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

Abstract

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.

Digging for answers: contributions of density- and frequency-dependent factors on ectoparasite burden in a social mammal

“…However, host density has been shown to be negatively correlated with home range size (Bordes et al 2009;Morand 2015) and hence the burrow systems of C. h. hottentotus in the arid site may have been larger than those in the mesic site. Although burrows were not excavated for the current study a previous assessment of burrow architecture of the study species corroborates this hypothesis and C. h. hottentotus burrows from an arid population extended over a larger area than those of the mesic population (Spinks et al 2000a). Hence, the greater ectoparasite burden observed in arid populations of C. h. hottentotus may be a result of larger home ranges and the associated greater exposure potential in this population.…”

Plasticity and constraints on social evolution in African mole-rats: ultimate and proximate factors

“…Within-species comparisons of philopatry and dispersal in arid and mesic-dwelling populations of the common mole-rat (Cryptomys hottentotus hottentotus) in South Africa have also shown that immigration and emigration were lower at an arid site than at a mesic one, indicating that constraints on dispersal are higher in areas of low and unpredictable rainfall [23]. Furthermore, behavioural tests on animals from the arid population revealed substantially higher levels of rejection of foreign conspecifics in dyadic encounters than the mesic population, suggesting increased xenophobia in the former [24]. These differences in dispersal indicate adaptive variation in social behaviour between the regions, and strongly suggest that delayed dispersal, sociality and cooperation may be more crucial to individual survival in arid than in mesic areas.…”

Burrow architecture of the Damaraland mole-rat (Fukomys damarensis) from South Africa

“…Food stores were not found in any of the excavated burrow systems in this study, instead it appears that the mole-rats "farm" the geophytes similar to that of the social C.h.hottentotus (Spinks et al, 2000) and is contradictory to solitary species B. suillus (Davies and Jarvis, 1986) and G. capensis (Thomas et al, 2012) which create large food stores. It has been suggested that the food storage method is dependent upon food size (Spinks et al, 2000) as in the case of Damaraland mole-rats where food supply is scattered and clumped, therefore farming geophytes provides a longer term food supply than storing small geophytes in a food cache.…”

“…It has been suggested that the food storage method is dependent upon food size (Spinks et al, 2000) as in the case of Damaraland mole-rats where food supply is scattered and clumped, therefore farming geophytes provides a longer term food supply than storing small geophytes in a food cache. Lovegrove and Painting (1987) found spiralled burrows located around large food resources indicated by a collection of three mounds fairly close to each other.…”

“…Once a food resource has been located it will either be taken back to a food storage area or if the geophyte is too large to be stored the colony eats parts of the geophyte in situ. It has been posited by Heth (1989) that once a large food resource has been located the burrowing technique changes from digging linear to a more reticulate pattern that explores the area more efficiently with numerous foraging branches (Lovegrove and Painting, 1987), as the likelihood of encountering another food resource is high (Heth, 1989;Brett 1991;Spinks et al, 2000). This area restricted search strategy has been suggested to be an adaptation to the clumped distribution of geophytes (Heth, 1989).…”