A natural experiment identifies an impending ecological trap for a neotropical amphibian in response to extreme weather events

Abstract

Extreme weather events are predicted to increase as a result of climate change, yet amphibian responses to extreme disturbance events remain understudied, especially in the Neotropics. Recently, an unprecedented windstorm within a protected Costa Rican rainforest opened large light gaps in sites where we have studied behavioral responses of diurnal strawberry poison frogs (Oophaga pumilio) to ultraviolet radiation for nearly two decades. Previous studies demonstrate that O. pumilio selects and defends perches where ultraviolet radiation (UV-B) is relatively low, likely because of the lethal and sublethal effects of UV-B. In this natural experiment, we quantified disturbance to O. pumilio habitat, surveyed for the presence of O. pumilio in both high-disturbance and low-disturbance areas of the forest, and assessed UV-B levels and perch selection behavior in both disturbance levels. Fewer frogs were detected in high-disturbance habitat than in low-disturbance habitat. In general, frogs were found vocalizing at perches in both disturbance levels, and in both cases, in significantly lower UV-B levels relative to ambient adjacent surroundings. However, frogs at perches in high-disturbance areas were exposed to UV-B levels nearly 10 times greater than males at perches in low-disturbance areas. Thus, behavioral avoidance of UV-B may not reduce the risks associated with elevated exposure under these novel conditions, and similarly, if future climate and human-driven land-use change lead to sustained analogous environments.

Keywords: Costa Rica; amphibians; disturbance; natural experiment; trade offs; ultraviolet radiation.

FIGURE 1

The impact of a novel extreme disturbance at a tropical field station. Photos show the impacts of a novel windstorm along study transects that we characterized as (a) high or (b) low‐ disturbance. (c) A map of the location of the study site at La Selva Biological Station (Heredia Province, Costa Rica, 10.43, −84.00) shows the focal species and main trail where transects were performed. Note that low‐disturbance areas are representative of the typical habitat that our focal species, the strawberry poison frog (Oophaga pumilio), inhabits

FIGURE 2

Impacts of the windstorm disturbance on the ecology of strawberry poison frog. (a) Significantly fewer frogs were detected in areas of the rainforest where more trees were felled and large light gaps were created along our transects. (b) In high‐disturbance areas, male frogs remained located in microhabitat with significantly lower UV‐B levels compared to ambient, but they still called from perches with significantly greater UV‐B levels relative to males in low‐ disturbance sections (GLM, p < .001, z = −4.06, df = 43)