Sharing the Top of the Bottom: Environmental Influences on Trophic Niche Dimensions and Overlap of Two Common Benthivorous Fishes of Boreal Lakes

Studies on the trophic ecology of large-bodied benthivorous fishes in boreal lakes are relatively rare, despite their abundance and interesting position as terminal nodes of short food chains. We used stable isotopes of nitrogen (¹⁵N / ¹⁴N) and carbon (¹³C / ¹²C) in muscle tissue to investigate how resource and habitat partitioning between lake whitefish (Coregonus clupeaformis) and common white sucker (Catostomus commersoni) are related to sympatry and environmental characteristics in Boreal Shield lakes. In lakes containing both species, lake whitefish exhibited a stronger reliance on pelagic primary production (inferred from δ¹³C), occupied a higher trophic position (inferred from δ¹⁵N), and had smaller trophic niche dimensions (inferred from variance ellipses in δ¹³C - δ¹⁵N space) compared to white sucker.  Overlap in the trophic niches of the two species in sympatry was generally low, and white sucker niche dimensions were not significantly larger in lakes where lake whitefish were absent, suggesting that they have relatively distinct trophic niches.  Niche overlap between these species was more strongly related to indices of ecosystem productivity than ecosystem size.  This research sheds light on the trophic interactions of benthivorous fishes in boreal food webs, and how these interactions are influenced by environmental conditions.