Inter-individual differences in ontogenetic trophic shifts among three marine predators
Ontogenetic niche shifts are widespread. However, individual differences in size at birth, morphology, sex, and personalities can 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 and optimizing ecological monitoring. Using stable carbon and nitrogen isotope values from concurrently sampled tissues, we quantified the direction and magnitude of intraspecific variation in trophic shifts among three shark species, and how these changed with body size: spurdogs (Squalus spp.) in deep-sea habitats off La Réunion, bull sharks (Carcharhinus leucas) in estuarine habitats of the Florida Everglades, and blacktip reef sharks (Carcharhinus melanopterus) in coral reef ecosystems of Moorea, French Polynesia. Intraspecific variation in trophic shifts was limited among spurdogs, and decreased with body size, while bull sharks exhibited greater individual differences in trophic shifts, but also decreased in variability through ontogeny. 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 populations, and ecosystems with greater spatial and/or temporal variability in environmental conditions, and those with more diverse food webs may facilitate greater individual differences in trophic interactions, and thus ontogenetic trophic shifts. In light of concerns over environmental disturbance, elucidating the contexts that promote or dampen phenotypic variability is invaluable for predicting population- and community-level responses to environmental changes.
KeywordsDietary shifts Elasmobranchs Foraging development Juveniles Nursery
Data collection and sample analysis were funded by the National Science Foundation through the Florida Coastal Everglades LTER Program (DEB1237517, DBI0620409, DEB9910514), Florida International University’s Marine Sciences Program, the PADI Foundation, and National Geographic. J Mourier was supported by funding from the Ministère de l’Environnement, du Développement Durable et de l’Energie (MEDDE) together with Agence Nationale des Aires Marines Protégées (AAMP). We thank the many volunteers who assisted with shark fishing in both Moorea and the Florida Everglades, and sample preparation and processing. We thank IFREMER La Réunion and ARVAM (especially JP Quod) for providing sharks in La Réunion. We thank the Texas Research Institute for Environmental Studies for providing logistical support in preparation for the manuscript. Research was approved by and conducted under the protocols of Florida International University’s Institutional Animal Care and Use Committee, and in accordance to sampling permits EVER-2013-SCI-0020, EVER-2011-SCI-0031, EVER-2009-SCI-0024, and EVER-2007-SCI-0025 granted by Everglades National Park. This is the sixth publication for the Coastal Marine Ecology Program, and contribution #121 from the Center for Coastal Oceans Research within the Institute of Water and Environment at Florida International University. Data are made available through the Florida Coastal Everglades LTER program (http://fce.lternet.edu).
Author contribution statement
PM, JJK, MRH, BLB, and JM conceived and designed the sampling protocols. PM, JJK, and JM conducted the fieldwork and collected the data. PM analyzed the data. PM, JJK, MRH, BLB, and JM developed the questions investigated within the manuscript. PM, JJK, MRH, BLB, and JM wrote the manuscript.
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