Ecosystem-Wide Morphological Structure of Leaf-Litter Ant Communities along a Tropical Latitudinal Gradient

Abstract

General principles that shape community structure can be described based on a functional trait approach grounded on predictive models; increased attention has been paid to factors accounting for the functional diversity of species assemblages and its association with species richness along environmental gradients. We analyze here the interaction between leaf-litter ant species richness, the local communities' morphological structure and fundamental niche within the context of a northeast-southeast latitudinal gradient in one of the world's most species-rich ecosystems, the Atlantic Forest, representing 2,700 km of tropical rainforest along almost 20o of latitude in eastern Brazil. Our results are consistent with an ecosystem-wide pattern in communities' structure, with relatively high species turnover but functionally analogous leaf-litter ant communities' organization. Our results suggest directional shifts in the morphological space along the environmental gradient from overdispersed to aggregated (from North to South), suggesting that primary productivity and environmental heterogeneity (altitude, temperature and precipitation in the case) determine the distribution of traits and regulate the assembly rules, shaping local leaf-litter ant communities. Contrary to the expected and most common pattern along latitudinal gradients, the Atlantic Forest leaf litter ant communities show an inverse pattern in richness, that is, richer communities in higher than in lower latitudes. The morphological specialization of communities showed more morphologically distinct communities at low latitudes and species redundancy at high latitudes. We claim that an inverse latitudinal gradient in primary productivity and environmental heterogeneity across the Atlantic forest may affect morphological diversity and species richness, enhancing species coexistence mechanisms, and producing thus the observed patterns. We suggest that a functional framework based on flexible enough traits should be pursued to allow comparisons at local, regional and global levels.

Morphological structure of ant assemblages in tropical and temperate forests

“…Our null model analysis may be 22, 2016; potentially biased because the analyzed scale may be inadequate to detect niche differentiation evidences. However, similar analyses for the tropical data set by Silva and Brandão (2014) using a smaller number of traits and constrained pool null models also did not find strong evidences of under-or overdispersion in the leaf-litter ant fauna, but suggested shifts in the morphospace structure along the latitudinal gradient. In this case, co-occurrence analysis at sample point scale (1 m 2 ) or constrained by guilds can be particularly informative (Silva and Brandão 2014) because patterns of morphological structure should be more probable within, rather than across feeding guilds.…”

“…For the tropical data set, we used the Atlantic Forest regions defined by Silva and Brandão (2014) and for the temperate data set we used the five different EPA Level II ecoregions (Del Toro 2013). The following regions were used in the analysis: temperate data set: (1) Appalachian Forests (18 sites and 63 species), (2) Atlantic Highlands (22 sites and 65 species), (3) Mixed Wood Plains (13 sites and 53 species), (4) Southeastern Coastal Plains (7 sites and 54 species), (7) Southeastern US Plains (7 sites and 44 species); tropical data set: (1) high southeastern-south areas (8 sites, 262 species), (2) low southeastern-south areas (6 sites, 229 species), (3) intermediate latitude areas (4 sites, 239 species), and (4) north Atlantic Forest areas northeastern (8 sites, 233 species).…”

An assessment of leaf-litter and epigaeic ants (Hymenoptera: Formicidae) living in different landscapes of the Atlantic Forest Biome in the State of Bahia, Brazil

“…In a recent study using Winkler traps, Silva & Brandão (2014) found a considerable diversity for the family Formicidae in the Brazilian Atlantic Forest, with 530 ant species. The geographic coverage of their study was much larger than our, since the sampling sites were distributed over a latitude gradient up to 20°, all over the biome (about 3,400 km, following an approximate northeast-southwest axe).…”

Simple does not mean poor: grasslands and forests harbor similar ant species richness and distinct composition in highlands of southern Brazil

“…Atlantic Forest stricto sensu or Atlantic Rainforest; e.g. Silva & Lopes 1997, Freitas et al 2014, Silva & Brandão 2014. Comparatively little is known about highland mixed forests and grasslands (Ulysséa et al 2011), which only recently started to be systematically investigated (Pinheiro et al 2010, Dröse et al 2017, Franco & Feitosa 2018.…”