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).