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Why do small isolated habitat patches increase the risk of inbreeding?

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wetland restoration — ecological restoration Wetland restoration along the Târnava Mică (Tîrnava Mică) River in Romania. A former gravel mine (left) was transformed into a functional wetland (right).

Small, isolated habitat patches increase the risk of inbreeding primarily because they restrict the available pool of potential mates. When a population is confined to a small, fragmented area, individuals are more likely to mate with close relatives, which narrows the genetic base and increases the probability that offspring will inherit identical alleles from a common ancestor.123

This process is exacerbated by the limited number of reproducing individuals within these patches. In such small groups, the lack of immigration from other populations prevents the introduction of new, diverse genes, forcing the population to rely on its existing, often limited, genetic pool. Over time, this leads to higher rates of inbreeding, which can result in "inbreeding depression"—a condition characterized by reduced fertility, slower growth rates, and increased susceptibility to disease.4153

Conservation biologists address these risks by attempting to foster ecological linkages between patches and increasing the overall size of habitat areas to maintain healthy, genetically diverse populations.1