Resource and Top-Predator Regulation in the Pitcher Plant (Sarracenia Purpurea) Inquiline Community

The effects of top-down and bottom-up forces on species abundance and diversity were quantified in the inquiline communities found in the water-filled leaves of the pitcher plant, Sarracenia purpurea. A press field experiment was conducted in which the abundances of resources (dead ants) and the top predators (larva of the mosquito Wyeomiia smithii) were each maintained at three levels in a factorial design for 23 d. Abundances of mites, rotifers, protozoans, and bacteria increased significantly with prey addition. Protozoan species richness also increased with increasing resource levels, whereas additional resources did not affect bacterial species richness. Increases in top-predator density decreased rotifer abundance but increased bacterial abundance and species richness. Increases in bacterial abundance and richness indicate that a trophic cascade occurs via the larvae, rotifer, and bacteria pathway; omnivory appears to be not strong enough to affect the trophic cascade. Top-down and bottom-up forces both had strong, but different, effects on the abundance and richness of intermediate trophic levels. For most components of the inquiline community, species richness and population sizes are resource limited, whereas predator limitation targets a limited set of groups.