EEB215H1 Lecture Notes - Lecture 16: Effective Population Size, Bighorn Sheep, Risk Assessment
6 Nov 2016
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Document Summary
Ne lower than population counts reveal: age, health, sterility, body size, social structure. Only a few males mating even if there are many: dormancy. Unequal sex ratio: chance, selective mortality or harvest, sociality. Variation in reproductive output: variation in offspring number reduces effective population size, some individuals disproportiantely represented in a gene pool of next generation. Result of chance fluctuations in demographic events: ex. Lower breeding potential in individual in a small population; has big consequences at low numbers. Can cause: fluctuations/trophic web imbalances, or direct population fluctuations. In small populations this can lead to dramatic decline. Medecrease in population"s ability to increase in numbers. When population growth rates decreases rather than increases because population sizes are so small. Unable to find a mate because pop size is too low: low density due to low population size. Group that protects itself in large numbers, but pop size so small that they lose that behavioural ability.
