Interactive Effects of Resources and a Processing Chain Interaction in Treehole Habitats

The degree to which the outcome of biotic interactions is sensitive to resource levels is a fundamental issue in ecology. Conversely, resource availability may be affected by processing chain interactions, where organisms specialize on a resource in different states of decay. An organism upstream in the decay sequence can affect availability of resources to downstream consumers. Experimental microcosms that mimic tree-hole habitats were used to test the hypothesis that leaf-shredders process resources and facilitate populations of downstream consumers under conditions of resource limitation in a detritus-based community. Resources were varied independently of presence of leaf-shredding scirtid beetles (Helodes pulchella and Prionocyphon discoideus) to examine interactions among resource level, scirtids, and the mosquito Aedes triseriatus. Scirtids facilitated growth of A. triseriatus only when resource quantity was low. Survival of mosquitoes was negatively affected by the lowest resource level only when scirtids were absent. At the highest resource levels, scirtids hindered growth of mosquitoes in comparison to high resources without scirtids. Leaf-shredders affect resource availability, and resource processing by scirtids has significant repercussions on populations of A. triseriatus that are dependent upon resource level. Although resources alone had large effects on mosquito growth, these bottom-up effects were conditionally mediated by shredders.