Direct effects influence larval salamander size and density more than indirect effects

Demographic effects of phenological variation in natural populations of two pond-breeding salamanders

Phenology is a key driver of population and community dynamics. Phenological metrics (e.g., first date that an event occurred) often simplify information from the full phenological distribution, which may undermine efforts to determine the importance of life history events. Data regarding full phenological distributions are especially needed as many species are shifting phenology with climatic change which can alter life-history patterns and species dynamics. We tested whether skewness, kurtosis or maximum duration of breeding phenology affected juvenile emigration phenology and survival in natural populations of ringed (Ambystoma annulatum) and spotted salamanders (A. maculatum) spanning a 7-year period at two study locations. We evaluated the relative importance of different phenological metrics in breeding phenology and larval density dependence on emigration phenology and survival. We found that variability in emigration phenology differed by species, with ringed salamanders having a shorter duration and distributions that were more often right-skewed and leptokurtic compared to spotted salamanders. Emigration phenology was not linked to any measure of variability in breeding phenology, indicating phenological variability operates independently across life stages and may be subject to stage-specific influences. Emigration duration and skewness were partially explained by larval density, which demonstrates how phenological distributions may change with species interactions. Further tests that use the full phenological distribution to link variability in timing of life history events to demographic traits such as survival are needed to determine if and how phenological shifts will impact species persistence.