Data from: Differential resource consumption in leaf litter mixtures by native and non-native amphipods

Leaf litter processing is an essential ecosystem function in freshwater
systems, since much of the carbon and nutrients moving through freshwater
food webs come from the surrounding terrestrial ecosystems. Thus, it is
important to understand how the species performing this function differ,
especially because many native species are being replaced by non-native
species in aquatic ecosystems. We used a field experiment to examine leaf
consumption rates of two common shredding macroinvertebrates (the native
Gammarus fossarum and the non-native Gammarus roeselii). Leaves from three
species, varying in resource quality, were added both in leaf monocultures
and as a three-species mixture. Biomass-adjusted daily consumption rates
were similar between the two amphipod species, and each consumed
nitrogen-rich alder leaves faster than oak or beech leaves. However,
because adult G. roeselii are approximately twice the size of G. fossarum,
this led to systematic, though nonsignificant, differences in consumption
rates at the per-capita or population level. Furthermore, we found nuanced
effects of decomposer identity on leaf decomposition in mixtures. Only G.
roeselii showeding increased consumption of the preferred resource (alder)
in the mixture, while G. fossarum consumed all leaves at the same
proportional rates as in monocultures. This is an important distinction,
as most measures of macroinvertebrate leaf shredding are made in the
laboratory with only a single leaf resource available. Our results, based
on a field experiment which could control the presence of dominant
macroinvertebrates while still providing natural, biologically realistic
context, suggests that even functionally-similar species may subtly shift
ecosystem processes.