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

The aridity food distribution hypothesis (AFDH) maintains that ecological constraints in arid habitats curtail dispersal and promote the evolution of cooperative foraging social groups within the African mole-rats. To evaluate the validity of the AFDH, we investigated inter-habitat differences in food resource characteristics, foraging behaviour, colony size and individual body mass in two common mole-rat populations, one from a mesic and one from an arid habitat. Although food was clumped at both localities, the geophyte density was lower at the arid site. However, geophytes from the arid site were larger than those from the mesic region, and this is suggested to compensate for the reduced geophyte density, enabling colonies to meet their energy requirements. Differences in food resource characteristics in turn influenced the pattern of foraging, the burrow systems at the arid site being longer and more linear than those from the mesic site. Mean colony size did not differ between the two sites, but animals from the arid site exhibited a reduced individual mass relative to those from the mesic area, probably an adaptation to reduce total colony energy expenditure given the elevated foraging costs in arid environments. The common mole-rat from the arid localities should occur in larger colonies than their mesic counterparts. The results from this investigation do not support this contention.