The European green crab (Carcinus maenas) is invasive on the West coast of North America, but the ecological consequences of this invasion remain poorly understood. Comparative functional response analysis has arisen as a method of elucidating ecological consequences of invasive species by comparing the impact of these species to native analogues. Through comparative functional response experiments of green crabs and native red rock crabs (Cancer productus) we found that green crab predation increased asymptotically (Type II functional response) when fed increasing densities of Pacific oysters (Magallana gigas), while red rock crab predation displayed a sigmoidal (Type III) response. At high oyster densities red rock crabs consume more Pacific oysters than green crabs do, due to their reduced handling time, though green crabs consume more Pacific oysters relative to their size than red rock crabs. However, compared to red rock crabs, green crabs consume more oysters at low prey densities, which implies that they have a larger, potentially destabilizing impact on low densities of Pacific oysters. As green crabs continue to spread across the West coast of North America, Pacific oysters will face increased predation pressure. Our results show the advantage of using functional response analysis to compare density dependent predation between an invasive species and a native species to predict the ecological consequences of invasions.

欧洲的绿蟹（Carcinus maenas）在北美西海岸具有入侵性，但对这种入侵的生态后果仍知之甚少。通过比较这些物种与天然类似物的影响来阐明入侵物种的生态后果的一种方法已经出现了比较功能响应分析。通过比较绿蟹和天然红岩蟹（巨蟹座）的功能反应实验，我们发现，当饲喂密度增加的太平洋牡蛎（Magallana gigas）时，绿蟹的捕食性逐渐增加（II型功能反应）），而红色的石蟹捕食显示出S型（III型）响应。在牡蛎密度高的情况下，由于减少了处理时间，红岩蟹比绿蟹要消耗更多的太平洋牡蛎，尽管相对于它们的大小，绿蟹比红岩蟹要消耗更多的太平洋牡蛎。但是，与红岩蟹相比，绿蟹在低密度捕食时会消耗更多的牡蛎，这意味着它们对低密度的太平洋牡蛎具有更大的潜在破坏作用。随着绿蟹继续在北美西海岸蔓延，太平洋牡蛎将面临更大的捕食压力。我们的结果表明，使用功能响应分析来比较入侵物种和本地物种之间依赖密度的捕食来预测入侵的生态后果的优势。