HABITAT FRAGMENTATION AND MOVEMENTS OF 3 SMALL MAMMALS (SIGMODON, MICROTUS, AND PEROMYSCUS)

We studied the effects of habitat fragmentation on the movements of co tton rats (Sigmodon hispidus), deer mice (Peromyscus maniculatus), and prairie voles (Microtus ochrogaster) living in a fragmented landscape using 7.7 yr (1984-1992) of mark-recapture data. The study area inclu ded three kinds of 0.5-ha blocks: single large patches (5000 m(2)), cl usters of medium patches (288 m(2)), and clusters of small patches (32 m(2)). We tested three predictions regarding animal movements. First, animals should move longer distances as fragmentation increases. Seco nd, the proportion of animals moving will decrease as fragmentation in creases. Third, species will show more movement from putative sources to putative sinks. In support of our first two predictions, all specie s (except male cotton rats) moved farther, and lower proportions of an imals moved, as fragmentation increased. In testing our third predicti on, we found no trends, for all species, between patch size and the ne t number of animals a block either imported or exported, indicating so urce-sink dynamics were probably not occurring on our study site. Furt hermore, animals of all species (except female deer mice) switched mor e frequently to blocks of larger patches. For prairie voles in the spr ing and deer mice in the summer, relative abundances among blocks pred icted from a Markov matrix model of switching probabilities showed hig h congruence with the actual abundances, indicating movement and abund ances were related. In both cotton rats and prairie voles but not in d eer mice, more juveniles and nonreproductive animals switched between blocks than did adults or reproductive animals. Deer mice switched mor e frequently than did either cotton rats or prairie voles; the latter species switched in similar frequencies. We discuss the implications o f our data for modeling and conservation.