Data from Long et al. 2012 JEMBE: Cannibalism in red king crab, Paralithodes camtschaticus (Tilesius, 1815): Effects of habitat type and predator density on predator functional response

Red king crab, Paralithodes camtschaticus, an important fishery species in Alaska, exhibits cannibalism both within and among age classes. Cannibalism in crab species can be an important determinant of recruitment success, and this might be especially important in king crab because year-0 and year-1 crab occupy the same habitat types in the wild. In this study we used laboratory experiments to determine the predator functional response, or the effect of prey density on predation rates of year-1 crab preying on year-0 crab in three different habitat types: Sand, which was unstructured soft sediment, Whole Shell, which was whole clam valves, and Shell Hash, which was smaller pieces of crushed shell. We also examined how predator density (one or two predators) affects the functional response. The data was fit to Type I, or density independent, Type II, or inversely density dependent, and Type III, or density dependent, functional response models and the best fit model was chosen using Akaike's information criterion. The functional response was a Type II in all habitat types; however, the predation rate was lower at all prey densities in the Whole Shell habitat than in Shell Hash and Sand. The functional response was a Type II at both predator densities as well. The presence of a second predator decreased both the attack rate and the handling time, resulting in slightly lower predation rates at low prey densities, and slightly higher predation rates at high prey densities when compared to the single predator treatment. This indicates a low level of predator interference. This work has implications for potential stock enhancement activities, as year-1 crab could inhibit enhancement success though cannibalism of introduced year-0 crab, especially given the destabilizing nature of the Type II functional response. A potential solution would be to enhance a given area only every other year to give previous cohorts a chance to start podding in less complex habitats. Future work should examine whether the pres- ence of alternative prey changes the functional response to a Type III, as this would give year-0 crabs a low‐density refuge from predation.<br>

红帝王蟹（Paralithodes camtschaticus）是阿拉斯加地区的重要渔业物种，其不同龄级间均存在同类相食行为。蟹类的同类相食是决定种群补充成功率的关键因素之一，而帝王蟹的同类相食行为可能尤为关键——野外环境中，0龄与1龄幼蟹共享相同的栖息生境。本研究通过室内实验，探究了1龄幼蟹捕食0龄幼蟹的捕食者功能响应（predator functional response），即猎物密度对捕食率的影响，实验设置了三种不同栖息生境：无结构软底质沙地、完整蛤壳生境以及破碎蛤壳碎屑生境；同时还考察了捕食者密度（1头或2头捕食者）对该功能响应的调控作用。研究将实验数据分别拟合至I型（密度独立，density independent）、II型（逆密度依赖，inversely density dependent）与III型（密度依赖，density dependent）捕食功能响应模型，并通过赤池信息准则（Akaike's information criterion）筛选最优拟合模型。结果显示，所有生境下的功能响应均为II型，但完整蛤壳生境中，各猎物密度下的捕食率均低于破碎蛤壳碎屑生境与沙地。两种捕食者密度下的功能响应同样均为II型。与单捕食者处理组相比，添加第二头捕食者会同时降低攻击率与处理时间：在低猎物密度下捕食率略有下降，而在高猎物密度下捕食率略有上升，这表明捕食者间存在轻度干扰。本研究结果对帝王蟹种群增殖放流活动具有重要参考价值：1龄幼蟹通过捕食投放的0龄幼蟹的同类相食行为，可能会抑制增殖放流的成效，尤其是II型功能响应具有种群不稳定特性的情况下。潜在的解决策略是每隔一年开展一次增殖放流，以便先前世代的幼蟹能够在结构相对简单的生境中完成集群栖息。未来研究可进一步探究替代猎物的存在是否会将功能响应转变为III型，若如此，0龄幼蟹将能在低密度下获得捕食庇护。