Results of model selection procedure.

Distance refers to the physical distance (in river km) between pools, while DD refers to the difference in degree days between pools over the previous 1 or 2 years. Threshold temperatures of 0°C, 5°C, 10°C, 15°C, 20°C and 25°C were compared, but only the threshold with the strongest support (assessed with AICC) was parameterized for these purposes (bolded models). For example, if a model with DD0 had a lower ΔAICC than an otherwise identical model with DD5, we only parameterized the model with DD0. B-C Sim = Bray-Curtis similarity; βDIST = standardized slope relating distance to B-C Sim; βDD = standardized slope relating difference in degree days to B-C Sim. Because temperature data are relatively limited, only 72 observations were included in this analysis.