How anthropogenic global warming will affect not just individual species but entire communities is an ecological question urgently requiring investigation. Recent research has shown that species’ thermal traits, including temperature preferences and critical thermal maxima (CTmax), can be used to rapidly estimate species’ direct and indirect responses to warmer temperatures. We used these criteria to assess invertebrate communities found in lowland, premontane, and montane tropical forests.
Specifically, we measured the thermal preferences and CTmax of invertebrates living in the young rolled leaves of Zingiberales plants, including heliconias and gingers, along a Costa Rican elevation gradient. After collecting invertebrates, we measured their thermal preferences by offering invertebrates choices between 5°C intervals ranging from 15°C/20°C to 30°C/35°C. We also measured CTmax by heating invertebrates at a steady rate until they lost motor control. Invertebrates were collected for identification using traditional and molecular methods. We hypothesized that invertebrates’ thermal traits would be primarily determined by elevational site due to local adaption, but that ecological guild and order-level evolutionary constraints would also influence thermal traits. We predicted that invertebrates from lower elevation forests would prefer and tolerate higher temperatures than montane invertebrates and that herbivores would prefer and tolerate higher temperatures than predators.
Results/Conclusions
We sampled rolled-leaf communities from over 25 species of Zingiberales at four elevational sites. Rolled leaves from different host species at the same elevation contain homologous invertebrate communities. The communities were dominated by multiple life stages of Coleoptera, Diptera, Hemiptera, and Hymenoptera, although invertebrates from nine other orders were also collected. We found that invertebrates preferred lower temperatures and that guild was the only factor that significantly affected temperature preference. Predators preferred warmer temperatures than herbivores. We found that thermal tolerance (CTmax) was strongly affected by elevation, guild, and taxonomic order, with elevation having the largest effect. Invertebrates from montane forest sites and predators had lower CTmax. Of the invertebrate orders, Diptera had the lowest mean CTmax and Coleoptera had the highest. In these communities, it appears that invertebrate thermal preference is primarily determined by guild, while thermal tolerance is determined by elevation, guild, and taxonomic order. Rising temperatures in the next century are unlikely to exceed these invertebrates’ CTma, but montane invertebrates cannot tolerate high temperatures as well as lowland invertebrates and may respond negatively to temperatures well below CTmax. Furthermore, differences in herbivores’ and predators’ thermal tolerances and temperature preferences may alter community interactions.