title: Community structure affects trophic ontogeny in a predatory fish.
abstract: While most studies have focused on the timing and nature of ontogenetic niche shifts, information is scarce about the effects of community structure on trophic ontogeny of top predators. We investigated how community structure affects ontogenetic niche shifts (i.e., relationships between body length, trophic position, and individual dietary specialization) of a predatory fish, brown trout (Salmo trutta). We used stable isotope and stomach content analyses to test how functional characteristics of lake fish community compositions (competition and prey availability) modulate niche shifts in terms of (i) piscivorous behavior, (ii) trophic position, and (iii) individual dietary specialization. Northern Scandinavian freshwater fish communities were used as a study system, including nine subarctic lakes with contrasting fish community configurations: (i) trout-only systems, (ii) two-species systems (brown trout and Arctic charr [Salvelinus alpinus] coexisting), and (iii) three-species systems (brown trout, Arctic charr, and three-spined sticklebacks [Gasterosteus aculeatus] coexisting). We expected that the presence of profitable small prey (stickleback) and mixed competitor-prey fish species (charr) supports early piscivory and high individual dietary specialization among trout in multispecies communities, whereas minor ontogenetic shifts were expected in trout-only systems. From logistic regression models, the presence of a suitable prey fish species (stickleback) emerged as the principal variable determining the size at ontogenetic niche shifts. Generalized additive mixed models indicated that fish community structure shaped ontogenetic niche shifts in trout, with the strongest positive relationships between body length, trophic position, and individual dietary specialization being observed in three-species communities. Our findings revealed that the presence of a small-sized prey fish species (stickleback) rather than a mixed competitor-prey fish species (charr) was an important factor affecting the ontogenetic niche-shift processes of trout. The study demonstrates that community structure may modulate the ontogenetic diet trajectories of and individual niche specialization within a top predator.
authors.affiliation: Department of Zoology, Genetics and Physical Anthropology University of Santiago de Compostela Santiago de Compostela Spain; Department of Arctic and Marine Biology UiT The Arctic University of Norway Tromsø Norway; Department of Natural History NTNU University Museum Trondheim Norway.
authors.forename: Javier
authors.identifier: 0000-0001-9684-4774
authors.initials: J
authors.lastname: Sánchez-Hernández
authors.affiliation: Aquatic Ecology Department Norwegian Institute for Nature Research (NINA)Trondheim Norway; Department of Biological and Environmental Sciences University of Jyväskylä Jyväskylä Finland.
authors.forename: Antti P
authors.initials: AP
authors.lastname: Eloranta
authors.affiliation: Department of Natural History NTNU University Museum Trondheim Norway; Aquatic Ecology Department Norwegian Institute for Nature Research (NINA)Trondheim Norway.
authors.forename: Anders G
authors.initials: AG
authors.lastname: Finstad
authors.affiliation: Department of Arctic and Marine Biology UiT The Arctic University of Norway Tromsø Norway.
authors.forename: Per-Arne
authors.initials: PA
authors.lastname: Amundsen
keywords: dietary switch; fish assemblage; individual specialization; interindividual variation; niche shift; predation