Stable isotope analysis clarifies the trophic ecology of pond insects

Despite their abundance on the landscape, ponds and associated aquatic insect assemblages have largely been underrepresented in scientific studies, which usually focus on lakes or streams. Similar to other waterbodies, ponds can harbor high levels of insect biodiversity, particularly within the orders Coleoptera and Hemiptera. However, some aquatic insects are experiencing declines due to habitat destruction, pollution, climate change, and invasive species introductions. To assess how these threats are affecting pond insects, and possibly the ecosystem services they provide, knowledge of their ecology is necessary but large knowledge gaps still exist, particularly for trophic position and diet at the species level. To address these knowledge gaps, we are using Carbon and Nitrogen stable isotopes to estimate the trophic position and prevalent diet items of common Coleoptera and Hemiptera from ponds in Northern Louisiana. Preliminary results from three ponds have estimated that most species ranged from trophic level 2-2.6 (primary consumer to omnivore), while one species of predaceous diving beetle (Thermonectus basillaris basillaris) had the highest trophic position at 4.03 ± 0.14 (tertiary predator), surpassing the predicted top predator: backswimmers (Notonecta irrorata) at 2.61 ± 0.26. Future results for this project will contribute novel information on the diet and distribution of aquatic insect species and provide more insight into the trophic dynamics of ponds.