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Emerging aquatic insects as predators in terrestrial systems across a gradient of stream temperature in North and South America


Jeff S. Wesner, Department of Fish, Wildlife, and Conservation Biology, Colorado State University, Fort Collins, CO 80523, U.S.A.


1. Empirical and theoretical research over the past decade has demonstrated the widespread importance of aquatic subsidies to terrestrial food webs. In particular, adult aquatic insects that emerge from streams and lakes are prey for terrestrial predators. While variation in the magnitude of this subsidy is clearly important, the potential top-down effects of the predatory adults of some aquatic insects in terrestrial food webs are largely unknown.

2. I used published data on benthic insect density (as a proxy for emergence) in North and South America to explore how the proportion of benthic insects that are predatory as adults varies across a gradient of mean annual stream temperature.

3. The proportion of benthic insects that are predatory as adults varied widely across sites (0–12% by abundance; 0–86% by biomass). There was a positive relationship between mean annual stream temperature and the proportion of predatory adults across all sites, driven largely by the greater abundance/biomass of predatory taxa (e.g. odonates), relative to non-predators (e.g. midges, mayflies, caddisflies), in tropical than in temperate streams.

4. The ‘trophic structure’ (i.e. the proportion of predators) of emerging adult aquatic insects is an understudied source of variation in aquatic–terrestrial interactions. Incorporation of trophic structure in future studies is needed to understand how future modification of fresh waters may affect adjacent terrestrial food webs through both bottom-up and top-down effects.

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