Canopy Openings Reduce Functional Volume in Amphibian Populations of a Neotropical Forest

Abstract

The study of amphibian functional traits in response to natural disturbance treefall regimes provides a key framework for understanding natural disturbances in tropical forests. In the tropical rainforest of Los Tuxtlas, Mexico, we measured five traits—body biomass and volume, cephalic width, mouth width, and snout–vent length—in three amphibian species that exhibit distinct responses to canopy openings: Rheohyla miotympanum, which occurs exclusively beneath the closed canopy; Incilius cavifrons, which is abundant in canopy openings but less frequent under closed canopy conditions; and Pseudoeurycea werleri, which is common under the closed canopy and rare in openings. No significant differences were observed in the traits of I. cavifrons between open and closed canopy habitats. In P. werleri, only mouth width differed significantly, being greater under the closed canopy. Rheohyla miotympanum, abundant under closed canopy, exhibited the lowest functional richness values, while I. cavifrons and P. werleri displayed higher values under the closed canopy. Contrary to our initial hypothesis, the results indicate that some amphibian species respond differentially to canopy openings through feeding-related traits (e.g., mouth width) rather than body size traits such as snout–vent length, biomass, or volume. Environmental filtering associated with canopy disturbance appears to constrain the functional trait space of certain populations, leaving ecological niches vacant and intensifying interspecific competition for resources. These findings underscore the complexity of amphibian responses to environmental change and emphasize the critical role of functional traits in elucidating the ecological dynamics of tropical forest systems.