Ecological, geographic and phylogenetic dimensions of food webs and their response to global change

世界正在经历气候、城市化和栖息地碎片化方面的快速变化。这些变化不仅会对物种的生存和分布产生直接影响，还会通过将物种联系在一起的摄食相互作用网络(“食物网”)来影响物种。然而，由于食物网包含可移动的动物，而且往往占据大量空间，因此很难通过实验操纵它们来测试有关全球变化影响的理论。我的解决方案是使用天然的水生食物网，比如菠萝或树洞中发现的那种。这些系统还有一个额外的优势，那就是发生在新大陆的大部分地区，使我们能够了解哪些过程是普遍的，哪些过程取决于地理环境，以及为什么。在这项提案中，我和我的学生将结合实验、理论模型和全球数据库的合成，我们已经开发了这些数据库来理解食物网背后的过程。为了理清不同气候对食物网结构的影响，我们将沿着厄瓜多尔安第斯山脉的海拔梯度和从阿根廷到墨西哥的纬度梯度来研究食物网。我们还将研究食物资源中营养物质的比例，以了解能量如何通过食物网中的“通道”流动。生物体需要一定比例的营养物质来支持生长，而这种个人需求可能会扩大到影响整个生态系统。物种的特征也决定了它们可以消耗哪些猎物或资源(以及它们是否可以避免自己被吃掉)，它们是否对环境条件具有生理抵抗力，以及它们如何利用信息来避开捕食者或危险的栖息地。物种的某些特征和营养需求在进化过程中可能是高度保守的，从而限制了食物网利用所有特征和营养组合(即多变量“空间”)的潜力。在其他情况下，代表缺失组合的物种存在于世界其他地方，但尚未分散到研究地点。理解这些进化和扩散的限制，使我们能够理解为什么食物网在不同的地方有不同的结构。这些限制对于理解环境变化--无论是通过气候、城市化还是碎片化--如何影响食物网也很重要。例如，支离破碎的雨林是由年轻的、快速生长的树木组成的，这些树木产生的落叶比完整的森林营养更丰富。这可能会在以落叶为基础的食物网中产生景观级的变化--我们可以通过实验改变落叶中营养物质的比例来测试这种机制。在城市，食物网络结构可能会受到殖民者可获得性的限制，而在有许多花园的富裕社区，这种殖民者池可能会更大。总之，我提出了一个多方面的研究计划，以了解食物网的基本制约因素，以便预测它们对不断变化的世界的反应。

The world is undergoing rapid change in terms of climate, urbanization and habitat fragmentation. These changes will affect species not only through direct effects on their survival and distribution but also via the web of feeding interactions ("food webs") that knit together species. However, because food webs contain mobile animals and often occupy large amounts of space, they are difficult to experimentally manipulate to test theory about global change impacts. My solution is to use naturally contained aquatic food webs, such as those found in bromeliads or tree holes. These systems have the additional advantage of occurring in much of the New World, allowing us to understand which processes are universal, which depend on geographic context, and why. In this proposal, my students and I will combine experiments, theoretical models and syntheses of global databases that we have developed to understand the processes underlying food webs. In order to disentangle different climatic influences on food web structure, we will examine food webs along elevational gradients in the Ecuadorian Andes and a latitudinal gradient from Argentina to Mexico. We will also examine the ratio of nutrients in food resources to understand how energy flows through `channels' in food webs. Organisms require certain ratios of nutrients to support growth, and such individual needs can scale up to affect the entire ecosystem. Species also have traits that determine which prey or resources they can consume (and whether they can avoid being eaten themselves), whether they are physiologically resistant to environmental conditions, and how they use information to avoid predators or risky habitats. Some traits and nutrient requirements of species may be strongly conserved through evolutionary time, restricting the potential of food webs to exploit all combinations (i.e. multivariate "space") of traits and nutrients. In other cases, species representing missing combinations exist elsewhere in the world, but have not yet dispersed to the study location. Understanding these evolutionary and dispersal constraints allow us to understand why food webs are structured differently in different places. These constraints are also important to understanding how a changed environment - whether through climate, urbanization or fragmentation - can affect food webs. For example, fragmented rainforest is composed of young, fast-growing trees that produce leaf litter richer in nutrients than intact forest. This could create landscape-scale changes in litter-based food webs- a mechanism that we can test by experimentally changing the ratio of nutrients within leaf litter. In cities, food web structure may be limited by the availability of colonists, and this colonist pool may be greater in affluent neighbourhoods with many gardens. In sum, I propose a multifaceted research program to understand the fundamental constraints of food webs in order to predict their responses to a changing world.