Abstract:
Understanding factors that drive species richness and turnover across ecological gradients is important
for insect conservation planning. To this end, we studied species richness e energy relationships and
regional versus local factors that influence dung beetle diversity in game reserves along an aridity and
trophic resource gradient in the Botswana Kalahari. Dung beetle species richness, alpha diversity, and
abundance declined with increasing aridity from northeast to southwest and differed significantly between
dung types (pig, elephant, cattle, sheep) and carrion (chicken livers). Patterns of between-study
area species richness on ruminant dung (cattle, sheep) differed to other bait types. Patterns of species
richness between bait types in two southwest study areas differed from those in four areas to the
northeast. Regional species turnover between study areas was higher than local turnover between bait
types. Patterns of southwest to northeast species loss showed greater consistency than northeast to
southwest losses from larger assemblages. Towards the southwest, similarity to northeast assemblages
declined steeply as beta diversity increased. High beta diversity and low similarity at gradsect extremes
resulted from two groups of species assemblages showing either northeast or southwest biogeographical
centres. The findings are consistent with the energy hypothesis that indicates insect species richness in
lower latitudes is indirectly limited by declining water variables, which drive reduced food resources
(lower energy availability) represented, here, by restriction of large mammals dropping large dung types
to the northeast and dominance of pellet dropping mammals in the arid southwest Kalahari. The influence
of theoretical causal mechanisms is discussed.
