Department of Ecology, Evolution and Marine Biology and Marine Science Institute, University of California, Santa Barbara, Santa Barbara, CA 93106, USA.
Oecologia. 2013 Apr;171(4):945-60. doi: 10.1007/s00442-012-2449-y. Epub 2012 Sep 16.
The effects of invasive species on native communities often depend on the characteristics of the recipient community and on the food habits of the invasive species, becoming complicated when the invader is omnivorous. In field enclosure experiments, we assessed the direct and interactive effects of an invasive omnivorous crayfish (Procambarus clarkii) and either native herbivorous snails (Physella gyrina) or shrimp (Atyoida bisulcata) on stream communities in California and Hawaii, respectively. Based on literature data and the characteristics of each study site, we predicted that crayfish would affect primarily algal-based trophic linkages in an open California stream but detritus-based trophic linkages in a shaded Hawaiian stream, with trophic cascades mediated through crayfish effects on primary consumers being observed in both systems. As predicted, crayfish in California directly reduced periphyton, filamentous algae, sediment, and snail levels, but generated a cascade by decreasing snail densities and increasing periphyton biomass. Contrary to prediction, crayfish did not reduce total invertebrate biomass. As predicted, crayfish in Hawaii reduced leaf litter, filamentous algae, and benthic invertebrate biomass. Contrary to our predictions, however, a trophic cascade was not observed because shrimp did not affect periphyton levels, crayfish did not reduce shrimp abundance, and crayfish had greater negative impacts on filamentous algae than did shrimp. Our findings highlight that the same invasive species can generate different effects on disparate systems, probably as mediated through the availability of different food types, flexibility in the invasive species' food habits, and complex pathways of trophic interaction.
入侵物种对本地群落的影响通常取决于受体群落的特征和入侵物种的食性，当入侵者是杂食性时，情况会变得复杂。在野外围栏实验中，我们评估了入侵的杂食性螯虾（Procambarus clarkii）以及本地草食性蜗牛（Physella gyrina）或虾（Atyoida bisulcata）对加利福尼亚州和夏威夷州溪流群落的直接和交互影响。根据文献数据和每个研究地点的特点，我们预测螯虾将主要影响加利福尼亚州开阔溪流中的藻类为基础的营养联系，但在夏威夷的遮荫溪流中影响碎屑为基础的营养联系，通过螯虾对初级消费者的影响介导的营养级联在两个系统中都观察到。正如预测的那样，加利福尼亚州的螯虾直接减少了周丛生物、丝状藻类、沉积物和蜗牛的数量，但通过降低蜗牛密度和增加周丛生物量，引发了级联效应。与预测相反，螯虾并没有减少总无脊椎动物生物量。正如预测的那样，夏威夷的螯虾减少了落叶、丝状藻类和底栖无脊椎动物的生物量。然而，与我们的预测相反，没有观察到营养级联，因为虾没有影响周丛生物量，螯虾没有减少虾的数量，而且螯虾对丝状藻类的负面影响大于虾。我们的研究结果表明，同一入侵物种可能对不同的系统产生不同的影响，这可能是由于不同食物类型的可利用性、入侵物种食性的灵活性以及复杂的营养相互作用途径所致。
