Effects of leaf-litter species and chemistry on aquatic insect habitat selection

Habitat selection-the choice of particular habitat patches by organisms-plays a large role in structuring communities. Habitat selection is typically driven by avoidance of risk (e.g., predation) and attraction to reward (e.g., nutrients, prey). Leaf litter in ponds is typically perceived to be a reward for potential colonizers because of nutrient content and support of primary and secondary production, but leaf litter also contains plant secondary compounds that may be a risk to colonizers. To examine the importance of leaf-litter species and chemistry to aquatic insect habitat selection, we created artificial ponds by placing mesocosms on a field-forest edge to serve as colonization sites. Leaves of 1 of 14 tree species were placed in each mesocosm to create variability in leaf and water chemistry. We then used an information-theoretic approach to determine whether leaf chemistry, water chemistry, water depth, or leaf species best predicted aquatic insect colonizer abundance and species richness. We found that the environmental variables that best predicted insect abundance differed among taxa and that the most common taxa had species-specific relationships with predictors. We did not find a clear indication that insects were responding to either risk or reward. We also assessed whether similarity in leaf chemistry was related to the similarity of insect communities between pairs of mesocosms, but we did not find such a relationship. Changes in tree species composition and foliar chemistry due to anthropogenic causes may affect aquatic community assembly in forested ponds and wetlands, though additional studies will be needed to confirm this effect.