Population bottleneck

A population bottleneck or genetic bottleneck is a sharp reduction in the size of a population due to environmental events such as famines, earthquakes, floods, fires, disease, and droughts; or human activities such as specicide, widespread violence or intentional culling, and human population planning. Such events can reduce the variation in the gene pool of a population; thereafter, a smaller population, with a smaller genetic diversity, remains to pass on genes to future generations of offspring through sexual reproduction. Genetic diversity remains lower, increasing only when gene flow from another population occurs or very slowly increasing with time as random mutations occur. This results in a reduction in the robustness of the population and in its ability to adapt to and survive selecting environmental changes, such as climate change or a shift in available resources. Alternatively, if survivors of the bottleneck are the individuals with the greatest genetic fitness, the frequency of the fitter genes within the gene pool is increased, while the pool itself is reduced. The genetic drift caused by a population bottleneck can change the proportional random distribution of alleles and even lead to loss of alleles. The chances of inbreeding and genetic homogeneity can increase, possibly leading to inbreeding depression. Smaller population size can also cause deleterious mutations to accumulate. Population bottlenecks play an important role in conservation biology (see minimum viable population size) and in the context of agriculture (biological and pest control). Scientists have witnessed population bottlenecks in American bison, greater prairie chickens, northern elephant seals, golden hamsters, and cheetahs. The New Zealand black robins experienced a bottleneck of five individuals, all descendants of a single female. Geneticists have found evidence for past bottlenecks in pandas, golden snub-nosed monkeys, and humans. Minimum viable population In conservation biology, minimum viable population (MVP) size helps to determine the effective population size when a population is at risk for extinction.