5 - Population Persistance

M519 population bottlenecks and founder effects a

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Unformatted text preview: in size. founder effects occur when a few individuals from the ancestral population establish a new population. In both cases, the gene pool is dramatically reduced, such that genetic variability is also reduced. Population size Bio 3115 Université d’Ottawa / University of Ottawa Bottleneck Time Ancestral population New population M5.20 Bio 3115 Université d’Ottawa / University of Ottawa M5 2009-2010.10 BIO 3115 Conservation Biology After population bottlenecks or founding events, Ne is dramatically reduced, so variability declines due to drift and/or inbreeding. The % of the original variation remaining (in ancestral population or before the bottleneck) decreases with the severity of the bottleneck and increases with the number of founders. % original variation remaining Loss of genetic variation after population bottlenecks 100 90 80 70 60 50 40 0 20 40 60 80 100 120 Effective population size (N e) M5.21 Bio 3115 Université d’Ottawa / University of Ottawa Founder effects in natural populations of Poeciliopsis monacha Heterozygosity declined to zero during extinction, was low after recolonization due to founder effects, but increased as gene pool supplemented by translocation (immigration). 0.5 Heterozygosity Translocation of 30 individuals 0.4 0.3 0.2 0.1 Tributary Main stream Drought/ extinction Recolonization 1975 1976 1978 1981 1983 1985 Year M5.22 Bio 3115 Université d’Ottawa / University of Ottawa M5 2009-2010.11 BIO 3115 Conservation Biology Evidence for inbreeding depression from population bottlenecks: the Cheetah (Acinonyx jubatus) Cheetah from southern Africa shows such low level of genetic variability that skin grafts can be used between two “unrelated” individuals Low genetic variability is a result of one or two historical population bottlenecks Low genetic variability is coupled with inbreeding depression; including high percentage of abnormal sperm, high infant mortality, and low resistance to diseases M5.23 Bio 3115 Université d’Ottawa / University of Ottawa The lions of Ngorongoro Crater M5.24 Bio 3115 Université d’Ottawa / University of Ottawa M5 2009-2010.12 BIO 3115 Conservation Biology History of the crater population In 1962, population of over 60 adults reduced to less than a dozen due to an epidemic of biting flies. Of these, 4 surviving females bred with 7 immigrant males. Virtually no immigration since population bottleneck. (One male in 45 years.) 5 of 6 extant prides descended directly from original 11 adults; evidence of considerable inbreeding. M5.25 Bio 3115 Université d’Ottawa / University of Ottawa Ngorongoro crater lion population 125 Cubs (<2 Years) Subadults (2-3 years) Adults 100 Number of lions 75...
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