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.
Savannahs are structurally complex ecosystems consisting of a diverse community of plants and animals such as arthropods. Arthropods are essential in many ecosystem processes that help maintain life on Earth. The anthropogenic conversion of natural landscapes into croplands, residential and industrial areas has a negative impact on surface-active arthropods that have limited dispersal abilities and narrow habitat preferences. This study investigated the effect of disturbance on assemblages of ants, beetles and spiders in the savannah vegetation in Mpumalanga province, South Africa. We compared species richness, abundance and composition of these three taxa between the pristine savannah and the savannah that is exposed to a variety of anthropogenic activities (disturbed savannah). Arthropods were collected using pitfall traps in 15 sites in pristine savannah and 15 sites in disturbed savannah. We found that disturbance affects species richness and abundance of these taxa differently. Disturbance did not affect species richness of spiders and abundance of beetles, while greater species richness of ants and beetles, as well as abundance of ants and spiders was in disturbed than in pristine savannah. Furthermore, the species compositions of all taxa were different between disturbed and pristine savannah. The disturbed savannah had twice more unique indicator species than the pristine savannah. Differences in assemblages of arthropods between pristine and disturbed habitats suggest that it may be important to consider habitats in and outside protected areas in the conservation of arthropods, particularly in areas with greater percentage of natural and semi-natural landscapes occurring outside protected areas.
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