Vertical niche and trait associations in Central African amphibians

Abstract

Tropical forests are vertically complex and offer unique niche opportunities in the form of resources, climate, and habitat gradients from the forest floor to the canopy. Rainforest amphibians have diversified within this vertical space, resulting in partitioned niches and corresponding morphological, behavioral, and reproductive traits. However, a lack of data regarding the vertical niche space used by amphibian species has prevented a nuanced analysis of the form-function relationship between traits and vertical height. We performed 74 ground-to-canopy surveys for amphibians in the tropical rainforest of Gabon and described the vertical stratification patterns of the assemblage in terms of richness, abundance, and species-specific vertical niches. We determined that the community shift in richness and abundance between the ground and understory was pronounced, while the community change from understory to canopy was gradual. We analyzed the relationships between amphibian traits with vertical height using linear mixed effects models, finding strong support (>60% variance explained) that frogs with bigger toes in relation to their length access greater height in the canopy. This relationship provides support for the form-function hypothesis: that morphology changes predictably to meet the functional demands of species along niche gradients. Furthermore, we documented differences in the vertical heights of species according to their reproductive modes, highlighting the potential impact of reproductive mode diversity on the vertical stratification patterns of amphibian assemblages.