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>

阿拉斯加重要渔业物种——红王蟹（Red king crab，*Paralithodes camtschaticus*）存在种内同类相食行为，该现象既发生于同年龄组内部，也存在于不同年龄组之间。蟹类的同类相食是影响种群补充成功的关键决定因素之一，而这一点在王蟹中尤为关键：野生环境下0龄与1龄王蟹共享相同的栖息生境。
本研究通过室内受控实验，探究1龄王蟹捕食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，实验设置了三类不同生境：无结构软沉积物沙质生境（Sand）、完整蛤壳生境（Whole Shell）以及碎壳碎屑生境（Shell Hash）。本研究同时考察了捕食者密度（1头或2头捕食者）对功能响应的调控作用。
研究将实验数据分别拟合至三类功能响应模型：I型（密度非依赖型）、II型（密度逆依赖型）与III型（密度依赖型），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，所有猎物密度下的捕食率均低于碎壳碎屑与沙质生境。
两种捕食者密度下的功能响应同样均为II型。相较于单捕食者处理组，加入第二头捕食者会同时降低攻击率与处理时间，进而在低猎物密度下略微降低捕食率，而在高猎物密度下则小幅提升捕食率，这表明捕食者间的干扰效应较弱。
本研究结果对潜在的渔业资源增殖活动具有指导意义：1龄王蟹可能通过捕食人工放流的0龄幼蟹，抑制增殖效果，而II型功能响应本身具有种群动态不稳定的特性，进一步加剧了这一风险。一种潜在的解决方案是每隔一年对特定区域开展一次增殖活动，以使前一年龄组的蟹群有机会在生境复杂度更低的区域集群栖息。
未来的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龄幼蟹便可在低猎物密度下获得捕食庇护。