Data from: Thermal tolerances and species interactions determine the elevational distributions of insects

<b>Abstract</b><br/><p><b>Aim:</b> While physiological limits to thermal extremes are often thought to determine the abundance and geographic distribution of species, more recent evidence suggests that species interactions may be equally important. Moreover, the relative importance of these constraints may shift with changing abiotic conditions, such as climate change. Here, we explore the relative importance of physiological tolerances to heat and species interactions in determining the distribution of insects along two elevational gradients. The gradients contrast in precipitation but not temperature, allowing us to separate these two climatic factors.</p> <p><b>Location:</b> Montane rainforest in Costa Rica.</p> <p><b>Time period:</b> 2015-2016.</p> <p><b>Major taxa studied:</b> Bromeliad-dwelling aquatic insect larvae.</p> <p><b>Methods:</b> We estimated the elevation preferences of five insect taxa by surveying 170 bromeliads along the moist Atlantic and the dry Pacific slopes of Monteverde, and experimentally determined their critical thermal maxima (CT<sub>max</sub>). We determined if species-specific heat tolerances predict their elevation preferences, using Deming regressions, and tested if potential predators mediated elevation effects on species distributions, using structural equation models.</p> <p><b>Results:</b> On the moist Atlantic slope, heat tolerances of insects explained their elevational distributions: taxa with high heat tolerances preferred low elevations where conditions are warmest, while taxa with low heat tolerances preferred high elevations where it is coldest. By contrast, on the drier Pacific slope, the elevational abundance pattern of many insects reflected negative interactions from cranefly larvae. These larvae are known to become predatory under drought conditions and were disproportionally abundant at low elevations on the Pacific slope.</p> <p><b>Main conclusions: </b>We show that under drought, indirect effects mediated by species interactions can override any direct physiological effects of environmental conditions on insect distributions. The relative importance of limits to physiological tolerance and species interactions thus depends on environmental context, an important insight given that environmental conditions are expected to shift with climate change.</p>