PREDATION BY ENALLAGMA NYMPHS (ODONATA, ZYGOPTERA) UNDER DIFFERENT CONDITIONS OF SPATIAL HETEROGENEITY

Macrophyte beds of the lake littoral host a diverse community of macro invertebrates, from primary consumers to top predators. Different macr ophyte species often support different macroinvertebrate communities. Complex leaf morphologies (plants with finely dissected leaves) usuall y support richer and/or more diverse invertebrate assemblages, probabl y because of the larger availability of microhabitats and refuges (spa tial heterogeneity) that allow for coexistence of otherwise mutually e xclusive species. Odonate nymphs are sometimes associated with complex leaf macrophytes. Because of their wide prey spectrum, colonization o f spatially heterogeneous macrophyte habitats may be due to a higher p redation success in such a habitat rather than to the presence of part icular prey species. Odonate (Enallagma sp.) nymph predation success w as tested under conditions of high (complex leaf Ceratophyllum demersu m L. leaf packs) and low (simple leaf Potamogeton illinoensis Morong l eaf packs) spatial heterogeneity. Prey species included two pulmonate gastropods, an amphipod, and a turbellarian that were common in the na tural habitat of Enallagma. Enallagma significantly reduced the amphip od and the turbellarian populations and the prey assemblage as a whole , but did not have any statistically significant impact on the snail p opulations, which increased their absolute and relative abundance in t he presence of the odonate. Numerical losses by Enallagma predation (i f any) were not related to macrophyte architecture, suggesting that pr ey vulnerability to Enallagma predation is species-specific rather tha n habitat-determined. Enallagma's preferential distribution in spatial ly heterogeneous macrophyte habitats, when occurring, may be due to ot her factors such as a refuge from fish predation and/or a generally gr eater prey availability and diversity in complex leaf than in simple l eaf macrophyte habitats.