MEPS prepress abstract  -  DOI:

Diverse resource-use strategies in a large-bodied marine predator guild: evidence from differential use of resource subsidies and intraspecific isotopic variation

Oliver N. Shipley*, Austin J. Gallagher, David S. Shiffman, Leslie Kaufman, Neil Hammerschlag


ABSTRACT: Observations of resource use dynamics are sparse for higher trophic level species in marine systems, but important given their role in driving the distribution and functional roles of species. For a guild comprised of seven large-bodied shark species captured in Florida Bay, we use multi-tissue stable isotope analysis to evaluate the extent of resource use diversity within and between two time periods. We examine: 1) variation in community-wide isotopic niche structure across time (i.e., Layman’s community metrics); 2) variation in species’ trophic position (TP); 3) reliance upon dominant resource pools (inland mangroves vs. coastal neritic [i.e. seagrass and/or reef-associated prey]; and 4) patterns of intraspecific isotopic variation across species (i.e., standard ellipse area [SEAc], ellipse eccentricity [E], ellipse inclination [θ], and total isotopic overlap). Community-wide isotopic niche characteristics varied with tissue type, suggesting temporal plasticity in community resource use. Our novel approach integrating multiple isotopic baselines resulted in consistently high trophic position estimates (> 5.0), but the utilization of available resource subsidies varied with species and tissue type. Whole blood suggested recent use of inland mangrove-derived prey resources while fin tissue suggested differential use of both inland mangroves and coastal neritic-derived subsidies. Our results suggest that sharks display dynamic resource use in space and time, with limited functional complementarity across species. The adoption of diverse resource use strategies, both within and among species, could facilitate the co-occurrence of large-bodied predator species and underscores the role of sharks as vectors of ecosystem connectivity.