Abstract Prey selection by predators is of interest to community ecologists. By choosing some prey over others, predators affect prey population dynamics and the strength of food webs. According to Optimal Diet Theory (ODT), as prey density increases predators will select more profitable prey. Thereby, prey population dynamics can also affect predator behaviour. Prey profitability involves the prey energetic value, energetic costs associated to predation (time spent searching, capturing and handling prey) and certain characteristics such as body size, abundance and behaviour. We examined the effect of the blue mussel (Mytilus edulis) association with conspecifics at different densities on prey selection and behaviour by the seastar Asterias rubens. Contrary to ODT prediction, when mussels were tightly clumped in high densities, the size range of the mussels consumed by A. rubens did not differ of the size range of the mussel population. Mussel association at high density caused seastars to feed locally, reducing their exposition to risks. Moreover, preying without selecting for a specific mussel size did not result in a decrease of net profit, rather it was increased. We concluded that under certain circumstances, not selecting prey results in an increase of net profit at prey size. We discuss our results in the context of the mussel industry where the effect of prey selection on the prey population dynamics is of importance. Mussel size selection by seastars, as described in previous works, will impact the size distribution of mussels within cultured populations affecting growth of the population and reproductive output among others, thus increasing the impact of seastar predation beyond that of just removing mussels from the population. However, this study shows that seastars prey upon availability at high densities, typically encountered in cultivated populations, and therefore their effect on mussel population is restricted to removal of mussels without affecting the size distribution of the population.

中文翻译：

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蓝贻贝 (Mytilus edulis L.) 与同种的关联会影响普通海星 (Asterias rubens L.) 对贻贝大小的选择

摘要 捕食者的猎物选择是社区生态学家的兴趣所在。通过选择一些猎物而不是其他猎物，捕食者会影响猎物种群动态和食物网的强度。根据最佳饮食理论 (ODT)，随着猎物密度的增加，捕食者将选择利润更高的猎物。因此，猎物种群动态也会影响捕食者的行为。猎物盈利能力涉及猎物的能量价值、与捕食相关的能量成本（搜索、捕获和处理猎物所花费的时间）以及某些特征，例如体型、丰度和行为。我们研究了蓝贻贝 (Mytilus edulis) 与不同密度的同种物种对海星 Asterias rubens 的猎物选择和行为的影响。与 ODT 预测相反，当贻贝以高密度紧密聚集时，A. rubens 食用的贻贝的大小范围与贻贝种群的大小范围没有区别。高密度的贻贝组合导致海星在当地觅食，减少了它们面临的风险。此外，不选择特定大小的贻贝捕食并没有导致净利润减少，反而增加了。我们得出的结论是，在某些情况下，不选择猎物会导致按猎物大小增加净利润。我们在贻贝产业的背景下讨论我们的结果，其中猎物选择对猎物种群动态的影响很重要。如先前工作所述，海星选择贻贝大小将影响养殖种群中贻贝的大小分布，影响种群增长和繁殖产量等，从而增加捕食海星的影响，而不仅仅是从种群中清除贻贝。然而，这项研究表明，海星以高密度捕食，通常在养殖种群中遇到，因此它们对贻贝种群的影响仅限于去除贻贝，而不影响种群的大小分布。