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Energetic mismatch induced by warming decreases leaf litter decomposition by aquatic detritivores
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International audience. The balance of energetic losses and gains is of paramount importance for understanding and predicting the persistence of populations and ecosystem processes in a rapidly changing world. Previous studies suggested that metabolic rate often increases faster with warming than resource ingestion rate, leading to an energetic mismatch at high temperature. However, little is known about the ecological consequences of this energetic mismatch for population demographyand ecosystem functions.2. Here, we combined laboratory experiments and modelling to investigate the energetic balance of a stream detritivore Gammarus fossarum along a temperaturegradient and the consequences for detritivore populations and organic matterdecomposition.3. We experimentally measured the energetic losses (metabolic rate) and supplies (ingestion rate) of Gammarus and we modelled the impact of rising temperaturesand changes in Gammarus body size induced by warming on population dynamics and benthic organic matter dynamics in freshwater systems.4. Our experimental results indicated an energetic mismatch in a Gammarus population where losses via metabolic rate increase faster than supplies via food ingestion with warming, which translated in a decrease in energetic efficiency withtemperature rising from 5 to 20°C. Moreover, our consumer–resource model predicts a decrease in the biomass of Gammarus population with warming, associated with lower maximum abundances and steeper abundance decreases after biomass annual peaks. These changes resulted in a decrease in leaf litter decomposition rate and thus longer persistence of leaf litter standing stock over years in the simulations. In addition, Gammarus body size reductions led to shorter persistence for both leaf litter and Gammarus biomasses at low temperature and the opposite trend at high temperature, revealing that body size reduction was weakening the effect of temperature on resource and consumer persistence.
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