Collaborative Research: The role of branching complexity in driving food chain length in rivers

食物链长度变化的起源——食物网中从生产者到顶端消费者的喂养环节的数量——几十年来一直引起生态学家的兴趣。了解对食物链长度的控制是很重要的，因为它会影响生态系统中的能量流动和人类经常食用的顶级捕食者体内的污染物浓度。流行的观点认为，食物链的长度是由生态系统的大小决定的。大型生态系统可以提供更多的基础资源，支持更大的组成物种种群规模，和/或减轻环境变化的影响。然而，尽管在空间简单的系统（如海洋岛屿和湖泊）中存在丰富的生态系统规模假设的经验证据，但在空间更复杂的系统（如分支河流网络）中却缺乏明确的支持。在空间复杂系统中，生态系统规模假说的混合结果表明，存在被忽视的控制食物链长度的因素。该项目将探索生态系统复杂性的作用，这是生态系统动力学中的一个关键因素。具体来说，研究人员将关注河流网络的分支复杂性，并研究其在驱动食物链长度方面的重要性。本项目的更广泛影响包括以下组成部分。首先，研究人员将通过与K-12学校的正式合作伙伴关系参与外展活动。其次，该项目将为未被充分代表的少数民族和一名博士后科学家提供研究培训机会。最后，研究人员将通过在线存储库分发开源软件，以促进研究成果的应用。该项目将结合理论和实证方法来检验以下假设：(1)复杂的河流网络，分支水平更高，支持长食物链，因为拥有更多具有不同地质和/或气候背景的分支（即支流系统）可能提供多样化的栖息地，缓冲环境波动的影响；(2)河流（流域）生态系统规模对食物链长度的影响较弱，主要表现为环境异质性与生态系统规模的相关关系。研究人员将开发一系列数学模型来预测食物链长度与分支复杂性/生态系统大小之间的关系。理论预测将通过对全球食物链长度和环境协变量的现有数据集进行荟萃分析来验证。总体而言，该项目将为生态群落如何在空间复杂系统中构建提供重要见解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The origin of variation in food chain length - the number of feeding links from producers to apex consumers in a food web - has intrigued ecologists for decades. Understanding controls of food chain length is important because it influences energy flow through ecosystems and contaminant concentrations in top predators that humans often consume. The prevailing thought has held that food chain length is determined by the size of an ecosystem. Large ecosystems can provide greater amounts of basal resources, support larger population sizes of constituent species, and/or mitigate the impact of environmental changes. However, while ample empirical evidence for the ecosystem size hypothesis exists in spatially simple systems (e.g., oceanic islands and lakes), there is less clear support in more spatially complex systems, such as branching river networks. The mixed results for the ecosystem size hypothesis in spatially complex systems imply the existence of overlooked factors that control food chain length. The project will explore the role of ecosystem complexity that is emerging as a key factor in ecosystem dynamics. Specifically, researchers will focus on the branching complexity of river networks and investigate its importance in driving food chain length. The broader impacts of this project include the following components. First, researchers will participate in outreach events through formal partnerships with K-12 schools. Second, the project will provide research training opportunities for underrepresented minorities and a postdoctoral scientist. Lastly, researchers will distribute open-source software through online repositories to facilitate the application of research products.The project will combine theoretical and empirical approaches to test the following hypotheses: (1) complex river networks, with greater levels of branching, support long food chains because having more branches (i.e., tributary systems) with distinct geological and/or climatic backgrounds may provide diverse habitats that buffer the impact of environmental fluctuations; (2) ecosystem size in rivers (watershed area) has weak effects on food chain length due to the context-dependent association between environmental heterogeneity and ecosystem size. Researchers will develop a series of mathematical models to generate predictions for the association between food chain length and branching complexity/ecosystem size. Theoretical predictions will be validated by meta-analyses of existing datasets of food chain length and environmental covariates across the globe. Overall, the project will provide important insights into how ecological communities are structured in spatially complex systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.