The hypolithic invertebrate community in the eastern Karoo: the role of rock size, microclimate and recolonization

Hypolithic habitats are important for the persistence of fauna that utilize these habitats as refuges and resource patches. Little is known, however, about the composition and structure of this community in the semi-arid Karoo. The current study therefore aims to explore the patterns and processes behind hypolithic communities, through determining the effect of rock size and baboon presence on the hypolithic community, the influence of rock size on the microclimate experienced under rocks, as well as determining the short- (over five days) and long- (over 12 months) term colonisation of the hypolithic habitat following a rock rolling disturbance, in a semi-arid Karoo environment. The hypolithic fauna encountered, and the temperature and moisture content experienced under a range of rock sizes were measured. Additionally, hypolithic fauna under rocks that were rolled to mimic rock rolling by baboons were sampled after a set period (i.e. over five days and 12 months). Large rocks were found to provide a more stable microclimate than small rocks. The probability of hypolithic fauna presence was influenced by rock size and season, and hypolithic fauna abundance (except in the dry season), richness, body size and biomass did not correlate with rock size. Additionally, the probability of detecting hypolithic fauna under intermediate sized and larger rocks was greater in the presence of baboons than in the absence of baboons, and in the presence of baboons hypolithic fauna richness increased with rock size. Furthermore, it was shown that hypolithic fauna abundance and biomass did not differ under rolled rocks over a short- (i.e. over five days) or long- (i.e. over 12 months) term period. The short-term colonisation of hypolithic habitats was not influenced by season or rock density. Lastly, most of the change in hypolithic community composition (over 12 months) occurred in the first three months and thereafter the hypolithic community composition approached pre-disturbance levels in month 12. The hypolithic habitat was shown to be influenced by a variety of conditions and processes affecting hypolithic community composition and structure. This study therefore contributes to our understanding of the hypolithic invertebrate community in the eastern Karoo, and the influence of rock size, baboon presence, microclimate and colonisation on hypolithic community composition and structure