Bishop Melanie J, Peterson Charles H
University of North Carolina at Chapel Hill, Institute of Marine Sciences, Morehead City, North Carolina 28557, USA.
Ecol Appl. 2006 Apr;16(2):718-30. doi: 10.1890/1051-0761(2006)016[0718:wrmnpi]2.0.co;2.
Predicting outcomes of species introductions may be enhanced by integrating life-history theory with results of contained experiments that compare ecological responses of exotic and analogue native species to dominant features of the recipient environment. An Asian oyster under consideration for introduction to the Chesapeake Bay, USA, the rapidly growing Suminoe oyster (Crassostrea ariakensis), may not be as successful an invader as its r-selected life history suggests if the trade-off for rapid growth and maturation is lower investment in defenses against blue crab (Callinectes sapidus) predation than the native Eastern oyster (Crassostrea virginica). In laboratory trials, blue crabs simultaneously offered equal numbers of Suminoe and Eastern oysters consumed more nonnatives, irrespective of whether the crabs had previous experience with Suminoe oysters as prey. Satiated blue crabs consumed nearly three times as many Suminoe oysters as Eastern oysters of 25-mm shell height, and eight times as many of 35-mm shell height. Despite blue crabs consuming small (30 mm) Suminoe oysters at twice the rate of large (40 mm) Suminoe oysters, when 40-mm Suminoe were paired with 30-mm Eastern oysters, seven times as many of the larger (Suminoe) oysters were consumed. The greater susceptibility of C. ariakensis than C. virginica to blue crab predation appears to be based upon the biomechanics of shell strength rather than active selection of a more attractive food. Much less force was required to crush shells of Suminoe than Eastern oysters of similar shell height. Tissue transplant experiments demonstrated greater predation on oyster tissues in weaker C. ariakensis shells independent of tissue identity, and duration of handling time before rejection of C. virginica exceeded the time to crush C. ariakensis. These results, coupled with the present importance of blue crab predation in limiting recovery of native Eastern oysters, imply a role for blue crabs in inhibiting Suminoe oysters, if introduced, from attaining high adult densities required to restore a fishery, provide appreciable reef habitat, and reduce turbidity through filtration. Thus, in high-predation environments, allocation of resources to rapid growth and development rather than to predation defenses reflects a life-history trade-off that may promote early stages of invasion, yet prevent attainment of dense adult populations.
将生活史理论与封闭式实验结果相结合，有望提高对物种引入结果的预测能力。此类实验比较外来物种和类似本地物种对受纳环境主要特征的生态反应。拟引入美国切萨皮克湾的亚洲牡蛎——快速生长的滑顶薄壳鸟蛤（Crassostrea ariakensis），若其为快速生长和成熟所付出的代价是，相较于本地的东部牡蛎（Crassostrea virginica），对蓝蟹（Callinectes sapidus）捕食的防御投资减少，那么它可能不会像其r-选择生活史所暗示的那样，成为一个成功的入侵物种。在实验室试验中，同时提供等量滑顶薄壳鸟蛤和东部牡蛎时，蓝蟹会捕食更多的外来物种，无论这些蓝蟹之前是否有捕食滑顶薄壳鸟蛤的经验。饱腹的蓝蟹捕食的25毫米壳高的滑顶薄壳鸟蛤数量几乎是东部牡蛎的三倍，35毫米壳高的则是八倍。尽管蓝蟹捕食小（30毫米）滑顶薄壳鸟蛤的速度是大（40毫米）滑顶薄壳鸟蛤的两倍，但当40毫米的滑顶薄壳鸟蛤与30毫米的东部牡蛎配对时，被吃掉的大（滑顶薄壳鸟蛤）牡蛎数量是小牡蛎的七倍。相较于东部牡蛎，滑顶薄壳鸟蛤对蓝蟹捕食的易感性更高，这似乎是基于壳强度的生物力学原理，而非对更具吸引力食物的主动选择。碾碎相同壳高的滑顶薄壳鸟蛤所需的力量远小于东部牡蛎。组织移植实验表明，无论组织类型如何，蓝蟹对壳更脆弱的滑顶薄壳鸟蛤组织的捕食量更大，而且东部牡蛎被拒绝前的处理时间超过了碾碎滑顶薄壳鸟蛤所需的时间。这些结果，再加上蓝蟹捕食目前对限制本地东部牡蛎恢复的重要作用，意味着如果引入滑顶薄壳鸟蛤，蓝蟹可能会抑制其达到恢复渔业、提供可观礁石栖息地以及通过过滤减少浊度所需的高成年密度。因此，在高捕食环境中，将资源分配给快速生长和发育而非捕食防御，反映了一种生活史权衡，这可能会促进入侵的早期阶段，但会阻止形成密集的成年种群。
