Sprenkel, Marley, Biology, Susquehanna University, 514 University Ave, Selinsgrove, PA, 17870, sprenkelm@susqu.edu; Matlaga, Tanya, Biology, Susquehanna University, 514 University Ave, Selinsgrove, PA, 17870, matlagat@susqu.edu.
Forest ecosystems are comprised of organisms that occupy different trophic levels, all of which affect one another. In Pennsylvania, the Eastern hemlock tree, Tsuga canadensis, is a key player in food webs because it affects soil chemistry, carbon, and nitrogen content, as well as providing shading for species in the understory. Since T. canadensis is undergoing a population decline due to the invasive wooly adelgid, understanding how its loss affects other species is crucial. Using outdoor pond mesocosms, we created simple food webs by adding zooplankton, phytoplankton, and two amphibian species, larval wood frogs (Lithobates sylvaticus) and spotted salamanders (Ambystoma maculatum). Then we manipulated leaf litter composition (majority eastern hemlock detritus or majority mixed detritus) and the rate of pond-drying. We measured treatment impacts on abiotic factors (pH, conductivity, dissolved oxygen, temperature) and quantified mass, developmental stage, and survival of wood frogs and spotted salamanders. Using linear regression and mixed model analyses, we found an interaction between increased drying and the leaf litter treatment, in that wood frog mass decreased with 10, 50 and 60% drying in the mixed leaf litter treatment. Wood frog survival did not differ between treatments, perhaps due to the asynchronous hatching between the two species. Our findings suggest that ponds will dry faster because of the loss of dependable shade coverage from T. canadensis, resulting in decreased amphibian performance due to more rapid pond-drying from increased evaporation.
amphibians, mesocosms, ephemeral ponds, Eastern hemlock