6 - Ecological factors in population persistence

The smaller the population the greater the chance

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Unformatted text preview: may lead to extinction. E.g. Dusky Seaside Sparrow doomed to extinction when in 1978-1979, all remaining females died, leaving only 6 surviving males in 1980 (extinct in 1987). Ammodramus maritimus nigrescens M6.13 BIO 3115 Université d’Ottawa / University of Ottawa Sources of uncertainty (stochasticity) II: environmental uncertainty Unpredictable events such as changes in weather, food supply and population density of competitors, parasites and predators result in random reductions in mean (population) birth rates and/or survivorship The smaller the population, the greater the chance that these events may lead to extinction. E.g. Black-footed ferret (endangered sp) declined in July 1985 due to outbreak of plague killing the prairie dogs (prey) and canine distemper. In 1987 only 18 left in the wild. Mustela nigripes M6.14 BIO 3115 Université d’Ottawa / University of Ottawa M6.7 BIO 3115 Conservation Biology Sources of uncertainty (stochasticity) III: natural catastrophes Large-scale unpredictable events (floods, fires, hurricanes), short in duration but wide in impact, which result in wide-spread mortality and/or reduced fecundity. Natural catastrophes may have large impacts even on populations that are quite large, especially if the population has a restricted geographical range. E.g. effects of flooding and rinderpest virus pandemic on large mammal populations in southern Africa in late 19th century. M6.15 BIO 3115 Université d’Ottawa / University of Ottawa Inbreeding and/or genetic drift can lead to reduced genetic variability (and hence, reduced adaptability) and increased juvenile mortality, thereby increasing extinction risk. 1.0 0.8 Outbred (F=0) Inbred (F=1) 0.6 0.4 0.2 0.0 aa Aa AA Genotype Frequency ( ) Genotype frequency Sources of uncertainty (stochasticity) IV: genetic uncertainty Small Ne Large Ne Generations M6.16 BIO 3115 Université d’Ottawa / University of Ottawa M6.8 BIO 3115 Conservation Bio...
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