title: High intraspecific variability in the functional niche of a predator is associated with ontogenetic shift and individual specialization.
abstract: Investigations on the functional niche of organisms have primarily focused on differences among species and tended to neglect the potential effects of intraspecific variability despite the fact that its potential ecological and evolutionary importance is now widely recognized. In this study, we measured the distribution of functional traits in an entire population of largemouth bass (Micropterus salmoides) to quantify the magnitude of intraspecific variability in functional traits and niche (size, position, and overlap) between age classes. Stable isotope analyses (δ (13)C and δ (15)N) were also used to determine the association between individual trophic ecology and intraspecific functional trait variability. We observed that functional traits were highly variable within the population (mean coefficient variation: 15.62% ± 1.78% SE) and predominantly different between age classes. In addition, functional and trophic niche overlap between age classes was extremely low. Differences in functional niche between age classes were associated with strong changes in trophic niche occurring during ontogeny while, within age classes, differences among individuals were likely driven by trophic specialization. Each age class filled only a small portion of the total functional niche of the population and age classes occupied distinct portions in the functional space, indicating the existence of ontogenetic specialists with different functional roles within the population. The high amplitude of intraspecific variability in functional traits and differences in functional niche position among individuals reported here supports the recent claims for an individual-based approach in functional ecology.
authors.affiliation: CNRS, Université Paul Sabatier, ENFA, UMR 5174 EDB (Laboratoire Évolution & Diversité Biologique) 118 route de Narbonne, F-31062, Toulouse, France ; Université Toulouse 3 Paul Sabatier, CNRS, UMR5174 EDB F-31062, Toulouse, France.
authors.forename: Tian
authors.initials: T
authors.lastname: Zhao
authors.affiliation: Laboratoire Écologie des Systèmes Marins Côtiers UMR 5119 CNRS-UM2-IFREMER-IRD-UM1, Université Montpellier 2 CC 093, 34 095, Montpellier Cedex 5, France.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Villéger
authors.affiliation: CNRS, Université Paul Sabatier, ENFA, UMR 5174 EDB (Laboratoire Évolution & Diversité Biologique) 118 route de Narbonne, F-31062, Toulouse, France ; Université Toulouse 3 Paul Sabatier, CNRS, UMR5174 EDB F-31062, Toulouse, France.
authors.forename: Sovan
authors.initials: S
authors.lastname: Lek
authors.affiliation: CNRS, Université Paul Sabatier, ENFA, UMR 5174 EDB (Laboratoire Évolution & Diversité Biologique) 118 route de Narbonne, F-31062, Toulouse, France ; Université Toulouse 3 Paul Sabatier, CNRS, UMR5174 EDB F-31062, Toulouse, France.
authors.forename: Julien
authors.initials: J
authors.lastname: Cucherousset
keywords: Functional traits; niche; ontogeny; overlap; stable isotope analyses