Inbreeding effects in wild populations

USA. Small and isolated populations are inherently more vulnerable to external environmental perturbations and chance fluctuations in local survival and fecundity [termed ‘ENVIRONMENTAL STOCHASTICITY’ and ‘DEMOGRAPHIC STOCHASTICITY’, respectively (see Glossary)]. Are they also threatened by inbreeding and the loss of genetic diversity? With data on the effects of inbreeding in wild populations scarce, some zoologists questioned its importance (or even its existence) in natural populations [1–3]. Recent evidence, however, now suggests that both inbreeding and inbreeding depression are more pervasive than previously realized. In addition, some studies point to inbreeding as an important threat that can directly affect population persistence, making it a key concern for conservation biologists. Here, we review this recent work, including studies of both plant and animal populations that exploit a range of traditional and molecular genetic techniques. Although we emphasize the empirical results, we also present the background theory needed to evaluate critically these approaches and place the results into context.