Ecological correlates of relative brain size in some South African rodents

Abstract

Relative brain size (size of the brain once body size effects have been removed) has been calculated for 16 species of rodent from South Africa and is shown to vary with six species having a positive RBS (that is a brain larger than expected) and 10 a negative RBS. Arboreal species such as Paraxerus cepapi and Graphiurus murinus and omnivores (G. murinus) have relatively larger brains than do the fossoriai root eaters such as Cryptomys hottentotus and terrestrial follivores (Otomys irroratus). It is suggested that the relatively large brains can be linked to the complex behavioural patterns necessary for locomotion in three dimensions and for utilization of a food resource such as insects that is randomly distributed in time and space. The three sciuromorph rodents (Xerus inauris, Paraxerus cepapi and Pedetes capensis) have very different life styles but all have a positive RBS and it is suggested that a relatively large brain may be a characteristic of the suborder.