The high diversity of soil communities is crucial for the process of decomposition in terrestrial ecosystems such as tropical forests. However, the leaf litter that these communities consume is of particularly poor quality as indicated by elemental stoichiometry. Recently, the biomass density of temperate litter consumer communities has been shown to be jointly driven by stoichiometric and allometric variables. We expanded this previous approach to the tropics and additionally investigated the effects of seven stoichiometric and three habitat structural predictor variables on consumer diversity across ten major taxonomic groups and four functional feeding guilds of tropical litter macro-invertebrates. We tested a set of well-established hypotheses predicting responses of consumer diversity, abundance or biomass to variation in basal resource stoichiometry and habitat structure, namely the ecosystem size hypothesis, the growth rate hypothesis, the secondary productivity hypothesis, the structural elements hypothesis and the sodium shortage hypothesis. Using a standardized model averaging approach, the joint assessment of consumer biomass density and diversity responses enabled us to identify contrasting patterns in the magnitude and direction of such responses to resource stoichiometric and habitat structural variation.
Results/Conclusions
We found support for all tested hypotheses, evoking the idea of a non-Liebig world in tropical forest systems, whereby consumers are controlled by multiple rather than single limiting factors. While consumer diversity was driven by litter mass and phosphorus availability, consumer biomass densities were dominated by direct effects of litter mass, calcium and sulphur, as well as interactions of population-averaged body mass with other predictors, such as nitrogen and potassium. The observed patterns provide striking insights to the consumer dependence on resource quantity and quality in tropical litter communities. Interestingly, consumer diversity and biomass density exhibited diverse response patterns caused by varying habitat structure and basal resource stoichiometry, such as parallel and opposing effects. We describe contrasts in consumer diversity and biomass density responses and offer a conceptual framework explaining variable response patterns in the two community variables.