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

植物有各种各样的天敌，但定量预测这些植物饲养者（食草动物）之间的相互作用的后果仍然很困难。基本的，未解决的问题包括：（一）草食动物之间的相互作用如何影响植物种群？(ii)互动是否具有协同或冲突的影响？（3）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认识。这些信息对于我们对自然界中生物相互作用的基本理解至关重要。此外，关于这种相互作用的知识对于推进有效的、环境安全的杂草生物防治具有实际意义。本研究以本地高蓟（Cirsium altissimum）为模式植物，探讨本地昆虫与高蓟的相互作用。这些标准是为了确定：（1）植物表现是否与主要类型的食草昆虫的摄食有关;（2）食草动物是否对植物动态具有中性、协同或抑制作用，（3）结果是否与资源可用性有关;（4）当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。这些主要假设是：第一，当植物暴露于单一的、高效的食草昆虫物种时，植物繁殖和密度的降低是最高的;第二，当多种食草昆虫攻击不同的植物器官（例如根、叶、花）时，这些降低是最大的。 这四个目标将通过在天然C. altissimum种群沿着资源梯度，昆虫排除实验，并通过发展一个整体的投影模型。这项研究是重要的，因为它解决了重要的，未充分探索的问题，无处不在的生物相互作用，因为它在杂草生物防治的实际应用。该研究项目还将扩大农村社区学生的教育机会，这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.