Amid growing concern over the impacts of long-term climate change, a fundamental challenge for wildlife biologists is determining how animal populations will respond to a changing climate. In amphibians, little research has addressed how climate variation may affect vital rates and overall population size and viability. We evaluated relationships between annual age- and sex-specific vital rates and local climate variables using a nine-year mark-recapture dataset of Columbia spotted frogs (Rana luteiventris) from the Bitterroot Mountains, western Montana. Climate variables included peak snowpack, winter length, summer length, and growing degree days. We examined correlations between climate variables and both breeding probability and egg to one year survival. We estimated annual survival and growth probability from the mark-recapture data using multistage robust design models in program MARK for four age classes: juveniles, subadult and adult females, and adult males. Finally, we calculated the simultaneous effects of snowpack on population growth rates by calculating asymptotic lambda for a low snow year (less severe winter) and a high snow year (more severe winter).
Results/Conclusions
We found that summer length was positively correlated with probability of breeding the following spring (Pearson’s correlation coefficient=0.752, p=0.051).There was no relationship between any of the climate variables and egg to one year survival. From the mark-recapture models, we found that survival and growth probability were best predicted by snowpack and winter length. Increases in snowpack resulted in a decrease in juvenile (b= -0.076 ±0.007), adult male (b= -0.037±0.016), and adult female (b= -0.032±0.015) survival, and had no effect on subadult survival (b= -0.025±0.035). An increase in winter length led to a slight increase in survival, but only for juveniles (b=0.0083±0.0039) and adult males (b=0.026±0.011). Higher snowpack led to an increase in growth probability for subadults (0.049±0.022), but a decrease for juveniles (-0.039±0.007). Longer winters were associated with higher growth probability for juveniles (0.017±0.005), but not subadults. The population showed an increasing growth rate for the low snow year (lambda=1.1), and a decreasing growth rate for the high snow year (lambda=0.57). These results suggest that a warming climate with less severe winters might lead to higher survival rates and subsequent population growth rates for this montane frog population. In environments that are naturally harsh for amphibian populations, changing climatic conditions may prove to be positive, at least in the short term.
