The trend towards sociality in three species of southern African mole-rats (Bathyergidae) : causes and consequences

Includes bibliographies.Three species of southern African mole-rats, possessing a wide range of social organisation were used to investigate the trend towards increasing sociality occurring in species inhabiting increasingly arid environments. The strictly solitary Georychus capensis, the weakly social Cryptomys hottentotus hottentotus and the highly social Cryptomys damarensis were chosen for this investigation and my findings are compared, where possible, with the eusocial Heterocephalus glaber. The level of social organisation exhibited by a particular mole-rat species appears to be dependent upon a number of physical factors as well as on the food resource distribution, its nutritional properties and its availability. Thus the soil moisture content, the annual rainfall pattern and the wear upon the extrabuccal incisors limit the amount of burrowing which can be undertaken by a single mole-rat, both on a daily and seasonal basis. These factors together with the size, distribution, digestible energy and fibre content of the geophytes on which they feed and nearest-neighbour distances occurring between the belowground portions of the geophytes, may be crucial in determining whether a habitat is suitable for solitary or colonial mole-rats