castor canadensis'') dam in Tierra del Fuego]] [[File:Kudzu on trees in Atlanta, Georgia.jpg|thumb|Kudzu growing over and smothering trees in Atlanta, Georgia]] [[File:Kanadische Goldrute, Solidago canadensis - Invasives Unkraut.jpg|right|thumb|Canada goldenrod (''Solidago canadensis'') as a roadside weed in Poland]] [[File:Vinca spreading along a border.jpg|thumb|''Vinca'' in a garden<ref name=":6">{{Cite web |title=Challenge |url=https://myfwc.com/fishing/saltwater/recreational/lionfish/challenge/ |access-date=2026-04-30 |website=Florida Fish And Wildlife Conservation Commission |language=en}}</ref>]]
An '''invasive species''' is an introduced species that harms its new environment.{{r|davis}} Invasive species adversely affect habitats and bioregions, causing ecological, environmental, and/or economic damage. Since the 20th century, invasive species have become serious economic, social, and environmental threats worldwide.
Invasion of long-established ecosystems by organisms is a natural phenomenon, but human-facilitated introductions have greatly increased the rate, scale, and geographic range of invasion. For millennia, humans have served as both accidental and deliberate dispersal agents, beginning with their earliest migrations, accelerating in the Age of Discovery, and accelerating again with the spread of international trade.
Notable plant species that are invasive in many parts of the world include the kudzu vine (''Pueraria''), water hyacinth ''(Pontederia crassipes)'', common ragweed (''Ambrosia artemisiifolia''), and yellow starthistle (''Centaurea solstitialis''). Notable animal species that are invasive include European rabbits (''Oryctolagus cuniculus''), domestic cats (''Felis catus''), and red swamp crayfish (''Procambarus clarkii'').
== Terminology == {{See also |Glossary of invasion biology terms}}
Invasive species are the subset of established non-native species that pose a threat to native species and biodiversity.<ref name="SandlundSchei2001">{{cite book |author1=Odd Terje Sandlund |author2=Peter Johan Schei |author3=Åslaug Viken |title=Invasive Species and Biodiversity Management |url=https://books.google.com/books?id=QHgMqnqaW_YC&pg=PA2 |date=30 June 2001 |publisher=Springer Science & Business Media |isbn=978-0-7923-6876-2 |pages=2– |access-date=November 1, 2020 |archive-date=December 18, 2021 |archive-url=https://web.archive.org/web/20211218042441/https://books.google.com/books?id=QHgMqnqaW_YC&pg=PA2 |url-status=live}}</ref> The term "invasive" is poorly defined and often very subjective.<ref name=neutral/> Invasive species may be plants, animals, fungi, and microbes; some include native species that have invaded human habitats such as farms and landscapes.<ref name="Inderjit2006">{{cite book |author=S. Inderjit |title=Invasive Plants: Ecological and Agricultural Aspects |url=https://books.google.com/books?id=c-aMIwmis-wC&pg=PA252 |date=16 January 2006 |publisher=Springer Science & Business Media |isbn=978-3-7643-7380-1 |pages=252– |access-date=November 1, 2020 |archive-date=December 18, 2021 |archive-url=https://web.archive.org/web/20211218042441/https://books.google.com/books?id=c-aMIwmis-wC&pg=PA252 |url-status=live}}</ref> Some broaden the term to include indigenous or "native" species that have colonized natural areas.<ref name=neutral/> Some sources name ''Homo sapiens'' as an invasive species,<ref name=":7">{{Cite news |last=Luscombe |first=Richard |date=2026-02-05 |title=Florida euthanizes 5,000 iguanas after cold snap stuns the invasive reptiles |url=https://www.theguardian.com/us-news/2026/feb/05/florida-frozen-iguanas-euthanized |access-date=2026-04-30 |work=The Guardian |language=en-GB |issn=0261-3077}}</ref><ref name=":9">{{Cite web |title=Green Iguana |url=https://myfwc.com/wildlifehabitats/profiles/reptiles/lizards/green-iguana/ |access-date=2026-04-30 |website=Florida Fish And Wildlife Conservation Commission |language=en}}</ref> but broad appreciation of human learning capacity and their behavioral potential and plasticity may argue against any such fixed categorization.<ref name="root">{{cite journal |last1=Root-Bernstein |first1=Meredith |last2=Ladle |first2=Richard |year=2019 |title=Ecology of a widespread large omnivore, Homo sapiens, and its impacts on ecosystem processes |journal=Ecology and Evolution |volume=9 |issue=19 |pages=10874–94 |bibcode=2019EcoEv...910874R |doi=10.1002/ece3.5049 |pmc=6802023 |pmid=31641442 |s2cid=203370925 |doi-access=free}}</ref>
The definition of "native" can also be controversial. For example, the ancestors of modern horses (''Equus ferus)'' evolved in North America and radiated to Eurasia before becoming extinct in North America. Their reintroduction to North America, by Spanish conquistadors, led to a 1943 debate over whether the feral horses were native or exotic to the continent of their evolutionary ancestors.<ref name=":10">{{Cite web |last=Kinsey |first=John |date=2020 |title=Nuisance Wildlife in Texas: Wild Pigs |url=http://tpwd.texas.gov/huntwild/wild/nuisance/feral_hogs/ |access-date=2026-04-30 |website=tpwd.texas.gov |language=en-US}}</ref>
While invasive species can be studied within many subfields of biology, most research on invasive organisms has been in ecology and biogeography. Much of the work has been influenced by Charles Elton's 1958 book ''The Ecology of Invasion by Animals and Plants'' which creates a generalized picture of biological invasions.<ref name=IE>{{cite book |last=Lockwood |first=Julie L. |title=Invasion Ecology |year=2007 |publisher=Blackwell Publishing |page=7 |url=http://www.planta.cn/forum/files_planta/invasion_ecology1_208.pdf |author2=Hoopes, Martha F. |author3=Marchetti, Michael P. |access-date=January 21, 2014 |archive-date=September 24, 2015 |archive-url=https://web.archive.org/web/20150924074044/http://www.planta.cn/forum/files_planta/invasion_ecology1_208.pdf}}</ref><ref name=Lowry>{{cite journal |pmid=23404636 |year=2012 |last1=Lowry |first1=E |last2=Rollinson |first2=EJ |last3=Laybourn |first3=AJ |last4=Scott |first4=TE |last5=Aiello-Lammens |first5=ME |last6=Gray |first6=SM |last7=Mickley |first7=J |last8=Gurevitch |first8=J |author-link8=Jessica Gurevitch |title=Biological invasions: A field synopsis, systematic review, and database of the literature |volume=3 |issue=1 |pages=182–96 |doi=10.1002/ece3.431 |pmc=3568853 |journal=Ecology and Evolution}}</ref> Studies remained sparse until the 1990s.<ref name=Lowry/> This research, largely field observational studies, has disproportionately been concerned with terrestrial plants.<ref name=Lowry/> The rapid growth of the field has driven a need to standardize the language used to describe invasive species and events. Despite this, little standard terminology exists. The field lacks any official designation but is commonly referred to as "invasion ecology" or more generally "invasion biology".<ref name=IE/><ref name=Lowry/> This lack of standard terminology has arisen due to the interdisciplinary nature of the field, which borrows terms from disciplines such as agriculture, zoology, and pathology, as well as due to studies being performed in isolation.<ref name=":11">{{Cite web |title=Nuisance Wildlife in Texas: Wild Pigs |url=http://tpwd.texas.gov/huntwild/wild/nuisance/feral_hogs/ |access-date=2026-04-30 |website=tpwd.texas.gov |language=en-US}}</ref><ref name=IE/>
{|class="wikitable" style="float:right;" |+Colautti and MacIsaac nomenclature<ref name=neutral/> |- ! Stage ! Characteristic |- |0 |Propagules residing in a donor region |- |I |Traveling |- |II |Introduced |- |III |Localized and numerically rare |- |IVa |Widespread but rare |- |IVb |Localized but dominant |- |V |Widespread and dominant |}
In an attempt to avoid the ambiguous, subjective, and pejorative vocabulary that so often accompanies discussion of invasive species, even in scientific papers, Colautti and MacIsaac proposed a new nomenclature system. Based on biogeography rather than on taxa, <ref name=neutral>{{cite journal |last1=Colautti |first1=Robert I. |last2=MacIsaac |first2=Hugh J. |title=A neutral terminology to define 'invasive' species: Defining invasive species |journal=Diversity and Distributions |date=24 February 2004 |volume=10 |issue=2 |pages=135–141 |doi=10.1111/j.1366-9516.2004.00061.x |s2cid=18971654 |doi-access=free }}</ref> the proposed system emphasizes ecology over taxonomy, human health, and economic factors. The model evaluated individual populations rather than entire species. It classified each population based on its success in that environment. This model applied equally to indigenous and to introduced species, and did not automatically categorize successful introductions as harmful.<ref name=neutral/>
The USDA's National Invasive Species Information Center defines invasive species very narrowly. According to Executive Order 13112, {{" '}}Invasive species' means an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health."<ref name=":12">{{Cite web |title=Fishing Seasons and Rules {{!}} Idaho Fish and Game |url=https://idfg.idaho.gov/rules/fish |access-date=2026-04-30 |website=idfg.idaho.gov}}</ref>
== Causes == Typically, an introduced species must persist at low population densities before it can become invasive in a new environment.<ref name="tilm">{{cite journal |last=Tilman |first=D. |year=2004 |title=Niche tradeoffs, neutrality, and community structure: A stochastic theory of resource competition, invasion, and community assembly |journal=Proceedings of the National Academy of Sciences |volume=101 |pages=10854–10861 |doi=10.1073/pnas.0403458101 |pmid=15243158 |issue=30 |pmc=503710 |bibcode=2004PNAS..10110854T |doi-access=free }}</ref> At low densities, introduced species often face difficulties in reproducing and sustaining a viable population—sometimes requiring multiple introductions before establishment occurs. Patterns of repeated human movement, such as ship traffic between ports or vehicles travelling along major highways, can create recurring opportunities for arrival and establishment, a phenomenon known as high propagule pressure.<ref name="verl">{{cite journal |last=Verling |first=E. |year=2005 |title=Supply-side invasion ecology: characterizing propagule pressure in coastal ecosystems |journal=Proceedings of the Royal Society B |volume=272 |pages=1249–1256 |doi=10.1098/rspb.2005.3090 |pmid=16024389 |issue=1569 |pmc=1564104}}</ref>
=== Ecosystem-based mechanisms === In ecosystems, the availability of resources determines the impact of additional species on the ecosystem. Stable ecosystems have a resource equilibrium, which can be changed fundamentally by the arrival of invasive species.<ref name="Byers 2002">{{cite journal |last1=Byers |first1=James E. |title=Impact of non-indigenous species on natives enhanced by anthropogenic alteration of selection regimes |journal=Oikos |date=June 2002 |volume=97 |issue=3 |pages=449–458 |doi=10.1034/j.1600-0706.2002.970316.x |bibcode=2002Oikos..97..449B }}</ref> When changes such as a forest fire occur, normal ecological succession favors native grasses and forbs. An introduced species that can spread faster than natives can outcompete native species for food, squeezing the natives out. Nitrogen and phosphorus are often the limiting factors in these situations.<ref name="Davis 2000 528–534">{{cite journal |last1=Davis |first1=M.A. |last2=Grime |first2=J.P. |last3=Thompson |first3=K. |s2cid=14573817 |year=2000 |title=Fluctuating resources in plant communities: A general theory of invisibility |journal=Journal of Ecology |volume=88 |issue=3 |pages=528–534 |doi=10.1046/j.1365-2745.2000.00473.x|doi-access=free |bibcode=2000JEcol..88..528D }}</ref> Every species occupies an ecological niche in its native ecosystem; some species fill large and varied roles, while others are highly specialized. Invading species may occupy unused niches, or create new ones.<ref name=":13">{{Cite web |last=Resources |first=Indiana Department of Natural |date=2026-03-09 |title=Indiana Department of Natural Resources |url=https://www.in.gov/dnr/ |access-date=2026-04-30 |website=Indiana Department of Natural Resources |language=en}}</ref> For example, edge effects describe what happens when part of an ecosystem is disturbed, as in when land is cleared for agriculture. The boundary between the remaining undisturbed habitat and the newly cleared land itself forms a distinct new habitat, creating new winners and losers, and potentially hosting species that would not otherwise thrive outside the boundary habitat.<ref>{{Cite journal |last1=Alverson |first1=William S. |last2=Waller |first2=Donald M. |last3=Solheim |first3=Stephen L. |date=1988 |title=Forests Too Deer: Edge Effects in Northern Wisconsin |journal=Conservation Biology |volume=2 |issue=4 |pages=348–358 |doi=10.1111/j.1523-1739.1988.tb00199.x |jstor=2386294|bibcode=1988ConBi...2..348A }}</ref>
In 1958, Charles S. Elton claimed that ecosystems with higher species diversity were less subject to invasive species because fewer niches remained unoccupied.<ref name="elton">{{cite book |last=Elton |first=C.S. |others=Foreword by Daniel Simberloff |title=The Ecology of Invasions by Animals and Plants |orig-date=1958 |year=2000 |publisher=University of Chicago Press |location=Chicago |isbn=978-0-226-20638-7 |page=196}}</ref> Other ecologists later pointed to highly diverse, but heavily invaded ecosystems, arguing that ecosystems with high species diversity were more susceptible to invasion.<ref name=Schell>{{cite journal |last1=Stohlgren |first1=Thomas J. |last2=Binkley |first2=Dan |last3=Chong |first3=Geneva W. |last4=Kalkhan |first4=Mohammed A. |last5=Schell |first5=Lisa D. |last6=Bull |first6=Kelly A. |last7=Otsuki |first7=Yuka |last8=Newman |first8=Gregory |last9=Bashkin |first9=Michael |last10=Son |first10=Yowhan |display-authors=6 |title=Exotic Plant Species Invade Hot Spots of Native Plant Diversity |journal=Ecological Monographs |date=February 1999 |volume=69 |issue=1 |pages=25–46 |doi=10.1890/0012-9615(1999)069[0025:EPSIHS]2.0.CO;2 }}</ref> This debate hinged on the spatial scale of invasion studies. Small-scale studies tended to show a negative relationship between diversity and invasion, while large-scale studies tended to show the reverse, perhaps a side-effect of invasives' ability to capitalize on increased resource availability and weaker species interactions that are more common when larger samples are considered.<ref>{{cite journal |last1=Byers |first1=James E. |last2=Noonburg |first2=Erik G. |title=Scale Dependent Effects of Biotic Resistance to Biological Invasion |journal=Ecology |date=June 2003 |volume=84 |issue=6 |pages=1428–1433 |doi=10.1890/02-3131 |bibcode=2003Ecol...84.1428B }}</ref><ref>{{cite journal |last1=Levine |first1=Jonathan M. |title=Species Diversity and Biological Invasions: Relating Local Process to Community Pattern |journal=Science |date=5 May 2000 |volume=288 |issue=5467 |pages=852–854 |doi=10.1126/science.288.5467.852 |pmid=10797006 |bibcode=2000Sci...288..852L }}</ref> However, this pattern does not seem to hold true for invasive vertebrates.{{r|ivey2019}}
[[File:Brown tree snake (Boiga irregularis) (8387580552).jpg|thumb|right|The brown tree snake (''Boiga irregularis'') has had an impact on the native bird population of the island ecosystem of Guam.]]
Island ecosystems may be more prone to invasion because their species face few strong competitors and predators, and because their distance from colonizing species populations makes them more likely to have "open" niches.<ref name="stach">{{cite book |last=Stachowicz |first=J.J. |editor=D.F. Sax |editor2=J.J. Stachowicz |editor3=S.D. Gaines |title=Species Invasions: Insights into Ecology, Evolution, and Biogeography |publisher=Sinauer Associates |location=Sunderland, Massachusetts |isbn=978-0-87893-811-7 |chapter=Species invasions and the relationships between species diversity, community saturation, and ecosystem functioning |year=2005 |url-access=registration |url=https://archive.org/details/speciesinvasions0000unse }}</ref> For example, native bird populations on Guam have been decimated by the invasive brown tree snake (''Boiga irregularis'').<ref>{{Cite web |title=Brown Tree Snake |url=https://www.invasivespeciesinfo.gov/profile/brown-tree-snake |url-status=live |archive-url=https://web.archive.org/web/20190824120114/https://www.invasivespeciesinfo.gov/profile/brown-tree-snake |archive-date=24 August 2019 |website=USDA National Invasive Species Information Center}}</ref> However, the geographical distance and open water characteristic of island ecosystems can also delay colonisation by invasive species. For example, island nations such as Australia and the Galapagos have a high proportion of their island ecology consisting of endemic species due to immigration of other species being limited by oceans and their geographical isolation.<ref>{{Cite web |last=Unit |first=Biosafety |date=2010-05-19 |title=Invasive Alien Species |url=https://www.cbd.int/island/invasive.shtml#:~:text=Islands,%20such%20as%20Australia,%20New,and%20public%20health%20of%20inhabitants. |access-date=2026-03-02 |website=www.cbd.int |language=en}}</ref>
In New Zealand the first invasive species were the dogs and rats brought by Polynesian settlers around 1300. These and other introductions devastated endemic New Zealand species.<ref>{{cite book |last=Howe |first=K. R. |title=The Quest for Origins |year=2003 |page=179 |publisher=Penguin Books |isbn=0-14-301857-4}}</ref><ref>{{Cite news |date=4 June 2008 |title=Rat remains help date New Zealand's colonisation |work=New Scientist |url=https://www.newscientist.com/article/mg19826595-200-rat-remains-help-date-new-zealands-colonisation/?ignored=irrelevant |url-status=live |url-access=subscription |access-date=23 June 2008 |archive-url=https://web.archive.org/web/20220611120716/https://www.newscientist.com/article/mg19826595-200-rat-remains-help-date-new-zealands-colonisation/?ignored=irrelevant |archive-date=11 June 2022}}</ref> The colonization of Madagascar brought similar harm to its ecosystems.<ref>{{cite journal |last1=Goodman |first1=Steven M. |date=1997 |title=The birds of southeastern Madagascar |journal=Fieldiana |issue=87 |doi=10.5962/bhl.title.3415 |doi-access=free}}</ref> Logging has caused harm directly by destroying habitat, and has allowed non-native species such as prickly pear (''Opuntia'') and silver wattle (''Acacia dealbata'') to invade.<ref>{{cite journal |last1=Brown |first1=Kerry A. |last2=Gurevitch |first2=Jessica |title=Long-term impacts of logging on forest diversity in Madagascar |journal=Proceedings of the National Academy of Sciences |date=20 April 2004 |volume=101 |issue=16 |pages=6045–6049 |doi=10.1073/pnas.0401456101 |pmid=15067121 |pmc=395920 |bibcode=2004PNAS..101.6045B |doi-access=free }}</ref><ref>{{cite journal |last1=Kull |first1=Ca |last2=Tassin |first2=J |last3=Carriere |first3=Sm |title=Approaching invasive species in Madagascar |journal=Madagascar Conservation & Development |date=26 February 2015 |volume=9 |issue=2 |page=60 |doi=10.4314/mcd.v9i2.2 |doi-access=free }}</ref> The water hyacinth (''Pontederia crassipes'') forms dense mats on water surfaces, limiting light penetration and hence harming aquatic organisms, and creating substantial management costs.<ref>{{cite journal |last1=Villamagna |first1=A. M. |last2=Murphy |first2=B. R. |title=Ecological and socio-economic impacts of invasive water hyacinth (''Eichhornia crassipes''): a review |journal=Freshwater Biology |date=February 2010 |volume=55 |issue=2 |pages=282–298 |doi=10.1111/j.1365-2427.2009.02294.x |bibcode=2010FrBio..55..282V }}</ref><ref name="Rakotoarisoa 365–379">{{cite journal |last1=Rakotoarisoa |first1=T. F. |last2=Richter |first2=T. |last3=Rakotondramanana |first3=H. |last4=Mantilla-Contreras |first4=J. |title=Turning a Problem Into Profit: Using Water Hyacinth (''Eichhornia crassipes'') for Making Handicrafts at Lake Alaotra, Madagascar |journal=Economic Botany |date=December 2016 |volume=70 |issue=4 |pages=365–379 |doi=10.1007/s12231-016-9362-y |bibcode=2016EcBot..70..365R |s2cid=255557151 |id = {{s2cid|18820290}} }}</ref> The shrub lantana (''Lantana camara'') is now considered invasive in over 60 countries, and has invaded large geographies in several countries prompting aggressive federal efforts to control it.<ref>{{Cite journal |last1=Bhagwat |first1=Shonil A. |last2=Breman |first2=Elinor |last3=Thekaekara |first3=Tarsh |last4=Thornton |first4=Thomas F. |last5=Willis |first5=Katherine J. |date=2012 |title=A Battle Lost? Report on Two Centuries of Invasion and Management of Lantana camara L. in Australia, India and South Africa |journal=PLOS ONE |language=en |volume=7 |issue=3 |article-number=e32407 |doi=10.1371/journal.pone.0032407 |doi-access=free |pmc=3293794 |pmid=22403653|bibcode=2012PLoSO...732407B }}</ref><ref>{{Cite journal |last1=Mungi |first1=Ninad Avinash |last2=Qureshi |first2=Qamar |last3=Jhala |first3=Yadvendradev V. |date=2020 |title=Expanding niche and degrading forests: Key to the successful global invasion of Lantana camara (sensu lato) |journal=Global Ecology and Conservation |volume=23 |article-number=e01080 |doi=10.1016/j.gecco.2020.e01080 |doi-access=free |bibcode=2020GEcoC..2301080M }}</ref>
Along with island ecosystems, intensively managed fenced areas are more prone to invasion. One reason is that species can enter through ways that fences cannot block. In the case of many plant species, dispersal can occur through wind, water, and birds carrying seeds either internally or externally. Small animals or insects are sometimes also able to make it through fenced areas.<ref>{{cite journal | last1=Egawa | first1=Chika | title=Wind dispersal of alien plant species into remnant natural vegetation from adjacent agricultural fields | journal=Global Ecology and Conservation | date=2017 | volume=11 | pages=33–41 | doi=10.1016/j.gecco.2017.04.008 | bibcode=2017GEcoC..11...33E | doi-access=free }}</ref><ref>{{cite journal | last1=Treep | first1=Jelle | last2=De Jager | first2=Monique | last3=Bartumeus | first3=Frederic | last4=Soons | first4=Merel B. | title=Seed dispersal as a search strategy: Dynamic and fragmented landscapes select for multi-scale movement strategies in plants | journal=Movement Ecology | date=2021 | volume=9 | issue=1 | article-number=4 | doi=10.1186/s40462-020-00239-1 | pmid=33514441 | pmc=7845050 | bibcode=2021MvEco...9....4T | doi-access=free }}</ref><ref>{{cite journal | last1=Connolly | first1=Trevor A. | last2=Day | first2=Tim D. | last3=King | first3=Carolyn M. | title=Estimating the potential for reinvasion by mammalian pests through pest-exclusion fencing | journal=Wildlife Research | date=2009 | volume=36 | issue=5 | pages=410–421 | doi=10.1071/WR09021 | bibcode=2009WildR..36..410C }}</ref> Another reason is that intensive management methods create opportunities for these invasive species to thrive. When fenced areas are established, they are intensively managed through clearing vegetation, mowing, and disturbing the soil. This reduces competition from the native plant species in the area and exposes the soil so that invasive species can easily populate the area.<ref>{{cite journal | last1=Halassy | first1=Melinda | last2=Krpán | first2=Emese | last3=Csákvári | first3=Edina | last4=Török | first4=Katalin | title=Mowing increases the vulnerability of sand grassland restoration to secondary invasion despite the sensitivity of invasive species to drought | journal=Global Ecology and Conservation | date=2025 | volume=60 | article-number=e03588 | doi=10.1016/j.gecco.2025.e03588 | bibcode=2025GEcoC..6003588H | doi-access=free }}</ref> The purpose of these fenced areas is often to keep unwanted herbivores out of the areas. Because there are no threats to the invasive plants that can take over intensively managed fenced areas, they can flourish without predatory threats.<ref>{{cite journal | last1=Shen | first1=Xiaoli | last2=Bourg | first2=Norman A. | last3=McShea | first3=William J. | last4=Turner | first4=Benjamin L. | title=Long-Term Effects of White-Tailed Deer Exclusion on the Invasion of Exotic Plants: A Case Study in a Mid-Atlantic Temperate Forest | journal=PLOS ONE | date=2016 | volume=11 | issue=3 | article-number=e0151825 | doi=10.1371/journal.pone.0151825 | pmid=27019356 | pmc=4809546 | bibcode=2016PLoSO..1151825S | doi-access=free }}</ref> Finally, in general, invasive species have traits that favor their survival. Most invasive species are extremely resilient and have traits that favor their establishment in areas where they are not native. These traits, along with the intensive management of the fenced areas, create an ideal environment in which these invasive species can thrive.<ref>{{cite journal | last1=Pepe | first1=Maria | last2=Gratani | first2=Loretta | last3=Fabrini | first3=Giuseppe | last4=Varone | first4=Laura | title=Seed germination traits of ''Ailanthus altissima'' , ''Phytolacca americana'' and ''Robinia pseudoacacia'' in response to different thermal and light requirements | journal=Plant Species Biology | date=2020 | volume=35 | issue=4 | pages=300–314 | doi=10.1111/1442-1984.12286 | bibcode=2020PSBio..35..300P }}</ref>
Primary geomorphological effects of invasive plants are bioconstruction and bioprotection. For example, kudzu (''Pueraria montana''), a vine native to Asia, was widely introduced in the southeastern United States in the early 20th century to control soil erosion. The primary geomorphological effects of invasive animals are bioturbation, bioerosion, and bioconstruction. For example, invasions of the Chinese mitten crab (''Eriocheir sinensis'') have resulted in higher bioturbation and bioerosion rates.<ref>{{cite journal |last1=Fei |first1=Songlin |last2=Phillips |first2=Jonathan |last3=Shouse |first3=Michael |title=Biogeomorphic Impacts of Invasive Species |journal=Annual Review of Ecology, Evolution, and Systematics |date=23 November 2014 |volume=45 |issue=1 |pages=69–87 |doi=10.1146/annurev-ecolsys-120213-091928 |doi-access=free }}</ref>
A native species can also become harmful and effectively invasive to its native environment after human alterations to its food web. This has been the case with the purple sea urchin (''Strongylocentrotus purpuratus''), which has decimated kelp forests along the northern California coast due to overharvesting of its natural predator, the California sea otter (''Enhydra lutris'').<ref>{{Cite web |title=Plague of purple sea urchins ravages California's offshore ecosystem, heads to Oregon |website=Los Angeles Times|date=October 24, 2019|url=https://www.latimes.com/california/story/2019-10-24/purple-sea-urchins-california-oregon-coasts|access-date=July 14, 2021 |archive-date=July 14, 2021 |archive-url=https://web.archive.org/web/20210714030639/https://www.latimes.com/california/story/2019-10-24/purple-sea-urchins-california-oregon-coasts |url-status=live}}</ref>
===Species-based mechanisms=== [[File:Riesenknoeterich.jpg|right|thumb|Japanese knotweed (''Reynoutria japonica'') is considered one of the world's worst invasive species.]] [[File:Ocicat-woodpecker.jpg|upright|thumb|Cats (''Felis catus'') (here, killing a woodpecker) are considered invasive species in Australia and negatively impact wildlife worldwide.]]
Invasive species appear to have specific traits or specific combinations of traits that allow them to outcompete native species. In some cases, these characteristics include rates of growth and reproduction. In other cases, invasive species interact with native species other more directly. One study found that 86% of invasive species could be identified from such traits alone.<ref name="kolar">{{cite journal |last=Kolar |first=C.S. |year=2001 |title=Progress in invasion biology: predicting invaders|journal=Trends in Ecology & Evolution |volume=16 |issue=4 |pages=199–204 |doi=10.1016/S0169-5347(01)02101-2 |pmid=11245943|s2cid=5796978 |url=https://figshare.com/articles/journal_contribution/24837945 }}</ref> Another study found that invasive species often had only a few of the traits, and that noninvasive species had these also.<ref name="kolar"/><ref name="theb">{{cite journal |last=Thebaud |first=C. |year=1996 |title=Assessing why two introduced Conyza differ in their ability to invade Mediterranean old fields |journal=Ecology |volume=77 |issue=3 |pages=791–804 |doi=10.2307/2265502 |jstor=2265502 |bibcode=1996Ecol...77..791T }}</ref><ref name="reichard">{{cite journal |last=Reichard |first=S.H. |s2cid=29816498 |year=1997 |title=Predicting invasions of woody plants introduced into North America |journal=Conservation Biology |volume=11 |issue=1 |pages=193–203 |doi=10.1046/j.1523-1739.1997.95473.x |pmc=7162396 |bibcode=1997ConBi..11..193R }}</ref> Common invasive species traits include fast growth and rapid reproduction, such as vegetative reproduction in plants;<ref name="kolar"/><!--high dispersal ability;--><!--Phenotype plasticity;--><!--ecological competence;--><!--generalist;--> association with humans;<ref name="Williams">{{cite book |last=Williams |first=J. D. |year=1998 |chapter=Non-indigenous Species |title=Status and Trends of the Nation's Biological Resources |location=Reston, Virginia |pages=117–29 |publisher=United States Geological Survey |isbn=978-0-16-053285-6 |id={{DTIC|ADA368849}} }}</ref> and prior successful invasions.<ref name="ewell">{{cite journal |last=Ewell |first=J.J. |year=1999 |title=Deliberate introductions of species: Research needs – Benefits can be reaped, but risks are high |journal=BioScience |volume=49 |pages=619–630 |doi=10.2307/1313438 |jstor=1313438 |issue=8 |doi-access=free |bibcode=1999BiSci..49..619E }}</ref> Domestic cats (''Felis catus'') are effective predators of wildlife. They have become feral and invasive in places such as the Florida Keys.<ref name="Cove Gardner 2018">{{cite journal |last1=Cove |first1=Michael V. |last2=Gardner |first2=Beth |last3=Simons |first3=Theodore R. |last4=Kays |first4=Roland |last5=O'Connell |first5=Allan F. |s2cid=3536174 |date=February 1, 2018 |title=Free-ranging domestic cats (''Felis catus'') on public lands: estimating density, activity, and diet in the Florida Keys |journal=Biological Invasions |volume=20 |issue=2 |pages=333–344 |doi=10.1007/s10530-017-1534-x|bibcode=2018BiInv..20..333C }}</ref>
An introduced species might become invasive if it can outcompete native species for resources. If these species evolved under great competition or predation, then the new environment may host fewer able competitors, allowing the invader to proliferate. Ecosystems used to their fullest capacity by native species can be modeled as zero-sum systems, in which any gain for the invader is a loss for the native. However, such unilateral competitive superiority (and extinction of native species with increased populations of the invader) is not the rule.<ref name="Schell"/><ref name="sax">{{cite journal |last1=Sax |first1=Dov F. |last2=Gaines |first2=Steven D. |last3=Brown |first3=James H. |title=Species Invasions Exceed Extinctions on Islands Worldwide: A Comparative Study of Plants and Birds |journal=The American Naturalist |date=December 2002 |volume=160 |issue=6 |pages=766–783 |doi=10.1086/343877 |pmid=18707464 |bibcode=2002ANat..160..766S |s2cid=8628360 }}</ref>
[[File:Lantana Invasion of abandoned citrus plantation Sdey Hemed Israel.JPG|right|thumb|upright=1.8|''Lantana'', abandoned citrus, Sdei Hemed]]
An invasive species might be able to use resources previously unavailable to native species, such as deep water accessed by a long taproot, or to live on previously uninhabited soil types. For example, barbed goatgrass (''Aegilops triuncialis'') was introduced to California on serpentine soils, which have low water-retention, low nutrient levels, a high magnesium/calcium ratio, and possible heavy metal toxicity. Plant populations on these soils tend to show low density, but goatgrass can form dense stands on these soils and crowd out native species.<ref>{{cite journal |last1=Huenneke |first1=Laura Foster |last2=Hamburg |first2=Steven P. |last3=Koide |first3=Roger |last4=Mooney |first4=Harold A. |last5=Vitousek |first5=Peter M. |title=Effects of Soil Resources on Plant Invasion and Community Structure in Californian Serpentine Grassland |journal=Ecology |date=1990 |volume=71 |issue=2 |pages=478–491 |doi=10.2307/1940302 |jstor=1940302 |bibcode=1990Ecol...71..478H }}</ref>
Invasive species may also alter their environment by releasing chemical compounds, modifying abiotic factors, or affecting the behavior of herbivores, all of which can impact other species. Some, like mother of thousands (''Kalanchoe daigremontana''), produce allelopathic compounds that inhibit competitors.<ref name="HERRERAFERRER-PARIS2018">{{cite journal |title=An Invasive Succulent Plant (Kalanchoe daigremontiana) Influences Soil Carbon and Nitrogen Mineralization in a Neotropical Semiarid Zone |journal=Pedosphere |volume=28 |issue=4 |year=2018 |pages=632–643 |doi=10.1016/S1002-0160(18)60029-3 |last1=Herrera |first1=Ileana |last2=Ferrer-Paris |first2=José R. |last3=Benzo |first3=Diana |last4=Flores |first4=Saúl |last5=García |first5=Belkis |last6=Nassar |first6=Jafet M. |bibcode=2018Pedos..28..632H |hdl=1959.4/unsworks_64013 |s2cid=104843296|url=https://unsworks.unsw.edu.au/bitstreams/12acbbad-8af9-444b-a478-e7dc9d941d9b/download |hdl-access=free }}</ref> Others like the toad plant (''Stapelia gigantea)'' facilitate the growth of seedlings of other species in arid environments by providing appropriate microclimates and preventing herbivores from eating seedlings.<ref>{{cite journal |last1=Herrera |first1=Ileana |last2=Ferrer-Paris |first2=José R. |last3=Hernández-Rosas |first3=José I. |last4=Nassar |first4=Jafet M. |title=Impact of two invasive succulents on native-seedling recruitment in Neotropical arid environments |journal=Journal of Arid Environments |date=2016 |volume=132 |pages=15–25 |doi=10.1016/j.jaridenv.2016.04.007 |bibcode=2016JArEn.132...15H}}</ref>
Changes in fire regimens are another form of facilitation. Cheatgrass (''Bromus tectorum'')'','' originally from Eurasia, is highly fire-adapted. It spreads rapidly after burning, and increases the frequency and intensity of fires by providing large amounts of dry detritus during the fire season in western North America. Where it is widespread, it has altered the local fire regimen so much that native plants cannot survive the frequent fires, allowing it to become dominant in its introduced range.<ref name="Brooks 2004 677–688">{{cite journal |last1=Brooks |first1=Matthew L. |last2=D'Antonio |first2=Carla M. |last3=Richardson |first3=David M. |last4=Grace |first4=James B. |last5=Keeley |first5=Jon E. |last6=DiTOMASO |first6=Joseph M. |last7=Hobbs |first7=Richard J. |last8=Pellant |first8=Mike |last9=Pyke |first9=David |title=Effects of Invasive Alien Plants on Fire Regimes |journal=BioScience |date=2004 |volume=54 |issue=7 |page=677 |doi=10.1641/0006-3568(2004)054[0677:EOIAPO]2.0.CO;2 |s2cid=13769125 |doi-access=free }}</ref>
Ecological facilitation occurs where one species, including invasive species, physically modifies a habitat in ways advantageous to other species. For example, zebra mussels (''Dreissena polymorpha'') increase habitat complexity on lake floors, providing crevices in which invertebrates live. This increase in complexity, together with the nutrition provided by the waste products of mussel filter-feeding, increases the density and diversity of benthic invertebrate communities.<ref name="silv">{{cite journal |last1=Silver Botts |first1=P. |last2=Patterson |first2=B.A. |last3=Schlosser |first3=D. |year=1996 |title=Zebra mussel effects on benthic invertebrates: Physical or biotic? |journal=Journal of the North American Benthological Society |issue=2 |volume=15 |doi=10.2307/1467947 |jstor=1467947 |pages=179–184 |bibcode=1996JNABS..15..179B |s2cid=84660670 }}</ref>
Introduced species may spread rapidly and unpredictably.<ref>{{Cite book |last=Keddy |first=Paul A. |url=https://books.google.com/books?id=ncloDgAAQBAJ&q=Plant+Ecology |title=Plant Ecology |publisher=Cambridge University Press |year=2017 |isbn=978-1-107-11423-4 |page=343 |access-date=October 6, 2020 |archive-date=August 16, 2021 |archive-url=https://web.archive.org/web/20210816224645/https://books.google.com/books?id=ncloDgAAQBAJ&q=Plant+Ecology |url-status=live}}</ref> When bottlenecks and founder effects cause a great decrease in the population size and may constrict genetic variation,<ref>{{Cite journal |last1=Xu |first1=Cheng-Yuan |last2=Tang |first2=Shaoqing |last3=Fatemi |first3=Mohammad |last4=Gross |first4=Caroline L. |last5=Julien |first5=Mic H. |last6=Curtis |first6=Caitlin |last7=van Klinken |first7=Rieks D. |date=September 1, 2015 |title=Population structure and genetic diversity of invasive Phyla canescens: implications for the evolutionary potential |journal=Ecosphere |volume=6 |issue=9 |pages=art162 |doi=10.1890/ES14-00374.1 |bibcode=2015Ecosp...6..374X |doi-access=free}}</ref> individuals begin to show additive variance as opposed to epistatic variance. This conversion can lead to increased variance in the founding populations, which permits rapid evolution.<ref name="Prentis 2008 288-294">{{cite journal |last=Prentis |first=Peter |title=Adaptive evolution in invasive species |journal=Trends in Plant Science|volume=13 |issue=6 |pages=288–294 |doi=10.1016/j.tplants.2008.03.004 |pmid=18467157 |year=2008|bibcode=2008TPS....13..288P |hdl=10019.1/112332 |hdl-access=free }}</ref> Selection may then act on the capacity to disperse as well as on physiological tolerance to new stressors in the environment, such as changed temperature and different predators and prey.<ref name="Eunmi 2002 386-391">{{cite journal |last=Lee |first=Carol Eunmi |title=Evolutionary genetics of invasive species |journal=Trends in Ecology & Evolution|volume=17 |issue=8 |pages=386–391 |doi=10.1016/s0169-5347(02)02554-5 |year=2002}}</ref>
Rapid adaptive evolution through intraspecific phenotypic plasticity, pre-adaptation, and post-introduction evolution lead to offspring that have higher fitness. Critically, plasticity permits changes to better suit the individual to its environment. Pre-adaptations and evolution after the introduction reinforce the success of the introduced species.<ref name="Zenni 2013 635-644">{{cite journal |last=Zenni |first=R.D. |title=Adaptive Evolution and Phenotypic Plasticity During Naturalization and Spread of Invasive Species: Implications for Tree Invasion Biology |journal=Biological Invasions |year=2013 |volume=16 |issue=3 |pages=635–644 |doi=10.1007/s10530-013-0607-8 |s2cid=82590}}</ref>
The enemy release hypothesis states that evolution leads to ecological balance in every ecosystem. No single species can occupy a majority of an ecosystem due to the presences of competitors, predators, and diseases. Introduced species moved to a novel habitat can become invasive, with rapid population growth, when these controls do not exist in the new ecosystem.{{r|amstutz2018}}
==Vectors== Non-native species have many vectors, but most are associated with human activity. Natural range extensions are common, but humans often carry specimens faster and over greater distances than natural forces.<ref>{{cite journal |last=Cassey |first=P |year=2005 |title=Concerning Invasive Species: Reply to Brown and Sax|journal=Austral Ecology |volume=30|issue=4 |pages=475–480 |doi=10.1111/j.1442-9993.2005.01505.x|bibcode=2005AusEc..30..475C |hdl=10019.1/119884 |hdl-access=free}}</ref> An early human vector occurred when prehistoric humans introduced the Pacific rat (''Rattus exulans'') to Polynesia.<ref>{{cite journal |last=Matisoo-Smith |first=E. |year=1998 |title=Patterns of prehistoric human mobility in Polynesia indicated by mtDNA from the Pacific rat|journal=Proceedings of the National Academy of Sciences of the United States of America |volume=95 |pages=15145–15150 |doi=10.1073/pnas.95.25.15145 |pmid=9844030 |issue=25 |pmc=24590 |bibcode=1998PNAS...9515145M |doi-access=free }}</ref>
Humans have historically acted as vectors, both deliberately and accidentally. During the colonial era, there were acclimatization societies that aimed to deliberately establish animals and plants that were recognizable to Europeans. These societies felt that this would be an "improvement" to nature by adding species that were nostalgic and valuable.<ref>{{Cite web | url=https://dspace.mit.edu/bitstream/handle/1721.1/72380/goingforth.ehversion.dec11.pdf?isAllowed=y&sequence=1 | title=Going Forth and Multiplying: Animal Acclimatization and Invasion | website=dspace.mit.edu}}</ref> Another reason for deliberate introduction was that some species are thought to act as biocontrol. The cane toad was introduced in Australia in hopes of controlling the cane beetle population. Cane beetles are pests of the sugar cane crop. While only 100 toads were initially imported, there are now over 200 million present in Australia.<ref>{{Cite web| title=The cane toad (bufo marinus) | url=https://www.dcceew.gov.au/sites/default/files/documents/cane-toad-fs.pdf | archive-url=https://web.archive.org/web/20221008121115/https://www.dcceew.gov.au/sites/default/files/documents/cane-toad-fs.pdf | archive-date=2022-10-08}}</ref> Another example of animal introduction is the Indian mongoose, which was introduced in Hawaii to control the rat population as the rats were damaging sugar cane yields. This, however, ended up being ineffective because rats are nocturnal while the mongoose is diurnal. Their introduction ended up causing new problems for the island's ecosystems.<ref>{{Cite book | last1=Fineran | first1=Katie E. | chapter=1.5 Non-Native Mongoose (Herpestes javanicus): A Threat to Hawaiian Islands |title=Environmental ScienceBites Volume 2 |editor-last1=Lower |editor-first1=Brian H. |editor-last2=Shaul | editor-first2=Travis R. | editor-last3=Shaul | editor-first3=Kylienne A. | editor-last4=Weaver | editor-first4=Ella M. | url=https://ohiostate.pressbooks.pub/sciencebitesvolume2/chapter/1-5-non-native-mongoose-herpestes-javanicus-a-threat-to-hawaiian-islands/ | access-date=2026-01-14}}</ref>
[[File:EriocheirSinensis1.jpg|thumb|left|The Chinese mitten crab (''Eriocheir sinensis'') may have been purposely introduced in Europe and North America because of its commercial value. ]]
Vectors also include plants or seeds imported for horticulture. The pet trade moves animals across borders, where they can escape and become invasive. Organisms may also stow away on transport vehicles. Incidental human assisted transfer is the main cause of introductions{{snd}}other than in polar regions.<ref name="Essl-et-al-2020">{{cite journal |last1=Essl |first1=Franz |last2=Lenzner |first2=Bernd |last3=Bacher |first3=Sven |last4=Bailey |first4=Sarah |last5=Capinha |first5=Cesar |last6=Daehler |first6=Curtis |last7=Dullinger |first7=Stefan |last8=Genovesi |first8=Piero |last9=Hui |first9=Cang |last10=Hulme |first10=Philip E. |last11=Jeschke |first11=Jonathan M. |last12=Katsanevakis |first12=Stelios |display-authors=6 |title=Drivers of future alien species impacts: An expert-based assessment |journal=Global Change Biology |date=September 2020 |volume=26 |issue=9 |pages=4880–4893 |doi=10.1111/gcb.15199 |pmid=32663906 |pmc=7496498 |bibcode=2020GCBio..26.4880E }}</ref> Diseases may be vectored by invasive insects: the Asian citrus psyllid (''Diaphorina citri'') carries the bacterial disease citrus greening.<ref name=r2/> The arrival of invasive propagules to a new site is a function of the site's invasibility.<ref>{{cite journal |last=Leung |first=B. |year=2007 |title=The risk of establishment of aquatic invasive species: joining invasibility and propagule pressure |journal=Proceedings of the Royal Society B |volume=274 |pages=2733–2739|doi=10.1098/rspb.2007.0841 |pmid=17711834 |issue=1625 |pmc=2275890}}</ref> Recreation is one of the most underestimated vectors for invasive species spread. Seeds, spores, larvae, and pathogens can hitchhike on boats, boots, waders, bikes, pets, vehicles, and firewood, moving farther and faster than natural dispersal ever could.<ref name=":17">{{Cite web |title=Recreation & Travel: How Outdoor Activities Spread Invasive Species |url=https://rewildingreport.com/invasive-species-recreation-pathway |access-date=2026-05-22 |website=rewildingreport.com |language=en}}</ref>
Many invasive species, once they are dominant in the area, become essential to the ecosystem of that area, and their removal could be harmful.<ref>{{cite journal |last1=Zavaleta |first1=Erika S. |last2=Hobbs |first2=Richard J. |last3=Mooney |first3=Harold A. |title=Viewing invasive species removal in a whole-ecosystem context |journal=Trends in Ecology & Evolution |date=August 2001 |volume=16 |issue=8 |pages=454–459 |doi=10.1016/s0169-5347(01)02194-2 }}</ref> Economics plays a major role in exotic species introduction. High demand for the valuable Chinese mitten crab is one explanation for the possible intentional release of the species in foreign waters.<ref>{{Cite book |last=Seinfeld |first=John H. |title=Marine Pollution and Climate Change |publisher=John Wiley & Sons |year=2016 |isbn=978-1-4822-9944-1 |editor-last=Arias |editor-first=Andres Hugo |editor-last2=Marcovecchio |editor-first2=Jorge Eduardo}}</ref>
=== Within the aquatic environment === Maritime trade has rapidly affected the way marine organisms are transported within the ocean; new means of species transport include hull fouling and ballast water transport. In fact, Molnar et al. 2008 documented the pathways of hundreds of marine invasive species and found that shipping was the dominant mechanism for the transfer of invasive species.<ref>{{cite journal |last1=Molnar |first1=Jennifer L. |last2=Gamboa |first2=Rebecca L. |last3=Revenga |first3=Carmen |last4=Spalding |first4=Mark D. |title=Assessing the global threat of invasive species to marine biodiversity |journal=Frontiers in Ecology and the Environment |date=November 2008 |volume=6 |issue=9 |pages=485–492 |doi=10.1890/070064 |bibcode=2008FrEE....6..485M }}</ref>
[[File:CSIRO ScienceImage 1010 Discharging ballast water.jpg |thumb |Cargo ship de-ballasting ]]
Many marine organisms can attach themselves to vessel hulls. Such organisms are easily transported from one body of water to another, and are a significant risk factor for a biological invasion event.<ref>{{Cite journal |last=Drake |first=John |date=2007 |title=Hull fouling is a risk factor for intercontinental species exchange in aquatic ecosystems |journal=Aquatic Invasions |volume=2 |issue=2 |pages=121–131 |doi=10.3391/ai.2007.2.2.7 |doi-access=free}}</ref> Controlling for vessel hull fouling is voluntary and there are no regulations currently in place to manage hull fouling. However, the governments of California and New Zealand have announced more stringent control for vessel hull fouling within their respective jurisdictions.<ref>{{cite web |url=http://www.gard.no/web/updates/content/24305557/biofouling-moves-up-the-regulatory-agenda. |title=Biofouling moves up the regulatory agenda – GARD |website=www.gard.no |access-date=September 19, 2018 |archive-date=January 13, 2020 |archive-url=https://web.archive.org/web/20200113231807/http://www.gard.no/web/updates/content/24305557/biofouling-moves-up-the-regulatory-agenda. |url-status=live}}</ref>
Another vector of non-native aquatic species is ballast water taken up at sea and released in port by transoceanic vessels.<ref name=cargo>{{cite web |url=http://www.jsonline.com/news/wisconsin/98880204.html |last=Egan |first=Dan |work=Journal Sentinel |date=October 31, 2005 |title=Noxious cargo |access-date=April 22, 2017 |archive-url=https://web.archive.org/web/20111021122316/http://www.jsonline.com/news/wisconsin/98880204.html |archive-date=October 21, 2011 }}</ref><ref>{{cite book |doi=10.1145/2623330.2623364 |chapter=Improving management of aquatic invasions by integrating shipping network, ecological, and environmental data |title=Proceedings of the 20th ACM SIGKDD international conference on Knowledge discovery and data mining |year=2014 |last1=Xu |first1=Jian |last2=Wickramarathne |first2=Thanuka L. |last3=Chawla |first3=Nitesh V. |last4=Grey |first4=Erin K. |last5=Steinhaeuser |first5=Karsten |last6=Keller |first6=Reuben P. |last7=Drake |first7=John M. |last8=Lodge |first8=David M. |pages=1699–1708 |isbn=978-1-4503-2956-9 |s2cid=2371978 }}</ref> Some 10,000 species are transported via ballast water each day.<ref>{{Cite journal |last1=Streftaris |first1=N |last2=Zenetos |first2=Argyro |last3=Papathanassiou |first3=Enangelos |date=2005 |title=Globalisation in marine ecosystems: The story of non-indigenous marine species across European seas |url=https://www.researchgate.net/publication/253862066 |journal=Oceanography and Marine Biology |volume=43 |pages=419–453 |access-date=September 19, 2018 |archive-date=September 20, 2018 |archive-url=https://web.archive.org/web/20180920011308/https://www.researchgate.net/publication/253862066 |url-status=live}}</ref> Many of these are harmful. For example, freshwater zebra mussels (''Dreissena polymorpha'') from Eurasia most likely reached the Great Lakes via ballast water.{{r|pnwaquaticinv}} The mussels outcompete native organisms for oxygen and food, and can be transported in the small puddle left in a supposedly empty ballast tank.<ref name=cargo/> Also, three lineages of the Asian clam genus ''Corbicula'' (''C. fluminea'', ''C. fluminalis'', ''C. leana'') are globally invasive. Molecular data confirm their taxonomic identity and reveal multiple independent introduction events.<ref name="Bespalaya2026">{{cite journal | vauthors= Bespalaya YV, Kropotin AV, Aksenova OV, Gofarov MY, Kondakov AV, Konopleva ES, Khrebtova IS, Mabrouki Y, Palatov DM, Prokin AA, Karabanov DP, Travina OV, Taybi AF, Izzatulaev ZI, Boymurodov KT, Tahirova EN, Snegovaya NY, Tien TV, Vikhrev IV, Vinarski MV, Kyi CT, Chan N, Lunn Z, Unnikrishnan SK, Pattnaik S, Raut D, Subba Rao NV, Bolotov IN |title=Global Molecular Taxonomy, Phylogeny and Biogeography of the Clam Genus Corbicula (Bivalvia: Cyrenidae) |journal=Zoologica Scripta |year=2026 |volume=55 |issue=1 |pages=74–101 |url=https://onlinelibrary.wiley.com/doi/10.1111/zsc.70022 |doi=10.1111/zsc.70022 |ref=Bespalaya2026 }}</ref> Regulations attempt to mitigate such risks,<ref>{{cite web |url=https://www.glc.org/wp-content/uploads/GLC-BW-Reg-Summary-11.14.16.pdf |title=Status of Ballast Water Discharge Regulations in the Great Lakes Region |last=Great Lake Commission |access-date=September 19, 2018 |archive-date=February 12, 2020 |archive-url=https://web.archive.org/web/20200212212419/http://www.glc.org/wp-content/uploads/GLC-BW-Reg-Summary-11.14.16.pdf |url-status=live}}</ref><ref>{{cite web |url=https://www.dco.uscg.mil/Portals/9/DCO%20Documents/5p/5ps/NVIC/2018/NVIC-01_18.pdf |title=Ballast Water Management for Control of Non-Indigenous Species in Waters of the United States |last=USCG |access-date=September 19, 2018 |archive-date=May 11, 2020 |archive-url=https://web.archive.org/web/20200511133624/https://www.dco.uscg.mil/Portals/9/DCO%20Documents/5p/5ps/NVIC/2018/NVIC-01_18.pdf |url-status=live}}</ref> not always successfully.{{r |trainer2012}} Climate change is causing an increase in ocean temperature. These changes to the environment in turn cause range shifts in organisms,<ref>{{Cite journal |last=Occhipinti-Ambrogi |first=Anna |date=2007 |title=Global change and marine communities: Alien species and climate change |journal=Marine Pollution Bulletin |volume=55 |issue=7–9 |pages=342–352 |doi=10.1016/j.marpolbul.2006.11.014 |pmid=17239404 |bibcode=2007MarPB..55..342O }}</ref><ref>{{cite journal |last1=Rahel |first1=Frank J. |last2=Olden |first2=Julian D. |title=Assessing the Effects of Climate Change on Aquatic Invasive Species |journal=Conservation Biology |date=June 2008 |volume=22 |issue=3 |pages=521–533 |doi=10.1111/j.1523-1739.2008.00950.x |pmid=18577081 |s2cid=313824 |doi-access=free |bibcode=2008ConBi..22..521R }}</ref> creating new species interactions. For example, organisms in a ballast tank of a ship traveling from the temperate zone through tropical waters may experience temperature fluctuations as much as 20 °C.<ref>{{Cite journal |last1=Hua |first1=J. |last2=Hwang |first2=W.H. |date=2012 |title=Effects of voyage routing on the survival of microbes in ballast water |journal=Ocean Engineering |volume=42 |pages=165–175 |doi=10.1016/j.oceaneng.2012.01.013|bibcode=2012OcEng..42..165H }}</ref> Heat challenges during transport may enhance the stress tolerance of species in their non-native range, by selecting for genotypes that will survive a second applied heat stress, such as increased ocean temperature in the founder population.<ref>{{Cite journal |last1=Lenz |first1=Mark |last2=Ahmed |first2=Yasser |last3=Canning-Clode |first3=João |last4=Díaz |first4=Eliecer |last5=Eichhorn |first5=Sandra |last6=Fabritzek |first6=Armin G. |last7=da Gama |first7=Bernardo A. P. |last8=Garcia |first8=Marie |last9=von Juterzenka |first9=Karen |s2cid=53082967 |date=May 24, 2018 |title=Heat challenges can enhance population tolerance to thermal stress in mussels: a potential mechanism by which ship transport can increase species invasiveness |journal=Biological Invasions |volume=20 |issue=11 |pages=3107–3122 |doi=10.1007/s10530-018-1762-8|bibcode=2018BiInv..20.3107L }}</ref>
=== Effects of wildfire and firefighting === Invasive species often exploit disturbances to an ecosystem (wildfires, roads, foot trails) to colonize an area. Large wildfires can sterilize soils, while adding nutrients.<ref name="Davis 2000 528–534"/> Invasive plants that can regenerate from their roots then have an advantage over natives that rely on seeds for propagation.<ref name="Brooks 2004 677–688"/>
==Adverse effects== Invasive species can affect the invaded habitats, communities, and ecosystems adversely, causing ecological, environmental, and/or economic damage.{{r|ehrenfeld2010}}<ref>{{Cite book |last=Simberloff |first=Daniel |title=Invasive species: what everyone needs to know |date=2013 |publisher=Oxford University Press |isbn=978-0-19-992201-7 |location=Oxford}}</ref><ref>{{Cite web |title=Environmental and Ecological Impacts {{!}} National Invasive Species Information Center |url=https://www.invasivespeciesinfo.gov/subject/environmental-and-ecological-impacts |access-date=2025-12-11 |website=www.invasivespeciesinfo.gov |language=en}}</ref>
===Ecological=== The European Union defines "Invasive Alien Species" as those that are outside their natural distribution area, and that threaten biological diversity.<ref>{{cite web |url=http://ec.europa.eu/environment/nature/invasivealien/docs/1_EN_resume_impact_assesment_part1_v3.pdf |title=Communication From The Commission To The Council, The European Parliament, The European Economic And Social Committee And The Committee Of The Regions Towards An EU Strategy On Invasive Species |access-date=May 17, 2011 |archive-date=March 5, 2016 |archive-url=https://web.archive.org/web/20160305033628/http://ec.europa.eu/environment/nature/invasivealien/docs/1_EN_resume_impact_assesment_part1_v3.pdf |url-status=live }}</ref><ref>{{cite journal |doi=10.2298/ZMSPN1834019L |title=Non-native and invasive tree species - their impact on biodiversity loss |year=2018 |last1=Lakicevic |first1=Milena |last2=Mladenovic |first2=Emina |journal=Zbornik Matice Srpske za Prirodne Nauke |issue=134 |pages=19–26 |doi-access=free}}</ref> Biotic invasion is one of the five top drivers for global biodiversity loss, and is increasing because of tourism and globalization.<ref>{{Cite book |url=https://www.nap.edu/read/10259/chapter/1 |year=2002 |doi=10.17226/10259 |pmid=25032288 |isbn=978-0-309-08264-8 |author1=National Research Council (US) Committee on the Scientific Basis for Predicting the Invasive Potential of Nonindigenous Plants Plant Pests in the United States |title=Predicting Invasions of Nonindigenous Plants and Plant Pests |bibcode=2002nap..book10259N |access-date=November 17, 2019 |archive-date=November 17, 2019 |archive-url=https://web.archive.org/web/20191117204337/https://www.nap.edu/read/10259/chapter/1 |url-status=live}}</ref><ref>{{cite journal |doi=10.1038/nature14258 |title=Defining the Anthropocene |year=2015 |last1=Lewis |first1=Simon L. |last2=Maslin |first2=Mark A. |s2cid=205242896 |journal=Nature |volume=519 |issue=7542 |pages=171–180 |pmid=25762280 |bibcode=2015Natur.519..171L |url=https://zotero.org/groups/5435545/items/CF2PI4C2 }}</ref> This may be particularly true in inadequately regulated fresh water systems, though quarantines and ballast water rules have improved the situation.<ref>{{cite web |url=http://www.millenniumassessment.org/documents/document.354.aspx.pdf |title=Ecosystems and Human Well-being: Biodiversity Synthesis |author=Millennium Ecosystem Assessment |year=2005 |publisher=World Resources Institute |author-link=Millennium Ecosystem Assessment |access-date=September 18, 2007 |archive-date=October 14, 2019 |archive-url=https://web.archive.org/web/20191014033601/http://www.millenniumassessment.org/documents/document.354.aspx.pdf |url-status=live}}</ref>
[[File:Gator and Python.jpg |thumb |right |American alligator (''Alligator mississippiensis'') combatting a Burmese python (''Python bivittatus'') in Florida ]]
Invasive species may drive local native species to extinction via competitive exclusion, niche displacement, or hybridization with related native species. Therefore, besides their economic ramifications, alien invasions may result in extensive changes in the structure, composition and global distribution of the biota at sites of introduction, leading ultimately to the homogenization of the world's fauna and flora and the loss of biodiversity.<ref>{{cite journal |doi=10.1098/rspb.2012.1651 |title=Pattern and process of biotic homogenization in the New Pangaea |year=2012 |last1=Baiser |first1=Benjamin |last2=Olden |first2=Julian D. |last3=Record |first3=Sydne |last4=Lockwood |first4=Julie L. |last5=McKinney |first5=Michael L. |journal=Proceedings of the Royal Society B: Biological Sciences |volume=279 |issue=1748 |pages=4772–4777 |pmid=23055062 |pmc=3497087}}</ref><ref name="Odendaal 2008">{{cite journal |last1=Odendaal |first1=L. J. |last2=Haupt |first2=T. M. |last3=Griffiths |first3=C. L. |year=2008 |title=The alien invasive land snail ''Theba pisana'' in the West Coast National Park: Is there cause for concern? |journal=Koedoe |volume=50 |issue=1 |pages=93–98 |doi=10.4102/koedoe.v50i1.153 |doi-access=free }}</ref> It is difficult to unequivocally attribute extinctions to a species invasion, though for example there is strong evidence that the extinction of about 90 amphibian species was caused by the chytrid fungus (''Batrachochytrium dendrobatidis'') spread by international trade.<ref>{{cite journal |doi=10.1038/s41579-020-0335-x |title=Chytrid fungi and global amphibian declines |year=2020 |last1=Fisher |first1=Matthew C. |last2=Garner |first2=Trenton W. J. |s2cid=211266075 |journal=Nature Reviews Microbiology |volume=18 |issue=6 |pages=332–343 |pmid=32099078 |url=https://discovery.ucl.ac.uk/id/eprint/10092667/1/NRMICRO-19-244_FINAL_ACCEPTED.pdf |hdl=10044/1/78596 |hdl-access=free |access-date=September 28, 2020 |archive-date=November 7, 2020 |archive-url=https://web.archive.org/web/20201107202307/https://discovery.ucl.ac.uk/id/eprint/10092667/1/NRMICRO-19-244_FINAL_ACCEPTED.pdf |url-status=live}}</ref>
Multiple successive introductions of different non-native species can worsen the total effect, as with the introductions of the amethyst gem clam (''Gemma gemma'') and the European green crab (''Carcinus maenas''). The gem clam was introduced into California's Bodega Harbor from the US East Coast a century ago. On its own, it did not displace native clams (''Nutricola'' spp.). However, in the mid-1990s, the introduction of the European green crab resulted in an increase of the amethyst gem at the expense of the native clams.<ref>{{cite journal |last=Grosholz |first=E.D. |year=2005 |title=Recent biological invasion may hasten invasional meltdown by accelerating historical introductions |journal=Proceedings of the National Academy of Sciences |volume=102 |pages=1088–1091 |doi=10.1073/pnas.0308547102 |pmid=15657121 |issue=4 |pmc=545825 |bibcode=2005PNAS..102.1088G |doi-access=free }}</ref> In India, multiple invasive plants have invaded 66% of natural areas, reducing the densities of native forage plants, declining the habitat-use by wild herbivores and threatening the long-term sustenance of dependent carnivores, including tigers.<ref>{{Cite journal |last=Mungi |first=Ninad Avinash |title=Distribution, drivers and restoration priorities of plant invasions in India |journal=Journal of Applied Ecology |date=2023 |volume=60 |issue=11 |pages=2400–2412|doi=10.1111/1365-2664.14506 |bibcode=2023JApEc..60.2400M |doi-access=free }}</ref><ref>{{Cite journal |last=Rastogi |first=Rajat |title=Multiple invasions exert combined magnified effects on native plants, soil nutrients and alters the plant-herbivore interaction in dry tropical forest |url=https://www.sciencedirect.com/science/article/pii/S0378112723000142 |journal=Forest Ecology and Management |date=2023 |volume=531 |article-number=120781|doi=10.1016/j.foreco.2023.120781 |bibcode=2023ForEM.53120781R |url-access=subscription }}</ref>
Invasive species can change the functions of ecosystems. For example, invasive plants can alter the fire regime (e.g., cheatgrass, ''Bromus tectorum''), nutrient cycling (e.g., smooth cordgrass, ''Spartina alterniflora''), and hydrology (e.g.,''Tamarix'') in native ecosystems.<ref name="causesepidemiology" /> Invasive species that are closely related to rare native species have the potential to hybridize with the native species. Harmful effects of hybridization have led to a decline and even extinction of native species.<ref>{{cite journal |last=Hawkes |first=C.V. |year=2005 |title=Plant invasion alters nitrogen cycling by modifying the soil nitrifying community |journal=Ecology Letters |volume=8 |pages=976–985 |doi=10.1111/j.1461-0248.2005.00802.x |issue=9 |pmid=34517683 |bibcode=2005EcolL...8..976H }}</ref><ref name="rhymer">{{cite journal |last=Rhymer |first=J. M. |author2=Simberloff, D. |year=1996 |title=Extinction by hybridization and introgression |journal=Annual Review of Ecology and Systematics |issue=1 |pages=83–109 |doi=10.1146/annurev.ecolsys.27.1.83 |volume=27|bibcode=1996AnRES..27...83R }}</ref> For example, hybridization with introduced cordgrass threatens the existence of California cordgrass (''Spartina foliosa'') in San Francisco Bay.<ref name="ayres">{{cite journal |last=Ayres |first=D. |s2cid=24732543 |year=2004 |title=Spread of exotic cordgrasses and hybrids (''Spartina'' sp.) in the tidal marshes of San Francisco Bay, California, USA |journal=Biological Invasions |volume=6 |pages=221–231 |doi=10.1023/B:BINV.0000022140.07404.b7 |issue=2 |bibcode=2004BiInv...6..221A |display-authors=etal}}</ref> Invasive species cause competition for native species, and because of this 400 of the 958 endangered species under the Endangered Species Act are at risk.<ref>{{cite journal |last=Primtel |first=David |year=2005 |title=Update on the environmental and economic costs associated with alien-invasive species in the United States |journal=Ecological Economics |volume=52 |issue=3 |pages=273–288 |doi=10.1016/j.ecolecon.2004.10.002|bibcode=2005EcoEc..52..273P }}</ref>
[[File:Firewoodposter white web.pdf |thumb |left |Poster from the State of California asking campers to not move firewood around, avoiding the spread of invasive species]]
The unintentional introduction of forest pest species and plant pathogens can change forest ecology and damage the timber industry. Overall, forest ecosystems in the U.S. are widely invaded by exotic pests, plants, and pathogens.<ref>{{cite journal |last1=Liebhold |first1=S. |year=2013 |title=A highly aggregated geographical distribution of forest pest invasions in the USA |doi=10.1111/ddi.12112 |journal=Diversity and Distributions |volume=19 |issue=9 |pages=1208–1216 |s2cid=85799394 |display-authors=etal |doi-access=free |bibcode=2013DivDi..19.1208L }}</ref><ref>{{cite journal |last1=Oswalt |first1=C. |year=2015 |title=A subcontinental view of forest plant invasions |journal=NeoBiota |volume=24 |pages=49–54 |display-authors=etal |doi=10.3897/neobiota.24.8378 |doi-access=free }}</ref>
The Asian long-horned beetle (''Anoplophora glabripennis'') was first introduced into the U.S. in 1996, and was expected to infect and damage millions of acres of hardwood trees. As of 2005 thirty million dollars had been spent in attempts to eradicate this pest and protect millions of trees in the affected regions.<ref name="pimental"/> The woolly adelgid (''Adelges tsugae'') has inflicted damage on old-growth spruce, fir and hemlock forests and damages the Christmas tree industry.<ref>{{Cite web |title=South/Adelges piceae - Bugwoodwiki |url=https://wiki.bugwood.org/Archive:South/Balsam_Woolly_Aphid |url-status=live |archive-url=https://web.archive.org/web/20110722063118/http://wiki.bugwood.org/Archive:South/Balsam_Woolly_Aphid |archive-date=22 July 2011 |access-date=2022-06-26 |website=wiki.bugwood.org}}</ref> Chestnut blight (''Cryphonectria parasitica'') and Dutch elm disease (Ascomycota) are plant pathogens with serious impacts.<ref>Schlarbaum, Scott E., Frederick Hebard, Pauline C. Spaine, and Joseph C. Kamalay. (1998) [https://research.fs.usda.gov/treesearch/745 "Three American Tragedies: Chestnut Blight, Butternut Canker, and Dutch Elm Disease'] . In: Britton, Kerry O., Ed. Exotic Pests of Eastern Forests Conference Proceedings; 1997 April 8–10; Nashville, TN. U.S. Forest Service and Tennessee Exotic Pest Plant Council., pp. 45–54.</ref><ref name="USDA-Forest Service-Schlarbaum-1997">{{cite web |author1=Schlarbaum, Scott E. |author2=Hebard, Frederick |author3=Spaine, Pauline C. |author4=Kamalay, Joseph C. |url=https://www.srs.fs.usda.gov/pubs/ja/ja_schlarbaum002.htm |title=Three American Tragedies: Chestnut Blight, Butternut Canker and Dutch Elm Disease |publisher=Southern Research Station, Forest Service, United States Department of Agriculture |year=1997 |work=(originally published via: Proceedings: Exotic Pests of Eastern Forests; (1997 April 8–10); Nashville, TN. Tennessee Exotic Pest Plant Council: 45–54.) |access-date=June 22, 2012 |archive-date=April 24, 2012 |archive-url=https://web.archive.org/web/20120424101943/http://www.srs.fs.usda.gov/pubs/ja/ja_schlarbaum002.htm |url-status=live }}</ref><ref>{{Cite journal | last1=Schlarbaum | first1=Scott E. | last2=Hebard | first2=Frederick | last3=Spaine | first3=Pauline C. | last4=Kamalay | first4=Joseph C. | last5=Schlarbaum | first5=Scott E. | last6=Hebard | first6=Frederick | last7=Spaine | first7=Pauline C. | last8=Kamalay | first8=Joseph C. | url=http://www.treesearch.fs.fed.us/pubs/745 | title=Southern Research Station | archive-url=https://web.archive.org/web/20121123093613/http://www.treesearch.fs.fed.us/pubs/745 | archive-date=November 23, 2012 | publisher=US Forest Service, USDA | website=Tree Search}}</ref> Garlic mustard (''Alliaria petiolata)'' is one of the most problematic invasive plant species in eastern North American forests, where it is highly invasive of the understory, reducing the growth rate of tree seedlings and threatening to modify the forest's tree composition.<ref>{{cite journal |last1=Rodger |first1=Vikki |last2=Stinson |first2=Kristin |last3=Finzi |first3=Adrian |year=2008 |title=Ready or Not, Garlic Mustard Is Moving In: ''Alliaria petiolata'' as a Member of Eastern North American Forests |doi=10.1641/b580510 |journal=BioScience |volume=58 |issue=5 |page=5 |bibcode=2008BiSci..58..426R |doi-access=free }}</ref> [[File:Strigops habroptilus, face.jpg|thumb|The Kākāpō is a threatened species partially because of predation by invasive species (mostly rats and cats), there are only ≈240 individuals left worldwide <ref>{{Cite web |date=2024-07-10 |title=Kākāpō Recovery Programme |url=https://www.meridianenergy.co.nz/community-support/kakapo-recovery-programme |access-date=2026-02-26 |website=Meridian Energy |language=en-US}}</ref>]] Native species can be threatened with extinction<ref name=":1">{{cite journal |pmc=33232 |title=The evolutionary impact of invasive species |year=2001 |volume=98 |issue=10 |pmid=11344292 |last1=Mooney |first1=HA |last2=Cleland |first2=EE |pages=5446–51 |doi=10.1073/pnas.091093398 |journal=Proceedings of the National Academy of Sciences of the United States of America |bibcode=2001PNAS...98.5446M |doi-access=free }}</ref> through the process of genetic pollution. Genetic pollution is unintentional hybridization and introgression, which leads to homogenization or replacement of local genotypes as a result of either a numerical or fitness advantage of the introduced species.<ref>{{cite web |url=http://www.nativeseednetwork.org/article_view?id=13 |title=Glossary: definitions from the following publication: Aubry, C., R. Shoal and V. Erickson. 2005. Grass cultivars: their origins, development, and use on national forests and grasslands in the Pacific Northwest. USDA Forest Service. 44 pages, plus appendices.; Native Seed Network (NSN), Institute for Applied Ecology, 563 SW Jefferson Ave, Corvallis, OR 97333, USA |publisher=Nativeseednetwork.org |access-date=May 17, 2011 |archive-url=https://web.archive.org/web/20060222092651/http://www.nativeseednetwork.org/article_view?id=13 |archive-date=February 22, 2006 }}</ref> Genetic pollution occurs either through introduction or through habitat modification, where previously isolated species are brought into contact with the new genotypes. Invading species have been shown to adapt to their new environments in a remarkably short amount of time.<ref name=":1"/> The population size of invading species may remain small for a number of years and then experience an explosion in population, a phenomenon known as "the lag effect".<ref name = causesepidemiology >{{cite journal |last1=Mack |first1=Richard N. |last2=Simberloff |first2=Daniel |author2-link=Daniel Simberloff |last3=Mark Lonsdale |first3=W. |last4=Evans |first4=Harry |last5=Clout |first5=Michael |last6=Bazzaz |first6=Fakhri A. |title=Biotic Invasions: Causes, Epidemiology, Global Consequences, and Control |journal=Ecological Applications |date=June 2000 |volume=10 |issue=3 |pages=689–710 |doi=10.1890/1051-0761(2000)010[0689:BICEGC]2.0.CO;2 |s2cid=711038 }}</ref>
[[File:Linepithema Argentine ant.jpg|thumb|Argentine ants (''Linepithema humile''), which form supercolonies across continents, are ranked among the world's 100 worst invasive animal species.<ref>{{cite report |last1=Boudjelas |first1=Souyad |year=2000 |title=100 of the world's worst invasive alien species |website=iucn.org |publisher=International Union for Conservation of Nature |url=https://portals.iucn.org/library/sites/library/files/documents/2000-126.pdf |access-date=20 July 2018 }} </ref>]] Hybrids resulting from invasive species interbreeding with native species can incorporate their genotypes into the gene pool over time through introgression. Similarly, in some instances a small invading population can threaten much larger native populations. For example, cordgrass (''Spartina alterniflora)'' was introduced in the San Francisco Bay and hybridized with native ''California cordgrass (Spartina foliosa).'' The higher pollen count and male fitness of the invading species resulted in introgression that threatened the native populations due to lower pollen counts and lower viability of the native species.<ref>{{cite journal |title=Reciprocal hybrid formation of Spartina in San Francisco Bay |journal=Molecular Ecology |volume=9 |issue=6 |pages=765–770 |doi=10.1046/j.1365-294x.2000.00935.x |pmid=10849292 |year=2000 |last1=Anttila |first1=C. K. |last2=King |first2=R. A. |last3=Ferris |first3=C. |last4=Ayres |first4=D. R. |last5=Strong |first5=D. R. |bibcode=2000MolEc...9..765A |s2cid=32865913}}</ref> Reduction in fitness is not always apparent from morphological observations alone. Some degree of gene flow is normal, and preserves constellations of genes and genotypes.<ref name="rhymer"/><ref>{{Cite book |url=http://www.rirdc.gov.au/reports/AFT/01-114.pdf |title=Genetic Pollution from Farm Forestry using eucalypt species and hybrids; A report for the RIRDC/L&WA/FWPRDC]; Joint Venture Agroforestry Program; by Brad M. Potts, Robert C. Barbour, Andrew B. Hingston; September 2001; RIRDC Publication No 01/114; RIRDC Project No CPF – 3A; |year=2001 |isbn=978-0-642-58336-9 |publisher=Australian Government, Rural Industrial Research and Development Corporation |access-date=April 22, 2017 |archive-url=https://web.archive.org/web/20040102175403/http://www.rirdc.gov.au/reports/AFT/01-114.pdf |archive-date=January 2, 2004 }}</ref> An example of this is the interbreeding of migrating coyotes (''Canis latrans'') with the critically endangered red wolf (''Canis rufus''), in areas of eastern North Carolina where the red wolf was reintroduced, reducing wolf numbers.<ref>{{cite journal |doi=10.1016/j.biocon.2015.01.013 |title=Factors influencing red wolf–coyote hybridization in eastern North Carolina, USA |journal=Biological Conservation |volume=184 |pages=108–116 |year=2015 |last1=Bohling |first1=Justin H. |last2=Waits |first2=Lisette P.|bibcode=2015BCons.184..108B }}</ref>
=== Environmental === In South Africa's Cape Town region, analysis demonstrated that the restoration of priority source water sub-catchments through the removal of thirsty alien plant invasions (such as Australian acacias, pines, eucalyptus, and Australian black wattle) would generate expected annual water gains of 50 billion liters within 5 years compared to the business-as-usual scenario (which is important as Cape Town experiences significant water scarcity). This is the equivalent to one-sixth of the city's current supply needs. These annual gains will double within 30 years. The catchment restoration is significantly more cost-effective then other water augmentation solutions (1/10 the unit cost of alternative options).<ref>{{Cite web |title=Cape Town is Facing Day Zero |url=https://www.nature.org/en-us/about-us/where-we-work/africa/stories-in-africa/cape-town-faces--day-zero-/ |access-date=2023-11-06 |website=The Nature Conservancy}}</ref> A water fund has been established, and these exotic species are being eradicated.<ref>{{Cite web |url=https://www.nature.org/content/dam/tnc/nature/en/documents/GCTWF-summary-11.14.18.pdf |title=Greater cape town water fund |access-date=November 16, 2020 |archive-date=February 28, 2021 |archive-url=https://web.archive.org/web/20210228175854/https://www.nature.org/content/dam/tnc/nature/en/documents/GCTWF-summary-11.14.18.pdf |url-status=live}}</ref>
=== Human health === Invasive species can affect human health. With the alteration in ecosystem functionality (due to homogenization of biota communities), invasive species have resulted in negative effects on human well-being, which includes reduced resource availability, unrestrained spread of human diseases, recreational and educational activities, and tourism.<ref name=":8">{{cite journal |last1=Mazza |first1=G. |last2=Tricarico |first2=E. |last3=Genovesi |first3=P. |last4=Gherardi |first4=F. |title=Biological invaders are threats to human health: an overview |journal=Ethology Ecology & Evolution |volume=26 |issue=2–3 |date=2013-12-19 |doi=10.1080/03949370.2013.863225 |pages=112–129|s2cid=58888740 }}</ref><ref name=":22">{{Cite journal |last1=Pyšek |first1=P. |last2=Richardson |first2=D.M. |date=2010 |title=Invasive Species, Environmental Change and Management, and Health |journal=Annual Review of Environment and Resources |volume=35 |issue=1 |pages=25–55 |doi=10.1146/annurev-environ-033009-095548 |doi-access=free|hdl=11104/0189317 |hdl-access=free }}</ref> Alien species have caused diseases including human immunodeficiency virus (HIV), monkey pox, and severe acute respiratory syndrome (SARS).<ref name=":22"/>
Invasive species and accompanying control efforts can have long term public health implications. For instance, pesticides applied to treat a particular pest species could pollute soil and surface water.<ref name="pimental"/> Encroachment of humans into previously remote ecosystems has exposed exotic diseases such as HIV to the wider population.<ref name="pimental"/> Introduced birds (e.g. pigeons), rodents, and insects (e.g. mosquito, flea, louse and tsetse fly pests) can serve as vectors and reservoirs of human afflictions. Throughout recorded history, epidemics of human diseases, such as malaria, yellow fever, typhus, and bubonic plague, spread via these vectors.<ref name="elton"/> A recent example of an introduced disease is the spread of the West Nile virus, which killed humans, birds, mammals, and reptiles.<ref>{{cite journal |last1=Lanciotti |first1=R. S. |last2=Roehrig |first2=J. T. |last3=Deubel |first3=V. |last4=Smith |first4=J. |last5=Parker |first5=M. |last6=Steele |first6=K. |last7=Crise |first7=B. |last8=Volpe |first8=K. E. |last9=Crabtree |first9=M. B. |last10=Scherret |first10=J. H. |last11=Hall |first11=R. A. |last12=MacKenzie |first12=J. S. |last13=Cropp |first13=C. B. |last14=Panigrahy |first14=B. |last15=Ostlund |first15=E. |date=17 December 1999 |title=Origin of the West Nile Virus Responsible for an Outbreak of Encephalitis in the Northeastern United States |journal=Science |volume=286 |issue=5448 |pages=2333–2337 |doi=10.1126/science.286.5448.2333 |pmid=10600742 |last16=Schmitt |first16=B. |last17=Malkinson |first17=M. |last18=Banet |first18=C. |last19=Weissman |first19=J. |last20=Komar |first20=N. |last21=Savage |first21=H. M. |last22=Stone |first22=W. |last23=McNamara |first23=T. |last24=Gubler |first24=D. J. |display-authors=6}}</ref> The introduced Chinese mitten crabs (''Eriocheir sinensis'') are carriers of Asian lung fluke.{{r|pnwaquaticinv}} Waterborne disease agents, such as cholera bacteria (''Vibrio cholerae''), and causative agents of harmful algal blooms are often transported via ballast water.<ref>{{cite journal |last=Hallegraeff |first=G.M. |year=1998 |title=Transport of toxic dinoflagellates via ships' ballast water: Bioeconomic risk assessment and efficacy of possible ballast water management strategies |journal=Marine Ecology Progress Series |volume=168 |pages=297–309 |bibcode=1998MEPS..168..297H |doi=10.3354/meps168297 |doi-access=free}}</ref>
=== Economic === [[File:Pasig River Intramuros Escolta Water Hyacinths.jpg|thumb|Invasive water hyacinths (''Pontederia crassipes'') clog the Pasig River in Manila, Philippines in October 2020.<ref>{{cite news |last1=Dela Cruz |first1=Raymond Carl |title=Water hyacinths ground Pasig River Ferry ops |url=https://www.pna.gov.ph/articles/1117832 |access-date=10 August 2024 |work=Philippine News Agency |date=October 7, 2020 |archive-url=https://web.archive.org/web/20231028150214/https://www.pna.gov.ph/articles/1117832 |archive-date=October 28, 2023}}</ref>]]
Globally, invasive species management and control are substantial economic burdens, with expenditures reaching approximately $1.4 trillion annually.{{r|amstutz2018}} The economic impact of invasive species alone was estimated to exceed $423 billion annually as of 2019. This cost has exhibited a significant increase, quadrupling every decade since 1970, underscoring the escalating financial implications of these biological invasions.<ref>{{Cite web |last=Environment |first=U. N. |date=2023-09-04 |title=Invasive Alien Species Report |url=http://www.unep.org/resources/report/invasive-alien-species-report |access-date=2024-05-29 |website=www.unep.org |language=en}}</ref>
Invasive species contribute to ecological degradation, altering ecosystem functionality and reducing the services ecosystems provide. This necessitates additional expenditures to control the spread of biological invasions, mitigate further impacts, and restore affected ecosystems. For example, the damage caused by 79 invasive species between 1906 and 1991 in the United States has been estimated at US$120 billion. Similarly, in China, invasive species have been reported to reduce the country's gross domestic product (GDP) by 1.36% per year.<ref name=":22" /><ref>{{cite journal |last1=Xu |first1=Haigen |last2=Ding |first2=Hui |last3=Li |first3=Mingyan |last4=Qiang |first4=Sheng |last5=Guo |first5=Jianying |last6=Han |first6=Zhengmin |last7=Huang |first7=Zongguo |last8=Sun |first8=Hongying |last9=He |first9=Shunping |last10=Wu |first10=Hairong |last11=Wan |first11=Fanghao |date=2006 |title=The distribution and economic losses of alien species invasion to China |journal=Biological Invasions |volume=8 |issue=7 |pages=1495–1500 |bibcode=2006BiInv...8.1495X |doi=10.1007/s10530-005-5841-2 |s2cid=25890246}}</ref>
The management of biological invasions can be costly. In Australia, for instance, the expense to monitor, control, manage, and research invasive weed species is approximately AU$116.4 million per year, with costs directed solely to central and local governments.<ref name=":22" />
While, in some cases, invasive species may offer economic benefits—such as the potential for commercial forestry from invasive trees—these benefits are generally overshadowed by the substantial costs associated with biological invasions.<ref name="potential" /> In most cases, the economic returns from invasive species are far less than the costs they impose.<ref name=":32">{{cite journal |last1=Molnar |first1=Jennifer L |last2=Gamboa |first2=Rebecca L |last3=Revenga |first3=Carmen |last4=Spalding |first4=Mark D |date=2008 |title=Assessing the global threat of invasive species to marine biodiversity |journal=Frontiers in Ecology and the Environment |volume=6 |issue=9 |pages=485–492 |bibcode=2008FrEE....6..485M |doi=10.1890/070064 }}</ref><ref name=":22" />
==== United States ==== In the Great Lakes region the sea lamprey (''Petromyzon marinus'') is an invasive species. In its original habitat, it had co-evolved as a parasite that did not kill its host. However, in the Great Lakes region, it acts as a predator and can consume up to 40 pounds of fish in its 12–18 month feeding period.<ref name=":0">{{cite web |url=http://www.glfc.org/sea-lamprey.php |title=Great Lakes Fishery Commission – Sea Lamprey |website=www.glfc.org |access-date=October 24, 2017 |archive-date=October 25, 2017 |archive-url=https://web.archive.org/web/20171025023343/http://www.glfc.org/sea-lamprey.php |url-status=live}}</ref> Sea lampreys prey on all types of large fish such as lake trout (''Salvelinus namaycush'') and salmon. The sea lampreys' destructive effects on large fish negatively affect the fishing industry and have helped cause the collapse of the population of some species.<ref name=":0"/>
Economic costs from invasive species can be separated into direct costs through production loss in agriculture and forestry, and management costs. Estimated damage and control costs of invasive species in the U.S. amount to more than $138 billion annually.<ref name="pimental">{{cite journal |last1=Pimentel |first1=D. |last2=R. |first2=Zuniga |last3=Morrison |first3=D |year=2005 |title=Update on the environmental and economic costs associated with alien-invasive species in the United States |journal=Ecological Economics |volume=52 |issue=3 |pages=273–288 |doi=10.1016/j.ecolecon.2004.10.002 |bibcode=2005EcoEc..52..273P }}</ref> Economic losses can occur through loss of recreational and tourism revenues.<ref name="simb">{{cite journal |last=Simberloff |first=D. |year=2001 |jstor=41717176 |title=Biological invasions – How are they affecting us, and what can we do about them? |journal=Western North American Naturalist |volume=61 |issue=3 |pages=308–315}}</ref> When economic costs of invasions are calculated as production loss and management costs, they are low because they do not consider environmental damage; if monetary values were assigned to the extinction of species, loss in biodiversity, and loss of ecosystem services, costs from impacts of invasive species would drastically increase.<ref name="pimental"/> It is often argued that the key to invasive species management is early detection and rapid response.<ref>{{Cite book |url=https://www.doi.gov/sites/doi.gov/files/migrated/invasivespecies/upload/2008-2012-National-Invasive-Species-Management-Plan.pdf |title=2008–2012 National Invasive Species Management Plan. |publisher=National Invasive Species Council, Department of the Interior |year=2008 |location=Washington, DC. |archive-url=https://web.archive.org/web/20150929011911/https://www.doi.gov/sites/doi.gov/files/migrated/invasivespecies/upload/2008-2012-National-Invasive-Species-Management-Plan.pdf |archive-date=29 September 2015 |url-status=live}}</ref> However, early response only helps when the invasive species is not frequently reintroduced into the managed area, and the cost of response is affordable.<ref>{{Cite journal |last1=Holden |first1=Matthew H. |last2=Nyrop |first2=Jan P. |last3=Ellner |first3=Stephen P. |date=June 1, 2016 |title=The economic benefit of time-varying surveillance effort for invasive species management |journal=Journal of Applied Ecology |volume=53 |issue=3 |pages=712–721 |doi=10.1111/1365-2664.12617 |doi-access=free|bibcode=2016JApEc..53..712H }}</ref>
[[File:Parthenium smothering native flora in Biodiversity Rich Forest.jpg |thumb |''Parthenium hysterophorus'', Achanakmar Tiger Reserve]]
Weeds reduce yield in agriculture. Many weeds are accidental introductions that accompany imports of commercial seeds and plants. Introduced weeds in pastures compete with native forage plants, threaten young cattle (e.g., leafy spurge, ''Euphorbia virgata'') or are unpalatable because of thorns and spines (e.g., yellow starthistle, ''Centaurea solstitialis''). Forage loss from invasive weeds on pastures amounts to nearly US$1 billion in the U.S.<ref name="pimental"/> A decline in pollinator services and loss of fruit production has been caused by honey bees (''Apis mellifera'') infected by the invasive varroa mite (''Varroa destructor''). Introduced rats (''Rattus rattus'' and ''R. norvegicus'') have become serious pests<ref>{{cite journal |last1=Gougherty |first1=Andrew V. |last2=Davies |first2=T. Jonathan |title=Towards a phylogenetic ecology of plant pests and pathogens |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |date=8 November 2021 |volume=376 |issue=1837 |article-number=20200359 |doi=10.1098/rstb.2020.0359 |pmid=34538142 |pmc=8450633 }}</ref> on farms, destroying stored grains.<ref name="pimental"/> The introduction of leaf miner flies (Agromyzidae), including the American serpentine leaf miner (''Liriomyza trifolii''), to California has caused losses in California's floriculture industry, as the larvae of these invasive species feed on ornamental plants.<ref>{{cite web |url=http://entnemdept.ufl.edu/creatures/veg/leaf/a_serpentine_leafminer.htm |title=American serpentine leafminer – Liriomyza trifolii (Burgess) |website=entnemdept.ufl.edu |access-date=November 20, 2019 |archive-date=November 25, 2019 |archive-url=https://web.archive.org/web/20191125043634/http://entnemdept.ufl.edu/Creatures/veg/leaf/a_serpentine_leafminer.htm |url-status=live}}</ref>
Invasive plant pathogens and insect vectors for plant diseases can suppress agricultural yields and harm nursery stock. Citrus greening is a bacterial disease vectored by the invasive Asian citrus psyllid (''Diaphorina citri''). As a result, citrus is under quarantine and highly regulated in areas where the psyllid has been found.<ref name="r2">{{Cite web |title=Citrus Greening |url=http://www.clemson.edu/public/regulatory/plant_industry/invasive_exotic_programs/Pest%20Alerts/citrus_greening.html |archive-url=https://archive.today/20130616000111/http://www.clemson.edu/public/regulatory/plant_industry/invasive_exotic_programs/Pest%20Alerts/citrus_greening.html |archive-date=16 June 2013 |website=Clemson Public Service Activities - The Department of Plant Industry}}</ref>
Invasive species can impact outdoor recreation, such as fishing, hunting, hiking, wildlife viewing, and water-based activities. They can damage environmental services including water quality, plant and animal diversity, and species abundance, though the extent of this is under-researched.<ref>{{cite journal |last1=Eiswerth |first1=M.E. |year=2005 |title=Input-output modeling, outdoor recreation, and the economic impacts of weeds |journal=Weed Science |volume=53 |pages=130–137 |doi=10.1614/WS-04-022R |last2=Darden |first2=Tim D. |last3=Johnson |first3=Wayne S. |last4=Agapoff |first4=Jeanmarie |last5=Harris |first5=Thomas R. |issue=1 |bibcode=2005WeedS..53..130E |s2cid=85608607 }}</ref> Eurasian watermilfoil (''Myriophyllum spicatum'') in parts of the US, fills lakes with plants, complicating fishing and boating.<ref>{{Cite web |date=1 November 2006 |title=Eurasian Watermilfoil in the Great Lakes Region |url=http://great-lakes.net/envt/flora-fauna/invasive/milfoil.html |archive-url=https://web.archive.org/web/20080725034837/http://great-lakes.net/envt/flora-fauna/invasive/milfoil.html#overview |archive-date=25 July 2008 |website=Great Lakes Information Network}}</ref> The loud call of the introduced common coqui (''Eleutherodactylus coqui'') depresses real estate values in affected neighborhoods of Hawaii.<ref>{{cite book |url=http://www.aphis.usda.gov/wildlife_damage/nwrc/symposia/invasive_symposium/content/Sin157_167_MVIS.pdf |last1=Sin |first1=Hans |last2=Radford |first2=Adam |year=2007 |chapter =Coqui frog research and management efforts in Hawaii |title=Managing Vertebrate Invasive Species: Proceedings of an International Symposium (G. W. Witmer, W. C. Pitt, K. A. Fagerstone, Eds) |publisher=USDA/APHIS/WS, National Wildlife Research Center |location=Fort Collins, Colorado |access-date=June 26, 2013 |archive-date=May 25, 2017 |archive-url=https://web.archive.org/web/20170525103353/http://www.aphis.usda.gov/wildlife_damage/nwrc/symposia/invasive_symposium/content/Sin157_167_MVIS.pdf}}</ref> The large webs of the orb-weaving spider (''Zygiella x-notata''), invasive in California, disrupts garden work.<ref>{{Cite web |title=Spider Invaders |url=https://www.kqed.org/quest/9595/spider-invaders |access-date=2020-12-13 |website=KQED |date=October 18, 2010 |archive-date=November 5, 2020 |archive-url=https://web.archive.org/web/20201105170805/https://www.kqed.org/quest/9595/spider-invaders |url-status=live}}</ref>
==== Europe ==== The overall economic cost of invasive alien species in Europe between 1960 and 2020 has been estimated at around US$140 billion (including potential costs that may or may not have actually materialized) or US$78 billion (only including observed costs known to have materialized). These estimates are very conservative. Models based on these data suggest a true ''annual'' cost of around US$140 billion in 2020.<ref>{{Cite journal |last1=Haubrock |first1=Phillip J. |last2=Turbelin |first2=Anna J. |last3=Cuthbert |first3=Ross N. |last4=Novoa |first4=Ana |last5=Taylor |first5=Nigel G. |last6=Angulo |first6=Elena |last7=Ballesteros-Mejia |first7=Liliana |last8=Bodey |first8=Thomas W. |last9=Capinha |first9=César |last10=Diagne |first10=Christophe |last11=Essl |first11=Franz |last12=Golivets |first12=Marina |last13=Kirichenko |first13=Natalia |last14=Kourantidou |first14=Melina |last15=Leroy |first15=Boris |last16=Renault |first16=David |last17=Verbrugge |first17=Laura |last18=Courchamp |first18=Franck |display-authors=6 |title=Economic costs of invasive alien species across Europe |year=2021 |journal=Neobiota |volume=67 |pages=153–190 |hdl=10138/333320 |s2cid=237460752 |hdl-access=free |doi=10.3897/neobiota.67.58196 |bibcode=2021NeoBi..67..153H |doi-access=free }}</ref>
{{visible anchor |Italy |'''Italy'''}}is one of the most invaded countries in Europe, with an estimate of more than 3,000 alien species. The impacts of invasive alien species on the economy has been wide-ranging, from management costs, to loss of crops, to infrastructure damage. The overall economic cost of invasions to Italy between 1990 and 2020 was estimated at US$819.76 million (EUR€704.78 million). However, only 15 recorded species have more reliably estimated costs, hence the actual cost may be much larger than the aforementioned sum.<ref>{{cite journal |last1=Haubrock |first1=Phillip J. |last2=Cuthbert |first2=Ross N. |last3=Tricarico |first3=Elena |last4=Diagne |first4=Christophe |last5=Courchamp |first5=Franck |last6=Gozlan |first6=Rodolphe E. |title=The recorded economic costs of alien invasive species in Italy |journal=NeoBiota |date=29 July 2021 |volume=67 |pages=247–266 |doi=10.3897/neobiota.67.57747 |bibcode=2021NeoBi..67..247H |s2cid=238819772 |url=https://hal.archives-ouvertes.fr/hal-03410329/file/CostsinItaly.pdf |doi-access=free |hdl=2158/1262519 }}</ref>
{{visible anchor |France |'''France'''}}has an estimated minimum of 2,750 introduced and invasive alien species. Renault et al. (2021) obtained 1,583 cost records for 98 invasive alien species and found that they caused a conservative total cost between US$1.2 billion and 11.5 billion over the period 1993–2018. This study extrapolated costs for species invading France, but for which costs were reported only in other countries but not in France, which yielded an additional cost ranging from US$151 million to $3.03 billion. Damage costs were nearly eight times higher than management expenditure. Insects, and in particular the Asian tiger mosquito (''Aedes albopictus'') and the yellow fever mosquito (''A. aegypti''), created the highest economic costs, followed by non-graminoid terrestrial flowering and aquatic plants (''Ambrosia artemisiifolia'', ''Ludwigia'' sp. and ''Lagarosiphon major''). Over 90% of alien species currently recorded in France had no costs reported in the literature, resulting in high biases in taxonomic, regional and activity sector coverages. However, the lack of reports does not mean there are no negative consequences or costs.<ref>{{cite journal |last1=Renault |first1=David |last2=Manfrini |first2=Eléna |last3=Leroy |first3=Boris |last4=Diagne |first4=Christophe |last5=Ballesteros-Mejia |first5=Liliana |last6=Angulo |first6=Elena |last7=Courchamp |first7=Franck |title=Biological invasions in France: Alarming costs and even more alarming knowledge gaps |journal=NeoBiota |date=29 July 2021 |volume=67 |pages=191–224 |doi=10.3897/neobiota.67.59134 |bibcode=2021NeoBi..67..191R |s2cid=237462170 |doi-access=free }}</ref>
==Favorable effects==
{{see also|Introduced species}}
The consensus of the scientific community is that the effects of invasive species on biodiversity are primarily negative, despite the potential for some favorable impacts.<ref name="doubtingthomas">{{cite journal |last=Halley |first=John |date=2019 |title=Doubting Thomas and the Love of Invasive Species |department=Book Review |journal=Conservation Biology |volume=33 |issue=6 |pages=1451–1453 |bibcode=2019ConBi..33.1451H |doi=10.1111/cobi.13413 |doi-access=free}}</ref><ref>{{Cite journal |last=Cadotte |first=Marc W. |date=2015-10-01 |title=Taming the 'New Wild': tackling the good and the bad with invasive species |url=https://doi.org/10.1007/s10530-015-0933-0 |journal=Biological Invasions |language=en |volume=17 |issue=10 |pages=3067–3072 |doi=10.1007/s10530-015-0933-0 |issn=1573-1464|url-access=subscription }}</ref><ref name="potential" /> The entomologist Chris D. Thomas argues that most introduced species are neutral or beneficial with respect to other species<ref>{{cite book |last=Thomas |first=Chris |author-link=Chris D. Thomas |title=Inheritors of the Earth: How Nature Is Thriving in an Age of Extinction |publisher=PublicAffairs |year=2017 |isbn=978-1-61039-727-8 |pages=}}</ref> but this is a minority opinion.<ref>{{Cite web |last=Jr |first=Tom Zeller |date=2017-05-30 |title=The Fascist History of De-Extinction |url=https://undark.org/2017/05/30/nazis-aurochs-deextinction-mammoth/ |access-date=2025-04-27 |website=Undark Magazine |language=en-US}}</ref><ref name=":5">{{Cite journal |last1=Fletcher |first1=Rebecca A. |last2=Brooks |first2=Rachel K. |last3=Lakoba |first3=Vasiliy T. |last4=Sharma |first4=Gourav |last5=Heminger |first5=Ariel R. |last6=Dickinson |first6=Christopher C. |last7=Barney |first7=Jacob N. |date=2019 |title=Invasive plants negatively impact native, but not exotic, animals |url=https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.14752 |journal=Global Change Biology |language=en |volume=25 |issue=11 |pages=3694–3705 |doi=10.1111/gcb.14752 |pmid=31389131 |bibcode=2019GCBio..25.3694F |issn=1365-2486|url-access=subscription }}</ref>
Some invasive species can provide a suitable habitat or food source for other organisms. In areas where a native has become extinct or reached a point that it cannot be restored, non-native species can fill their role despite having negative impacts elsewhere. For instance, in the US, the endangered southwestern willow flycatcher (''Empidonax traillii'') mainly nests in the non-native tamarisk.<ref name="potential" /> The introduced mesquite (''Neltuma juliflora'') is an aggressive invasive species in India, but is the preferred nesting site of native waterbirds in small cities like Udaipur in Rajasthan.<ref>{{cite journal |last1=Mehta |first1=Kanishka |last2=Koli |first2=Vijay K. |last3=Kittur |first3=Swati |last4=Sundar |first4=K. S. Gopi |title=Can you nest where you roost? Waterbirds use different sites but similar cues to locate roosting and breeding sites in a small Indian city |journal=Urban Ecosystems |date=21 February 2024 |volume=27 |issue=4 |pages=1279–1290 |doi=10.1007/s11252-023-01454-5 |bibcode=2024UrbEc..27.1279M |s2cid=267973120 }}</ref> Similarly, Ridgway's rail (''Rallus obsoletus'') has adapted to the invasive hybrid of ''Spartina alterniflora'' and ''Spartina foliosa'', which offers better cover and nesting habitat.<ref>{{Cite report |url=https://spartina.org/project_documents/revegetation_program/CLRA%20Report%202012.pdf |title=Clapper Rail Surveys for the San Francisco Estuary Invasive Spartina Project |last=McBroom |first=Jen |date=December 2012 |publisher=State Coastal Conservancy |location=Oakland, California |access-date=30 November 2020 |archive-url=https://web.archive.org/web/20170305070303/http://spartina.org/project_documents/revegetation_program/CLRA%20Report%202012.pdf |archive-date=5 March 2017 |url-status=live}}</ref> In Australia, saltwater crocodiles (''Crocodylus porosus''), which had become endangered, have recovered by feeding on introduced feral pigs (''Sus domesticus'').<ref>{{cite news |last1=Ham |first1=Anthony |title=Pigs to the Rescue: An Invasive Species Helped Save Australia's Crocodiles |url=https://www.nytimes.com/2022/08/15/science/invasive-species-pigs-crocodiles.html |work=The New York Times |date=15 August 2022 }}</ref>
Non-native species can provide ecosystem services, functioning as biocontrol agents to limit the effects of invasive agricultural pests.<ref name=potential>{{cite journal |last1=Schlaepfer |first1=Martin A. |last2=Sax |first2=Dov F. |last3=Olden |first3=Julian D. |title=The Potential Conservation Value of Non-Native Species: Conservation Value of Non-Native Species |journal=Conservation Biology |date=June 2011 |volume=25 |issue=3 |pages=428–437 |doi=10.1111/j.1523-1739.2010.01646.x |pmid=21342267 |s2cid=2947682 }}</ref> Some species have invaded an area so long ago that they are considered to have naturalised there. In the US, the endangered Taylor's checkerspot butterfly (''Euphydryas editha taylori'') has come to rely on invasive ribwort plantain (''Plantago lanceolata'') as the food plant for its caterpillars.<ref>Thomas, Chris D.. Inheritors of the Earth (p. 148). PublicAffairs. Kindle Edition.</ref>
Some invasions offer potential commercial benefits. For instance, silver carp (''Hypophthalmichthys molitrix'') and common carp (''Cyprinus carpio'') can be harvested for human food and exported to markets already familiar with the product, or processed into pet foods or mink feed. Water hyacinth (''Pontederia crassipes'') can be turned into fuel by methane digesters,<ref name=wolv>{{cite journal|doi=10.1007/BF02858689|title=Energy from vascular plant wastewater treatment systems|journal=Economic Botany|volume=35|issue=2|pages=224–232 |year=1981 |last1=Wolverton |first1=B. C.|last2=McDonald|first2=Rebecca C.|bibcode=1981EcBot..35..224W |s2cid=24217507}}. Cited in Duke, J. (1983) [http://www.hort.purdue.edu/newcrop/duke_energy/dukeindex.html ''Handbook of Energy Crops''] {{Webarchive|url=https://web.archive.org/web/20130212071515/http://www.hort.purdue.edu/newcrop/duke_energy/dukeindex.html |date=February 12, 2013 }}. Purdue University, Center for New Crops & Plants Products</ref> and other invasive plants can be harvested and utilized as a source of bioenergy.<ref>{{cite journal |title=Biomass of invasive plant species as a potential feedstock for bioenergy production |first1=Koenraad |last1=Van Meerbeek |first2=Lise |last2=Appels |first3=Raf |last3=Dewil|first4=Annelies|last4=Calmeyn|first5=Pieter|last5=Lemmens |first6=Bart |last6=Muys |first7=Martin |last7=Hermy |date=May 1, 2015 |journal=Biofuels, Bioproducts and Biorefining |volume=9 |issue=3 |pages=273–282 |doi=10.1002/bbb.1539 |s2cid=83918875 }}</ref>
== Control, eradication, and study == {{owidslider |start = 2022 |list = Template:OWID/Budget to manage invasive alien species#gallery |location = commons |caption = |title = |language = |file = link=|thumb|upright=1.6|right|Budget to manage invasive alien species |startingView = World }}
Humans are versatile enough to remediate adverse effects of species invasions.<ref>{{cite book |isbn=978-0-8166-9329-0 |title=Making Other Worlds Possible: Performing Diverse Economies |last1=Roelvink |first1=Gerda |last2=Martin |first2=Kevin St |last3=Gibson-Graham |first3=J. K. |year=2015 |publisher=University of Minnesota Press }}</ref><ref name="root"/><ref name="Garrido">{{cite journal |last1=Garrido-Pérez |first1=Edgardo I. |last2=Tella Ruiz |first2=David |date=2016 |title=Homo sapiens (Primates: Hominidae): ¿una especie invasora o aún peor? Un reto para potenciar la Ecología y la Biología de la conservación |url=https://www.researchgate.net/publication/317083729 |journal=Puente Biológico |volume=8 |pages=43–55}} <br/>Translated as {{cite web |last1=Garrido-Pérez |first1=Edgardo I. |last2=Tella Ruiz |first2=David |date=2016 |title=''Homo sapiens'' (Primates: Hominidae): an invasive species or even worse? A challenge for strengthening ecology and conservation biology |via=ResearchGate |url=https://www.researchgate.net/publication/319234497 |access-date=August 19, 2020 |archive-date=June 11, 2022 |archive-url=https://web.archive.org/web/20220611120711/https://www.researchgate.net/publication/319234497_Homo_sapiens_Primates_Hominidae_an_invasive_species_or_even_worse_A_challenge_for_strengthening_ecology_and_conservation_biology_Translated_from_Spanish |url-status=live }}</ref> The public is motivated by invasive species that impact their local area.<ref>{{cite web |url=http://depts.washington.edu/oldenlab/wordpress/wp-content/uploads/2013/02/Invasive-Species-Survey_Hakam_August2016.pdf#page=8 |title=Invasive Species: Public Awareness and Education |last=Hakam |first=Lara |date=February 2013 |website=University of Washington |access-date=September 30, 2020 |archive-date=November 5, 2021 |archive-url=https://web.archive.org/web/20211105154129/http://depts.washington.edu/oldenlab/wordpress/wp-content/uploads/2013/02/Invasive-Species-Survey_Hakam_August2016.pdf#page=8 |url-status=live }}</ref> The control of alien species populations is important in the conservation of biodiversity in natural ecosystem. Previous studies and control programs that target invasives are the most effective during the earlier phases of invasion, such as eliminating founder population quickly before the introduced species can spread.<ref>{{Cite book |last=Williams |first=Peter A. |url=https://www.doc.govt.nz/Documents/science-and-technical/csp07-entire.pdf |title=Ecology and Management of Invasive Weeds |date=November 1997 |publisher=Dept. of Conservation, Wellington, N.Z. |year=1997 |isbn=0-478-01956-4 |pages=22}}</ref> One of the most promising methods for controlling alien species is genetic.<ref>{{cite journal |last1=Makhrov |first1=A. A. |last2=Karabanov |first2=D. P. |last3=Koduhova |first3=Yu. V. |title=Genetic methods for the control of alien species |journal=Russian Journal of Biological Invasions |date=July 2014 |volume=5 |issue=3 |pages=194–202 |doi=10.1134/S2075111714030096 |bibcode=2014RuJBI...5..194M |s2cid=256073288 }}</ref>
=== <span class="anchor" id="Cargo inspection"></span><span class="anchor" id="Quarantine"></span> Cargo inspection and quarantine === The original motivation was to protect against agricultural pests while still allowing the export of agricultural products. In 1994 the first set of global standards were agreed to, including the Agreement on the Application of Sanitary and Phytosanitary Measures (SPS Agreement). These are overseen by the World Trade Organization. The International Maritime Organization oversees the International Convention for the Control and Management of Ships' Ballast Water and Sediments (the Ballast Water Management Convention). Although primarily targeted at other, more general environmental concerns, the Convention on Biological Diversity does specify some steps that its members should take to control invasive species. The CBD is the most significant international agreement on the environmental consequences of invasive species; most such measures are voluntary and unspecific.<ref name="Lodge-et-al-2016">{{cite journal |last1=Lodge |first1=David M. |last2=Simonin |first2=Paul W. |last3=Burgiel |first3=Stanley W. |last4=Keller |first4=Reuben P. |last5=Bossenbroek |first5=Jonathan M. |last6=Jerde |first6=Christopher L. |last7=Kramer |first7=Andrew M. |last8=Rutherford |first8=Edward S. |last9=Barnes |first9=Matthew A. |last10=Wittmann |first10=Marion E. |last11=Chadderton |first11=W. Lindsay |last12=Apriesnig |first12=Jenny L. |display-authors=6 |title=Risk Analysis and Bioeconomics of Invasive Species to Inform Policy and Management |journal=Annual Review of Environment and Resources |date=1 November 2016 |volume=41 |issue=1 |pages=453–488 |doi=10.1146/annurev-environ-110615-085532 |doi-access=free }}</ref>
=== Slowing spread === Firefighters are becoming responsible for decontamination of their own equipment, public water equipment, and private water equipment, due to the risk of aquatic invasive species transfer.<ref name="Sea-Grant-NY">{{cite web |url=http://www.slocounty.ca.gov/Departments/Public-Works/Forms-Documents/Water-Resources/Invasive-Mussels/NY-Fire-Control-Equipment.pdf |title=Zebra Mussels and Fire Control Equipment |last=O'Neill, Jr. |first=Charles R. |date=2002 |publisher=Sea Grant |place=SUNY College at Brockport |access-date=May 23, 2021 |archive-date=November 5, 2021 |archive-url=https://web.archive.org/web/20211105212840/https://www.slocounty.ca.gov/Departments/Public-Works/Forms-Documents/Water-Resources/Invasive-Mussels/NY-Fire-Control-Equipment.pdf |url-status=live }}</ref> In the United States this is especially a concern for wildland firefighters because quagga (''Dreissena bugensis'') and zebra (''Dreissena polymorpha'') mussel invasion and wildfires co-occur in the American West.<ref name="wildland-firefight-NPR">{{cite web |last=Ouellet |first=Nicky |date=2017-08-23 |title=Wildland Firefighters Try to Combat Spread of Invasive Species |url=http://www.npr.org/2017/08/23/545617315/wildland-firefighters-try-to-combat-spread-of-invasive-species |access-date=2021-05-23 |archive-date=June 13, 2021 |archive-url=https://web.archive.org/web/20210613005731/https://www.npr.org/2017/08/23/545617315/wildland-firefighters-try-to-combat-spread-of-invasive-species |url-status=live |publisher=NPR |work=All Things Considered }}</ref><ref name="Montana-firefight-MtPR">{{cite news |last=Ouellet |first=Nicky |title=How Montana Is Fighting Invasive Hitchhikers On Firefighting Aircraft |website=Montana Public Radio |date=2017-07-27 |url=http://www.mtpr.org/post/how-montana-fighting-invasive-hitchhikers-firefighting-aircraft |access-date=2021-05-23 |archive-date=May 23, 2021 |archive-url=https://web.archive.org/web/20210523185157/https://www.mtpr.org/post/how-montana-fighting-invasive-hitchhikers-firefighting-aircraft |url-status=live }}</ref><ref name="NWCG">{{cite web |url=http://www.nwcg.gov/sites/default/files/publications/pms444.pdf |title=Guide to Preventing Aquatic Invasive Species Transport by Wildland Fire Operations |date=January 2017 |author=National Wildfire Coordinating Group |access-date=May 23, 2021 |archive-date=April 19, 2021 |archive-url=https://web.archive.org/web/20210419034257/https://www.nwcg.gov/sites/default/files/publications/pms444.pdf |url-status=live }}</ref><ref name="Mt-DNRC">{{cite web |url=http://dnrc.mt.gov/divisions/forestry/docs/fire-and-aviation/2018-nrcg-how-to-guide_aquatic-invasive-species_final.pdf |date=June 11, 2018 |title=Decontaminating Firefighting Equipment to Reduce the Spread of Aquatic Invasive Species |author=National Wildfire Coordinating Group |access-date=May 23, 2021 |archive-date=April 28, 2021 |archive-url=https://web.archive.org/web/20210428072947/http://dnrc.mt.gov/divisions/forestry/docs/fire-and-aviation/2018-nrcg-how-to-guide_aquatic-invasive-species_final.pdf |url-status=live }}</ref>
=== Reestablishing species === [[File:Takahe and chick.jpg|thumb|Takahē (''Porphyrio hochstetteri'') have bred after translocation to restored islands, like these on Kapiti Island, off New Zealand.]]
Island restoration deals with the eradication of invasive species on islands. A 2019 study suggests that if eradications of invasive animals were conducted on just 169 islands, the survival prospects of 9.4% of the Earth's most highly threatened terrestrial insular vertebrates would be improved.<ref>{{cite journal |last1=Holmes |first1=Nick |date=March 27, 2019 |title=Globally important islands where eradicating invasive mammals will benefit highly threatened vertebrates |journal=PLOS ONE |volume=14 |issue=3 |article-number=e0212128 |doi=10.1371/journal.pone.0212128 |pmid=30917126 |pmc=6436766 |bibcode=2019PLoSO..1412128H |doi-access=free }}</ref>
Invasive vertebrate eradication on islands aligns with United Nations Sustainable Development Goal 15 and associated targets.<ref name="de WitZilliacus2020">{{cite journal |last1=de Wit |first1=Luz A. |last2=Zilliacus |first2=Kelly M. |last3=Quadri |first3=Paulo |last4=Will |first4=David |last5=Grima |first5=Nelson |last6=Spatz |first6=Dena |last7=Holmes |first7=Nick |last8=Tershy |first8=Bernie |last9=Howald |first9=Gregg R. |last10=Croll |first10=Donald A. |display-authors=6 |title=Invasive vertebrate eradications on islands as a tool for implementing global Sustainable Development Goals |journal=Environmental Conservation |date=September 2020 |volume=47 |issue=3 |pages=139–148 |doi=10.1017/S0376892920000211 |bibcode=2020EnvCo..47..139D |s2cid=221990256 |doi-access=free }}</ref><ref>{{cite web |title=Pursuing Sustainable Development for Island Communities by Removing Invasive Species |url=https://www.islandconservation.org/sustainable-development-communities-removing-invasive-species/ |publisher=Island Conservation |access-date=13 August 2020 |date=13 August 2020 |archive-date=September 26, 2020 |archive-url=https://web.archive.org/web/20200926042621/https://www.islandconservation.org/sustainable-development-communities-removing-invasive-species/ |url-status=live}}</ref>
Rodents were carried to South Georgia, an island in the southern Atlantic Ocean with no permanent inhabitants, in the 18th century by sealing and whaling ships. They soon wrought havoc on the island's bird population, eating eggs and attacking chicks. In 2018, the South Georgia Island was declared free of invasive rodents after a multi-year extermination effort. Bird populations have rebounded, including the South Georgia pipit (''Anthus antarcticus'') and South Georgia pintail (''Anas georgica georgica''), both endemic to the island.<ref>{{Cite news |url=https://www.science.org/content/article/rat-begone-record-eradication-effort-rids-sub-antarctic-island-invasive-rodents |title=Rat begone: Record eradication effort rids sub-Antarctic island of invasive rodents |last=Warren |first=Matt |date=May 8, 2018 |work=Science |access-date=May 9, 2018 |archive-date=May 9, 2018 |archive-url=https://web.archive.org/web/20180509035618/http://www.sciencemag.org/news/2018/05/rat-begone-record-eradication-effort-rids-sub-antarctic-island-invasive-rodents |url-status=live}}</ref><ref>{{cite web |url=https://www.atlasobscura.com/articles/how-to-exterminate-rats-on-an-island |title=The Intrepid Rat-Sniffing Terriers of South Georgia Island |date=May 17, 2018 |author=Hester, Jessica Leight |work=Atlas Obscura |access-date=June 6, 2018 |archive-date=May 22, 2018 |archive-url=https://web.archive.org/web/20180522041931/https://www.atlasobscura.com/articles/how-to-exterminate-rats-on-an-island |url-status=live}}</ref>
=== Taxon substitution === [[File:Aldabra Giant Tortoise, Ile aux Aigrettes Nature Reserve, Mauritius.JPG|thumb|The Aldabra giant tortoise (''Aldabrachelys gigantea'') has helped to restore ecological equilibrium on two islets off Mauritius, including the Île aux Aigrettes (pictured). ]]
Non-native species can be introduced to fill an ecological engineering role that previously was performed by a native species now extinct. The procedure is known as taxon substitution.<ref name=potential/><ref>{{cite web |url=https://www.sciencedaily.com/releases/2011/02/110211095555.htm |title=Invasive plants can create positive ecological change |work=Science Daily |date=February 14, 2011 |quote="Invasive species could fill niches in degraded ecosystems and help restore native biodiversity...." |access-date=June 22, 2017 |archive-date=May 25, 2017 |archive-url=https://web.archive.org/web/20170525102601/https://www.sciencedaily.com/releases/2011/02/110211095555.htm |url-status=live}}</ref><ref>{{cite journal |last1=Searcy |first1=Christopher A. |last2=Rollins |first2=Hilary B. |last3=Shaffer |first3=H. Bradley |title=Ecological equivalency as a tool for endangered species management |year=2016 |journal=Ecological Applications |volume=26 |issue=1 |pages=94–103 |pmid=27039512 |doi=10.1890/14-1674 |doi-access=free|bibcode=2016EcoAp..26...94S }}</ref> On many islands, tortoise extinction has resulted in dysfunctional ecosystems with respect to seed dispersal and herbivory. On the offshore islets of Mauritius, tortoises now extinct had served as the keystone herbivores. Introduction of the non-native Aldabra giant tortoises (''Aldabrachelys gigantea'') on two islets in 2000 and 2007 has begun to restore ecological equilibrium. The introduced tortoises are dispersing seeds of several native plants and are selectively grazing invasive plant species. Grazing and browsing are expected to replace ongoing intensive manual weeding, and the introduced tortoises are already breeding.<ref>{{cite journal |last1=Hansen |first1=Dennis M. |last2=Donlan |first2=C. Josh |last3=Griffiths |first3=Christine J. |last4=Campbell |first4=Karl J. |title=Ecological history and latent conservation potential: Large and giant tortoises as a model for taxon substitutions |year=2010 |journal=Ecography |volume=33 |issue=2 |pages=272–284 |doi=10.1111/j.1600-0587.2010.06305.x |doi-access=free|bibcode=2010Ecogr..33..272H }}</ref>
=== By using them as food === {{further|List of edible invasive species}}
The practice of eating invasive species to reduce their populations has been explored. In 2005, Chef Bun Lai of Miya's Sushi in New Haven, Connecticut, created the first menu dedicated to invasive species. At that time, half the items on the menu were conceptual because those invasive species were not yet commercially available.<ref name=r1>{{cite news |title=The Invasivore's Dilemma |url=https://www.outsideonline.com/1922351/invasivores-dilemma |access-date=May 28, 2019 |magazine=Outside |last=Jacobsen |first=Rowan |date=March 24, 2014 |archive-date=May 28, 2019 |archive-url=https://web.archive.org/web/20190528211949/https://www.outsideonline.com/1922351/invasivores-dilemma |url-status=live}}</ref> By 2013, Miya's offered invasive aquatic species such as Chesapeake blue catfish (''Ictalurus furcatus''), Florida lionfish (''Pterois'' ''sp.''), Kentucky silver carp (''Hypophthalmichthys molitrix)''''',''' Georgia cannonball jellyfish (''Stomolophus meleagris''), and invasive plants such as Japanese knotweed (''Reynoutria japonica'') and autumn olive (''Elaeagnus umbellata'').<ref>{{cite journal |title=Invasive Species Menu of a World-Class Chef |journal=Scientific American |volume=309 |issue=3 |pages=40–43 |date=September 1, 2013 |last=Lai |first=Bun |doi=10.1038/scientificamerican0913-40 |pmid=24003552 |bibcode=2013SciAm.309c..40L}}</ref><ref>{{cite web |url=https://www.smithsonianmag.com/travel/indulge-invasive-species-restaurants-across-country-180957899/ |title=Bite Back Against Invasive Species at Your Next Meal |author=Billock, Jennifer |work=Smithsonian Magazine |date=February 9, 2016 |access-date=May 28, 2019 |archive-date=March 22, 2019 |archive-url=https://web.archive.org/web/20190322193509/https://www.smithsonianmag.com/travel/indulge-invasive-species-restaurants-across-country-180957899/ |url-status=live}}</ref><ref>{{cite web |url=https://www.scientificamerican.com/article/can-we-really-eat-invasive-species-into-submission/?redirect=1 |title=Can We Really Eat Invasive Species into Submission? |work=Scientific American |author=Snyder, Michael |date=May 19, 2017 |access-date=May 28, 2019 |archive-date=August 1, 2020 |archive-url=https://web.archive.org/web/20200801204428/https://www.scientificamerican.com/article/can-we-really-eat-invasive-species-into-submission/?redirect=1 |url-status=live}}</ref><ref>{{Cite news |last=Kolbert |first=Elizabeth |date=2 December 2012 |title=Alien Entrées |work=New Yorker |url=https://www.newyorker.com/magazine/2012/12/10/alien-entrees |url-status=live |access-date=13 February 2020 |archive-url=https://web.archive.org/web/20191018202041/https://www.newyorker.com/magazine/2012/12/10/alien-entrees |archive-date=18 October 2019}}</ref> Joe Roman, a Harvard and University of Vermont conservation biologist and recipient of the Rachel Carson Environmental award, runs a website named "Eat The Invaders".<ref>{{Cite web |title=Bio |url=http://www.joeroman.com/new/bio/ |url-status=live |archive-url=https://web.archive.org/web/20190528213031/http://www.joeroman.com/bio/ |archive-date=28 May 2019 |access-date=2022-06-26 |website=Joe Roman |date=March 12, 2015}}</ref><ref>{{Cite web |title=Eat The Invaders — Fighting Invasive Species, One Bite At A Time! |url=http://eattheinvaders.org/ |url-status=live |archive-url=https://web.archive.org/web/20190519015542/http://eattheinvaders.org/ |archive-date=19 May 2019 |access-date=2022-06-26 |website=eattheinvaders.org}}</ref><ref name=r1/> In the 21st century, organizations including Reef Environmental Educational Foundation and the Institute for Applied Ecology have published cookbooks and recipes using invasive species as ingredients.<ref>{{cite book |author=Parks |first1=Mary |title=The Green Crab Cookbook |last2=Thanh |first2=Thai |publisher=Green Crab R&d |year=2019 |isbn=978-0-578-42794-2 }}</ref><ref>{{Cite web |url=https://www.reef.org/products/lionfish-cookbook-2nd-edition |title=Lionfish Cookbook 2nd Edition | Reef Environmental Education Foundation |website=www.reef.org |access-date=May 28, 2019 |archive-date=May 28, 2019 |archive-url=https://web.archive.org/web/20190528212729/https://www.reef.org/products/lionfish-cookbook-2nd-edition |url-status=live}}</ref> Invasive plant species have been explored as a sustainable source of beneficial phytochemicals and edible protein.<ref>{{Cite journal |last1=Iyer |first1=Ajay |last2=Bestwick |first2=Charles S. |last3=Duncan |first3=Sylvia H. |last4=Russell |first4=Wendy R. |date=2021-02-15 |title=Invasive Plants Are a Valuable Alternate Protein Source and Can Contribute to Meeting Climate Change Targets |journal=Frontiers in Sustainable Food Systems |volume=5 |article-number=575056 |doi=10.3389/fsufs.2021.575056 |bibcode=2021FrSFS...575056I |doi-access=free |hdl=2164/15875 |hdl-access=free }}</ref><ref>{{Cite journal |last1=Iyer |first1=Ajay |last2=Guerrier |first2=Lisa |last3=Leveque |first3=Salomé |last4=Bestwick |first4=Charles S. |last5=Duncan |first5=Sylvia H. |last6=Russell |first6=Wendy R. |date=2022 |title=High throughput method development and optimised production of leaf protein concentrates with potential to support the agri-industry |url=https://link.springer.com/10.1007/s11694-021-01136-w |journal=Journal of Food Measurement and Characterization |volume=16 |issue=1 |pages=49–65 |doi=10.1007/s11694-021-01136-w |s2cid=244407388 |hdl=2164/19275 |hdl-access=free }}</ref><ref>{{Cite journal |last1=Nuñez |first1=Martin A. |last2=Kuebbing |first2=Sara |last3=Dimarco |first3=Romina D. |last4=Simberloff |first4=Daniel |date=December 2012 |title=Invasive Species: to eat or not to eat, that is the question |url=https://conbio.onlinelibrary.wiley.com/doi/10.1111/j.1755-263X.2012.00250.x |journal=Conservation Letters |language=en |volume=5 |issue=5 |pages=334–341 |doi=10.1111/j.1755-263X.2012.00250.x |bibcode=2012ConL....5..334N |hdl=11336/198362 |hdl-access=free }}</ref>
Proponents of eating invasive organisms argue that humans have the ability to eat away any species that it has an appetite for, pointing to the many animals which humans have been able to hunt to extinction—such as the Caribbean monk seal (''Neomonachus tropicalis'') and the passenger pigeon (''Ectopistes migratorius''). They further point to Jamaica's success in significantly decreasing the population of lionfish by encouraging the consumption of the fish.<ref>{{cite web |url=https://news.yahoo.com/invasive-lionfish-kings-caribbean-may-met-match-011600208.html |title=Invasive Lionfish, the Kings of the Caribbean, May Have Met Their Match |date=January 24, 2014 |work=Yahoo News |last=Conniff |first=Richard |archive-url=https://web.archive.org/web/20140127033047/https://news.yahoo.com/invasive-lionfish-kings-caribbean-may-met-match-011600208.html |archive-date=January 27, 2014}}</ref> Skeptics point out that once a foreign species has entrenched itself in a new place—such as the Indo-Pacific lionfish that has now virtually taken over the waters of the western Atlantic Ocean, Caribbean and Gulf of Mexico—eradication is almost impossible. Critics argue that encouraging consumption might have the unintended effect of spreading harmful species even more widely.<ref>{{cite news |url=https://www.theguardian.com/environment/world-on-a-plate/2015/feb/06/cooking-cant-solve-the-invasive-threat |title=Cooking can't solve the threat of invasive species |author=Bryce, Emma |date=February 6, 2015 |access-date=October 16, 2017 |work=The Guardian |archive-date=October 17, 2017 |archive-url=https://web.archive.org/web/20171017201839/https://www.theguardian.com/environment/world-on-a-plate/2015/feb/06/cooking-cant-solve-the-invasive-threat |url-status=live}}</ref>
===Pesticides and herbicides=== Pesticides are commonly used to control invasives.<ref name="Goss2020">{{cite journal |last1=Goss |first1=EM |last2=Kendig |first2=AE |last3=Adhikari |first3=A |last4=Lane |first4=B |last5=Kortessis |first5=N |last6=Holt |first6=RD |last7=Clay |first7=K |last8=Harmon |first8=PF |last9=Flory |first9=SL |title=Disease in Invasive Plant Populations |journal=Annual Review of Phytopathology |date=August 2020 |volume=58 |issue=1 |pages=97–117 |doi=10.1146/annurev-phyto-010820-012757 |pmid=32516034 |bibcode=2020AnRvP..58...97G |s2cid=219563975 }}</ref> Herbicides used against invasive plants include fungal herbicides.<ref name="Goss2020"/> Although the effective population size of an introduced population is bottlenecked, some genetic variation has been known to provide invasive plants with resistance against these fungal bioherbicides.<ref name="Goss2020"/> Invasive populations of cheatgrass (''Bromus tectorum'') exist with resistance to ''Ustilago bullata'' used as a biocontrol, and a similar problem has been reported in Japanese stiltgrass ''(Microstegium vimineum'') subject to ''Bipolaris microstegii'' and ''B. drechsleri''.<ref name="Goss2020"/> This is not solely a character of invasive plant genetics but is normal for wild plants such as the weed wild flax (''Linum marginale)'' and its fungal pathogen flax rust (''Melampsora lini)''.<ref name="Goss2020"/> Crops have another disadvantage over any uncontrolled plant – wild native or invasive – namely their greater uptake of nutrients, as they are deliberately bred to increase nutrient intake to enable increased product output.<ref name="Goss2020"/>
=== Gene drive === A gene drive could be used to eliminate invasive species and has, for example, been proposed as a way to eliminate invasive mammal species in New Zealand.<ref name="Kalmakoff2016">{{cite web |last=Kalmakoff |first=James |url=http://www.merlinnz.com/blog/crispr-pest-free-nz/ |title=CRISPR for pest-free NZ |date=11 October 2016 |access-date=19 October 2016 |archive-date=October 19, 2016 |archive-url=https://web.archive.org/web/20161019152322/http://www.merlinnz.com/blog/crispr-pest-free-nz/ }}</ref> Briefly put, an individual of a species may have two versions of a gene, one with a desired coding outcome and one not, with offspring having a 50:50 chance of inheriting one or the other. Genetic engineering can be used to inhibit inheritance of the non-desired gene, resulting in faster propagation of the desired gene in subsequent generations.<ref name="GeneDrive" /> Gene drives for biodiversity conservation purposes are being explored as part of The Genetic Biocontrol of Invasive Rodents program because they offer the potential for reduced risk to non-target species and reduced costs when compared to traditional invasive species removal techniques.<ref>{{cite web |url=http://www.geneticbiocontrol.org/wp-content/uploads/2018/05/GBIRD-FactSheet-April-2018.pdf |title=GBIRd Fact Sheet |date=1 April 2018 |access-date=14 November 2018 }}</ref> A wider outreach network for gene drive research exists to raise awareness of the value of gene drive research for the public good.<ref name="GeneDrive">{{cite web |url=https://genedrivenetwork.org |title=Mission & Principles Statement |date=1 July 2018 |access-date=14 November 2018 }}</ref> Some scientists are concerned that the technique could wipe out species in their original native habitats.<ref>{{cite web |url=http://theconversation.com/gene-drives-could-wipe-out-whole-populations-of-pests-in-one-fell-swoop-81681 |title='Gene drives' could wipe out whole populations of pests in one fell swoop |work=The Conversation|date=August 8, 2017 }}</ref> The gene could mutate, causing unforeseen problems,<ref>{{cite web |url=http://blogs.plos.org/dnascience/2017/11/30/an-argument-against-gene-drives-to-extinguish-new-zealand-mammals-life-finds-a-way/ |title=An Argument Against Gene Drives to Extinguish New Zealand Mammals: Life Finds a Way |work=Plos blogs |date=30 November 2017 }}</ref> or hybridize with native species.<ref name="NZ gene drive risks">{{cite web |last=Campbell |first=Colin |url=https://www.odt.co.nz/opinion/risks-may-accompany-gene-drive-technology#comment-1086 |title=Risks may accompany gene drive technology |publisher=Otago Daily Times |date=17 October 2016 |access-date=19 October 2016}}</ref>
=== Predicting invasive plants === Accurately predicting the impacts of non-native plants can be an especially effective management option because most introductions of non-native plant species are intentional.<ref>{{cite journal |last1=Ööpik |first1=Merle |last2=Kukk |first2=Toomas |last3=Kull |first3=Kalevi |last4=Kull |first4=Tiiu |title=The importance of human mediation in species establishment: analysis of the alien flora of Estonia |journal=Boreal Environment Research |date=2008 |volume=13 |issue=Supplement A |pages=53–67 |hdl=10138/235238 |hdl-access=free }}</ref><ref>{{cite journal |last1=Lehan |first1=Nora E. |last2=Murphy |first2=Julia R. |last3=Thorburn |first3=Lukas P. |last4=Bradley |first4=Bethany A. |title=Accidental introductions are an important source of invasive plants in the continental United States |journal=American Journal of Botany |date=July 2013 |volume=100 |issue=7 |pages=1287–1293 |doi=10.3732/ajb.1300061 |pmid=23825135 }}</ref><ref>{{cite book |last1=Virtue |first1=J.G. |last2=Bennett |first2=Sarita |last3=Randall |first3=R.P. |chapter=Plant introductions in Australia: how can we resolve 'weedy' conflicts of interest?: Plant introductions in Australia: how can we resolve 'weedy' conflicts of interest? |pages=42–48 |s2cid=82300163 |editor1-last=Sindel |editor1-first=Brian Mark |editor2-last=Johnson |editor2-first=Stephen Barry |title=Weed Management: Balancing People, Planet, Profit: 14th Australian Weeds Conference: Papers & Proceedings |date=2004 |publisher=Weed Society of New South Wales |isbn=978-0-9752488-0-5 }}</ref> Weed risk assessments attempt to predict the chances that a specific plant will have negative effects in a new environment, often using a standardized questionnaire. The resulting total score is associated with a management action such as "prevent introduction".<ref name=":2">{{cite journal |last1=Pheloung |first1=P.C. |last2=Williams |first2=P.A. |last3=Halloy |first3=S.R. |title=A weed risk assessment model for use as a biosecurity tool evaluating plant introductions |journal=Journal of Environmental Management |date=December 1999 |volume=57 |issue=4 |pages=239–251 |doi=10.1006/jema.1999.0297 |bibcode=1999JEnvM..57..239P }}</ref><ref name=":3">{{cite journal |last1=Koop |first1=Anthony L. |last2=Fowler |first2=Larry |last3=Newton |first3=Leslie P. |last4=Caton |first4=Barney P. |title=Development and validation of a weed screening tool for the United States |journal=Biological Invasions |date=February 2012 |volume=14 |issue=2 |pages=273–294 |doi=10.1007/s10530-011-0061-4 |bibcode=2012BiInv..14..273K |s2cid=254280051 }}</ref> Assessments commonly use information about the physiology,<ref name=":2" /> life history,<ref name=":3" /> native ranges,<ref>{{cite journal |last1=Pfadenhauer |first1=William G. |last2=Nelson |first2=Michael F. |last3=Laginhas |first3=Brit B. |last4=Bradley |first4=Bethany A. |title=Remember your roots: Biogeographic properties of plants' native habitats can inform invasive plant risk assessments |journal=Diversity and Distributions |date=January 2023 |volume=29 |issue=1 |pages=4–18 |doi=10.1111/ddi.13639 |s2cid=253220107 |url=https://scholarworks.umass.edu/cgi/viewcontent.cgi?article=1002&context=oeb_grad_pubs |doi-access=free |bibcode=2023DivDi..29....4P }}</ref> and phylogenetic relationships of the species evaluated. The effectiveness of the approach is debated.<ref>{{cite journal |last1=Gordon |first1=Doria R. |last2=Flory |first2=S. Luke |last3=Lieurance |first3=Deah |last4=Hulme |first4=Philip E. |last5=Buddenhagen |first5=Chris |last6=Caton |first6=Barney |last7=Champion |first7=Paul D. |last8=Culley |first8=Theresa M. |last9=Daehler |first9=Curt |last10=Essl |first10=Franz |last11=Hill |first11=Jeffrey E. |last12=Keller |first12=Reuben P. |last13=Kohl |first13=Lisa |last14=Koop |first14=Anthony L. |last15=Kumschick |first15=Sabrina |last16=Lodge |first16=David M. |last17=Mack |first17=Richard N. |last18=Meyerson |first18=Laura A. |last19=Pallipparambil |first19=Godshen R. |last20=Panetta |first20=F. Dane |last21=Porter |first21=Read |last22=Pyšek |first22=Petr |last23=Quinn |first23=Lauren D. |last24=Richardson |first24=David M. |last25=Simberloff |first25=Daniel |last26=Vilà |first26=Montserrat |display-authors=6 |title=Weed Risk Assessments Are an Effective Component of Invasion Risk Management |journal=Invasive Plant Science and Management |date=March 2016 |volume=9 |issue=1 |pages=81–83 |doi=10.1614/IPSM-D-15-00053.1 |bibcode=2016IPSM....9...81G |s2cid=86276601 |hdl=10019.1/116927 |hdl-access=free }}</ref><ref>{{cite journal |last1=Hulme |first1=Philip E. |title=Weed risk assessment: a way forward or a waste of time?: Weed risk assessment: a way forward or waste of time? |journal=Journal of Applied Ecology |date=February 2012 |volume=49 |issue=1 |pages=10–19 |doi=10.1111/j.1365-2664.2011.02069.x |doi-access=free }}</ref>
=== Predicting invasive animals === Invasive alien animal species can seriously affect human well-being and biodiversity. A hierarchical approach underpins the management measures used to lessen these effects, ranging from invasive species management to invasion prevention through early warning and quick response.<ref name=":4">{{Cite journal |last1=Bertolino |first1=Sandro |last2=Sciandra |first2=Chiara |last3=Bosso |first3=Luciano |last4=Russo |first4=Danilo |last5=Lurz |first5=Peter W.W. |last6=Di Febbraro |first6=Mirko |date=2020 |title=Spatially explicit models as tools for implementing effective management strategies for invasive alien mammals |url=https://onlinelibrary.wiley.com/doi/abs/10.1111/mam.12185 |journal=Mammal Review |language=en |volume=50 |issue=2 |pages=187–199 |doi=10.1111/mam.12185 |bibcode=2020MamRv..50..187B |issn=1365-2907|hdl=2318/1737199 |hdl-access=free }}</ref><ref>{{Cite journal |last1=Shackleton |first1=Ross T. |last2=Shackleton |first2=Charlie M. |last3=Kull |first3=Christian A. |date=2019-01-01 |title=The role of invasive alien species in shaping local livelihoods and human well-being: A review |url=https://www.sciencedirect.com/science/article/pii/S0301479718305267 |journal=Journal of Environmental Management |series=The human and social dimensions of invasion science and management |volume=229 |pages=145–157 |doi=10.1016/j.jenvman.2018.05.007 |pmid=30049620 |bibcode=2019JEnvM.229..145S |hdl=10019.1/122761 |issn=0301-4797|url-access=subscription }}</ref><ref>{{Cite journal |last1=Pejchar |first1=Liba |last2=Mooney |first2=Harold A. |date=2009-09-01 |title=Invasive species, ecosystem services and human well-being |url=https://www.cell.com/trends/ecology-evolution/abstract/S0169-5347(09)00176-1 |journal=Trends in Ecology & Evolution |language=English |volume=24 |issue=9 |pages=497–504 |doi=10.1016/j.tree.2009.03.016 |issn=0169-5347 |pmid=19577817|bibcode=2009TEcoE..24..497P |url-access=subscription }}</ref> Currently, a small number of research on invading mammals have employed spatially explicit models, and the majority of them only looked at a small number of species. The majority of the research employed climate matching to assess the appropriateness of global geographic regions or the potential for established species to spread farther. For species that are not yet established but are anticipated to do so, modelling techniques may be a helpful tool to evaluate the risk of establishment; nevertheless, there aren't many research of this kind for mammals.<ref name=":4" /><ref>{{Cite book |last1=Bender |first1=Emily M. |last2=Gebru |first2=Timnit |last3=McMillan-Major |first3=Angelina |last4=Shmitchell |first4=Shmargaret |chapter=On the Dangers of Stochastic Parrots: Can Language Models be Too Big? 🦜 |date=2021-03-01 |title=Proceedings of the 2021 ACM Conference on Fairness, Accountability, and Transparency |series=FAccT '21 |location=New York, NY, USA |publisher=Association for Computing Machinery |pages=610–623 |doi=10.1145/3442188.3445922 |isbn=978-1-4503-8309-7|doi-access=free }}</ref>
=== Returning invasive species to origin country === In 2025, for the first time in history, a project to return an invasive species to the country it came from has been started in the Hebrides in Scotland. Hedgehogs "native to the UK mainland" were brought to those islands decades ago to fight garden pests, but the introduction caused severe harm to birds which nested on the ground. The authorities decided to move them back to the mainland, helping the birds without harming the hedgehogs.<ref>{{cite news |last1=Elliards |first1=Xander |title=Hedgehogs to be evicted from Scottish island in world-first trial |url=https://www.thenational.scot/news/25075393.hedgehogs-evicted-scottish-island-world-first-trial/ |access-date=10 April 2025 |agency=The National |date=9 April 2025}}</ref>
=== Government Regulations === Government regulations offer another way to eradicate invasive species. The Florida Fish and Wildlife Commission (FWC) sponsors competitions aimed at removing lionfish from Florida waters.<ref name=":6" /> The challenge offers divers with prizes contingent on the number of lionfish each competitor successfully removes. Similarly, the FWC encourages local Floridians to collect invasive green iguanas and turn them into local government facilities.<ref name=":7" /> When the state undergoes cold snaps, these non-native lizards often freeze and become stunned allowing for the ease of collecting them. The FWC permits the killing of green iguanas year-round to combat the population.<ref name=":9" />
The state of Texas classifies feral hogs as invasive species. As such, hunting of these hogs is permitted and highly encouraged by the Texas government year-round. Methods described by the Texas State Government include trapping, corralling, aerial gunning (high-powered rifles discharged from individuals aboard helicopters), and tracking dogs.<ref name=":10" /> Many local governments across Texas also provide bounties that encourage hunters to increase pressure on the feral hog populations.<ref name=":11" />
The state of Idaho classifies walleye as an invasive species in their waters. These predatory fish pose a threat to native aquatic populations. Idaho Fish and Game officials strongly encourage anglers to harvest caught walleye year-round with no limits regarding amount or size.<ref name=":12" /> Similarly, the Indiana Department of Natural Resources classifies thirteen species of fish, including bighead carp and walking catfish, as invasive to Indiana waters and finds anglers not in violation of the Exotic Fish Rule only if the fish are killed immediately after being caught.<ref name=":13" />
== Criticisms of the invasive species discourse == The process of removing and classifying animals as invasive species is not without controversy. Several animal welfare movements have attempted to dissuade the eradication of invasive species. A main point of contention for these activists is the treatment of the invasive species during the eradication process. These proponents argue that the stigma surrounding an invasive species seemingly outweighs the notion that all animals are living beings that deserve respect and care.<ref name=":14">{{Cite web |title=Detailed Discussion of the Ethical Treatment of Invasive Species {{!}} Animal Legal & Historical Center |url=https://www.animallaw.info/article/detailed-discussion-ethical-treatment-invasive-species |access-date=2026-04-30 |website=www.animallaw.info}}</ref> These activists acknowledge that invasive species contribute to more economic and environmental damage than every natural disaster combined but find the removal process largely unethical and cruel.<ref name=":14" />
Other animal activists reject the idea of labeling a species as invasive altogether. These activists posit the labeling of a species as ‘invasive’ constitutes wrongful discrimination that permits systemic violence on the creatures.<ref name=":15">{{Cite journal |last1=Abbate |first1=C.E. |last2=Fischer |first2=Bob |date=2019-10-27 |title=Don't Demean "Invasives": Conservation and Wrongful Species Discrimination |journal=Animals |language=en |volume=9 |issue=11 |pages=871 |doi=10.3390/ani9110871 |doi-access=free |issn=2076-2615 |pmc=6912556 |pmid=31717868}}</ref> Proponents of this subset of animal activism profess invasive species labeling is inherently arbitrary and a perpetuator of speciesism, a term coined by Peter Singer to describe the “misguided belief that one species is more important than another.”<ref>{{Cite web |date=2019-04-09 |title=What Is Speciesism and How You Can Overcome It |url=https://www.peta.org/features/what-is-speciesism/ |access-date=2026-04-30 |website=PETA |language=en-US}}</ref> Once a species is determined to be legally invasive, those animals often fail to be protected by anti-cruelty statutes and inhumane killings of the species, like cane toads in Australia, become commonplace.<ref name=":15" />
A growing contingent of scientists, ecologists, and animal welfare activists caution utilizing the term ‘invasive’ for species migrating to new ecosystems. Scientists disclose that climate change has begun pushing species such as white-tailed deer, armadillos, lobsters, unicorn snails, and even maple trees to pursue new ecosystems, a migration necessary to survive hotter temperatures.<ref name=":16">{{Cite web |last=Bolotnikova |first=Marina |date=2021-11-28 |title=It's time to stop demonizing "invasive" species |url=https://www.vox.com/down-to-earth/22796160/invasive-species-climate-change-range-shifting |access-date=2026-04-30 |website=Vox |language=en-US}}</ref> Rather than labeling these species as invasive, this contingent urges these animals should be welcomed as refugees.<ref name=":16" /> The term ‘invasive’ compares these species to enemies in war which warps the public perception of the innocent animals’ livelihood and welfare.
==See also== * Adventive plant * Archaeophyte * Climate change and invasive species * Ecologically based invasive plant management * Escaped plant * Hemerochory * Invasion genetics * Lists of invasive species * Naturalisation (biology) * Neophyte (botany) * Seed dispersal * 100 of the World's Worst Invasive Alien Species
== References == === Attribution === This article incorporates CC-BY-3.0 text from the reference<ref name="Odendaal 2008"/>
=== Citations === {{Reflist|refs= <ref name=amstutz2018>{{Cite book|last=Amstutz|first=Lisa J|title=Invasive Species|publisher=Abdo Publishing|year=2018|isbn=978-1-5321-1024-5|location=Minneapolis, MN|pages=8–10}}</ref> <ref name=davis>{{cite journal |last1=Davis |first1=Mark A. |last2=Thompson |first2=Ken |year=2000 |title=Eight Ways to be a Colonizer; Two Ways to be an Invader: A Proposed Nomenclature Scheme for Invasion Ecology |journal=Bulletin of the Ecological Society of America |volume=81 |number=3 |pages=226–230 |jstor=20168448}}</ref> <ref name=ehrenfeld2010>{{cite journal |last1=Ehrenfeld |first1=Joan G. |title=Ecosystem Consequences of Biological Invasions |journal=Annual Review of Ecology, Evolution, and Systematics |date=1 December 2010 |volume=41 |issue=1 |pages=59–80 |doi=10.1146/annurev-ecolsys-102209-144650 }}</ref> <ref name=ivey2019>{{cite journal |last1=Ivey |first1=Matthew R. |last2=Colvin |first2=Michael |last3=Strickland |first3=Bronson K. |last4=Lashley |first4=Marcus A. |date=June 14, 2019 |title=Reduced vertebrate diversity independent of spatial scale following feral swine invasions |journal=Ecology and Evolution |volume=9 |issue=13 |pages=7761–7767 |doi=10.1002/ece3.5360 |pmid=31346438 |pmc=6635915|bibcode=2019EcoEv...9.7761I }}</ref> <ref name=pnwaquaticinv>Aquatic invasive species. A Guide to Least-Wanted Aquatic Organisms of the Pacific Northwest. 2001. University of Washington</ref> <ref name=trainer2012>{{Cite journal|last1=Trainer|first1=Vera L.|last2=Bates|first2=Stephen S.|last3=Lundholm|first3=Nina|last4=Thessen|first4=Anne E.|last5=Cochlan|first5=William P.|last6=Adams|first6=Nicolaus G.|last7=Trick|first7=Charles G.|date=2012|title=Pseudo-nitzschia physiological ecology, phylogeny, toxicity, monitoring and impacts on ecosystem health|journal=Harmful Algae|volume=14|pages=271–300|doi=10.1016/j.hal.2011.10.025|bibcode=2012HAlga..14..271T |hdl=1912/5118|hdl-access=free}}</ref> }}<ref name=":17" />
== Further reading == * {{cite journal |last1=Mitchell |first1=Heidi J. |last2=Bartsch |first2=Detlef |title=Regulation of GM Organisms for Invasive Species Control |journal=Frontiers in Bioengineering and Biotechnology |date=21 January 2020 |volume=7 |article-number=454 |doi=10.3389/fbioe.2019.00454 |pmid=32039172 |pmc=6985037 |doi-access=free }} * [https://sitn.hms.harvard.edu/flash/2014/removing-threat-from-invasive-species-with-genetic-engineering/ Removing Threat from Invasive Species with Genetic Engineering]—''Science in the News'' * {{cite web |url=https://theconversation.com/the-true-damage-of-invasive-alien-species-was-just-revealed-in-a-landmark-report-heres-how-we-must-act-211893|title=The true damage of invasive alien species was just revealed in a landmark report. Here's how we must act|last=Sheppard|first=Andy|display-authors=etal.|date= September 4, 2023|website=The Conversation |publisher= |quote=}} * White, Michael (13 Dec 2017) [6 Dec 2017]. [https://psmag.com/environment/should-we-fight-invasive-species-with-genetic-engineering "Should We Fight Invasive Species with Genetic Engineering?"] ''Pacific Standard''.
== External links == * [https://www.naisn.org/ North American Invasive Species Network], a consortium that uses a coordinated network to advance science-based understanding and enhance management of non-native, invasive species. * [https://www.nonnativespecies.org/ Great Britain Non-native Species Secretariat (NNSS) website] * [https://www.cabi.org/ISC/ CABI Invasive Species Compendium], an encyclopaedic resource of scientific information * [https://www.invasivespeciesinfo.gov/ Invasive Species], National Invasive Species Information Center, United States National Agricultural Library * [https://web.archive.org/web/20110406095350/http://issg.org/database/welcome/ Invasive Species Specialist Group] – Global Invasive Species Database * [http://www.hear.org/pier/ Pacific Island Ecosystems at Risk] project * [http://www.invadingspecies.com/ invadingspecies.com] of the Ontario Ministry of Natural Resources and Ontario Federation of Anglers and Hunters * [https://www.fisheriesireland.ie/what-we-do/research/research-theme-invasive-species Aquatic invasive species in Ireland], Inland Fisheries Ireland * [http://ias.biodiversity.be/ Invasive alien species in Belgium] Belgian Forum on Invasive Species (BFIS) *
{{Invasive species by country}} {{Globalization |state=autocollapse }} {{Modelling ecosystems |state=collapsed }} {{Pollution}} {{Authority control}}
{{DEFAULTSORT:Invasive Species}} Category:Invasive species Category:Environmental conservation Category:Environmental terminology Category:Forest pathology Category:Habitat Category:Pest control