Ground-dwelling arthropod community structure responds to an experimental gradient of tropical tree diversity.

Plant biodiversity can influence the structure of other trophic levels, with cascading effects on ecosystem functioning. Biodiversity-ecosystem function (BEF) experiments that manipulate tree diversity provide information on the mechanisms that drive these bottom-up effects. In this study, conducted in a seasonally dry tropical forest BEF experiment in South America, we tested the hypotheses that ground-dwelling arthropod abundance and diversity are positively affected by tree species richness and a gradient of plant facilitation which can potentially increase community productivity, resource heterogeneity, and soil conditions. Using generalised additive models (GAM), we found that tree richness, which directly affects leaf litter heterogeneity, positively affected total arthropod richness, as well as the richness of Hemiptera, Hymenoptera, and predators. Contrary to expectations, facilitation had no detectable effect on the structure of the arthropod community. Nutrient availability and mean tree height, used as a proxy for community productivity, emerged as the main drivers of arthropod abundance. Our results indicate that the effect of tree diversity on ecosystem functioning can be mediated by ground-dwelling arthropods.