Dietary and morphometric variation in some Peruvian rodent communities: the effect of feeding strategy on evolution

Abstract

This study examines the relationship between feeding strategy and the evolutionary radiation of three genera of broadly sympatric cricetid rodents (Phyllotis, Akodon, Calomys) found in the Andes of southern Peru. Stomach contents from 13 species reveal that although food habits are variable, both intra- and interspecifically, there are two general feeding strategies: diurnal insectivory and nocturnal herbivory-omnivory. Intraspecific variation in diet was sometimes correlated with altitude. Patterns which might suggest competitive exclusion or ecological release were generally not observed. Interspecific dietary variation is related to morphological variation in both size and shape as revealed by regression and discriminant function analyses. There is a significant negative relationship between the degree of insectivory and body size (wt). The existence of correlated patterns of dietary variation with environment and morphology supports the hypothesis that feeding strategy is adaptive and has been a factor in the evolutionary radiation of these groups. We propose that both phyllotines and akodonts arose from small, insectivorous ancestors. In conjunction with shifts toward herbivory, most phyllotines have evolved larger size plus tooth and jaw modifications. Calomys sorellus is atypical of other phyllotines; it is small, and insectivorous. Most Peruvian Akodon are also small and insectivorous; A. jelskii is an exceptional akodont being large and principally herbivorous.