Size-selective predation and drillhole-site selectivity in Euspira fortunei (Gastropoda: Naticidae): implications for ecological and palaeoecological studies

摘要

We explored the prey-size preference and drillhole-site selectivity in Euspira fortunei preying on Ruditapes philippinarum by means of laboratory experiments. Euspira fortunei was a size-selective predator and there was a positive correlation between predator and prey sizes. Our experiments and observations showed that prey-size limits in E. fortunei were determined by the size of its foot, which is the organ used for capturing and handling prey, as in other naticid species. Within the manipulation limits, attacks on relatively small or large prey were detected after prey of the preferred size classes became scarce. Our experiments also suggested that there was no size refuge for R. philippinarum (shell length range 0–35 mm) from attack by E. fortunei and that R. philippinarum of shell length range 10–25 mm were especially vulnerable to predation. These results imply that introduction of E. fortunei probably causes significant loss in R. philippinarum stocks. The sizes of E. fortunei individuals were significantly correlated with the diameters of the drillholes left on the shells of prey. Drillhole location was generally stereotypical in size-matched prey but anomalous drillhole placements commonly occurred in size-mismatched prey. Because E. fortunei captured prey using its foot and manipulated prey in a stereotypical manner, handling of size-mismatched prey was difficult and thus attacks on such prey tended to result in anomalous drillhole placements. Euspira fortunei did not make drillholes on the edges of bivalve prey when it competed for prey.