Complexity and Stability of an Old-field Ecosystem: The Role of Asymmetrical Interaction Strengths and Food Web Toplology

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Biodiversity provides important environmental services that support human health and economic well-being. One important and as yet unanswered question is: How do species fit together to provide the most stable supply of those services? This question will be answered by experimentation with species of insect predators and herbivores, and grassland plants. The study will test new theory that the most stable supply of services comes from complex systems in which many weakly interacting species counterbalance the effects of a few strongly interacting species. The four-year field project will test this theory by assembling experimental food webs containing different mixtures of strongly and weakly interacting predator and herbivore species. The study will measure how well the different species mixtures sustain important life-support services such as plant production for forage and the nitrogen cycle. Human activities are fundamentally changing ecological systems with attendant loss of biodiversity. This study will test the resilience of ecological systems by quantifying the risks to ecological function of species loss. It will show how seemingly benign, weakly interacting species can, in combination with many other weakly interacting species, end up being the important threads that hold ecosystems together. The results will help guide conservation strategies that ensure long-term sustainability of vital environmental services. The project will also train the next generation of undergraduate and graduate students in methods for experimental analysis of natural ecosystem function in ways that enable them to make productive, direct contributions to environmental policy.