INTRODUCTION AND OBJECTIVES

The worrying prospect that genetic deterioration may threaten the viability of wildlife populations was first brought to the attention of the conservation community by Frankel & Soulé (1981). The issue has since been hotly debated and widely researched. It is reasonable to assume that wildlife may suffer inbreeding and associated inbreeding depression resulting from continuing erosion of natural habitats and increasing reliance on captive breeding. Indeed all evidence points to this being the case (Ralls et al., 1988; Crnokrak & Roff, 1999). In any case there exists a series of simple relationships providing a clear expectation that population viability may be threatened by inbreeding and loss of genetic variation. It is worth briefly reviewing those here.

Since genetic variability is the raw material for evolutionary adaptation, it follows that genetically invariant populations cannot adapt to environmental change, and are thus not ‘buffered’ against it (see Ryan et al., Chapter 6). A corollary of this is that any trait that evolves must have genetic variation, and is consequently open to the effects of loss of genetic variation.

Demographic bottlenecks reduce genetic variability in a manner described by a series of theoretical relationships (Falconer & Mackay, 1996). In general, prolonged small population size is expected to cause a decline in allelic diversity and, to a lesser extent, heterozygosity. Conversely, if a population recovers quickly from a bottleneck then loss of genetic variation, especially heterozygosity, may be minimal.