Latitudinal gradient of termite diversity indicates higher diversification and narrower thermal niches in the tropics

Aim To investigate the contributions of ecosystem productivity, temperature-dependent metabolism and climatic tolerances to the latitudinal gradient in species richness and changes in species composition in tropical and subtropical regions. Location Global. Time period Contemporary. Major taxa studied Termites. Methods We compiled termite occurrence data from papers using the standardized sampling protocol proposed 20 years ago by Jones and Eggleton. Three continents, 28 countries and 494 sampling plots were included in our database. We used structural equation models to determine the direct and indirect effects of productivity, and the average and extreme values of temperature and precipitation on termite species richness. We also compared the observed association between diversity and temperature with predictions from the metabolic theory of ecology and compared how the similarity in species composition relates to geographic distance and environmental differences in tropical versus subtropical regions. Results Termite species richness was, directly and indirectly, related to average and extreme temperatures, but not to productivity. However, the association of species richness and temperature was much stronger than predicted by the metabolic theory of ecology. Moreover, species composition changed more rapidly with geographic distance and temperature differences between plots in the tropics than in the subtropics. Main conclusions These results suggest that the increase of species richness toward the equator cannot be explained by productivity gradients. Instead, the increase in the speciation rates and the narrow species niches along the temperature gradient in tropical regions likely determine the distribution of termites at broad spatial scales.