population fragmentation

Population fragmentation can be the cause of natural forces or human actions, although in modern times, human activity is the most common cause.Disrupting evolutionary processes: The effect of habitat fragmentation on collared lizards in the Missouri Ozarks Alan R. Templeton, Robert J. Robertson, Jennifer Brisson, Jared Strasburg Proceedings of the National Academy of Sciences May 2001, 98 (10) 5426-5432; {{doi|10.1073/pnas.091093098}} Some general causes of fragmentation are:

• the development of land around a protected area, even through the addition of a single road lane or fence line,
• the captivity, capture or killing of species in an area that links populations,
• the movement of a population away from other individuals of that species, such as the natural introduction of wolves and moose on Isle Royale,
• geologic processes, such as landslides or volcanoes, dividing a habitat
• rising sea levels separating islands from what was once a common landmass,
• global warming, especially when coupled with mountains, reducing movement from one habitat to another.{{Cite journal|last1=Hermes|first1=Claudia|last2=Keller|first2=Klaus|last3=Nicholas|first3=Robert E.|last4=Segelbacher|first4=Gernot|last5=Schaefer|first5=H. Martin|date=2018-01-24|title=Projected impacts of climate change on habitat availability for an endangered parakeet|journal=PLOS ONE|volume=13|issue=1|pages=e0191773|doi=10.1371/journal.pone.0191773|pmid=29364949|issn=1932-6203|pmc=5783391|bibcode=2018PLoSO..1391773H|doi-access=free}}

Population fragmentation may cause inbreeding depression, which leads to a decrease in genetic variability in the species involved.{{Citation |last1=Proctor |first1=M. F. |last2=McLellan |first2=B. N. |last3=Strobeck |first3=C. |name-list-style=amp |last4=Barclay |first4=R. M. R. |year=2005 |title=Genetic analysis reveals demographic fragmentation of grizzly bears yielding vulnerably small populations |journal=Proceedings of the Royal Society B |volume=272 |issue=1579 |pages=2409–2416 |doi=10.1098/rspb.2005.3246 |pmid=16243699 |pmc=1559960 }}. This decreases the fitness of the population for several reasons. First, inbreeding forces competition with relatives, which decreases the evolutionary fitness of the species. Secondly, the decrease in genetic variability causes an increased possibility a lethal homozygous recessive trait may be expressed; this decreases the average litter size reproduced, indirectly decreasing the population.{{Citation |last=Krebs |first=C. J. |year=2009 |title=Ecology: The Experimental Analysis of Distribution and Abundance |edition=6th |publisher=Benjamin Cummings |location=San Francisco |isbn=978-0-321-50743-3 }}. When a population is small, the influence of genetic drift increases, which leads to less and/or random fixation of alleles. In turn, this leads to increased homozygosity, negatively affecting individual fitness. The performance of plants may be compromised by less effective selection which causes an accumulation of deleterious mutations in small populations. Since individuals in small populations are more likely to be related, they are more likely to inbreed. A reduction in fitness may occur in small plant populations because of mutation accumulation, reduced genetic diversity, and increased inbreeding.Young, A., Boyle, T., & Brown, T. (1996). The population genetic consequences of habitat fragmentation for plants. Trends in Ecology & Evolution, 11(10), 413-418. {{doi|10.1016/0169-5347(96)10045-8}} Over time, the evolutionary potential and ability of a species to adapt to a changing environment, such as climate change, is decreased.Leimu, R., Vergeer, P., Angeloni, F., & Ouborg, N. J. 2010. Habitat fragmentation, climate change, and inbreeding in plants. The Year in Ecology and Conservation Biology 1195:84-98. In addition, the limited ability to adapt to changes due to inadequate gene flow can also increase a species susceptibility to extinction.{{Cite journal |last1=Richard |first1=Frankham |last2=D. |first2=Ballou, Jonathan |last3=Katherine |first3=Ralls |last4=Eldridge, Mark D. B. |last5=R. |first5=Dudash, Michele |last6=B. |first6=Fenster, Charles |last7=C. |first7=Lacy, Robert |last8=Paul |first8=Sunnucks |date=2019-10-23 |title=Population fragmentation causes inadequate gene flow and increases extinction risk |url=https://academic.oup.com/book/35098/chapter-abstract/299165314?redirectedFrom=fulltext |journal=OUP Academic |language=en |doi=10.1093/o |doi-broken-date=1 May 2025 |archive-url=http://web.archive.org/web/20230530034302/https://academic.oup.com/book/35098/chapter-abstract/299165314?redirectedFrom=fulltext |archive-date=2023-05-30}}

Other instances of population fragmentation show that while population bottlenecks resulting from fragmentation should lower genetic diversity over time, as mentioned, some species that experience these changes are able to maintain high levels of genetic diversity.{{Cite journal |last1=Hill |first1=Peta |last2=Dickman |first2=Chris R. |last3=Dinnage |first3=Russell |last4=Duncan |first4=Richard P. |last5=Edwards |first5=Scott V. |last6=Greenville |first6=Aaron |last7=Sarre |first7=Stephen D. |last8=Stringer |first8=Emily J. |last9=Wardle |first9=Glenda M. |last10=Gruber |first10=Bernd |date=2023-10-24 |title=Episodic population fragmentation and gene flow reveal a trade-off between heterozygosity and allelic richness |url=https://pubmed.ncbi.nlm.nih.gov/37873908 |journal=Molecular Ecology |volume=32 |issue=24 |pages=6766–6776 |doi=10.1111/mec.17174 |issn=1365-294X |pmid=37873908|bibcode=2023MolEc..32.6766H |doi-access=free }} Population fragmentation into multiple, smaller subpopulations, and with periods of low gene flow, is able to adequately preserve allelic richness, the number of alleles in a population, at the expense of heterozygosity - increases the Loss of heterozygosity.

Population fragmentation by habitat fragmentation has been shown to increase the genetic differentiation between different subpopulations as there is less gene flow due to the physical separation.{{Cite journal |last1=Alcaide |first1=M. |last2=Serrano |first2=D. |last3=Negro |first3=J. J. |last4=Tella |first4=J. L. |last5=Laaksonen |first5=T. |last6=Müller |first6=C. |last7=Gal |first7=A. |last8=Korpimäki |first8=E. |date=2008-10-15 |title=Population fragmentation leads to isolation by distance but not genetic impoverishment in the philopatric Lesser Kestrel: a comparison with the widespread and sympatric Eurasian Kestrel |url=https://www.nature.com/articles/hdy2008107 |journal=Heredity |language=en |volume=102 |issue=2 |pages=190–198 |doi=10.1038/hdy.2008.107 |issn=1365-2540|hdl=10261/38901 |hdl-access=free }}

Population fragmentation can result in reduced gene flow, increasing the risk for inbreeding depression and extinction overall. However, the implications of population fragmentation on conservation efforts requires further research. Gene flow, which is the introduction of new alleles into a population, leads to genetically and phenotypically similar organisms. Additionally, it can increase biodiversity in a population by introducing new alleles from various individuals. To reduce the effects, or prevent population fragmentation, researchers propose multiple solutions as it relates to human activity. First, they state that the removal of barriers (i.e., fencing, highways) could restore populations. {{Cite journal |last1=Beer |first1=Stephanie Dowell |last2=Bartron |first2=Meredith L. |last3=Argent |first3=David G. |last4=Kimmel |first4=William G. |date=May 2019 |title=Genetic Assessment Reveals Population Fragmentation and Inbreeding in Populations of Brook Trout in the Laurel Hill of Pennsylvania |url=https://academic.oup.com/tafs/article/148/3/620/7819465 |journal=Transactions of the American Fisheries Society |language=en |volume=148 |issue=3 |pages=620–635 |doi=10.1002/tafs.10153 |bibcode=2019TrAFS.148..620B |issn=0002-8487|url-access=subscription }} This is especially relevant for urban areas, where building infrastructure can physically prevent back-and-forth movement between habitats, forcing them to relocate or even form new populations. However, barrier removal is not always possible, especially in rapidly urbanizing environments.

A second proposed solution is to maintain connectivity between habitats located beyond barriers, as well as high-quality habitats (i.e., climate control, reduced pollution levels). It must be noted, though, that researchers had aquatic species in mind when proposing these solutions and they may not have the same applications for terrestrial organisms. Furthermore, the effects of climate change may make it difficult to achieve these solutions without relevant legislation. Similarly, researchers from a separate study proposed resisting policies that support habitat fragmentation and controlling human access to habitats as to not disrupt them. {{Cite journal |last1=Proctor |first1=Michael F. |last2=Paetkau |first2=David |last3=Mclellan |first3=Bruce N. |last4=Stenhouse |first4=Gordon B. |last5=Kendall |first5=Katherine C. |last6=Mace |first6=Richard D. |last7=Kasworm |first7=Wayne F. |last8=Servheen |first8=Christopher |last9=Lausen |first9=Cori L. |last10=Gibeau |first10=Michael L. |last11=Wakkinen |first11=Wayne L. |last12=Haroldson |first12=Mark A. |last13=Mowat |first13=Garth |last14=Apps |first14=Clayton D. |last15=Ciarniello |first15=Lana M. |date=2012 |title=Population fragmentation and inter-ecosystem movements of grizzly bears in western Canada and the northern United States |url=https://wildlife.onlinelibrary.wiley.com/doi/10.1002/wmon.6 |journal=Wildlife Monographs |language=en |volume=180 |issue=1 |pages=1–46 |doi=10.1002/wmon.6 |issn=1938-5455|url-access=subscription }} Again, this may only be achievable through policy implementation. Lastly, understanding the implications of climate change and differing species can be impacted based on their ecological niche requires further research.

• Metapopulation
• Wildlife corridor
• Habitat fragmentation

Fragmentation

Category:Habitat

Category:Environmental conservation

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