SG RUI: Snow melt-induced changes in phenology as direct and indirect drivers of herbivore abundance

地球上植物种类繁多，分布广泛，尽管有许多不同的动物以植物为食，即食草动物。由于多种因素限制了草食的强度，世界上的植物仍然是绿色的。了解这些限制因素是生态学的一个重要目标。这项研究的重点是植物和食草性昆虫之间相互作用的季节性时间如何限制食草性。该项目研究了植物与它们的食草性蚜虫之间的相互作用，这些蚜虫在植物的花茎上形成了巨大的群体，使它们成为一个理想的实验操作研究系统。蚜虫群落与其他昆虫相互作用，包括为它们提供保护免受捕食者攻击的蚂蚁。六年的数据显示，当春季积雪融化得更早时，寄主植物开花更早，而这种更早开花往往与蚜虫数量的增加有关。为了了解是什么导致了这种联系，研究人员将通过实验改变积雪，作为改变植物与昆虫相互作用的时间的一种方式。这项工作很重要，因为它增加了我们对生物体相互作用时间的变化如何影响食物网以及由此产生的生态群落的理解。这一结果将对预测受较早到来的春季影响的自然和农业系统中昆虫食草动物的丰度具有重要意义。该项目还将为缺乏服务的社区的本科生提供野外生态学方面的培训，并将为K-12教师和学生提供学习机会。本研究将采用观察和实验相结合的方法，确定植物物候变化对草食动物丰度的直接和间接影响。在这个研究系统中，蚜虫(Aphis Helianthi)在其寄主植物(Ligusticum Porteri)的花序上定殖，6年的监测表明，寄主植物物候的进步(早花)与蚜虫丰度的增加有关。植物物候与食草动物丰度之间的这种相关性可能是由于物候对植物营养品质的直接影响和/或蚂蚁、捕食者和竞争对手之间相互作用的间接调节。这项研究将应用结构方程模型方法来评估关于物候信号如何通过这些直接和间接的营养相互作用影响节肢动物丰度的假说。这项研究将通过利用沿海拔梯度发现的植物种群对积雪融化的实验操作，直接改变寄主植物的物候。这些实验还将采用析因设计，将植物物候处理与改变互助者和/或捕食者对蚜群的可及性的处理相结合。不同处理间蚜虫群体生长的差异将显示出植株阶段的直接和间接影响的相对大小。实验室测定韧皮部汁液和蚜虫质量(如C/N比、次生代谢物含量等)。将补充这些田间实验，并提供一种寄主植物物候可以影响蚜虫种群增长或蚂蚁-蚜虫互惠共生的机制。

Plants are abundant and widely distributed on earth, despite the fact that many different species of animals feed on them, i.e., herbivores. The world remains green with plants because a variety of factors limit the intensity of herbivory. Understanding these limiting factors is an important goal of ecology. This research focuses on how the seasonal timing of interactions between plants and herbivorous insects could limit herbivory. The project examines interactions between plants and their herbivorous aphids, which form vast colonies on the flowering stalks of the plants, making them an ideal study system for experimental manipulation. The aphid colonies interact with other insects, including ants that provide them with protection from predators. Six years of data show that when snow melts earlier in spring, host plants flower earlier, and this earlier flowering tends to be associated with an increase in aphid numbers. To understand what is causing this association, the researchers will experimentally alter snow cover as a way to vary the timing of plant-insect interactions. This work is important because it adds to our understanding of how changes in the timing of when organisms interact with each other, affect food webs, and the resulting ecological communities. The results will have implications for predicting the abundance of insect herbivores in natural and agricultural systems affected by an earlier arrival of spring. This project will also provide undergraduate students from under-served communities with training in field ecology, and will develop learning opportunities for K-12 teachers and students.Using a combination of observational and experimental approaches, this research will determine the direct and indirect effects of changes in plant phenology on herbivore abundance. In this study system, aphids (Aphis helianthi) colonize the inflorescences of their host plant (Ligusticum porteri), and six years of monitoring indicates that advances in host-plant phenology (earlier flowering) are associated with increases in the abundance of aphids. This correlation between plant phenology and the abundance of herbivores may be due to the direct effects of phenology on plant nutritional quality and/or to the indirect mediation of interactions among ants, predators and competitors. This study will apply a structural equation modeling approach to evaluate hypotheses about how phenological cues influence arthropod abundance through these direct and indirect trophic interactions. The study will directly vary host plant phenology through the experimental manipulation of snow melt using plant populations found along an elevational gradient. These experiments will also employ a factorial design to combine plant phenology treatments with treatments that alter the accessibility of aphid colonies to their mutualists and/or predators. Differences in aphid colony growth among treatments will show the relative magnitudes of direct and indirect effects of plant stage. Laboratory assays of phloem sap and aphid quality (e.g., C/N ratio, secondary metabolite content etc.) will complement these field experiments and provide a mechanism by which host plant phenology could affect aphid population growth or the ant-aphid mutualism.