LONG-TERM DYNAMICS IN A METAPOPULATION OF THE AMERICAN PIKA

A 20-yr study of a metapopulation of the American pika revealed a regi onal decline in occupancy in one part of a large network of habitat pa tches. We analyze the possible causes of this decline using a;spatiall y realistic metapopulation model, the incidence function model. The pi ka metapopulation is the best-known mammalian example of a classical m etapopulation with significant population turnover, and it satisfies c losely the assumptions of the incidence function model, which was para meterized with data on patch occupancy. The model-predicted incidences of patch occupancy are consistent with observed incidences, and the m odel predicts well the observed turnover rate between four metapopulat ion censuses. According to model predictions, the part of the metapopu lation where the decline has been observed is relatively unstable and prone to large oscillations in patch occupancy, whereas the other part of the metapopulation is predicted to be persistent. These results de monstrate how extinction-colonization dynamics may produce spatially c orrelated patterns of patch occupancy without any spatially correlated processes in local dynamics or extinction rate. The unstable part of the metapopulation gives an empirical example of multiple quasi equili bria in metapopulation dynamics. Phenomena similar to those observed h ere may cause fluctuations in species' range limits.