Canopy Openings Reduce Functional Volume in Amphibian Populations of a Neotropical Forest
Description
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, exhibited the lowest functional richness, 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.
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Steps to reproduce
We calculated trait probability density functions (TPD) for Body volume (VM), biomass (BS), snout-vent length (SVL/TL), head width (HW), and mouth width (MW) for populations of I. cavifrons and P. werleri, both present in canopy openings and under the closed forest canopy, as well as for R. miotympanum, a species exclusive to closed-canopy forest. The TPD approach accounts for intraspecific trait variability priori to estimating the distribution of functional traits across species, thereby reflecting the probabilistic nature of functional niches in ecological systems (Carmona et al., 2019). In this framework, some trait values are more likely than others, and these probabilities define how trait space is occupied by individuals in a given population or assemblage. This method enables more realistic and informative assessments of functional diversity (Carmona et al., 2016). This analysis was conducted using the TPD package (Carmona et al., 2019) in the RStudio software version 1.2.5033 (RStudio Team, 2020).
Institutions
- Universidad Autonoma del Estado de MorelosMorelos, Cuernavaca