Preliminary patterns of seasonal changes in species composition of surface-active arthropods in a South African savannah

Surface-active arthropods have limited dispersal abilities and their abundances are responsive to changes in the environment. Their sensitivity allows for the identification of aspects of environmental variation that are responsible for changes in community assemblages of these arthropods. Limited dispersal abilities allow for changes in the populations of surface-active arthropods to be linked reliably to changes in their local environment. In this study, we tested the hypothesis that seasonal variation in resource availability drives assemblages of three groups of surface-active arthropods (ants, beetles and spiders). Ten study sites were selected, where sampling was carried out continually during the wet, austral summer season (December 2018-February 2019) and then repeated at the same sites in the dry winter season (June 2019-August 2019) in a mesic savannah of Mpumalanga province, South Africa. Pitfall trapping was used to sample the surface-active arthropods. We found 89 morphospecies of ants, 48% of which were members of the Myrmicinae, while 32% of the 163 morphospecies of beetles were the Scarabaeidae. There were 262 morphospecies of spiders, of these, 22% were from the Salticidae. We found similar abundance and species richness of ants between seasons but significantly greater abundance and species richness of beetles and spiders in summer than in winter. These results show that the impact of seasonal variation in resource availability differs among arthropod taxa. However, the species compositions of all three taxa were significantly different between summer and winter. These results can be explained by the 'niche differentiation hypothesis' coupled with the 'resource-ratio hypothesis'. Additionally, these results highlight the role that temporal and dietary niche differentiation play in driving the assemblage composition of surface-active arthropods in a mesic savannah.

Automated summary

The composition of surface-active arthropods is influenced by seasonal variation in resource availability, with lower abundance and species richness of beetles and spiders in winter compared to summer. These results highlight the importance of temporal and dietary niche differentiation in driving the assemblage composition of surface-active arthropods.