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Darker ants dominate the canopy: Testing macroecological hypotheses for patterns in colour along a microclimatic gradient.

ABSTRACT: Gradients in cuticle lightness of ectotherms have been demonstrated across latitudes and elevations. Three key hypotheses have been used to explain these macroecological patterns: the thermal melanism hypothesis (TMH), the melanism-desiccation hypothesis (MDH) and the photo-protection hypothesis (PPH). Yet the broad abiotic measures, such as temperature, humidity and UV-B radiation, typically used to detect these ecogeographical patterns, are a poor indication of the microenvironment experienced by small, cursorial ectotherms like ants. We tested whether these macroecological hypotheses explaining cuticle lightness held at habitat and microclimatic level by using a vertical gradient within a tropical rainforest. We sampled 222 ant species in lowland, tropical rainforest across four vertical strata: subterranean, ground, understory and canopy. We recorded cuticle lightness, abundance and estimated body size for each species and calculated an assemblage-weighted mean for cuticle lightness and body size for each vertical stratum. Abiotic variables (air temperature, vapour pressure deficit and UV-B radiation) were recorded for each vertical stratum. We found that cuticle lightness of ant assemblages was vertically stratified: ant assemblages in the canopy and understory were twice as dark as assemblages in ground and subterranean strata. Cuticle lightness was not correlated with body size, and there was no support for the TMH. Rather, we attribute this cline in cuticle lightness to a combination of the MDH and the PPH. Our findings indicate that broad macroecological patterns can be detected at much smaller spatial scales and that microclimatic gradients can shape trait variation, specifically the cuticle lightness of ants. These results suggest that any changes to microclimate that occur due to land-use change or climate warming could drive selection of ants based on cuticle colour, altering assemblage structure and potentially ecosystem functioning.

SUBMITTER: Law SJ

PROVIDER: S-EPMC7027836 | biostudies-literature | 2020 Feb

REPOSITORIES: biostudies-literature

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Darker ants dominate the canopy: Testing macroecological hypotheses for patterns in colour along a microclimatic gradient.

Law Stephanie J SJ Bishop Tom R TR Eggleton Paul P Griffiths Hannah H Ashton Louise L Parr Catherine C

The Journal of animal ecology 20191021 2

Gradients in cuticle lightness of ectotherms have been demonstrated across latitudes and elevations. Three key hypotheses have been used to explain these macroecological patterns: the thermal melanism hypothesis (TMH), the melanism-desiccation hypothesis (MDH) and the photo-protection hypothesis (PPH). Yet the broad abiotic measures, such as temperature, humidity and UV-B radiation, typically used to detect these ecogeographical patterns, are a poor indication of the microenvironment experienced ...[more]

PMID: 31637702

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Project description:The number of individuals within a population or community and their body size can be associated with changes in resource supply. While these relationships may provide a key to better understand the role of abiotic vs. biotic constraints in animal communities, little is known about the way size and abundance of organisms change along resource gradients. Here, we studied this interplay in ants, addressing two hypotheses with opposite predictions regarding variation in population densities along resource gradients- the 'productivity hypothesis' and the 'productivity-based thinning hypothesis'. The hypotheses were tested in two functional groups of ground-dwelling ants that are directly primary consumers feeding on seeds: specialized seed-eaters and generalist species. We examined variations in colony density and foraging activity (a size measurement of the forager caste) in six ant assemblages along a steep productivity gradient in a semi-arid region, where precipitation and plant biomass vary 6-fold over a distance of 250km. An increase in the density or foraging activity of ant colonies along productivity gradients is also likely to affect competitive interactions among colonies, and consequently clinal changes in competition intensity were also examined. Ant foraging activity increased with productivity for both functional groups. However, colony density revealed opposing patterns: it increased with productivity for the specialized seed-eaters, but decreased for the generalist species. Competition intensity, evaluated by spatial partitioning of species at food baits and distribution of colonies, was uncorrelated with productivity in the specialized seed-eaters, but decreased with increasing productivity in the generalists. Our results provide support for two contrasting hypotheses regarding the effect of resource availability on the abundance of colonial organisms- the 'productivity hypothesis' for specialized seed-eaters and the 'productivity-based thinning hypothesis' for generalist species. These results also stress the importance of considering the role of functional groups in studies of community structure.

Dataset Information

Darker ants dominate the canopy: Testing macroecological hypotheses for patterns in colour along a microclimatic gradient.

Publications

Darker ants dominate the canopy: Testing macroecological hypotheses for patterns in colour along a microclimatic gradient.

Similar Datasets

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