Collaborative research: Measuring and modeling the ecological consequences of associational effects

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This project will study how insect pests affect individual plant populations within the context of diverse assemblages of plant species. When insects search for plants to eat, they can be influenced by the look and smell of surrounding plants. Neighboring plants can both increase and decrease insect damage to plants, and the term for this is associational effects (AE). Although it is clear that associational effects can occur at the level of individual plants, little is known about whether these effects are important enough to alter plant populations in nature, or to what degree they contribute to affecting crop yield in agricultural fields. This project will use short-term experiments in combination with mathematical models to infer how associational effects influence populations of native plants. The methods developed in this project can also be used to determine how to use associational effects to maximize crop yields. The project will provide STEM training for undergraduate, graduate and postdoctoral students and a post-baccalaureate technician, and the researchers will partner with K-12 teachers to develop activities for teaching science using school gardens and associational effects between crops such as collards and mustards. This project will combine mathematical models and experiments to address whether and how associational effects influence the outcome of plant interspecific competition (coexistence and/or relative abundance) in an old-field system, using Solanum carolinense (Carolina horsenettle) and Solidago altissima (goldenrod) as focal species. The project will address three questions empirically: 1) What is the spatial scale of AE in this system? (using a Nelder fan design field experiment) 2) How do AE from multiple species combine? (using an experiment with monocultures, bicultures, and tricultures at two different densities) and 3) how do associational effects influence competition (using data from a previous competition experiment with and without herbivores). Spatially implicit and explicit models will address how plant spatial structure and the form of frequency dependence alter predicted effects of AE on plant populations. The researchers will parameterize models using data from the empirical studies to test how associational effects scale up to the population level. Overall, this project will quantify directly for the first time how associational effects influence plant competition and provide a general framework for understanding how different forms of associational effects influence population-level processes across different types of consumer-resource systems. This project will also suggest how best to manipulate associational effects in agriculture, in order to maximize crop yields.