Consumption of Native Green Ash and Nonnative Common Buckthorn Leaves by the Amphipod Gammarus pseudolimnaeus

Decomposition of allochthonous organic matter that enters shaded headwater streams during a short autumn leaf fall period provides much of the energy the streams receive throughout the year. As such, alterations of riparian communities, including those resulting from invasive species, should have a significant impact on these energy inputs and potentially alter microbial communities and the behavior of shredders that process leaf litter. We compared consumption of leaves of an abundant native species (green ash Fraxinus pennsylvanica) and nonnative species (common buckthorn Rhamnus cathartica) by the northern spring amphipod Gammarus pseudolimnaeus, with and without periods of stream conditioning. Amphipods consumed a very small proportion of the unconditioned leaves of common buckthorn and green ash and demonstrated no significant preference for the unconditioned leaves of either species. When leaves were stream-conditioned, there was a significant interaction between the effects of leaf species...