When does conservation genetics matter?

Is this short review we explore the genetic threats facing declining popula tions, focusing in particular on empirical studies and the emerging questio ns they raise. At face value, the two primary threats are slow erosion of g enetic variability by drift and short-term lowering of fitness owing to inb reeding depression, of which the latter appears the more potent force. Howe ver, the picture is not this simple. Populations that have passed through a severe bottleneck can show a markedly reduced ability to respond to change , particularly in the face of novel challenges. At the same time, several r ecent studies reveal subtle ways in which species are able to retain more u seful genetic variability than they 'should', for example by enhanced repro ductive success among the most outbred individuals in a population. Such fi ndings call into question the validity of simple models based on random mat ing, and emphasize the need for more empirical data aimed at elucidating pr ecisely what happens in natural populations.