OF MICE AND HABITATS - TESTS FOR DENSITY-DEPENDENT HABITAT SELECTION

We compared the demography, fitness (measured indirectly as a set of proxies), and interhabitat movements of white-footed mice occupying three contiguous habitats (woodlot, early successional old-field, and pasture) to determine if the populations conformed to the ideal-free or ideal-despotic model of density-dependent habitat selection. Population densities differed markedly among habitats: old-field > woodlot > pasture. No significant difference in the proportions of age-classes existed among habitats. However, the old-field population had a significantly higher proportion of pregnant females than the woodlot or pasture populations. An increase in subadult recruitment to old-field population, following a drastic decline in adult density during the autumn and winter, suggests that adult mice may have prevented recruitment prior to the decline through territoriality. Recruitment did not occur in the woodlot or pasture. We detected no influx of subadult mice into the old-field following the decline. We speculate that the recruits represent mice born within the habitat during the autumn/winter that subsequently occupied the vacant territories. The fitness components exhibited no significant differences among the populations, but trends indicate that young mice grew faster and adult females had longer residence times in the old-field, and males tended toward larger body size in the woodlot. When comparing only summer growth rates, young mice grew significantly faster in the old-field than young mice in the other habitats. Our results suggest that the P. leucopus populations we studied exhibit an ideal-despotic distribution; with fitness highest in the old-field, intermediate in the woodlot, and lowest in the pasture. This general trend was positively correlated with density; a key assumption of the ideal-despotic model.