Ecological clustering within a diverse minnow assemblage according to morphological, dietary and isotopic data

Summary The ecological role of an organism is a complex interaction between many factors, such as morphology, behaviour and physiology, which can act as functional constraints upon how an organism engages with the environment. We examined the ecological roles, guild structure and ecological convergence among 15 sympatric minnow species (Cyprinidae) in the New River (North Carolina, U.S.A.). Minnows often dominate fish species diversity and biomass in North American streams. We evaluated the ecological relationships among minnows using popular methods that correspond to different aspects of minnow biology: geometric morphometrics (landmark‐based PCA), gut content analysis and stable isotopes (13C, 15N, 2H). We then tested for clustering (i.e. guilds) and convergence among minnows using these traits. Important shape variation among species was primarily associated with mouth orientation and caudal peduncle morphology, implicating the importance of trophic and activity patterns. Minnows clustered into five guilds based on body shape. Gut contents revealed three discrete guilds: pelagic‐ and benthic‐oriented invertivory and benthic herbivory. Stable isotopes revealed only two discrete guilds: algivory and invertivory; however, all minnows preferentially assimilated invertebrates. Minnows thus exhibit dynamic ecologies based largely on utilisation of the benthic–pelagic resource axis.