Data from: Spatial separation without territoriality in shark communities

Spatial separation within predator communities can arise via
territoriality but also from competitive interactions between and within
species. However, linking competitive interactions to predator
distribution patterns is difficult and theoretical models predict
different habitat selection patterns dependent on habitat quality and how
competition manifests itself. While models generally consider competitors
to be either equal in ability, or for one phenotype to have a fixed
advantage over the other, few studies consider that an animal may only
have a competitive advantage in specific habitats. We used > 10
years of telemetry data, habitat surveys and behavioral experiments, to
show spatial partitioning between and within two species of reef shark
(grey reef, Carcharhinus amblyrhinchos, and blacktip reef sharks, C.
melanopterus) at an unfished Pacific atoll. Within a species, sharks
remained within small ‘sub-habitats’ with very few movements of
individuals between sub-habitats, which previous models have suggested
could be caused by intra-specific competition. Blacktip reef sharks were
more broadly distributed across habitat types but a greater proportion
used lagoon and backreef habitats, while grey reef sharks preferred
forereef habitats. Grey reef sharks at a nearby atoll where blacktip reef
sharks are absent, were distributed more broadly between habitat types
than when both species were present. A series of individual-based models
predict that habitat separation would only arise if there are competitive
interactions between species that are habitat-specific, with grey reefs
having a competitive advantage on the forereefs and blacktips in the
lagoons and backreef. We provide compelling evidence that competition
drives distribution patterns and spatial separation of a marine predator
community, and highlight that competitive advantages may not be constant
but rather dependent on habitats.