A comparison of the ecology of two populations of the common mole-rat, Cryptomys hottentotus hottentotus: the effect of aridity on food, foraging andbody mass

The aridity food distribution hypothesis (AFDH) maintains that ecological c onstraints in arid habitats curtail dispersal and promote the evolution of cooperative foraging social groups within the African mole-rats. To evaluat e the validity of the AFDH, we investigated inter-habitat differences in fo od resource characteristics, foraging behaviour, colony size and individual body mass in two common mole-rat populations, one from a mesic and one fro m an arid habitat. Although food was clumped at both localities, the geophy te density was lower at the arid site. However, geophytes from the arid sit e were larger than those from the mesic region, and this is suggested to co mpensate for the reduced geophyte density, enabling colonies to meet their energy requirements. Differences in food resource characteristics in turn i nfluenced the pattern of foraging, the burrow systems at the arid site bein g longer and more linear than those from the mesic site. Mean colony size d id not differ between the two sites, but animals from the arid site exhibit ed a reduced individual mass relative to those from the mesic area, probabl y an adaptation to reduce total colony energy expenditure given the elevate d foraging costs in arid environments. The common mole-rat from the arid lo calities should occur in larger colonies than their mesic counterparts. The results from this investigation do not support this contention.