Spatial Patterns of Coexistence and Separation in a Large-bodied Marine Predator Community

Species coexistence includes various diet, space, and/or habitat selection mechanisms. Species comprising predator communities should vary in spatial overlap to maximize their fitness. Elucidating how interspecific interactions affect space use and habitat selection in large-bodied marine predators, however, is challenging due to the infeasibility of conducting manipulative experiments. Consequently, the mechanisms enabling coexistence of constituent species remain generally poorly understood. Individual-based models of a predator community incorporating competition, predation, and asymmetrical intraguild predation (IGP) predicted that mesopredators should generally separate from apex predators in safe habitat, with stronger spatial separation occurring among species with strong interference (predator/prey), which becomes weaker as interference intensity decreases (e.g., IGP). Spatial overlap patterns within an elasmobranch (sharks and rays) community in Bimini, The Bahamas, based on biotelemetry with resource selection functions and movement models, generally matched theoretical predictions. For example, predator/prey (e.g., great hammerhead sharks versus southern stingrays) showed the clearest spatial separation, followed by IG_predator/IG_prey (e.g., great hammerhead versus blacktip sharks). A lack of specific diet data, however, impedes the functional inferences that could be made. Quantifying trophic relationships for many elasmobranchs is difficult because directly observing foraging behavior is challenging and stomach contents analysis is not always feasible. The development of a minimally invasive and efficient tool using DNA metabarcoding from cloacal swabs, validated in a controlled feeding experiment and in the field, has promise for elucidating diets in and interspecific interactions among elasmobranchs.

Understanding space use is also important for designing marine protected areas (MPAs). In The Bahamas, an MPA in North Bimini has been proposed, although it is unclear how this MPA would benefit elasmobranchs if implemented. Integrating elasmobranch movement models with systematic conservation planning revealed that although the NBMPA would improve conservation, adding an additional MPA southwest of Bimini would be necessary to protect important habitats.

Altogether, integrating ecological modeling, field data, and new DNA-based diet reconstruction tools will help to resolve space use and community organization drivers, by providing insights into whether interspecific interactions might drive habitat selection and elucidating species-specific trophic pathways and dietary partitioning, that can also provide the foundation of effective and adaptive management.