Species turnover in ant assemblages is greater horizontally than vertically in the world's tallest tropical forest

Abstract

Abiotic and biotic factors structure species assembly in ecosystems both horizontally and vertically. However, the way community composition changes along comparable horizontal and vertical distances in complex three‐dimensional habitats, and the factors driving these patterns, remains poorly understood. By sampling ant assemblages at comparable vertical and horizontal spatial scales in a tropical rainforest, we tested hypotheses that predicted differences in vertical and horizontal turnover explained by different drivers in vertical and horizontal space. These drivers included environmental filtering, such as microclimate (temperature, humidity, and photosynthetic photon flux density) and microhabitat connectivity (leaf area), which are structured differently across vertical and horizontal space. We found that both ant abundance and richness decreased significantly with increasing vertical height. Although the dissimilarity between ant assemblages increased with vertical distance, indicating a clear distance‐decay pattern, the dissimilarity was higher horizontally where it appeared independent of distance. The pronounced horizontal and vertical structuring of ant assemblages across short distances is likely explained by a combination of microclimate and microhabitat connectivity. Our results demonstrate the importance of considering three‐dimensional spatial variation in local assemblages and reveal how highly diverse communities can be supported by complex habitats.

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

“…There is limited information on how compositional differences of ant assemblages in the vertical space compares with differences in the horizontal space. In fact, to our knowledge, only two studies have addressed this question, but both have evaluated changes in the structure of ant assemblages within only a few hundred meters (Antoniazzi et al, 2021; Xing et al, 2022). In contrast to the findings of these studies, we found that the overall dissimilarity between the ground and the arboreal assemblages at a given site was, on average, greater rather than less than the dissimilarity between assemblages from the same stratum for horizontal distances up to 1500 km.…”

“…Finally, we asked how dissimilarity in species composition within each vertical stratum is affected by the geographical and the climatic distance between sampling sites and how the level of dissimilarity across the horizontal space compares with the dissimilarity across the vertical space. Studies performed at local scales indicate that the distance‐decay of similarity relationship can be different for assemblages from different vertical strata (Antoniazzi et al, 2021; Xing et al, 2022, but see Leponce et al, 2021), and that dissimilarity can be greater horizontally than vertically (Antoniazzi et al, 2021; Xing et al, 2022). However, it is not clear whether these patterns hold at geographical scales.…”

Ecological patterns and processes in the vertical dimension of terrestrial ecosystems

“…This pattern may be explained by connectivity in the canopy via lianas and higher territoriality in canopy ants than ground ants (Antoniazzi et al, 2021). At a smaller spatial scale, Xing et al (2022) only detected distance‐decay pattern vertically, but not horizontally for arboreal ant assemblages in tropical rainforest of Borneo. Such pattern can be attributed to distinct microclimate pattern and low horizontal microhabitat connectivity within the three‐dimensional rainforest (Xing et al, 2022).…”

“…At a smaller spatial scale, Xing et al (2022) only detected distance‐decay pattern vertically, but not horizontally for arboreal ant assemblages in tropical rainforest of Borneo. Such pattern can be attributed to distinct microclimate pattern and low horizontal microhabitat connectivity within the three‐dimensional rainforest (Xing et al, 2022). Thus, diversity patterns of different taxa reflect the challenges and opportunities provided by the vertical habitat (depending on their ecological requirements and movement/dispersal traits), resulting in a variety of community turnover patterns.…”

“…Ants (Antoniazzi et al, 2021) Species turnover is greater horizontally than vertically Microclimate, microhabitat connectivity Ants (Xing et al, 2022) scales (Adams et al, 2017;Xing et al, 2022). In Madagascar, Basham et al (2019) showed horizontal distance-decay patterns in the canopy and understorey, but no such pattern was found for amphibian assemblages on the ground, which they attribute to high habitat heterogeneity and low connectivity in forest canopies.…”