Viability analysis of endangered Gulf Coast beach mice ( Peromyscus polionotus) populations

Abstract

Beach mice, endangered subspecies of oldfield mice ( Peromyscus polionotus), occur in a few, isolated populations along the Gulf Coast of Alabama and Florida, USA. To provide information needed for the management of these species, we conducted population viability analyses (PVA) using a stochastic differential equation (Wiener-drift) model applied to long-term demographic data for four populations of beach mice. In the absence of catastrophic events, the probability that the mouse populations would decline to one mouse ranged from 0.002 for the population of Alabama beach mice ( P. p. ammobates) at the Perdue unit of Bon Secour National Wildlife Refuge (BSPU) to 1.00 for the Perdido Key beach mouse ( P. p. trissyllepsis) population at Gulf Island National Seashore (GINS). Modal time to extinction for those sample paths reaching extinction ranged from 5 years for the Fort Morgan population of Alabama beach mice to 21 years for the GINS population of Perdido Key beach mice. When the BSPU data set was extended to include data collected following Hurricane Opal, the probability of extinction increased to 0.479. If catastrophic events, which are frequent in the Gulf Coast habitats, are considered, virtually all populations of beach mice appear in substantial danger of extinction unless current levels of habitat fragmentation are reversed. In addition, ongoing development continues to reduce or fragment the habitat exacerbating the already precarious existence of these mice. It is our conclusion that the results obtained from the PVA analyses provide independent evidence that further loss of beach mouse habitat (including the scrub dune component) should be avoided, and that populations should be re-established within their historic range wherever feasible.