Regional coexistence and local dominance in Chaoborus: Species sorting along a predation gradient

Variation in the intensity of predation pressure across the well-known environmental gradient of lentic freshwater habitats from small, ephemeral ponds to large, permanent lakes is a key ecological interaction important in the development and maintenance of aquatic community structure. Here, we present data on the distribution and abundance of four species of Chaoborus (Diptera: Chaoboridae) that vary in species traits (i.e. pigmentation, diel vertical migration (DVM) behavior and size) and document the importance of fish predators as drivers of the pattern. In addition, we examined Chaoborus species sorting along an experimental gradient in bluegill sunfish (Lepomis macrochirus) density and tested bluegill prey choice for the four species of Chaoborus found in Southwestern, Michigan, USA. We found that a gradient in fish density can lead to clear species sorting, and that this response is consistent with distributional patterns observed in nature. Chaoborus americanus was most abundant in the fishless ponds, C. flavicans was neutral in response to fish and C. punctipennis was most abundant in the high fish biomass ponds. Furthermore, fish size selectivity and differences in Chaoborus species traits (i.e. pigmentation, DVM behavior and size) were all observed to contribute to the pattern of Chaoborus abundance and distribution.