Insect Herbivore Guild Interactions and Tall Thistle Population Dynamics: A Test of Conflicting Hypotheses

植物有各种各样的天敌，但对这些植食性动物（食草动物）之间相互作用的后果的定量预测仍然很困难。尚未解决的基本问题包括：(i)草食动物之间的相互作用如何影响植物种群？（ii）相互作用的影响是协同的还是相互冲突的？（三）结果是否取决于资源？迫切需要提高我们对这种相互作用的理解。这些信息对我们了解自然界生物间的相互作用至关重要。此外，了解这种相互作用对推进有效的、环境安全的杂草生物防治具有实际意义。该项目研究了本地昆虫与本地高蓟（Cirsium altissimum）的相互作用，作为一个有四个具体目标的模型系统。这些研究旨在确定：(1)植物的生产性能是否与主要食草昆虫的取食类型有关；(2)如果食草动物对植物动态具有中性、协同或抑制作用；(3)如果结果与资源可用性有关；(4)目前两种相互矛盾的假设中，哪一种最能解释多种食草动物的影响。这些主要的假设是：首先，当植物暴露于单一的、高效的食草昆虫物种时，植物繁殖和密度的减少是最大的；其次，当多种昆虫食草动物攻击不同的植物器官（如根、叶、花）时，这些减少是最大的。这四个目标将通过沿着资源梯度密集测量天然高棉种群的昆虫摄食，通过昆虫排斥实验，并通过开发一个积分投影模型来实现。这项研究具有重要意义，因为它解决了重要的，未被探索的普遍存在的生物相互作用问题，因为它在杂草生物防治方面具有实际应用。该研究项目还将扩大农村社区学生的受教育机会，农村社区学生是高等教育中代表性不足的群体。

Plants have a wide array of natural enemies, but the quantitative prediction of the consequences of interactions among these plant feeders (herbivores) remains difficult. Fundamental, unresolved questions include: (i) How do interactions among herbivores affect plant populations? (ii) Do interactions have synergistic or conflicting impacts? and, (iii) Does the outcome depend upon resources? There is an urgent need to improve our understanding of such interactions. The information is essential to our basic understanding of biological interactions in nature. Further, knowledge about such interactions has practical significance for advancing effective, environmentally safe biological control of weeds. This project examines the interaction of native insects with the native tall thistle (Cirsium altissimum) as a model system with four specific aims. These are to determine: (1) whether plant performance differs in relation to feeding by the main types of insect herbivores; (2) if herbivores have neutral, synergistic, or inhibitory effects on plant dynamics, (3) if the outcomes are related to resource availability; and (4) which of two current, conflicting hypotheses best explains the effects of multiple herbivores. These leading hypotheses are: first, that reductions in plant reproduction and density are highest when plants are exposed to a single, highly effective insect herbivore species; and, second, that these reductions are greatest when multiple insect herbivores attack different plant organs (e.g. roots, leaves, flowers). The four aims will be achieved by intensive measurement of insect feeding in natural C. altissimum populations along resource gradients, by insect exclusion experiments, and by development of an integral projection model. This research is significant because it addresses important, under-explored questions about ubiquitous biological interactions and because it has practical application in weed biocontrol. This research project also will expand educational opportunities for students from rural communities, an underrepresented group in higher education.