4.1 | Community-wide trophic structure metrics
Analysis of the fish community’s trophic structure suggested an overall reduction of trophic resource use following river regulation with a limited amount due to species turnover (Table 2). With probabilities > 0.90, core fish species experienced reductions in both δ13C (27.2% decrease in δ13C range) and δ15N (28.7% decrease in δ15N range), assimilated less diverse trophic resources (26.2% decrease in CD), and niches became more similar (27.9% decrease in NND). When including all species, the reduction in basal resource assimilation (δ13C range) decreased by 32.9%. The establishment of Red Shiner likely contributed to retaining the food chain length (probability of change in δ15N range = 0.55) as it assimilated the lowest δ15N values (mean δ15N = 11.0, SD = 1.5‰; Table1 and Figure 2). However, most of the reduction (probability ≥ 0.92) in degree of trophic diversity (CD) and niche similarity (NND) between time periods was due to factors other than species turnover as the average difference in the percent change between all and core species for these trophic metrics was 4.15%. The only community-wide trophic structure metric that did not change for either core (probability = 0.65) or all species (probability = 0.67) was the standard deviation in nearest neighbor distances (SDNND).