Climate change and long-term trends in a stream salamander population

Background/Question/Methods

Population declines of amphibians have been documented worldwide, and are often linked to climate change. However, we have been unable to assess population trends and responses to climate change in stream salamanders because long-term data on these species are extremely rare. I used 12 years of data to assess population trends in the stream salamander Gyrinophilus porphyriticus, and to test whether these trends were related to climate-associated changes in temperature and precipitation. Data from July surveys of a 1-km study stream in northern New Hampshire, USA, were used to test for trends in salamander abundance and size distribution between 1999 and 2010. Additionally, I used capture-mark-recapture (CMR) data from surveys in 1999 through 2004 to test for temporal variation in detection and survival probabilities. I then tested whether changes in annual temperature and precipitation during the 12-year study period were related to G. porphyriticus population trends.

Results/Conclusions

Total salamander abundance declined significantly over the 12-year period. This decline was caused by reductions in the abundance of post-metamorphic adults, and accompanied by an increase in median adult size. Larval abundance and size distribution did not change over the study period. CMR analyses showed no temporal trends in detection probability, validating the abundance data, and no temporal variation in larval or adult survival. Salamander abundance decreased with annual precipitation, and was unrelated to temperature. With the lack of declines in larval abundance, and in larval and adult survival, these results suggest that the population decline was caused by reduced adult recruitment from the larval stage (i.e., metamorphosis). More broadly, these data suggest that climate-associated increases in precipitation and streamflow in the Northeast may reduce metamorphosis rates in G. porphyriticus, leading to reductions in population size and thereby increasing vulnerability to other disturbances. North America is home to the greatest diversity of stream salamanders in the world, and greater understanding of these population trends may be crucial to protecting this diversity.