Amphibian and reptile declines over 35 years at La Selva, Costa Rica

Abstract

Amphibians stand at the forefront of a global biodiversity crisis. More than one-third of amphibian species are globally threatened, and over 120 species have likely suffered global extinction since 1980. Most alarmingly, many rapid declines and extinctions are occurring in pristine sites lacking obvious adverse effects of human activities. The causes of these "enigmatic" declines remain highly contested. Still, lack of long-term data on amphibian populations severely limits our understanding of the distribution of amphibian declines, and therefore the ultimate causes of these declines. Here, we identify a systematic community-wide decline in populations of terrestrial amphibians at La Selva Biological Station, a protected old-growth lowland rainforest in lower Central America. We use data collected over 35 years to show that population density of all species of terrestrial amphibians has declined by approximately 75% since 1970, and we show identical trends for all species of common reptiles. The trends we identify are neither consistent with recent emergence of chytridiomycosis nor the climate-linked epidemic hypothesis, two leading putative causes of enigmatic amphibian declines. Instead, our data suggest that declines are due to climate-driven reductions in the quantity of standing leaf litter, a critical microhabitat for amphibians and reptiles in this assemblage. Our results raise further concerns about the global persistence of amphibian populations by identifying widespread declines in species and habitats that are not currently recognized as susceptible to such risks.

Fig. 1.

Amphibian and reptile density over 35 years at La Selva Biological Station, Costa Rica. Each point indicates mean density for all quadrats in a given year. The closed symbols and solid line indicate data from primary forest. The open symbols and dashed line indicate data from abandoned cacao plantations. (A) Trends for all terrestrial amphibians and reptiles. (B) Trends for frogs only. (C) Trends for lizards only.

Fig. 2.

Climate data for 35 years at the La Selva Biological Station indicates that the climate is getting warmer and more consistently wet. The annual mean of daily mean temperature (A) has increased and the number of days with zero rainfall has decreased since 1970 (B).