Abstract
There is considerable variation among studies that evaluate how amphibian populations respond to global climate change. We used 23 years of annual survey data to test whether changes in climate have caused predictable shifts in the phenology and population characteristics of adult spotted salamanders (Ambystoma maculatum) during spring breeding migrations. Although we observed year-to-year correlation between seasonal climate variables and salamander population characteristics, there have not been long-term, directional shifts in phenological or population characteristics. Warm winters consistently resulted in early migration dates, but across the 23-year study, there was no overall shift towards warmer winters and thus no advanced migration timing. Warm summers and low variability in summer temperatures were correlated with large salamander body sizes, yet an overall shift towards increasing body sizes was not observed despite rising summer temperatures during the study. This was likely due to the absence of long-term changes of within-year variation in summer temperatures, which was a stronger determinant of body size than summer temperature alone. Climate-induced shifts in population characteristics were thus not observed for this species as long-term changes in important seasonal climate variables were not observed during the 23-years of the study. Different amphibian populations will likely be more resilient to climate change impacts than others, and the probability of amphibians exhibiting long-term population changes will depend on how seasonal climate change interacts with a species’ life history, phenology, and geographic location. Linking a wide range of seasonal climatic conditions to species or population characteristics should thus improve our ability for explaining idiosyncratic responses of species to climate change.
Highlights
Climate change impacts are likely to be profound for amphibians because they are ectothermic with life cycles and life history attributes that are tightly linked to climate [20]
We evaluated whether 1) the number of returning adults, 2) male to female sex ratios, 3) body size and 4) migration timing have responded to annual variation in climate during the seasonally active versus non-active times of the year
We only focus on the Spring migration period rather than the entire Spring season because 1) of the importance of local climate conditions during the actual migration period and 2) migrations typically span the Winter to Spring transition period, and springtime season conditions would be more reflective of post-migration conditions
Summary
The impacts from climate change on amphibians are diverse and include shifts in body size [7, 8, 9, 10, 11], increased vulnerability to diseases [12], range contractions [13, 14], and population declines/extirpations [15, 16, 17, 18]. For amphibians that inhabit shallow, non-permanent wetlands (e.g., ponds and marshes), the hydroperiod of these habitats is tightly linked to patterns in snowmelt, seasonal rainfall, or evapotranspiration rates, all of which are predicted to change survival, recruitment, and population size [18, 22, 23]. Temperature and precipitation serve as important triggers for the initiation of annual breeding migrations [24, 25, 26], and shifts in the timing of reproduction have been correlated with warming temperatures [27, 28]
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