WHY MORE PRODUCTIVE SITES HAVE MORE SPECIES - AN EXPERIMENTAL TEST OFTHEORY USING TREE-HOLE COMMUNITIES

One of the most common explanations for an increase in species richnes s with productivity is what we have dubbed the ''More Individuals Hypo thesis.'' According to this hypothesis, more productive sites can supp ort higher total abundances and, since species richness is an increasi ng function of total abundance, so will it be of productivity. This hy pothesis assumes that communities are limited by productivity. We test ed the More Individuals Hypothesis using the detritivorous aquatic ins ect communities of tree holes. When tree holes with varying levels of productivity (debris amount) were allowed to be colonized (through ovi position), more productive tree holes did have more species but not mo re individuals. Neither was total energy use strictly proportional to productivity. Only in communities forced to disassemble through produc tivity reductions were the predictions of the More Individuals Hypothe sis satisfied. Ovipositing adults may prefer productive tree holes not because they contain more resources but because they are anticipated to be less likely to dry out. In tree holes, and more generally, the M ore Individuals Hypothesis is an insufficient explanation for increase s in species richness with productivity because it neither accounts fo r the different processes of local colonization and extinction nor all ows body size to correlate with extinction risk.