Temporal shifts in abiotic resources are problematic for organisms with complex life cycles (i.e., amphibians) because temperature and precipitation influence the habitat suitable for life history events across their ontogeny (e.g., breeding phenology, recruitment, emigration phenology). Juvenile recruitment is a primary driver of amphibian population dynamics; thus, we tested how variation in breeding and emigration phenologies influence juvenile growth and survival in a capture-mark-recapture study. We manipulated emigration phenology by adding ringed salamanders (Ambystoma annulatum) to 3x3 meter terrestrial enclosures in two treatments: all individuals on one date or at the same density over three dates over a 4 week period. We crossed emigration treatments with identical manipulations of breeding phenology (larvae added on one or three dates), for a total of four treatments, each with six replicates. We expected survival to increase with the number of emigration events since the risks associated with environmental stochasticity would be spread among emigration pulses; thus, decreasing the probability of complete mortality. We implanted juveniles with passive integrated transponders (PIT) and recaptured animals bi-weekly (01-August 2018 – 01-May 2019) using visual surveys, pitfall traps, or PIT tag scans. We estimated survival, with and without carryover effects, using a Cormack-Jolly-Seber model fit in JAGS.
Results/Conclusions:
Overall, we re-detected 151 of the 192 individuals released. Of those, 81 individuals were confirmed alive at least once and four individuals experienced mortality. Size at metamorphosis did not vary across larval treatment; however, juveniles added to 3-date enclosures were significantly larger in mass (mean ± SD: 1.50 ± 0.42) than juveniles in 1-date enclosures (1.19 ± 0.33; t = -5.73; p < 0.01). Neither survival nor detection probability differed across treatments, with or without consideration of carryover effects from the larval environment. Since size at metamorphosis is a proxy for survival and lifetime fitness of amphibians, observed differences in survival between phenology treatments would lend support for abiotic factors influencing population dynamics. However, the lack of differences in size at metamorphosis and juvenile survival suggest that larval and juvenile Ambystoma annulatum life stages may be robust to the range of environmental perturbations tested in our phenological manipulations. In fact, many amphibians breed and emigrate over multiple pulses that correspond with rainfall events over a period of weeks in natural systems. Despite the lack of a strong effect of phenology on juvenile survival, these data provide important life history parameters for a critical life stage that has often been overlooked.