Latitudinal gradient and spatial covariance in species richness of tropical Lepidoptera in the Andes

We investigated whether Lepidoptera species richness in the tropical Andes is distributed evenly across the latitudinal gradient, explored the spatial correlations between different taxonomic groups, and investigated historical and ecological factors responsible for shaping the observed patterns. We interpolated species richness from collecting records of nine ecologically diverse taxa of montane Lepidoptera, eight of butterflies (Ithomiini, Acraeini, Callicorini, Pronophilina, Aporiina, Leptophobia, Penaincisalia, and Forsterinaria) and one of moths (Geometridae: Erateina) along elevational transects from 1000 to 3500 m every two degrees in latitude between 11°N and 27°S. We used multiple regression to assess the role of climatic and historical variables in shaping their species richness patterns, and Spearman's correlation coefficient to examine the correlation of species richness gradients between pairs of taxa. We found that Lepidoptera species richness in the tropical Andes is distributed unevenly across the latitudinal gradient, differing considerably between the least and the most diverse transects, with a peak at 3–11°S, and is strongly correlated among all nine taxa. Geological age of the Andes, area and climatic seasonality explained the most variation in species richness, with age dominating in the north and seasonality in the south. The latitudinal gradient in east Andean Lepidoptera species richness is likely a result of historical and contemporary factors, in particular temperature seasonality and the greater age of the Andes south of the Equator. Local aspects of species richness patterns are due to small-scale geological or climatic phenomena, for example, the peak at 3–5°S which results from local mixing of east-west Andean faunas in the Huancabamba Deflection area.