Editing Habitat fragmentation (section)

=== Habitat and biodiversity loss ===
{{Main|biodiversity loss}}
One of the major ways that habitat fragmentation affects [[biodiversity]] is by reducing the amount of suitable habitat available for organisms. Habitat fragmentation often involves both [[habitat destruction]] and the subdivision of previously continuous habitat.<ref>{{cite journal|last1=Fahrig|first1=Lenore|title=Effects of Habitat Fragmentation on Biodiversity|journal=Annual Review of Ecology, Evolution, and Systematics|date=November 2003|volume=34|issue=1|pages=487–515|doi=10.1146/annurev.ecolsys.34.011802.132419}}</ref> Plants and other [[Sessility (zoology)|sessile]] organisms are disproportionately affected by some types of habitat fragmentation because they cannot respond quickly to the altered spatial configuration of the habitat.<ref name="Lienert2004">{{cite journal|last1=Lienert|first1=Judit|title=Habitat fragmentation effects on fitness of plant populations – a review|journal=Journal for Nature Conservation|date=July 2004|volume=12|issue=1|pages=53–72|doi=10.1016/j.jnc.2003.07.002|bibcode=2004JNatC..12...53L }}</ref> Habitat fragmentation consistently reduces biodiversity by 13 to 75% and impairs key ecosystem functions by decreasing biomass and altering [[nutrient cycle]]s. This underscores the severe and lasting ecological impacts of fragmentation, which could be highlighted in the sections discussing the consequences of fragmentation.<ref name="ReferenceA">{{Cite journal |last1=Haddad |first1=Nick M. |last2=Brudvig |first2=Lars A. |last3=Clobert |first3=Jean |last4=Davies |first4=Kendi F. |last5=Gonzalez |first5=Andrew |last6=Holt |first6=Robert D. |last7=Lovejoy |first7=Thomas E. |last8=Sexton |first8=Joseph O. |last9=Austin |first9=Mike P. |last10=Collins |first10=Cathy D. |last11=Cook |first11=William M. |last12=Damschen |first12=Ellen I. |last13=Ewers |first13=Robert M. |last14=Foster |first14=Bryan L. |last15=Jenkins |first15=Clinton N. |date=2015-03-06 |title=Habitat fragmentation and its lasting impact on Earth's ecosystems |journal=Science Advances |language=en |volume=1 |issue=2 |pages=e1500052 |doi=10.1126/sciadv.1500052 |issn=2375-2548 |pmc=4643828 |pmid=26601154|bibcode=2015SciA....1E0052H }}</ref>

Habitat loss, which can occur through the process of habitat fragmentation, is considered to be the greatest threat to species.<ref>{{cite journal | last1 = Wilcove | first1 = David S. |display-authors=etal | year = 1998 | title = Quantifying Threats to Imperiled Species in the United States | jstor = 1313420 | journal = BioScience | volume = 48 | issue = 8| pages = 607–615 | doi=10.2307/1313420| doi-access = free}}</ref> But, the effect of the configuration of habitat patches within the landscape, independent of the effect of the amount of habitat within the landscape (referred to as fragmentation per se<ref name="Fahrig2003">{{cite journal | last1 = Fahrig | first1 = L | year = 2003 | title = Effects of habitat fragmentation on biodiversity | journal = Annual Review of Ecology, Evolution, and Systematics | volume = 34 | pages = 487–515 | doi=10.1146/annurev.ecolsys.34.011802.132419}}</ref>), has been suggested to be small.<ref name="Fahrig2013">{{cite journal | last1 = Fahrig | first1 = L | year = 2013 | title = Rethinking patch size and isolation effects: the habitat amount hypothesis | journal = J. Biogeogr. | volume = 40 | issue = 9| pages = 1649–1663 | doi = 10.1111/jbi.12130 | bibcode = 2013JBiog..40.1649F | doi-access = free}}</ref> A review of empirical studies found that, of the 381 reported significant effect of habitat fragmentation per se on species occurrences, abundances or diversity in the scientific literature, 76% were positive whereas 24% were negative.<ref name="Fahrig2017">{{cite journal | last1 = Fahrig | first1 = L | year = 2017 | title = Ecological Responses to Habitat Fragmentation Per Se | journal = Annual Review of Ecology, Evolution, and Systematics | volume = 48 | pages = 1–23 | doi = 10.1146/annurev-ecolsys-110316-022612}}</ref> Despite these results, the scientific literature tends to emphasize negative effects more than positive effects.<ref>{{Cite book |last=Fahrig |first=Lenore |url=https://academic.oup.com/book/26688/chapter/195480099 |title=Forty years of bias in habitat fragmentation research |date=2017-12-21 |publisher=Oxford University Press |volume=1 |language=en |doi=10.1093/oso/9780198808978.003.0005|isbn=978-0-19-880897-8 }}</ref> Positive effects of habitat fragmentation per se imply that several small patches of habitat can have higher conservation value than a single large patch of equivalent size.<ref name="Fahrig2017" /> Land sharing strategies could therefore have more positive impacts on species than land sparing strategies.<ref name="Fahrig2017" /> Although the negative effects of habitat loss are generally viewed to be much larger than that of habitat fragmentation, the two events are heavily connected and observations are not usually independent of one another.<ref>{{Cite journal |doi=10.1016/j.biocon.2018.07.022| s2cid=52839843 | title=Is habitat fragmentation good for biodiversity? | year=2018 | last1=Fletcher | first1=Robert J. | last2=Didham | first2=Raphael K. | last3=Banks-Leite | first3=Cristina | last4=Barlow | first4=Jos | last5=Ewers | first5=Robert M. | last6=Rosindell | first6=James | last7=Holt | first7=Robert D. | last8=Gonzalez | first8=Andrew | last9=Pardini | first9=Renata | last10=Damschen | first10=Ellen I. | last11=Melo | first11=Felipe P.L. | last12=Ries | first12=Leslie | last13=Prevedello | first13=Jayme A. | last14=Tscharntke | first14=Teja | last15=Laurance | first15=William F. | last16=Lovejoy | first16=Thomas | last17=Haddad | first17=Nick M. | journal=Biological Conservation | volume=226 | pages=9–15 | bibcode=2018BCons.226....9F | url=https://eprints.lancs.ac.uk/id/eprint/126675/1/Fletcher_etal_2018_Biological_Conservation.pdf }}</ref>[[File:Indiana Dunes Habitat Fragmentation.jpg|thumb|right|300px|Habitat fragmented by numerous roads near the [[Indiana Dunes National Park]].]]
Area is the primary determinant of the number of species in a fragment<ref name="Rosenzweig">{{cite book | last = Rosenzweig | first = Michael L. | author-link = Michael Rosenzweig | title = Species diversity in space and time | year = 1995 | publisher = [[Cambridge University Press]] | location = Cambridge}}</ref> and the relative contributions of demographic and genetic processes to the risk of global population extinction depend on habitat configuration, stochastic environmental variation and species features.<ref>{{cite journal | last1 = Robert | first1 = A | year = 2011 | title = Find the weakest link. A comparison between demographic, genetic and demo-genetic metapopulation extinction times | journal = BMC Evolutionary Biology | volume = 11 | issue = 1 | page = 260 | doi = 10.1186/1471-2148-11-260 | pmid = 21929788 | pmc = 3185286 | bibcode = 2011BMCEE..11..260R | doi-access = free }}</ref> Minor fluctuations in climate, resources, or other factors that would be unremarkable and quickly corrected in large populations can be catastrophic in small, isolated populations. Thus fragmentation of habitat is an important cause of species extinction.<ref name="Rosenzweig" /> Population dynamics of subdivided populations tend to vary [[wikt:asynchronous|asynchronous]]ly. In an unfragmented landscape a declining population can be "rescued" by immigration from a nearby expanding population. In fragmented landscapes, the distance between fragments may prevent this from happening. Additionally, unoccupied fragments of habitat that are separated from a source of [[Colonisation (biology)|immigrants]] by some barrier are less likely to be repopulated than adjoining fragments. Even small species such as the [[Columbia spotted frog]] are reliant on the [[rescue effect]]. Studies showed 25% of juveniles travel a distance over 200m compared to 4% of adults. Of these, 95% remain in their new locale, demonstrating that this journey is necessary for survival.<ref>{{cite journal |author1=Funk W.C. |author2=Greene A.E. |author3=Corn P.S. |author4=Allendorf F.W. | year = 2005 | title = High dispersal in a frog species suggests that it is vulnerable to habitat fragmentation | journal = [[Biology Letters|Biol. Lett.]] | volume = 1 | issue = 1| pages = 13–6 | doi=10.1098/rsbl.2004.0270|pmid=17148116 |pmc=1629065|bibcode=2005BiLet...1...13F }}</ref>

Additionally, habitat fragmentation leads to [[edge effect]]s. Microclimatic changes in light, temperature, and wind can alter the ecology around the fragment, and in the interior and exterior portions of the fragment.<ref>{{Cite journal|last1=Magnago|first1=Luiz Fernando Silva|last2=Rocha|first2=Mariana Ferreira|last3=Meyer|first3=Leila|last4=Martins|first4=Sebastião Venâncio|last5=Meira-Neto|first5=João Augusto Alves|date=September 2015|title=Microclimatic conditions at forest edges have significant impacts on vegetation structure in large Atlantic forest fragments|journal=Biodiversity and Conservation|language=en|volume=24|issue=9|pages=2305–2318|doi=10.1007/s10531-015-0961-1|bibcode=2015BiCon..24.2305M |s2cid=16927557|issn=0960-3115|url=http://www.locus.ufv.br/handle/123456789/21347|url-access=subscription}}</ref> [[wildfire|Fires]] become more likely in the area as humidity drops and temperature and wind levels rise. Exotic and pest species may establish themselves easily in such disturbed environments, and the proximity of domestic animals often upsets the natural ecology. Also, habitat along the edge of a fragment has a different climate and favours different species from the interior habitat. Small fragments are therefore unfavourable for species that require interior habitat. The percentage preservation of contiguous habitats is closely related to both genetic and species biodiversity preservation. Generally a 10% remnant contiguous habitat will result in a 50% [[biodiversity loss]].<ref>{{Cite book |last=Quammen |first=David |title=The song of the dodo: Island biogeography in an age of extinctions |date=2004 |publisher=Scribner |isbn=978-0-684-82712-4 |location=New York, NY}}</ref>

Much of the remaining terrestrial [[wildlife]] habitat in many third world countries has experienced fragmentation through the development of [[Urban sprawl|urban expansion]] such as roads interfering with [[habitat loss]]. Aquatic species’ habitats have been fragmented by [[dam]]s and [[Interbasin transfer|water diversions]].<ref name="Habitat Loss">{{Cite web|url=https://www.nwf.org/Home/Educational-Resources/Wildlife-Guide/Threats-to-Wildlife/Habitat-Loss|title=Habitat Loss|website=National Wildlife Federation|language=en|access-date=2020-03-06}}</ref> These fragments of habitat may not be large or connected enough to support species that need a large territory where they can find mates and food. The loss and fragmentation of habitats makes it difficult for migratory species to find places to rest and feed along their migration routes.<ref name="Habitat Loss" />

The effects of current fragmentation will continue to emerge for decades. Extinction debts are likely to come due, although the counteracting immigration debts may never fully be paid. Indeed, the experiments here reveal ongoing losses of biodiversity and ecosystem functioning two decades or longer after fragmentation occurred. Understanding the relationship between transient and long-term dynamics is a substantial challenge that ecologists must tackle, and fragmentation experiments will be central for relating observation to theory.<ref name="Haddad2015"/>