title: Size, sex and individual-level behaviour drive intrapopulation variation in cross-ecosystem foraging of a top-predator.
abstract: Large-bodied, top-predators are often highly mobile, with the potential to provide important linkages between spatially distinct food webs. What biological factors contribute to variation in cross-ecosystem movements, however, have rarely been examined. Here, we investigated how ontogeny (body size), sex and individual-level behaviour impacts intrapopulation variation in cross-ecosystem foraging (i.e. between freshwater and marine systems), by the top-predator Alligator mississippiensis. Field surveys revealed A. mississippiensis uses marine ecosystems regularly and are abundant in estuarine tidal creeks (from 0·3 to 6·3 individuals per km of creek, n = 45 surveys). Alligator mississippiensis captured in marine/estuarine habitats were significantly larger than individuals captured in freshwater and intermediate habitats. Stomach content analysis (SCA) showed that small juveniles consumed marine/estuarine prey less frequently (6·7% of individuals) than did large juveniles (57·8%), subadult (73%), and adult (78%) size classes. Isotopic mixing model analysis (SIAR) also suggests substantial variation in use of marine/estuarine prey resources with differences among and within size classes between sexes and individuals (range of median estimates for marine/estuarine diet contribution = 0·05-0·76). These results demonstrate the importance of intrapopulation characteristics (body size, sex and individual specialization) as key determinants of the strength of predator-driven ecosystem connectivity resulting from cross-ecosystem foraging behaviours. Understanding the factors, which contribute to variation in cross-ecosystem foraging behaviours, will improve our predictive understanding of the effects of top-predators on community structure and ecosystem function.
authors.affiliation: Department of Biology, University of Florida, Gainesville, FL, USA.
authors.forename: James C
authors.initials: JC
authors.lastname: Nifong
authors.affiliation: Department of Applied Ecology, North Carolina State University, Chapel Hill, NC, USA.
authors.forename: Craig A
authors.initials: CA
authors.lastname: Layman
authors.affiliation: Division of Marine Sciences and Conservation, Nicholas School of the Environment, Duke University, Beaufort, NC, USA.
authors.forename: Brian R
authors.initials: BR
authors.lastname: Silliman
mesh_terms: D000489:Alligators and Crocodiles / Q000254:growth & development / Q000502:physiology*; D000818:Animals; D049628:Body Size; D004032:Diet; D017753:Ecosystem; D063366:Estuaries; D005766:Gastrointestinal Contents; D005845:Georgia; D062312:Islands; D011235:Predatory Behavior; D012727:Sex Characteristics
keywords: Alligator mississippiensis; crocodilian; diet; ecosystem connectivity; estuary; food web; individual specialization; trophic coupling