Integrated population models for predicting spatial and temporal dynamics at range margins
Most species distribution models fail to include the demographic processes responsible for spatial and temporal variation in density or occurrence, yet process-based models are needed to understand the factors causing range shifts and to inform effective conservation efforts. A major obstacle has been the lack of mechanistic statistical models that can be fitted to field data. Spatially explicit integrated population models (IPMs) are a promising solution, allowing for inference about spatio-temporal population dynamics by combining count data collected at extensive spatial scales with demographic data from smaller plots. In addition, because spatial IPMs are based on point process models, they are not scale dependent and hence can be used to create distribution maps at any extent and resolution. We demonstrate the approach using point count and mist-netting data from a recently initiated study of avian population dynamics at low-latitude range margins in the southern Appalachian Mountains.
Preliminary results indicate that IPMs can yield precise estimates of spatial and temporal variation in density as well as the demographic parameters underlying range shifts. In the southern Appalachians, our findings support the hypothesis that the distributions of populations at low-latitude range margins will contract with rising temperatures. This has important implications because southern populations appear to have been diverging from northern populations prior to rapid, human-caused environmental change, and the loss of these populations could effectively reverse the speciation process.