TRICOMM: Structure, assembly and evolution of natural tritrophic communities

植物群落、食草昆虫和它们的昆虫寄生天敌提供了地球上大多数已知物种。这些群落包括导致经济损失的相互作用，如作物害虫，以及其他有益于人类社会的相互作用，如生物控制剂。尽管它们很重要，但我们仍然对是什么决定了哪些物种吃其他物种或被其他物种吃掉知之甚少。我们对植物和食草动物之间的联系了解得最多，对食草动物和寄生虫的了解较少，对所有三个层次的结合模式的了解也较少。一个关键的问题是，在何种程度上，这样的三个层次（三营养）的物种协会结构从“自下而上”的植物性状，从“自上而下”的寄生蜂，或这些的组合。“自下而上”的观点认为植食性寄生虫的相互作用是由发生在较低营养级的过程所构成的，通过植物对植食性寄生虫的影响。相反，“自上而下”的观点认为寄生虫-草食动物的相互作用推动了草食动物防御的进化，这些特征对于构建寄生虫群落比发现它们的宿主植物更重要。本项目使用最先进的统计方法评估这些替代模型及其组合的证据，需要三种类型的数据：（i）一个相互作用矩阵，总结了一个营养级的物种之间的联系，并在另一个;（ii）草食动物的防御性状数据和（iii）完整的植物，草食动物和他们的寄生虫物种水平的遗传。发现植物的寄生性是一个强有力的预测植物-草食动物和草食动物-寄生虫的相互作用将支持自下而上的观点。相比之下，发现草食动物的防御性状强烈预测草食动物寄生虫的相互作用将支持自上而下的观点。首先，我们将估计物种的身份和性状对植物-草食动物和草食动物-寄生虫相互作用的影响，提供自下而上与自上而下过程的相对重要性的第一个测试。我们将使用超过50，000个记录的特定植物-食草动物-寄生虫相互作用的自然群落，包括树木，gallwasp食草动物和小蜂寄生虫，采样从三个区域数据集，跨越北方半球。这些群落已经独立进化了足够长的时间，可以为我们的假设提供基本上独立的测试。

Communities of plants, insect herbivores, and their insect parasitoid enemies provide most of the known species on Earth. These communities include interactions that lead to economic damage, such as pests of crops, and others that benefit human societies, such as biocontrol agents. Despite their importance, we still know little about what determines which species eat, or are eaten by, other species. We know most about links between plants and herbivores, less about herbivores and parasitoids, and less again about patterns over all three levels combined. A key question is the extent to which such three level (tritrophic) species associations are structured from the 'bottom-up' by plant traits, from the 'top-down' by parasitoids, or some combination of these. The 'bottom-up' view regards herbivore-parasitoid interactions as structured by processes happening a trophic level lower, via the effects of plants on herbivores. In contrast, the 'top-down' view sees parasitoid-herbivore interactions as driving the evolution of herbivore defences, and these traits as more important for structuring parasitoid communities than the host plants on which they are found.This project assesses the evidence for these alternative models, and their combinations, using state of the art statistical methods that require three types of data: (i) an interaction matrix, summarising links between species in one trophic level and those in another; (ii) herbivore defence trait data and (iii) complete species-level phylogenies for plants, herbivores and their parasitoids. Finding that plant phylogeny is a strong predictor of both plant-herbivore and herbivore-parasitoid interactions would support the bottom-up view. In contrast, finding that herbivore-parasitoid interactions are strongly predicted by herbivore defensive traits would support a top-down view. First, we will estimate the effects of species identity and traits on plant-herbivore and herbivore-parasitoid interactions, providing the first test of the relative importance of bottom-up versus top-down processes. We will use over 50,000 records of specific plant-herbivore-parasitoid interactions for natural communities comprising trees, gallwasp herbivores, and chalcid parasitoids, sampled from three regional datasets that span the Northern Hemisphere. These communities have evolved independently for long enough to provide largely independent tests of our hypotheses.