Impacts of year-year variations of precipitation (snowpack and rainfall) on amphibian recruitment and survival
Research Project Summary
Year to year variation in snowpack (20-200% of average) and summer rain create large fluctuations in the volume of water in ponds and small lakes of the higher elevation (>3000 m) Sierra Nevada . These water bodies are critical habitat for the imperiled mountain yellow-legged frog, Rana muscosa, which has decreased in abundance by up to 90% during the past century, due in part to the loss of suitable habitat and introduction of a fish predator (trout, Oncorhynchus} spp.). Climate change is predicted to reduce the amount of snowpack, potentially impacting amphibian habitats throughout the Sierra Nevada by further reducing the lake and pond water levels and resulting in drying of small lakes during the summer.
Mountain yellow-legged frogs are closely tied to water during all life stages, and are unique in having a three- to four-year tadpole phase. Thus, tadpole survival and future recruitment of adult frogs requires adequate water in lakes and ponds throughout the year, but larger lakes are populated with fish that prey on frogs and tadpoles. Most successful frog breeding occurs in warm, shallow, fishless ponds that undergo wide fluctuations in volume. These water bodies would be most susceptible to the potential climate change effects of reduced snowpack, possibly resulting in lower tadpole survival.
This study explores the link between the changes in water availability – including complete pond drying – and the abundance and recruitment of mountain yellow-legged frog in Dusy Basin , Kings Canyon National Park , California , USA . We propose using the low-snowpack years (1999, 2002, 2004) as comparative case studies to predict future effects of climate change on aquatic habitat availability and amphibian abundance and survival.
METHODS AND DESIGN
To quantify the year to year variation and changes in water volume available to amphibians, we initiated GPS lake mapping in 2002 to quantify water volumes, water surface area, and shoreline length. We tracked these changes by repeated mapping of water surface and volume (bathymetry) during the summer, and concurrently counting all frogs seen for the life stages: adult, subadult/metamorph, and tadpole. As a baseline in this analysis, we present 2002 data when pond volume declined 40-100% during summer in three breeding lakes. The lakes that completely dried up in 2002 were repopulated by adults in 2003 but showed no recruitment of metamorphosed frogs from previous year’s tadpoles. The lakes that retained water – even if they underwent a large reduction in water volume (-60%), surface area (-70%) and shoreline length (-70%) during the summer – show consistent tadpole-to-subadult recruitment in the following year (2003). Similar results are obtained using frog counts from 1999-2000 and 2004-2005 and estimates of water volume in those years.
APPLICATION OF RESEARCH RESULTS
Our preliminary results suggest that more frequent summer drying of small ponds – as may be induced by climate change – will severely reduce frog recruitment. When combined with the invasive fish that prevent frog breeding in larger lakes, such effect of climate change may cause loss of local frog populations, and push the entire species towards extinction. While additional work is necessary to quantify the link between summer drying and frog recruitment, the results suggest that restoration efforts for mountain yellow-legged frogs include adequate fish-free larger water bodies that do not undergo periodic drying.
Dusy Basin, Kings Canyon National Park
1.)Matthews, Kathleen R. 2.)Lacan, Igor 1.) Feldman, Krishna
1)USDA Forest Service
Pacific Southwest Research Station
Sierra Nevada Research Center
2) UC Berkeley - Dept of ESPM
137 Mulford Hall # 3114
Berkeley , CA 94720-3114
PUBLICATIONS AND PRODUCTS
Lacan, I., Matthews, K. R., and Feldman, K. 2006. A Practical Method for Calculating Lake Volume Over Time: Using GPS to measure water availability in small lakes inhabited by the mountain yellow-legged frog (Rana muscosa) in Kings Canyon National Park, California. Proceedings of the 2006 ESRI International User Conference, Aug 2006, San Diego, CA
Lacan, I. and K.R. Matthews 2005. Potential for Loss of Breeding Habitat for Imperiled Mountain Yellow-legged Frog ( Rana muscosa ) in High Sierra Nevada Mountain Water Bodies due to Reduced Snowpack: Interaction of Climate Change and an Introduced Predator. Eos Trans. AGU, 86 (52), Fall Meet. Suppl., Abstract GC32A-07