Arctic char - friend or foe?: Climate driven seasonal variation in competitive impact of Arcticchar (Salvelinus alpinus L) on brown trout (Salmo truttaence L)
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- Institutt for biologi 
Here I test for climate driven seasonal effects on competition in lakes using brown trout (Salmo trutta L.) and Arctic char (Salvelinus alpinus L.) as model organisms. Winter and summer brown trout consumption rates were estimated by 1374 Cs tracer methodology using brown trout sampled in allopatric (brown trout) and 10 sympatric (brown trout/Arctic char) lakes, located along an altitudinal gradient in central Scandinavia. Lake catchment area vegetation properties ranged from southern boreal to alpine. All brown trout populations showed decreased energy intake during winter compared to summer and there was a significant impact of the presence of Arctic char on overall food consumption. Variation in food consumption between lakes was best described by a model including a three way interaction between season, secchi disk transparency and presence/absence of Arctic char.Despite the large environmental gradient no effect of water temperature was found on the impact of Arctic char on brown trout food consumption. Length of ice-covered period and export of allochthonous material from the catchment, affecting light regime in the lakes, are likely drivers of the seasonal and climatic variation in competitive impact. The study16 emphasizes the importance of adding indirect effects from alterations in catchment area properties to the direct effects of rising temperature when modelling future effects of climate change on freshwater biodiversity.