Inbreeding depression in conservation biology

Inbreeding depression is of major concern in the management and conservatio n of endangered species. Inbreeding appears universally to reduce fitness, but its magnitude and specific effects are highly variable because they dep end on the genetic constitution of the species or populations and on how th ese genotypes interact with the environment. Recent natural experiments are consistent with greater inbreeding depression in more stressful environmen ts. In small populations of randomly mating individuals, such as are charac teristic of many endangered species, all individuals may suffer from inbree ding depression because of the cumulative effects of genetic drift that dec rease the fitness of all individuals in the population. In three recent cas es, introductions into populations with low fitness appeared to restore fit ness to levels similar to those before the effects of genetic drift. Inbree ding depression may potentially be reduced, or purged, by breeding related individuals. However, the Speke's gazelle example, often cited as a demonst ration of reduction of inbreeding depression, appears to be the result of a temporal change in fitness in inbred individuals and not a reduction in in breeding depression.