Data from: Intraspecific predator inhibition, not a prey size refuge, enables oyster population persistence during predator outbreaks

Predators commonly structure natural communities, but predation effects
can vary greatly. For example, increasing predator densities may not
reduce prey populations as expected if intraspecific predator interactions
suppress foraging efficiency or if prey size refuges exist. In
northeastern Florida (USA), outbreaks of the predatory crown conch
Melongena corona have contributed to declines in oyster populations and
the commercial oyster fishery. However, despite expectations of oyster
population collapse, reefs have persisted, albeit with reduced adult
oyster size and living reef biomass. To investigate the mechanism(s)
underlying this unexpected persistence, we used field observations and
experiments to examine the effects of predator density and prey size on
predation rates. Multi-year surveys indicated that large oysters did not
experience a predation size refuge, and further suggested that predation
rates declined with increased predator density. Consistent with field
surveys, field experiments demonstrated that conchs selectively consumed
larger oysters (potentially explaining the absence of large oysters on
natural reefs) and that high conch densities suppressed per capita
predation rates, likely due to intraspecific antagonistic interactions. A
Type III ratio-dependent model best described the experimental conch
functional response, explaining >50% of the variation in per capita
prey consumption and including a signal of reduced attack rates at high
predator densities. Thus, although large aggregations of predators have
the potential to deplete prey populations, our study illustrates
intraspecific predator interactions that possibly prevent the local
extirpation of an important habitat-forming prey species.