DEMOGRAPHIC CONSEQUENCES OF INBREEDING IN REMNANT POPULATIONS

Although traditional population fragmentation theory and management ha s been strongly oriented toward concerns arising from inbreeding depre ssion, recent papers suggest that small populations will be eliminated by demographic and/or environmental events before inbreeding becomes a problem. We explore the interaction between these factors by develop ing a stochastic, discrete time Leslie model that incorporates inbreed ing depression. We model small population dynamics with three realisti c demographic schedules: low growth rate ''ungulates,'' medium growth rate ''felids,'' and high growth rate ''rodents,'' examining the impac t of survival and fertility depression commensurate with inbreeding ef fects reported in the literature. Focusing on the first few generation s after habitat fragmentation and isolation, we find that (a) high gro wth rate populations are affected only by strong inbreeding depression , but low growth rate populations are extremely vulnerable to even min or inbreeding depression; (b) vulnerability to extinction is affected more by survival depression than by fecundity depression; and (c) redu ctions in the sex ratio exacerbate inbreeding accumulation and hence e xtinction rate. Counter to the current fashion, which downplays the im portance of inbreeding in stochastic environments, we conclude that, w hile inbreeding depression is not necessarily the primary cause of ext inction, it can be critical.