OOS 47-1 - The vertical stratification of tropical forest vertebrates: A meta-analysis

Background/Question/Methods
Tropical forests harbour the highest levels of terrestrial biodiversity and represent some of the most complex ecosystems on the Earth, with a significant portion of this diversity above ground. Although the vertical dimension is a central aspect of the ecology of forest communities, there is little consensus as to prominence, evenness, and consistency of community-level stratification from ground to canopy. Here, we gather the results of 62 studies across the tropics to synthesize and assess broad patterns of abundance and richness vertical stratification in vertebrates, the best studied and not yet collated taxonomic group. Our review of the literature yielded sufficient data for bats, small mammals, birds and amphibians.

Results/Conclusions
Bat richness stratification was variable among studies but trended towards greater richness in the canopy, and bat abundance was strongly weighted towards the canopy. Bird richness and abundance stratification was variable, though slightly weighted towards the canopy. On the contrary, both amphibians and small mammals showed consistent patterns of decline in abundance and richness towards the canopy. We characterize research trends in drivers of stratification cited or investigated within studies, finding local habitat structure and food distribution/foraging to be the leading drivers. Further, we analyze the influence of macroecological variables on stratification patterns, finding elevation to be a key predictor of bird stratification in particular. Prominent differences among taxa are likely due to taxa-specific interactions with local drivers such as vertical habitat structure, food distribution, and vertical climate gradients, which may vary considerably across macroecological gradients such as elevation and biogeographic realm. Our study showcases the complexity in which animal communities organize within tropical forest ecosystems while demonstrating the canopy as a critical niche space for tropical vertebrates. We also see that significant effort is required to fill research gaps in terms of the adequate sampling across various under-sampled regions, taxa, and environments.