Editing Gene flow (section)

===Genetic pollution===

{{Main|Genetic pollution}}

Human activities such as movement of species and modification of landscape can result in genetic pollution, [[Hybrid (biology)|hybridization]], [[introgression]] and genetic swamping.  These processes can lead to homogenization or replacement of local [[genotypes]] as a result of either a numerical and/or [[Fitness (biology)|fitness]] advantage of introduced plant or animal.<ref>{{cite book |title=Grass cultivars: their origins, development, and use on national forests and grasslands in the Pacific Northwest |vauthors=Aubry C, Shoal R, Erickson V |publisher=USDA Forest Service; Native Seed Network (NSN), Institute for Applied Ecology |year=2005 |location=Corvallis, OR |pages=26–27 |chapter=Glossary |chapter-url=https://www.fs.usda.gov/wildflowers/Native_Plant_Materials/documents/cultivars_maindoc_040405_appendices.pdf |archive-url=https://web.archive.org/web/20230530092809/http://www.fs.usda.gov/wildflowers/Native_Plant_Materials/documents/cultivars_maindoc_040405_appendices.pdf |archive-date=2023-05-30 |url-status=dead |access-date=2023-11-16 }}</ref> Nonnative species can threaten native plants and animals with extinction by hybridization and introgression either through purposeful introduction by humans or through habitat modification, bringing previously isolated species into contact. These phenomena can be especially detrimental for rare species coming into contact with more abundant ones which can occur between island and mainland species. Interbreeding between the species can cause a 'swamping' of the rarer species' gene pool, creating hybrids that supplant the native stock. This is a direct result of evolutionary forces such as natural selection, as well as genetic drift, which lead to the increasing prevalence of advantageous traits and homogenization. The extent of this phenomenon is not always apparent from [[morphology (biology)|outward appearance]] alone. While some degree of gene flow occurs in the course of normal evolution, hybridization with or without introgression may threaten a rare species' existence.<ref>{{cite journal| vauthors = Rhymer JM, Simberloff D |year=1996|title=Extinction by Hybridization and Introgression|journal=Annual Review of Ecology and Systematics|volume=27|issue=1|pages=83–109|doi=10.1146/annurev.ecolsys.27.1.83|jstor=2097230|bibcode=1996AnRES..27...83R }}</ref><ref>{{cite book| vauthors = Potts BM, Barbour RC, Hingston AB |date=September 2001|title=Genetic Pollution from Farm Forestry using eucalypt species and hybrids; A report for the RIRDC/L&WA/FWPRDC; Joint Venture Agroforestry Program|url=http://www.rirdc.gov.au/reports/AFT/01-114.pdf|url-status=dead|publisher=Australian Government, Rural Industrial Research and Development Corporation|isbn=978-0-642-58336-9|issn=1440-6845|archive-url=https://web.archive.org/web/20040102175403/http://www.rirdc.gov.au/reports/AFT/01-114.pdf|archive-date=2004-01-02|work=RIRDC Publication No 01/114; RIRDC Project No CPF - 3A}}</ref> For example, the [[Mallard]] is an abundant species of duck that interbreeds readily with a wide range of other ducks and poses a threat to the integrity of some species.<ref>{{cite journal | vauthors = Bulgarella M, Quenu M, Shepherd LD, Morgan-Richards M | title = The ectoparasites of hybrid ducks in New Zealand (Mallard x Grey Duck) | journal = International Journal for Parasitology: Parasites and Wildlife | volume = 7 | issue = 3 | pages = 335–342 | date = December 2018 | pmid = 30258780 | pmc = 6154467 | doi = 10.1016/j.ijppaw.2018.09.005 | bibcode = 2018IJPPW...7..335B | url = }}</ref>{{Failed verification|date=November 2023}}