Dissertation Research: The effects of multispecies interactions on population dynamics of invading Centaurea solstitialis across a geographic range

植物与许多物种相互作用，包括传粉者、竞争对手和病原体。当与一个物种的相互作用改变了植物与后续物种相互作用的强度或频率时，就会产生非加性效应。虽然诸如此类的复杂相互作用在自然系统中可能很常见，但它们的净效应本身就难以预测，而且人们对其潜在机制知之甚少。即使相互作用影响到单个植物，它们也可能不会影响植物种群的大小。当种群增长对特定生命阶段的变化不太敏感时，个体表现和种群规模可以解耦；在这个阶段改变植物的相互作用对整个种群的影响很小。由于种群动态经常在一个物种的地理范围内变化，因此给定的生物相互作用可能会根据发生的地点产生不同的种群水平后果。本研究将利用入侵植物黄星蓟、其传粉媒介和两种生物防治剂（一种病原体和一种食草昆虫）来检验(1)多物种相互作用对单个植物的净结果，(2)个体性能的变化是否具有种群水平的影响，以及(3)该入侵物种范围外围的种群是否受到不同于其范围中心种群的影响。这项研究的学术价值在于，它解决了多物种相互作用在种群水平上的后果，这是生态学的一个核心主题，尽管研究不足。此外，它在地理背景下考虑这些后果，了解到人口水平的后果可能因其更广泛的生态背景而异。这项研究的广泛影响包括学生培训和潜在应用于农业系统中使用的生物控制计划，并限制入侵物种的传播。

Plants interact with numerous species, including pollinators, competitors, and pathogens. Nonadditive effects arise when an interaction with one species alters the intensity or frequency of the plant's interactions with subsequent species. While complex interactions such as these are probably common in natural systems, their net effects are inherently difficult to predict and the underlying mechanisms are poorly understood. Even when interactions impact individual plants, they may not affect the size of the plant population. Individual performance and population size can be decoupled when population growth is less sensitive to changes in a particular life stage; interactions that alter a plant at that stage will have little effect on the population as a whole. Because population dynamics often vary across the geographic range of a species, a given biotic interaction may have different population level consequences depending on where it takes place. This study will use an invasive plant, yellow starthistle, its pollinators, and two biological control agents (a pathogen and an insect herbivore) to examine (1) the net outcome of multispecies interactions for individual plants, (2) whether changes in individual performance have population level effects, and (3) whether populations at the periphery of the range of this invasive species are affected differently than populations at the center of its range. The intellectual merit of the study is that it addresses population-level consequences of multispecies interactions, a central, albeit under-studied, theme in ecology. Furthermore, it considers those consequences in a geographic context, with the understanding that population-level consequences may vary with their broader ecological context. Broader impacts of this study include student training and potential application to biological control programs that are used in agricultural systems and to limit the spread of invasive species.