He and his colleagues also compared both groups' DNA to preserved samples of prairie chicken DNA from the 1930s. The DNA from the earlier birds closely resembled that of modern birds from outside Illinois, confirming that the prairie chicken population at large was once part of a giant, interbreeding group. As the Illinois populations became more and more fragmented, each group's collective gene pool came to represent a smaller and smaller portion of the original whole. Genetic peculiarities became magnified thanks to lack of recruitment from other groups, until the two remaining Illinois populations barely resembled their common, ancestral population. There are many factors that conspire against small, isolated populations, and ecologists have long wondered how to weigh their relative importance.
Small populations are particularly vulnerable to catastrophic events.
An epidemic or an earthquake can wipe out all of a small group's members, while a larger, wide- ranging group would be barely perturbed. Isolated populations are also vulnerable to the genetic consequences of inbreeding, which can magnify the presence of harmful genes and reduce reproductive success. The cheetah, the Florida panther and the black-footed ferret have all fallen victim to this fate. Isolated groups of humans are vulnerable as well. The Amish of Pennsylvania experience higher rates of genetic disorders than are found in the population at large.