A spatially explicit hierarchical model to characterize population viability

摘要

Many of the processes that govern the viability of animal populations vary spatially, yet population viability analyses (PVAs) that account explicitly for spatial variation are rare. We develop a PVA model that incorporates autocorrelation into the analysis of local demographic information to produce spatially explicit estimates of demography and viability at relatively fine spatial scales across a large spatial extent. We use a hierarchical, spatial, autoregressive model for capture-recapture data from multiple locations to obtain spatially explicit estimates of adult survival (Φ_(ad)), juvenile survival (Φ_(juv)), and juvenile-to-adult transition rates (λ), and a spatial autoregressive model for recruitment data from multiple locations to obtain spatially explicit estimates of recruitment (R).We combine local estimates of demographic rates in stage-structured population models to estimate the rate of population change (k), then use estimates of λ (and its uncertainty) to forecast changes in local abundance and produce spatially explicit estimates of viability (probability of extirpation, P_(ex)). We apply the model to demographic data for the Sonoran desert tortoise (Gopherus morafkai) collected across its geographic range in Arizona. There was modest spatial variation in ^k (0.94-1.03), which reflected spatial variation in Φ_(ad) (0.85-0.95), Φ_(juv) (0.70-0.89), and λ (0.07-0.13). Recruitment data were too sparse for spatially explicit estimates; therefore, we used a range-wide estimate (R=0.32 1-yr-old females per female per year). Spatial patterns in demographic rates were complex, but Φ_(ad), Φ_(juv), and λ tended to be lower and λ higher in the northwestern portion of the range. Spatial patterns in P_(ex) varied with local abundance. For local abundances >500, P_(ex) was near zero (<0.05) across most of the range after 100 yr; as abundances decreased, however, P_(ex) approached one in the northwestern portion of the range and remained low elsewher