The Mesoamerican giant toad Rhinella horribilis as bioindicator of vegetation degradation in a tropical forest.

Abstract

Identifying species that can serve as bioindicators of environmental quality is essential for monitoring the anthropogenic impact. Common and widespread species can be ideal bioindicators due to their abundance and easy monitoring, but a confirmation of their differential responses as a function of habitat perturbation is needed. Because amphibians are known as good bioindicators of environmental perturbation, we conducted this work to identify whether a common, generalist amphibian species, the Mesoamerican giant toad (Rhinella horribilis), could serve as a bioindicator of environmental degradation in a tropical forest. We sampled toads in two areas of tropical forest that differed in anthropogenic degradation (primary vs. secondary forest), establishing in each of these areas two sections of the same surface area but differing in substrate (grass vs. sand). We analyzed toad abundance, sex ratio, body length and condition, and the amount and distribution across the body of ectoparasites (ticks). We analyzed 59 toads that were infested with 503 ticks. Based on a multi-model inference approach, the results suggested that toads were more abundant and had lower body condition in the secondary than in the primary forest. In the secondary forest, females were proportionally less abundant than males. The tick loads responded to an interaction of the body area with either the forest type or the substrate, with increased occurrence of ticks in toads from secondary forests and from grass sections. The differences found between the primary and secondary forests in sex ratio, toad abundance, body condition, and tick load across body regions are consistent with previous studies in other less common species of amphibians and thus posit R. horribilis as a good bioindicator of anthropic disturbance in this tropical forest.