Delayed density dependence are delays in the effect that density has on population size. They can contribute to population fluctuations and lead to time lags. When the time lag is small, the population shows logistic growth (with no fluctuations). When the time lag is intermediate, populations show damped oscillations (fluctuations become smaller over time). When the time lag is large, the population shows stable limit cycles (regular fluctuations around the carrying capacity). A.J. Nicholson in his experiments, showed that delayed density dependence was a cause of fluctuations in blowfly populations. Additionally, these fluctuations can increase the risk of extinction. Small populations are especially at higher risk due to a number of factors: Chance events are unpredictable events, and can be environmental conditions such as temperature and rainfall. Genetic drift are chance events influence the alleles passed on to the next generation, and can cause allele frequencies to change at random. Finally inbreeding, which is mating between relatives, can make individuals too closely related, and increase the frequency of homozygotes, including harmful alleles.
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