Joint effects of climate warming and exotic litter (Eucalyptus globulus Labill.) on stream detritivore fitness and litter breakdown
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Joint effects of climate warming and other stressors are potentially complex and difficult to predict. In stream ecosystems, exotic riparian species have the potential to alter leaf-shredding detritivorous invertebrate assemblages and leaf litter breakdown due to differences in the quality of litter inputs. This is the case for Eucalyptus plantations, which are widespread, occurring along riparian corridors of streams around the world. We hypothesised that the presence of Eucalyptus globulus (Labill.) litter (1) impairs detritivore fitness both directly (i.e., through leaf consumption) and indirectly (i.e., through leaf leachates in the water) and (2) impairs litter breakdown, (3) with stronger effects at higher temperatures. We tested these hypotheses in microcosm experiments with two detritivore species from two locations: the stonefly Diamphipnosis samali (Illies, 1960) in Chile and the caddisfly Calamoceras marsupus (Brauer 1865) in Spain. Eucalyptus leaves affected detritivore growth mainly by direct consumption, while the presence of both Eucalyptus leaves and leachates inhibited the breakdown of native litter. When both litter types were available, breakdown of Eucalyptus leaves was enhanced, possibly as a means of compensatory feeding. Increased temperature exacerbated the negative effect of Eucalyptus on native litter breakdown, possibly because it reduced detritivore survival. Our results add to the mounting evidence that joint effects of multiple stressors can be non-additive, and suggest that the sole presence of Eucalyptus leaves and leachates in the water may impact stream communities and ecosystem functions even if native litter is available, with further negative effects to be expected under a warmer climate.
KeywordsClimate change Exotic species Leaf litter breakdown Leaf-shredding detritivores Riparian vegetation Stream ecosystems Temperature
We thank Richard G. Pearson and two anonymous reviewers for their comments on the manuscript. The study was funded by MINECO’s project CGL2010-16285 (Spain) to LB and projects FONDAP CRHIAM 1513001 and CONAF 035-2010 (Chile) to RF.
LB and RF conceived the study; FCA conducted the field and laboratory work with help from LB, RF, CS, RA and ARG; LB, FCA and MASG wrote the ms with input from the other authors.
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