Smithsonian Tropical Research Institute, Box 0843-03092, Balboa, Ancon, Republic of Panama.
Ecol Lett. 2011 Nov;14(11):1093-100. doi: 10.1111/j.1461-0248.2011.01677.x. Epub 2011 Sep 8.
Natural enemies, especially host-specific enemies, are hypothesised to facilitate the coexistence of plant species by disproportionately inflicting more damage at increasing host abundance. However, few studies have assessed such Janzen-Connell mechanisms on a scale relevant for coexistence and no study has evaluated potential top-down influences on the specialized pests. We quantified seed predation by specialist invertebrates and generalist vertebrates, as well as larval predation on these invertebrates, for the Neotropical palm Attalea butyracea across ten 4-ha plots spanning 20-fold variation in palm density. As palm density increased, seed attack by bruchid beetles increased, whereas seed predation by rodents held constant. But because rodent predation on bruchid larvae increased disproportionately with increasing palm density, bruchid emergence rates and total seed predation by rodents and bruchids combined were both density-independent. Our results demonstrate that top-down effects can limit the potential of host-specific insects to induce negative-density dependence in plant populations.
天敌，特别是专性天敌，被假设通过在宿主丰度增加时不成比例地造成更大的伤害，从而促进植物物种的共存。然而，很少有研究在与共存相关的规模上评估这种 Janzen-Connell 机制，也没有研究评估专门害虫的潜在自上而下的影响。我们量化了十种 4 公顷的样地中，特化无脊椎动物和广脊椎动物对 Neotropical 棕榈 Attalea butyracea 的种子捕食，以及这些无脊椎动物的幼虫捕食情况，这些样地的棕榈密度跨度为 20 倍。随着棕榈密度的增加，豆象甲虫对种子的攻击增加，而啮齿动物对种子的捕食保持不变。但是，由于啮齿动物对豆象幼虫的捕食不成比例地随棕榈密度增加而增加，豆象的出芽率和啮齿动物和豆象共同造成的总种子捕食率都与密度无关。我们的研究结果表明，自上而下的影响可能会限制专性昆虫在植物种群中诱导负密度依赖性的潜力。
