Fish feeding niche characterization over space and time in a natural boreal river

Few studies have examined the temporal variability of fish feeding niche in response to variable flows and temperature or the temporal consistency of spatial differences in fish feeding niche within natural rivers. Using a 10-year dataset from the boreal Batchawana River in Northern Ontario, we found that fish feeding niche was temporally invariant in the lower sampled river reaches but increased over time in the upper reaches of the river. A significant relationship between the standard deviations of mean delta N-15 and mean daily summer flow was found. No other significant relationships between measures of flow or temperature variability and variability in delta C-13 or delta N-15 were observed. Fish feeding niche was significantly larger in the lower than in the upper Batchawana River, but there were no significant differences in mean fish community delta C-13 or delta N-15 between reaches. Fish assemblage vC, delta N-15 and standard ellipse area were consistent among years within river reaches despite flow and temperature variability over the same years. Results highlight that in natural undisturbed rivers, fish feeding niche appears to be temporally invariant in the face of naturally imposed environmental variability. Copyright (C) 2016 John Wiley & Sons, Ltd.