Abstract
Ontogenetic niche shifts are widespread. However, individual differences in size at birth, morphology, sex, and personalitiescan cause variability in behavior. As such, inherent inter-individual differences within populations may lead to context-dependent changes in behavior with animal body size, which is of concern for understanding population dynamics andoptimizing ecological monitoring. Using stable carbon and nitrogen isotope values from concurrently sampled tissues, wequantified the direction and magnitude of intraspecific variation in trophic shifts among three shark species, and how thesechanged with body size: spurdogs (Squalus spp.) in deep-sea habitats off La Réunion, bull sharks (Carcharhinus leucas) inestuarine habitats of the Florida Everglades, and blacktip reef sharks (Carcharhinus melanopterus) in coral reef ecosystemsof Moorea, French Polynesia. Intraspecific variation in trophic shifts was limited among spurdogs, and decreased with bodysize, while bull sharks exhibited greater individual differences in trophic shifts, but also decreased in variability throughontogeny. In contrast, blacktip reef sharks exhibited increased intraspecific variation in trophic interactions with body size.Variability in trophic interactions and ontogenetic shifts are known to be associated with changes in energetic requirements,but can vary with ecological context. Our results suggest that environmental stability may affect variability within popula-tions, and ecosystems with greater spatial and/or temporal variability in environmental conditions, and those with morediverse food webs may facilitate greater individual differences in trophic interactions, and thus ontogenetic trophic shifts. Inlight of concerns over environmental disturbance, elucidating the contexts that promote or dampen phenotypic variability isinvaluable for predicting population- and community-level responses to environmental changes.