Trophic redundancy within a diverse community of sympatric delphinids in the oligotrophic Caribbean Sea.

Understanding the trophic interactions of sympatric predators is essential to assess ecosystem structure, particularly in oligotrophic environments where resources are scarce. We examined the trophic structure of a diverse community of sympatric delphinids in the Lesser Antilles, in the eastern Caribbean Sea, using stable carbon (δ13C) and nitrogen (δ15N) isotope analysis. Isotope data suggest the existence of three distinct isotopic clusters. Killer whales (Orcinus orca) and false killer whales (Pseudorca crassidens) exhibited the highest δ15N and δ13C values, broad isotopic niches, and minimal overlap, indicating distinct apex predator roles. A cluster of mesopredators include short-finned pilot whales (Globicephala macrorhynchus), Risso's dolphins (Grampus griseus), melon-headed whales (Peponocephala electra), Fraser's dolphins (Lagenodelphis hosei), and Clymene dolphins (Stenella clymene) showed intermediate δ15N values and moderate to high isotopic overlap. In contrast, smaller delphinids (Stenella spp.) formed an isotopic cluster characterized by lower δ15N values, exhibited narrow isotopic niches, reflecting limited dietary variation and low trophic redundancy. Ontogenetic shifts and sex variation in isotopic niches were rarely detected. These findings provide novel insights into resource partitioning and ecological roles among a wide diversity of delphinids in a nutrient-poor tropical ecosystem.