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

Abstract

Aim: Arboreal 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. Location: Brazil.Taxon: Ants. Methods:We 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.Results: Species 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 Conclusions: We 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.

Macroecological patterns of functional and phylogenetic diversity vary between ground and arboreal assemblages in Neotropical savanna ants

“…Savanna ant species richness is much greater on the ground than in trees (Almeida et al 2023. Furthermore, species richness on the ground increases with latitude at a faster rate than in trees (Vasconcelos et al 2018(Vasconcelos et al , 2023.…”

“…Our data set derives from previous sampling of the arboreal and ground-foraging ant fauna at 32 sites in Brazil (Vasconcelos et al 2018(Vasconcelos et al , 2023. Except for two sites in the Amazon region and one in semi-arid Caatinga, all sampling sites were located in the Cerrado (savanna) biome of central Brazil (Vasconcelos et al 2023) (Fig. 1).…”

“…We have previously described how ground and arboreal ant assemblages in Brazilian savannas show different macroecological patterns of species richness and composition and, consequently, how the vertical stratification of these assemblages varies at large spatial scales (Vasconcelos et al 2023). Savanna ant species richness is much greater on the ground than in trees (Almeida et al 2023.…”

“…On the other hand, at warmer sites interspecific competition and niche partitioning may be of greater importance for the arboreal than for the ground communities. This is because although the proportion of arboreal species found foraging on the ground remains constant along a latitudinal temperature gradient, that of ground-dwelling species foraging in trees tend to increase as latitude decreases (Vasconcelos et al 2023).…”

Rates of species turnover across elevation vary with vertical stratum in rainforest ant assemblages

“…Vertical gradients in mean temperature and temperature variance have been well‐documented in this study system (Leahy et al 2021a), as has thermal overlap in ground and canopy temperature profiles across elevation bands (Scheffers and Williams 2018). Ants are ideal organisms for the study of biogeographic patterns as they are highly speciose (Kass et al 2022) and widely distributed across both vertical and elevation gradients (Sanders et al 2007, Bishop et al 2014, Longino et al 2019, Leahy et al 2020, Vasconcelos et al 2023). In addition to experiencing different microclimates, ground and arboreal ants also occupy different habitat templets with distinct nesting and food resources (Yanoviak and Kaspari 2000).…”