Collabrative Research: Does productivity drive diversity or vice versa? Empirical and theoretical investigations of the multivariate productivity-diversity hypothesis in streams

物种多样性与生态系统生产力之间的关系是生物学中最重要但也最具争议的话题之一。历史上，生物学家一直认为生态系统的生产力限制了该系统中物种共存的数量。在过去的二十年里，实验表明事实恰恰相反；同一生态系统中存在的物种数量限制了生产力。这导致了一个明显的悖论：物种多样性是生产力的原因还是结果？本研究试图通过检验多元生产力-多样性假设来解决这一悖论。这一假设提出，生产力和多样性之间的关系可以被提炼成三种类型的效应：1)营养供应的效应，它设定了生态系统潜在生产力的上限；2)物种丰富度的效应，它决定了给定营养供应下生态系统的实际生产力；3)营养供应对生产的额外影响，因为营养物质控制了可以共存的竞争物种的数量。这项研究将使用实地和实验室实验来量化这些影响，并将它们整合到一个数学模型中，该模型可以预测生态系统中植物和动物的生物量和物种数量。这项研究将对正在经历快速环境变化的生态系统的管理产生重大而广泛的影响。物种多样性正在以前所未有的速度在世界范围内消失，过度使用肥料正在改变生态系统的生产力。这项工作将处于开发模型的前沿，这些模型有助于预测环境变化的两个最普遍的方面（生物多样性丧失和营养过剩）如何共同影响生态群落。该项目还将为研究生和本科生提供研究培训。

The relationship between species diversity and the productivity of ecosystems is one of the most important yet controversial topics in biology. Historically, biologists have assumed that the productivity of an ecosystem limits how many species can coexist in that system. Over the past two decades, experiments have suggested that the opposite is true; that the number of species present in the same ecosystem limits the productivity. This has led to an apparent paradox: is species diversity the cause or the consequence of productivity? This study seeks to resolve this paradox by testing the Multivariate Productivity-Diversity hypothesis. This hypothesis proposes that the relationship between productivity and diversity can be distilled into three types of effects: 1) an effect of nutrient supply that sets an upper bound on an ecosystem's potential productivity, 2) an effect of species richness that determines how productive an ecosystem actually is for a given nutrient supply, and 3) an additional effect of nutrient supply on production that occurs as nutrients control the number of competing species that can coexist. This research will use field and laboratory experiments to quantify these effects and fit them together into a mathematical model that predicts both the biomass and number of species of plants and animals in an ecosystem. This research will have significant broader impacts on the management of ecosystems that are undergoing rapid environmental change. Species diversity is being lost worldwide at an unprecedented rate, and the productivity of ecosystems is being altered by over use of fertilizer. This work will be at the forefront of developing models that help forecast how two of the most pervasive aspects of environmental change (biodiversity loss and excessive nutrients) jointly impact ecological communities. This project will also provide research training to graduate and undergraduate students.