9-3 Effects of Generic Variations on Population Size

What Role Does Genetics Play in the Size of Populations? The Vulnerability of Small, Isolated Populations

In most large populations, genetic diversity is fairly constant. The loss or addition of individuals has little effect on the total gene pool. However, genetic factors can affect the survival and genetic diversity of small, isolated populations.

Several factors can play a role in the loss of genetic diversity and the survival of such populations.

One is the founder effect when a few individuals in a population colonize a new habitat that is geographically isolated from other members of the population. In such cases, limited genetic diversity or variability may threaten the survival of the colonizing population.

Another problem is a demographic bottleneck. It occurs when only a few individuals in a population survive a catastrophe such as a fire or hurricane. Lack of genetic diversity may limit the ability of these individuals to rebuild the population

A third factor is genetic drift. It involves random changes in the gene frequencies in a population that can lead to unequal reproductive success.

A fourth factor is inbreeding. It occurs when individuals in a small population mate with one another. This can increase the frequency of defective genes within a population and affect its long-term survival.

What Are Metapopulations? Exchanging Genes Now and Then

As a landscape becomes fragmented, populations become smaller and more spatially separated. Small disjunct populations can be subject to inbreeding depression and are more apt to be driven extinct by catastrophic events such as severe storms or extreme temperatures.

Such collections of interacting local populations of a species are called metapopulations.