Interspecific green leaf-litter selection by ground detritivore arthropods indicates generalist over specialist detritivore communities

Abstract

Reasons for the higher-than-expected soil and litter faunal diversity are still poorly understood – the so-called ‘enigma of soil animal diversity’ - especially regarding the extent of specialization of arthropod detritivores towards leaf-litter species. Here, we assess soil detritivorous arthropod diversity patterns in relation to eight, green leaf-litter species, in an old-growth, diverse southern Afrotemperate forest. Here, green leaves are often found scattered across the forest floors after turbulent weather, providing vital nutrients for ground-dwelling arthropods in a nutrient-poor system, possibly selecting for specialization. Litter bags containing species-specific green leaf litter of common southern Afrotemperate trees were placed in five forests. We found no evidence that leaf-litter species support unique detritivore assemblages, except for one species, nor did we find differences in richness between leaf-litter species. Significant differences in arthropod abundance were noted between some leaf-litter species, which did not relate to patterns for leaf-litter decomposition. Therefore, we support the hypothesis that ground-dwelling, detritivore arthropods are largely generalist towards leaf-litter species. Additionally, we demonstrate that decomposition rates were largely independent of the diversity of detritivorous arthropods. Competition for nutrients in the litter layer is predictably high, due to the nutrient poor quality of southern Afrotemperate forests. This competition could attract certain decomposers to leaf-litter species of higher nutrient status, as shown for one leaf-litter species here. The ‘enigma of soil diversity’ might best be explained not through specialized interactions between detritivorous arthropods and leaf-litter species, but rather through other mechanisms, such as microbial and fungal activity and their interactions with arthropods.