Background/Question/Methods Understanding how environmental factors influence the distribution of species richness is important for predicting future impacts of climate change on biodiversity. One way that we can quantify such patterns is through environmental gradients, such as elevation. Elevation gradients are important for maintaining and generating biodiversity, and due to their high turnover in environmental conditions, are an ideal system to investigate what environmental factors affect species richness. Despite this, the global trend in species richness of the most diverse group of animals, the insects, with elevation is unknown. The current evidence across studies is variable: there are patterns of decreasing, increasing, and mid-elevation peaks in richness with elevation. Moreover, most studies are from single-systems, different regions, various taxa, and use different sampling techniques. A global synthesis across systems is needed to provide a better understanding of how insect species richness changes with elevation, and the factors underlying those patterns. We conducted a meta-analysis and asked how does insect species richness change with elevation, and do these patterns differ with location, taxon, or climate? Results/Conclusions Our search yielded 67 studies and 120 elevation gradients across major insect taxonomic groups (e.g., Hymenoptera, Lepidoptera, Coleoptera) and biomes. The highest number of gradients was found in the tropics (n=50) with the fewest in the desert (n=10). Using a mixed effects model, richness peaked at mid-elevations. This relationship is similar to patterns from previous meta-analyses conducted in small mammals and plants, and an old literature review on insects. The mid-elevation peak in richness was not dependent on taxa or region studied. Restricting our data to studies with temperature data available (49 gradients), we found that despite upper elevation sites being cooler than lower elevation sites, mean annual temperature was not related to species richness. This suggests that another factor, such as a biotic factor (e.g., plant diversity) or another climatic factor (e.g. seasonality or precipitation) is driving insect richness across elevation. Assessing the generality of richness-elevation patterns is critical to predicting the effects of climatic changes on montane communities.
