EFFECT OF INTRASPECIFIC COMPETITION ON CANNIBALISTIC BEHAVIOR IN THE NATICID GASTROPOD NEVERITA DUPLICATA (SAY, 1822)

In order to shed insight into changes in cannibalism by predatory naticid gastropods associated with a series of extinctions in the Plio-Pleistocene of the Carolinas (Christie et al., 2009), we conducted experiments on cannibalism by the naticid Neverita duplicata. Cannibalism was monitored in three high competition tanks, in which three large (predator) Neverita competed for five small conspecific prey, and in three control tanks, in which one large predator Neverita without competition was offered five small conspecific prey. With no other prey choice offered each predator, Neverita was forced to cannibalize. Predator snails ranged in size from 33-37 mm and prey snails ranged from 17-23 mm. Predator snails in high competition tanks were hypothesized to consume less prey than predators in the control tanks. This result was expected because predators in control tanks can forage without interference from competitors, whereas predators in high competition tanks may be inhibited from foraging due to the presence of competitors. Tanks were checked every three days over a 4-week period between August 11 and September 7, 2009, and consumed prey replaced. At the end of the experiment a total of 32 prey snails were consumed from the control tanks, averaging 10.7 prey snails consumed per predator. Predator snails in the experimental tanks consumed a total of 53 prey snails, averaging 5.9 prey consumed per predator. As expected the high competition tanks yielded less cannibalism, with predators consuming only 55.2% of the total prey consumed per snail in the control tanks. Our results imply that the high competition predators drilled and consumed a prey item on average once every 5.6 days while control predators attacked prey once every 3.1 days. These results will help interpret the competitive context of naticid confamilial predation across the Plio-Pleistocene extinctions.