Interactions of Cotton Rats with a Patchy Environment: Dietary Responses and Habitat Selection

Previous studies on the Texas coastal prairie implicated habitat as the primary factor producing variation in demography and resource use of the cotton rat (Sigmodon hispidus). In this community, secondary succession has resulted in a patchy distribution of habitat types. Hence, dietary responses, individual occurrence, and the process of habitat selection were investigated to elucidate interactions with habitat. Diet measurements for animals constrained to known habitats in each season revealed little variation in diet relative to variation in resource availability. This pattern was maintained by dynamic shifts in resource selectivity. Grasses were most frequent in the diet, forbs were maintained at low levels, and berries were consumed opportunistically. Results of a 2-yr livetrapping census showed that individual cotton rats were nonrandomly distributed on the livetrapping grid. They were positively associated with habitat dominated by monocots and exhibited density-dependent occurrence in dicot and mixed habitat types. Overall, females were more specific to monocot habitat than males, but when lactating they occurred most frequently in mixed habitat, possibly to facilitate acquisition of a balance diet. Habitat selection was analyzed as a simple Markov chain or which transition probabilities were estimated from capture-recapture data. Transition matrices were stationary with respect to density and sex, but not age. Adults were most likely to select a monocot habitat, subadults selected both mixed and monocot habitats, and juveniles were least selective. Behavioral interactions were suggested to account for these age effects.