Body mass and environment: A study in Negev rodents

Seasonal body mass change in rodents could be due to: (1) an adaptive strat egy that reduces energy requirements during unfavorable seasons and (2) a r esponse to fluctuations in food resources. We measured seasonal body mass c hanges and habitat distribution in four Negev highland rodent species, Meri ones crassus, Gerbillus dasyurus, G. henleyi, and Acomys cahirinus. Analyse s were done to determine the effect of habitat, season, sex, and residence on body mass. The species exhibited differences in body mass (a) among seas ons, 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 habi tat. During summer and winter, M. crassus and G. henleyi made widespread mo vements whereas G. dasyurus and A. cahirinus did not. Meriones crassus exhi bited regular dispersal when most individuals moved to the same area and ch anged habitats seasonally, while movements of G. henleyi occurred non-direc tionally 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 spin y mouse, A. cahirinus. Thus the pattern of reduced body mass during the har sh, 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 a vailability.