Vertical stratification of ant assemblages varies along a latitudinal gradient in Brazilian savanna

Abstract

AbstractAimArboreal and ground‐dwelling species experience distinct microclimates, have contrasting thermal tolerances and thus may be expected to respond differentially to geographic climatic gradients. We tested this idea by evaluating if the degree of vertical stratification of savanna ant assemblages varies along a latitudinal climatic gradient, and by determining how compositional dissimilarities within each stratum varies across increased geographical and climatic distances.LocationBrazil.TaxonAnts.MethodsWe sampled ants foraging on the ground or in trees at 32 sites. Species were classified according to their main foraging stratum, as arboreal, ground‐dweller or strata generalist. We used linear models to evaluate the effects of latitude and sampling stratum on species richness, and the effect of latitude on the proportion of species typical from trees or from the ground in different sampling strata. The influence of geographic and climatic distances on the compositional differences between assemblages from the same stratum was assessed using regression on distance matrices.ResultsSpecies richness on the ground increased with latitude significantly faster than in trees. The turnover of species between strata was lower at lower latitudes, where there were proportionally more strata generalists and species typical from the ground stratum foraging in trees. Consequently, the compositional dissimilarity between vertical strata decreased with decreasing latitude. Despite that, the dissimilarities between vertical strata were, on average, as great or even greater than the dissimilarities between assemblages from the same stratum across the horizontal space.Main ConclusionsWe found support for the idea that climatic variation across latitude had different effects on arboreal compared with ground‐foraging assemblages. Overall, our results suggest that as Brazilian savanna becomes hotter and drier as forecast under climate change, ant assemblages may become not only less diverse, notably on the ground, but also more homogeneous vertically.