Direct and Indirect Effects on the Trophic Dynamics of Holly Leaf Miner Populations

9628929康奈尔大学是由天敌造成的自上而下效应还是由资源引起的自下而上效应控制食草动物种群的动态，这在生态学上一直是一个令人敬畏和分裂的争论。随着认识到自然系统的多样性和异质性，争论已经变得毫无结果，焦点必须转移到这两种力量的相对重要性以及在不同环境中控制它们的因素上。此外，最近变得明显的是，彻底探索这些相互作用需要区分直接和间接影响。间接效应意味着两个物种之间相互作用的强度和对称性可能会因第三个物种的存在而改变。例如，植物防御可能能够减少食草动物的丰度，但只有在有天敌的情况下才能，因为防御的主要效果是使食草动物更容易受到攻击。在这项研究中，研究人员采用多管齐下的方法，采用实验和统计路径分析相结合的方法，研究自上而下和自下而上对美国冬青上冬青潜叶蛾分布和丰度的影响。通径分析和实验的结合提供了一种新的方法，可以增加推理能力，而不是单独使用这两种技术。研究人员已经测量了冬青叶潜蝇及其寄主植物质量和天敌丰度的异质性，目前正在进行因子试验，以测试它们对潜叶潜蝇的直接和间接影响。这将是第一次使用这种综合方法来回答有关陆地食物网的结构和功能的基本问题的研究。它应该与营养动力学理论以及森林病虫害管理和生物防治的应用领域特别相关。

9628929 Cornell Whether top-down effects due to enemies or bottom-up effects due to resources control the dynamics of herbivore populations has been a venerable and divisive controversy in ecology. With the realization that natural systems are diverse and heterogeneous the argument has become sterile, and the focus must shift to the relative importance of these two forces and what controls them in different environments. Moreover, it has recently become obvious that exploring these interactions thoroughly requires differentiation between direct and indirect effects. Indirect effects mean that the intensity and symmetry of an interaction between two species may be altered by the presence of a third. For example, plant defenses might be able to reduce herbivore abundances but only in the presence of natural enemies because the primary effect of the defense is to make the herbivore more susceptible to attack. In this study, the investigators are employing a multi-pronged approach using a combination of experiments and statistical path analysis to study top-down and bottom-up effects on the distribution and abundance of the holly leaf miner on American holly. A combination of path analysis and experiments provides a new way of increasing inferential power beyond what is possible when either technique is used separately. The investigators have measured heterogeneity of plant quality and enemy abundance for the holly leaf miner and its host and are now setting up factorial experiments to test their direct and indirect effects on miners. This will be the first study to use such an integrated approach to answer fundamental questions about the structure and function of terrestrial food webs. It should have special relevance to theories of trophic dynamics as well as to the applied areas of forest pest management and biological control.