The precipitous loss of amphibians in recent years has been blamed on habitat loss, global warming, fungal infections, and pesticides. Globally, all of these factors probably combine for a multiple whammy. Now, research published online April 20 in Proceedings of the National Academy of Sciences U.S.A. reveals a new combo: climate change is causing some species to lose their leaf-layer habitat - and the damage is killing reptiles, too.

Steven Whitfield of Florida International University and colleagues examined 35 years' worth of data from the La Selva Biological Station in Costa Rica. The team found that populations of frogs and common reptiles such as lizards plummeted 75% since 1970. Globally, human activities are closely linked with disappearing frogs and salamanders. One-third of all amphibian species are threatened with extinction, according to a recent estimate, in large part because humans encroach on their habitats and introduce nonnative species. But even in areas without large human influences, such as the patch of protected old-growth rainforest that the researchers studied, many species are disappearing.

©Steven M. Whitfield
The strawberry poison frog (Oophaga pumilio) is one of many species of amphibians declining in lowland forests of Costa Rica.

These "enigmatic" declines, in which an entire species can disappear in months with no obvious human cause, "have aroused particular alarm" and have often been linked to chytrid fungi infections, the authors write. But the team could not point the finger at fungi in this case, because frogs in La Selva were free of fungal diseases, and the fungi don't infect reptiles. In addition, no agrochemical pesticides were reported to be present in the forest.

The researchers attributed the declines to a thinning layer of leaf litter on the forest floor. Warmer, wetter conditions could be decomposing the leaf litter that these species rely on as habitat, or may be causing trees to drop fewer leaves. They add that some populations "may be considered stable because of lack of long-term data, not lack of threats."