Detritivores feeding on poor quality food are more sensitive to increased temperatures
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As temperature increases the metabolic rates, the effect of warming on animals will also enhance animal-driven nutrient cycling with important consequences on ecosystem dynamics. We tested the effects of increased temperature (15 and 20°C, optimal and suboptimal temperatures, respectively) on metabolic rates of the shredder larvae Sericostoma vittatum fed on three diets, Alnus glutinosa (L.) Gaertn., Eucalyptus globulus Labill. and Quercus robur L. We measured P and N content in leaves, faeces and excreta and calculated C, N, and P assimilation efficiencies, and mass balances. Carbon assimilation efficiency (AE) was reduced at 20°C when larvae fed on Q. robur; nitrogen-AE was reduced at 20°C in all diets and phosphorus-AE was not affected by temperature. Larvae achieved a net N gain in all treatments, however, increased temperatures had a negative effect on N incorporation into body tissue. The mass balance of P was negatively affected by temperature; larvae fed on Q. robur and on E. globulus had null balances at 15°C and negative at 20°C. Our results showed that high temperature increased nutrient excretion and affected N:P ratios in excreta, thus changes in temperature may have severe consequences on larval mediated leaf litter processing and nutrient cycling. However, the type of diet seemed to modulate the way temperature affects larval metabolism regarding excretion rate and assimilation efficiencies. The extent to which optimal–suboptimal temperature variation will alter detritivore metabolism performance, internal nutrient balance and hence, cycling of elements in the environment seems crucial under global warming scenarios.
KeywordsTemperature Detritivores Ecological stoichiometry Nutrient cycling Streams
We thank Ana R. Calapez for laboratory work and chemical determinations, and E. Balseiro and M.A.S. Graça for suggestions in a previous version of this manuscript. D. Howell kindly advised us with the factorial analysis of variance and provided the statistical program for use on R statistical package. This work was supported by a bi-national Visiting Grant (SECYT, Argentina and GRICES, Portugal: PO/PA05-BXV-015), the Portuguese Science Foundation (Project: PTDC/CLI/67180/2006) and IMAR (Portugal), and by the CONICET (Grant #PIP 112-200801-01702) and FONCYT (Grant #PICT-2007-01747) (Argentina).
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