Aventuras en Costa Rica (1): overview of amphibian declines

The charismatic strawberry poison dart frog (Oophaga pumilio) is highly abundant at La Selva Biological Station.

The charismatic strawberry poison dart frog (Oophaga pumilio) is highly abundant at La Selva Biological Station.

This summer I spent six weeks in Costa Rica for a Tropical Biology field course with the Organization for Tropical Studies/Organización para Estudios Tropicales (OTS/OET). During the field course, the class visited several different biological stations across different habitats in Costa Rica, including Palo Verde (season dry forest/wetland), Monteverde (cloud forest), La Selva (lowland rain forest), and Las Cruces (botanical garden/mid-elevation rain forest). I also went on a post-course trip to the Smithsonian Tropical Research Institute‘s station at Barro Colorado Island (BCI) in Panamá. At each of these sites, we heard stories about how amphibians were being affected by global changes. In Palo Verde, densities of burrowing frogs had declined over the years, in Monteverde several species had gone extinct, in La Selva there have been long-term declines of both reptiles and amphibians, and at Las Cruces some rare species were believed to be recovering from declines.

A female yellow toad (Incilius luetkenii) at Palo Verde Biological Station.

A female yellow toad (Incilius luetkenii) at Palo Verde Biological Station.

Costa Rica was one of the first places in the Neotropics where amphibian declines due to the amphibian chytrid fungus were recorded. Now it is thought that most of the remaining amphibians are resistant to the chytrid fungus. However, long-term amphibian declines have been reported from Costa Rica, continuing into the present. Some scientists (i.e. Alan Pounds) have suggested that these amphibian declines, starting with the extinction of the Costa Rican Golden Toad (Incilius periglenes), are the result of climate change. Temperatures in tropical regions are usually fairly stable so many tropical organisms have a relatively low range of temperatures they can tolerate, meaning that they are particularly sensitive to global warming. In addition to temperature changes, there have also been changes in precipitation and in severity of climatic events such as El Niño/La Niña. With the El Niño this year (“Godzilla“), we observed an extended dry season in Palo Verde and at BCI in Panamá, but flooding at La Selva, on the Atlantic side of Costa Rica.

Carpenter's anole (Anolis carpenteri) at La Selva. Leaf litter lizards and frogs have both been declining over the past 30 years in La Selva.

Carpenter’s anole (Anolis carpenteri) at La Selva. Leaf litter lizards and frogs have both been declining over the past 30+ years in La Selva.

Amphibian and reptile declines at La Selva are particularly interesting because there are likely a variety of factors contributing to the long-term declines in abundance of leaf litter reptiles and amphibians. The area surrounding the biological station has been developed for pineapple plantations, where pesticides are often applied that may be traveling to the forest and affecting reptiles and amphibians in as yet undiscovered ways. Diseases such as the amphibian chytrid fungus (Batrachochytrium dendrobatidis) and Ranavirus are likely present at the reserve (if interested in learning more, see this paper on temporal variation of Bd infection at La Selva). In conclusion, there is a lot of research occurring in Costa Rica right now on amphibian and reptile declines, living up to Costa Rica’s reputation as one of the more well-studied neotropical countries.

Bransford's leaf litter frog (Craugastor bransfordi), one of the most common terrestrial frogs at La Selva.

Bransford’s leaf litter frog (Craugastor bransfordi), one of the most common terrestrial frogs at La Selva.

Stay tuned: In part (2) of my “Aventuras”, I will talk about the two independent mini-projects on reptiles and amphibians that I and some friends designed and carried out at La Selva and Las Cruces as part of the OTS course.

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