Activity patterns of some Namib Desert ants

Abstract

The activity patterns of eight epigaeic ant species from the Namib Desert were studied in summer and winter, and before and after a rainfall event. The patterns varied from unimodal to bimodal depending on species and season. Seven species exhibited seasonal changes in activity pattern, with a trend towards diurnalism in winter. One diurnal species exhibited similar activity in both seasons. Interspecific differences in activity pattern were greater in summer than winter. Activity levels increased significantly after rain, owing to an increase in foraging and nest construction. Multiple linear regression analysis indicated that surface temperature influenced ant activity more than vapour pressure deficit but a substantial amount of variation was not attributable to these two variables. Critical thermal limits were similar for all eight species irrespective of their normal activity period and some species were active over virtually the entire thermal range that they could withstand physiologically. Interspecific differences in activity may have evolved to minimise interference interactions which occur between ant species. Other possibilities that could explain the observed differences include navigational constraints and different thermal preferenda and, hence, the coincidental partitioning of time.