Variation in the trophic position of common stream fishes and its relationship to the presence of a rare fish, northern leatherside chub (Lepidomeda copei)

Abstract

AbstractVariation in trophic position can be caused by structural changes in food webs that may affect the presence of, or be affected by the presence of, individual species. We examined variation in the trophic position of fishes across 14 stream sites in the Bear River drainage, WY, USA. This drainage is the focus of ongoing conservation of northern leatherside chub (Lepidomeda copei). Our goals were (i) to describe variation in trophic position of individual species and (ii) to determine whether these measures differed between sites with and without northern leatherside chub. Mean trophic position of individual fish species varied between 0 and 3 trophic positions across sites. For two of these species, trophic position declined at sites without northern leatherside chub. Importantly, habitat surveys from a previous study at 10 of these sites revealed no differences in habitat suitability for northern leatherside chub. This suggests that trophic position revealed systematic differences among sites that were not apparent based on traditional species‐habitat modelling. We outline possible mechanisms behind these patterns and argue that monitoring variation in trophic position can complement traditional, habitat‐based methods for understanding species distributions.