Editing Biodiversity (section)

== Biodiversity changes (other than losses) ==

=== Natural seasonal variations ===
Biodiversity naturally varies due to seasonal shifts. Spring's arrival enhances biodiversity as numerous species breed and feed, while winter's onset temporarily reduces it as some insects perish and migrating animals leave. Additionally, the seasonal fluctuation in plant and invertebrate populations influences biodiversity.<ref>{{Cite web |title=Biodiversity loss {{!}} Causes, Effects, & Facts {{!}} Britannica |url=https://www.britannica.com/science/biodiversity-loss |access-date=2024-04-23 |website=www.britannica.com |language=en}}</ref>

=== Introduced and invasive species ===
{{Main|Introduced species|Invasive species}}

[[File:Male Silver Pheasant.jpg|thumb|right|Male ''Lophura nycthemera'' ([[silver pheasant]]), a native of [[East Asia]] that has been introduced into parts of [[Europe]] for ornamental reasons]]
Barriers such as large [[river]]s, [[sea]]s, [[oceans]], [[mountains]] and [[deserts]] encourage diversity by enabling independent evolution on either side of the barrier, via the process of [[allopatric speciation]]. The term [[invasive species]] is applied to species that breach the natural barriers that would normally keep them constrained. Without barriers, such species occupy new territory, often supplanting native species by occupying their niches, or by using resources that would normally sustain native species.

Species are increasingly being moved by humans (on purpose and accidentally). Some studies say that diverse ecosystems are more resilient and resist invasive plants and animals.<ref>{{cite journal|last=Levine|first=J. 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|bibcode = 2000Sci...288..852L|pmid=10797006}}</ref> Many studies cite effects of invasive species on natives,<ref>{{cite journal|last=GUREVITCH|first=J|author-link1=Jessica Gurevitch|author2=PADILLA, D|title=Are invasive species a major cause of extinctions?|journal=Trends in Ecology & Evolution|date=1 September 2004|volume=19|issue=9|pages=470–474|doi=10.1016/j.tree.2004.07.005|pmid=16701309}}</ref> but not extinctions. 

Invasive species seem to increase local ([[alpha diversity]]) diversity, which decreases turnover of diversity ([[beta diversity]]). Overall [[gamma diversity]] may be lowered because species are going extinct because of other causes,<ref>{{cite journal|last=Sax|first=Dov F.|author2=Gaines, Steven D. |author3=Brown, James H. |title=Species Invasions Exceed Extinctions on Islands Worldwide: A Comparative Study of Plants and Birds|journal=The American Naturalist|date=1 December 2002|volume=160|issue=6|pages=766–783|doi=10.1086/343877|pmid=18707464|bibcode=2002ANat..160..766S }}</ref> but even some of the most insidious invaders (e.g.: Dutch elm disease, emerald ash borer, chestnut blight in North America) have not caused their host species to become extinct. [[Local extinction|Extirpation]], [[population decline]] and [[Species homogeneity|homogenization]] of regional biodiversity are much more common. Human activities have frequently been the cause of invasive species circumventing their barriers,<ref>{{cite book|last=Jude|first=David|editor1-first=M.|editor1-last=Munawar|title=The lake Huron ecosystem: ecology, fisheries and management|year=1995|publisher=S.P.B. Academic Publishing|location=Amsterdam|isbn=978-90-5103-117-1}}</ref> by introducing them for food and other purposes. Human activities therefore allow species to migrate to new areas (and thus become invasive) occurred on time scales much shorter than historically have been required for a species to extend its range.

At present, several countries have already imported so many exotic species, particularly agricultural and ornamental plants, that their indigenous fauna/flora may be outnumbered. For example, the introduction of [[kudzu]] from Southeast Asia to Canada and the United States has threatened biodiversity in certain areas.<ref>{{cite press release |title=Are invasive plants a threat to native biodiversity? It depends on the spatial scale |url=https://www.sciencedaily.com/releases/2011/04/110408163917.htm |work=ScienceDaily |publisher=American Journal of Botany |date=11 April 2011 }}</ref> Another example are [[pine]]s, which have invaded forests, shrublands and grasslands in the southern hemisphere.<ref>{{Cite journal |last1=Higgins |first1=Steven I. |last2=Richardson |first2=David M. |year=1998 |title=Pine invasions in the southern hemisphere: Modelling interactions between organism, environment and disturbance |journal=Plant Ecology |volume=135 |issue=1 |pages=79–93 |doi=10.1023/a:1009760512895 |bibcode=1998PlEco.135...79H }}</ref>

===Hybridization and genetic pollution===
[[File:Wheat selection k10183-1.jpg|right|thumb|The Yecoro [[wheat]] (right) [[cultivar]] is sensitive to salinity, plants resulting from a hybrid cross with cultivar W4910 (left) show greater tolerance to high salinity]]Endemic species can be threatened with [[extinction]]<ref>{{cite journal |last1=Mooney |first1=H. A. |last2=Cleland |first2=EE |year=2001 |title=The evolutionary impact of invasive species |journal=Proceedings of the National Academy of Sciences |volume=98 |issue=10 |pages=5446–5451 |bibcode=2001PNAS...98.5446M |doi=10.1073/pnas.091093398 |pmc=33232 |pmid=11344292 |doi-access=free}}</ref> through the process of [[genetic pollution]], i.e. uncontrolled [[Hybrid (biology)|hybridization]], [[introgression]] and genetic swamping. Genetic pollution leads to homogenization or replacement of local [[genomes]] as a result of either a numerical and/or [[Fitness (biology)|fitness]] advantage of an introduced species.<ref>{{cite report |last1=Aubry |first1=Carol |last2=Shoal |first2=Robin |last3=Erickson |first3=Vicky |date=January 2005 |title=Grass cultivars: Their origins, development, and use on national forests and grasslands in the Pacific Northwest |publisher=USDA Forest Service |url=https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fsbdev7_015644.pdf }}</ref>
Hybridization and introgression are side-effects of introduction and invasion. These phenomena can be especially detrimental to [[rare species]] that come into contact with more abundant ones. The abundant species can interbreed with the rare species, swamping its [[gene pool]]. This problem is not always apparent from [[morphology (biology)|morphological]] (outward appearance) observations alone. Some degree of [[gene flow]] is normal adaptation and not all [[gene]] and [[genotype]] constellations can be preserved. However, hybridization with or without introgression may, nevertheless, threaten a rare species' existence.<ref>{{cite journal |last1=Rhymer |first1=Judith M. |last2=Simberloff |first2=Daniel |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 name="PottsBarbour2001">{{cite book |last1=Potts |first1=Bradley Michael |last2=Barbour |first2=Robert C. |last3=Hingston |first3=Andrew B. |title=Genetic Pollution from Farm Forestry Using Eucalypt Species and Hydrids: A Report for the RIRDC/L & WA/FWPRDC Joint Venture Agroforestry Program |date=2001 |publisher=RIRDC |isbn=978-0-642-58336-9 }}{{pn|date=October 2024}}</ref><!--this argument seems circular. hybridization is bad because...it limits future hybridization. so...the more genetic engineering the better to limit future hybridization? just sayin'...-->