Mountain passes are higher at low latitudes for madicolous insect communities of the Neotropical region

Abstract

Aim: To test whether spatial turnover patterns of mountain madicolous insect com- munities in the Southern Hemisphere support the ‘mountain passes are higher in the Tropic’ hypothesis (MPHT). To do this, we compared madicolous communities in the Amazon Mountains (equator) and the Atlantic Forest Mountains (23°S). Location: Brazil. Methods: We characterized madicolous insect communities in two elevational gradi- ents between 90 to 3000 m a.s.l. separated by 23° of latitude, totalling 108 sampling sites. Since the MPHT predicts a more intense turnover along elevational gradients at lower latitudes than at higher latitudes, we evaluated beta diversity in the Amazon mountains, at the equator, and in the Atlantic Forest mountains, in the subtropical region. We quantified multiple-site abundance-based dissimilarity to assess whether beta diversity was different between both regions. We also performed constrained ordination (db-RDA) analyses to assess whether community dissimilarity (balanced variation in abundances) was uniquely or jointly explained by environmental, spatial and/or elevational predictors. Additionally, we independently assessed the relation- ship between community dissimilarity and altitudinal difference in each region and tested for differences in model parameters between regions. Results: Although we found high species turnover in both regions, the community variation explained by environmental factors and altitude was higher in the Amazon than in the Atlantic Forest, as evidenced by db-RDA and altitudinal difference mod- els. In general, communities were remarkably constrained by spatial predictors, which result from low dispersion capacity of most madicolous insects and low connectivity of madicolous systems. Consequently, the composition of madicolous insects notably diverged between regions, highlighting the complementarity and high conservation value of both systems. Main Conclusions: Our results indicate that the MPHT explains, at the community level, the differences between low- and high-latitude mountain systems in community turnover along elevational gradients, even within a relatively short latitudinal distance in the Southern Hemisphere.