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Ecological role of the salamander Ensatina eschscholtzii: direct impacts on the arthropod assemblage and indirect influence on the carbon cycle in mixed hardwood/conifer forest in Northwestern California
Terrestrial salamanders are the most abundant vertebrate predators in northwestern California forests, fulfilling a vital role converting invertebrate to vertebrate biomass. The most common of these salamanders in northwestern California is the salamander Ensatina (Ensatina eschsccholtzii). I examined the top-down effects of Ensatina on leaf litter invertebrates, and how these effects influence the relative amount of leaf litter retained for decomposition, thereby fostering the input of carbon and nutrients to the forest soil. The experiment ran during the wet season (November - May) of two years (2007-2009) in the Mattole watershed of northwest California. In Year One results revealed a top-down effect on multiple invertebrate taxa, resulting in a 13% difference in litter weight. The retention of more leaf litter on salamander plots was attributed to Ensatina’s selective removal of large invertebrate shedders (beetle and fly larva) and grazers (beetles, springtails, and earwigs), which also enabled small grazers (mites; barklice in year two) to become more numerous. Ensatina’s predation modified the composition of the invertebrate assemblage by shifting the densities of members of a key functional group (shredders) resulting in an overall increase in leaf litter retention. Results from year two indicated that these effects were affected by moisture availability, and that direct salamander impacts on invertebrates, and the related indirect effects on the capacity for forest floor leaf litter retention were diminished in the second, wetter year.