The foraging ecology of two Namib Desert harvester ant species

Abstract

Forager abundance, activity, dispersion and diet of Messor denticornis and Tetramorium rufescens was studied on a monthly basis for 17 months. There were large fluctuations in forager abundance with both species exhibiting similar patterns; the first peak in abundance occurring five months after a peak in food availability and the second peak in abundance coinciding with a second, smaller pulse of food. Food supplementation experiments demonstrated that availability of food partially regulated the absolute numbers of ants foraging. Both species shared similar activity patterns with the majority of activity occurring at night. Foragers were randomly dispersed within the 16 ha study plot. Most of the food collected by both species was Enneapogon brachystachyus seeds. These seeds were collected during the first half of the study when seeds were apparently superabundant. With declining seed availability both species took more non·seed plant matter and arthropods. In both species, diet range fluctuated widely, reflecting opportunistic responses to food availability. Opportunism was particularly apparent when seeds were relatively scarce. Despite large interspecific differences in body size, the majority of food utilized was the same size for both species. The above patterns suggest that interspecific competition for food is not an important factor in the ecology of these ant species.