Collaborative Research: Interactive Effects of Exogenous and Endogenous Spatial Heterogeneity on Plant Diversity

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The spatial heterogeneity of the physical environment within a given area may be the primary determinant of the coexistence of multiple species and consequent species diversity therein. However, organisms themselves can contribute to species coexistence through their own processes of variable reproduction and dispersal, through interactions such as competition, and through ways that different organisms modify their environment locally and increase heterogeneity. The balance of the roles of the external environment and the organisms themselves in determining coexistence and diversity of species is a largely open question in ecology. This project will use a novel field experiment to examine this question for a grassland system in Kansas. The experiment will manipulate environmental heterogeneity using soil mixtures and will introduce differences in the effects of organisms by planting different mixtures of species in different ways. A computer simulation model will complement the experiment to explore the details of various processes. This work will contribute to knowledge on the maintenance of species diversity in plant communities, which is valuable in managing natural and modified (in this case, rangeland) plant communities to maintain ecosystem services. The project also contributes to the development of the next generation of scientists through training of graduate and undergraduate students and a well-developed connection to a local high school that involves students in the research.This research will examine the strengths of exogenous and endogenous spatial heterogeneity in mediating species coexistence and diversity in grassland communities. The exogenous spatial heterogeneity is taken here as the spatial heterogeneity in soils, and the endogenous heterogeneity is taken as the conditions created by spatial heterogeneity in response to dispersal limitation, demographic stochasticity, competitive interactions, and organism-environment feedbacks resulting in endogenous spatial structuring of populations and communities independent of underlying environment gradients. A novel experiment will compare mixed and unmixed soils in a block design. Seeds will be sown to vary species aggregation pattern and species pools (by functional and phylogenetic diversity). A smaller set of experiments will focus on plant-soil feedbacks. The experiments will be complemented by the development of a simulation model that can mimic the experimental design. The simulation will allow additional scales of heterogeneity to be considered. By combining experiments with models, the work will close a gap between theory and empirical work. The research will be extended to education through an associate scientist program involving a local high school students who will participate directly in data gathering and analysis. Graduate students will participate in training undergraduates and the high school students. The work will contribute to conservation through an understanding of the effects of plant community simplification.