Ecological dynamics of a terrestrial orchid symbiosis
Diez, Jeffrey Michael
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My dissertation research tested elements of niche theory by determining how the population dynamics of a terrestrial orchid, Goodyera pubescens, respond to abiotic gradients, and how mycorrhizal fungi influence patterns of orchid recruitment. Long-term study plots were established along a gradient from the southeastern Piedmont to the southern Appalachian Mountains, encompassing a wide range of environmental conditions. I generated predictive models to show how basic vital rates such as survival and reproduction depend on soil moisture and understory light availability using a combination of approaches including abiotic and demographic monitoring, soil analyses, targeted field experiments, genetic analysis, and computer modelling. I then used these findings to compare predicted population growth rates across abiotic gradients from modelling to realized distributions and abundances from field data. I also conducted the first study to jointly characterize the spatial genetic structure of a plant and its mycorrhizal fungi, in order to test hypotheses about how patterns of genetic diversity are shaped by demographic processes of a symbiotic plant-fungal system along environmental gradients. Through field experiments I found strong evidence for fungal limitations on patterns of plant recruitment that were context dependent (i.e. symbiotic recruitment increased with both soil organic content and moisture). A key to these studies has been the use of newly-available Bayesian statistical approaches to integrate multiple types of data from a range of spatial and temporal scales, in order to build predictive models with reasonable estimates of uncertainty.