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Phenological shifts are expected to affect species interactions, in part by influencing which size classes, life stages or species occur simultaneously in a community. Yet, changes in phenology beyond shifts to the first, mean or median date of an ontogenetic event are underexplored in their importance to community dynamics. Using outdoor mesocosms, we experimentally mimicked increasing variability in breeding phenology of a top predatory salamander in pond food webs (Ambystoma annulatum) to assess its impacts on its own demographic traits and survival. We also tested whether variability in predator breeding would cascade to impact survival and diversity of lower trophic levels (intermediate salamander predators, anuran tadpoles, zooplankton and periphyton). We found that only variability in body size at metamorphosis of A. annulatum was impacted by phenological manipulations, with size variability being greater at higher levels of phenological variability. Because size at metamorphosis is often correlated with adult fitness, covarying variability in body size and phenology may lead to altered population dynamics. We also found that the density and size of A. annulatum were better predictors of overall survival and diversity of amphibian prey compared to phenological variability. We speculate that overwintering mortality of A. annulatum due to pond freezing modulated the impacts of phenological variability, such that changes in demographic traits and cascading effects throughout the food web were mollified. [ABSTRACT FROM AUTHOR]

Predator species and body size represent critical factors that have differential effects on prey populations, as well as overall community structure. However, investigations of how morphologically-similar predator species, simultaneous to variation in predator body size, influence lower trophic levels are infrequently performed. We tested whether predator species and body size influenced the functional response curve of three larval ambystomatid salamanders (Ringed Salamander, Ambystoma annulatum Cope, 1886; Spotted Salamander, Ambystoma maculatum (Shaw, 1802); Marbled Salamander, Ambystoma opacum (Gravenhorst, 1807)) while eating congeneric prey. We combined larval salamanders of varying body sizes with up to six prey densities within experimental microcosms. We tested for the shape of the functional response curve and obtained parameter estimates for attack rate and handling time for each predator size - species combination. We found variability among both species and size classes, with a combination of type I and type II functional response curves. Large size classes of predators had higher attack rates than smaller size classes, but equivalently-sized larvae of different species exhibited differences in attack rates and handling time. Our study shows that predation risk varies depending on the size structure and diversity of predators present in a food web, and that grouping predators by either species or size class may reduce the ability to predict changes in community structure resulting from such interactions. [ABSTRACT FROM AUTHOR]

Loss or alteration of natural wetland habitats is a near ubiquitous global phenomenon. In the US, legislation mandates that all lost wetland habitats be replaced; manmade wetland habitats rarely have the same structural form or ecological function as natural wetlands. In the eastern US, these manmade pond habitats often serve as water sources for wildlife, but many are also utilized by amphibians for reproduction. Understanding the features that maximize species' abundance and diversity is critical to effective management. In this study, we surveyed for ambystomatid salamander larvae at 169 manmade ponds in a military training installation. Three species were present: Ambystoma maculatum, A. opacum and the regionally endemic A. annulatum. We estimated larval densities in each pond in relation to landscape- and pond-level covariates. Important factors relating to larval density were forest habitat surrounding each pond, canopy cover over a pond, the number of ponds within 300 m of the focal pond, presence of fish, slope of the pond basin, hydroperiod and amount of vegetation within the pond. Density estimates for each species were best predicted by different combinations of these factors, underscoring the need to provide a range of pond habitats to promote species diversity on the landscape. Our results indicate that manmade ponds are providing a valuable reproductive resource, but that future construction of ponds on the landscape will best serve the salamander and broader amphibian community if different combinations of hydroperiod and slope are utilized. [ABSTRACT FROM AUTHOR]