Frogs in the genus Atelopus have declined dramatically over recent decades, with 70 percent of the 113 known species thought to have suffered population crashes. In Venezuela, nine of the ten endemic Atelopus species are classified as Critically Endangered on the IUCN Red List, and one is thought to be extinct. The agent behind these declines is suspected to be chytridiomycosis, a disease caused by the pathogenic fungus Batrachochytrium dendrobatidis (4).
Once abundant and widespread across the coastal mountains of Venezuela, the Rancho Grande harlequin frog has undergone a steep decline to the point that, despite extensive surveys, there were no observations of this species for almost 20 years after 1986 (5) (6). In 2004, after eight years of intensive searching, a small population of the Rancho Grande harlequin frog was discovered in the Parque Nacional Henri Pittier (2) (6). A number of other small populations have since been found (4).
Analyses of specimens collected in 1986 confirmed that the Rancho Grande harlequin frog was suffering from infection by Batrachochytrium dendrobatidis (7). It is possible that an outbreak of chytridiomycosis occurred after severe droughts in 1988, which would have caused frogs to congregate at remaining water sources, increasing the speed of infection (2). Furthermore, over the last decade there has been a decrease in the maximum daily temperatures, which promotes the growth of Batrachochytrium dendrobatidis on amphibians. The fact that all surviving populations of the Rancho Grande harlequin frog occur below 350 metres above sea level, where temperatures are higher than at greater elevations, may be evidence of this (4).
Other potential threats to the Rancho Grande harlequin frog include droughts and flash floods, which could increase in frequency as a result of climate change, and pollution in the Valencia-Maracay area, where many industries are emitting toxic gases (1) (2).