US EPA

1. Sublethal effects of predation can affect both population and community structure. Despite this, little is known about how the frequency of injury varies in relation to habitat, aquatic community characteristics or between trophically similar, coexisting taxa. 2. In a tidal freshwater ecosystem, we first examined injuries (lamellae autotomy) of Enallagma and Ischnura damselfly larvae, which have unique behaviours and susceptibilities to predation, as a function of habitat type, body size and overall odonate density, using proportional odds multinomial logistic regression. We also examined relative abundance of these genera and potential anisopteran predators as a function of habitat type, using goodness-of-fit tests. 3. For Enallagma, when larvae were small and overall odonate densities were high, the frequency of injury increased. For Ischnura, however, the frequency of injury depended on habitat, and increased progressively for small larvae in less disturbed, lower elevation habitats. Ischnura were most frequently found in more disturbed, higher elevation habitats, whereas Enallagma were more frequently found in less disturbed, lower elevation habitats. 4. The relative importance of factors hypothesized to structure odonate communities varied between coexisting Enallagma and Ischnura. Unique distributions and patterns of injury for each genus provided new insights on the potential for intraguild interactions to modify habitat associations in tidal freshwater ecosystems.

The purpose of the study was to examine the injury rate for two coexisting damselfly larvae in a tidal freshwater habitat. This study has no direct bearing on EPA policies and is a carry-over project from prior effors (see Comments below).

Witt, J., R. Forkner, AND R. Kraus. Habitat Heterogeneity And Intraguild Interactions Modify Distribution And Injury Rates In Two Coexisting Genera Of Damselflies. FRESHWATER BIOLOGY. Blackwell Publishing, Malden, MA, 58(11):2380-2388, (2013).