Resource quantity, resource quality, and biodiversity: Caves as model ecosystems

The quantity and quality of resources have long been considered important drivers of biodiversity.  According to species energy theory, an increasing energy base should support greater numbers of species.  In addition, recent advances in ecological stoichiometry have made clear that resource quality is also tightly bound to the distribution, ecology, and evolution of species.   We are currently exploring how resource quantity and quality influence biodiversity in cave ecosystems, which are completely donor-controlled.  Caves are model ecosystems for testing these questions because the species are intricately linked to the allochthonous inputs that enter from the surface.  Through field collections, laboratory experiments, and analyses of compiled distribution data, we investigated relationships among the stoichiometry (C, N, P) of cave invertebrates and the species’ morphological adaptations, allometry, geographic range sizes, and large scale biodiversity patterns.  After quantifying inputs into twelve caves, we found species richness of cave residents to be correlated with the total energy present.  Analyses of cave resources demonstrated that they are very low in nutrient content (N, P), which may explain some morphological adaptations of cave species.  For example, total body nitrogen content and amino acid analyses of cave species show interesting differences from those of their surface-dwelling relatives, which may be in response to nitrogen deprivation.  Cave species also showed significant allometric relationships involving total nitrogen content that are not seen in their surface-dwelling counterparts.  Lastly, geographic patterns observed within genera and across trophic groups suggest that distributional patterns may be strongly supported by stoichiometric explanations in cave ecosystems.