Biology 2485B Lecture Notes - Lecture 18: Allele Frequency, Allele, Inbreeding Depression

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The balance of these processes determines whether the population grows, stays the same or decline s. 5 major current threats to biodiversity: they decrease birth and increase deaths. Population growth rate = birth + immigration deaths - emigration. If population size decreases below the blue line, it enters the zone of positive feedback: the population growth rate is smaller here and causes a low population size. Other reasons why a population might not rebound when its size is pushed too low: random demographic events (ex. skew in sex ratio, genetic effects (loss of genetic variation and inbreeding) These can also set up positive feedback loops that reduce population size further. Stochastic events and processes cannot be definitely predicted only their probability of occurrence can be known. Small populations are susceptible to: demographic stochasticity, environmental stochasticity, genetic stochasticity. Populations of hermaphrodite individuals: each individual can produce 0, 1 or 2 offspring with equal probability (each having the probability of 1/3)

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