Body mass and environment: A study in negev rodents

Seasonal body mass change in rodents could be due to: (1) An adaptive strategy that reduces energy requirements during unfavorable seasons and (2) a response to fluctuations in food resources. We measured seasonal body mass changes and habitat distribution in four Negev highland rodent species, Meriones crassus, Gerbillus dasyurus, G. henleyi, and Acomys cahirinus. Analyses were done to determine the effect of habitat, season, sex, and residence on body mass. The species exhibited differences in body mass (a) among seasons, except for A. cahirinus, and (b) between sexes, except for G. henleyi. G. dasyurus was the only species in which body mass was influenced by habitat. During summer and winter, M. crassus and G. henleyi made widespread movements whereas G. dasyurus and A. cahirinus did not. Meriones crassus exhibited regular dispersal when most individuals moved to the same area and changed habitats seasonally, while movements of G. henleyi occurred non-directionally within the same habitat. In the three gerbil species, M. crassus, G. dasyurus, and G. henleyi, there was a significant reduction in body mass in winter, ranging from 8.9% to 20.2%; but no change was found in the spiny mouse, A. cahirinus. Thus the pattern of reduced body mass during the harsh, non-breeding season is applicable to some desert rodents. However, more studies are required to examine whether these changes are an adaptational strategy to reduce energy requirements or simply a result of reduced food availability.