Habitat Associations and Relative Densities of Rodent Populations in Cultivated Areas of Central Argentina

Small mammals were livetrapped during 12 months in crop fields and weedy borders at 18 sites in central Argentina. A total of 1,652 mammals of 14 species was captured during 33,060 trap-nights. Six species of rodents comprised >95% of captures. Periodically disturbed fields of crops were dominated by Calomys musculinus and C. laucha, and to a lesser extent Mus musculus. A second group composed of Akodon azarae, Bolomys obscurus, and Oligoryzomys flavescens primarily inhabited the more stable, weedy borders of cultivated fields. Peaks in relative densities of C. musculinus, C. laucha, and M. musculus were observed in summer and early autumn, and populations declined to low numbers in winter, following harvest. In contrast, maxima for A. azarae, B. obscurus, and O. flavescens were in late autumn and early winter, and numbers never declined to low values seen for the other species. These characteristic differences in habitat associations and relative densities of pampas rodents may reflect colonizing potential, as both Calomys and Mus potentially are highly opportunistic genera.