Local Interactions in Pitcher Plant Communities Scale-Up to Regional Patterns in Distribution and Abundance

We used the aquatic communities living in the purple pitcher plant (Sarracenia purpurea L., Sarraceniaceae) to determine if patterns produced by trophic interactions at the local scale can be detected at larger spatial scales. Mosquitoes (Wyeomyia smithii Coq., Diptera: Culicidae) are known to have a negative effect on the aquatic microfauna within leaves. We compared the abundance of two microfaunal taxa, Bodo (Kinetoplastea: Bodonidae) and Habrotrocha rosa Donner (Rotifera: Bdelloidea), in bogs with and without pitcher plant mosquitoes. Bogs containing pitcher plant mosquitoes had lower densities of bacteria through the study period. However, within these bogs, leaves with mosquitoes did not have lower bacterial densities. We found that the pattern for Bodo was similar at the leaf and bog spatial scales. Abundance of Bodo was closely linked to bacterial densities and the presence of mosquitoes strengthened that relationship, because of greater predator impacts when bacteria were scarce. In contrast, different patterns emerged at the two scales for H. rosa. At the leaf scale, a predator effect was seen only for low bacterial densities (as for Bodo), but at the bog scale, H. rosa was less abundant in mosquito bogs, and abundance was not associated with bacterial levels. We suggest that differences in life history characteristics (population growth rate and average abundance) may influence the relative influence of local interactions and regional processes such as colonization.