Interactive effects of resource quality and temperature drive differences in detritivory among native and invasive freshwater amphipods

Abstract

Invasive non-native species and climate change are two of the greatest pressures facing freshwater communities; however, how they interact to impact ecosystem function remains poorly understood despite the potential for impacts on key functional behaviours, such as detritivory, which could have wide-reaching impacts. We quantified the rates of detrital processing and survival of one U.K. native (Gammarus pulex) and two invasive non-native (Dikerogammarus villosus and Dikerogammarus haemobaphes) freshwater amphipod species, across three temperatures (8°C, 14°C, and 20°C), and three leaf diets of varying resource quality (oak, sycamore, and alder) in laboratory microcosms. We also compared amphipod survival across the different temperature and diet treatments. Rates of detrital processing varied between the native and invasive non-native amphipod species, with native G. pulex having a faster processing rate than both invasive non-native species at the lower temperatures. However, as the temperature treatments increased, between-species differences decreased, while the effects of leaf diets became more apparent. Although the survival probability did not vary with amphipod species, amphipod survival was higher at lower temperatures and in treatments containing higher quality leaf diets. We propose that the invasive non-native Dikerogammarus species will affect native communities through lower rates of detrital processing; however, this impact may change under predicted climatic warming and be increasingly similar to native amphipod species.