6 - Ecological factors in population persistence

M69 bio 3115 universit dottawa university of ottawa

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Unformatted text preview: niversity of Ottawa Minimum Viable Population estimation based on genetic considerations: the 50/500 rule of thumb N = 50; the minimum size to required avoid inbreeding depression and thus to maintain genetic variability (based on animal breeding, if N = 50, only 1% of original variability/generationis lost) N = 500; If N = 500, the rate of new genetic variability arising through mutation approximately balances balance the variability lost due to small N. Problems (1) These estimates based on mathematical models and have not been empirically validated. Problems (2): concern is only with loss of genetic variability, which is relevant to population persistence on evolutionary time scales. M6.10 BIO 3115 Université d’Ottawa / University of Ottawa M6.5 BIO 3115 Conservation Biology Deterministic extinction forces are those associated with some inexorable and more or less predictable change or force (e.g. habitat loss of grizzly bears, commercial harvesting of sturgeon). Overexploitation leads to low catches (depletion)! 1992 Annual sturgeon CPUE (kg/licence) Extinction forces I: deterministic forces 1922 150 The Pas 120 A C u m b e r la n d H ouse 90 60 30 0 75 80 85 90 95 Y e a r (1 9 0 0 ) M6.11 BIO 3115 Université d’Ottawa / University of Ottawa Extinction forces II: stochastic forces Stochastic extinction forces are essentially unpredictable factors (e.g. weather) which can produce large-scale fluctuations in population size. Prediction: the larger the susceptibility/exposure of a population to stochastic forces, the larger the population size required to enable it to persist through potential extinction events (i.e. the larger the MVP) Stochastic events resulting in large reductions in population size Population size Time Extinction M6.12 BIO 3115 Université d’Ottawa / University of Ottawa M6.6 BIO 3115 Conservation Biology Sources of uncertainty (stochasticity) in population growth I: demographic uncertainty Effects of random events on the survival and/or reproduction of individuals cause demographic uncertainty. The smaller the population, the greater the chance that these events...
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