Climate change is driving changes in the elevations of hosts and pathogens. Our primary field site is in the Cordillera Vilcanota, a heavily glacierized range in Cusco Department, southern Peru, within a region of the tropical Andes where significant changes in temperature, glacier cover, and species distributions have been recorded in recent decades. As glaciers melt away, glacial runoff forms new ponds and frogs have expanded their ranges to new habitat created within the last 70 years between 5200-5400 masl, making these the highest recorded populations of amphibians on the planet. At the same time, the pathogenic amphibian chytrid fungus (Batrachochytrium dendrobatidis, Bd) has appeared in frogs that have colonized the deglaciated zone, causing mass mortality events. This 200-meter upward shift represents one of the largest elevational range expansions observed for any vertebrate, and the arrival of Bd is one of the clearest examples of climate change directly influencing the spread of an emerging infectious wildlife disease.
Results/Conclusions
We present the first detailed description of seasonal reproductive patterns for the highest-known frog populations on Earth. We conducted three years (including a strong El Niño year) of reproductive surveys for the frogs Pleurodema marmoratum and Telmatobius marmoratus above 5200 masl. We found that P. marmoratum reproduce from the onset of the wet season (late September) until late November. Tadpoles complete metamorphosis in 3-4 months and juveniles emerge from ponds from January-May. In 2013 we documented recovery of Telmatobius marmoratus in several study ponds. Telmatobius marmoratus had not been observed at the site since a Bd-induced mortality event in 2005. We found a seasonal pattern of Bd infection. Emerging P. marmoratum juveniles had a lower-than-expected infection load compared to adults. We determined the critical thermal maximum for P. marmoratum from 5250 masl. Despite living in such a cold environment, P. marmoratum has one of the highest CTmax (>32º C) reported from the tropical Andes of Peru. We completed occupancy surveys for amphibians at several new sites in the Vilcanota and Vilcabamba ranges. We documented additional examples of amphibian elevational range expansions into new habitat in recently deglaciated valleys, indicating that amphibians are likely moving upwards throughout the rapidly warming Peruvian Andes. Amphibians are not the only animals expanding into newly available habitat. We documented high levels of mammal activity at the edge of the recently deglaciated zone including vicuña (Vicugna vicugna), taruka deer (Hippocamelus antisensis), puma (Puma concolor), and pampas cat (Leopardus pajeros).