Trophic dynamics in the fine-root based food web: integrating resource heterogeneity, root herbivores, and root foraging
Stevens, Glen Noel
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Resources in the soil are heterogeneously distributed. We know that plant species differ in their root responses to nutrient patches and that these differences in foraging can influence plant competition. However, most studies of root-resource interactions overlook the potential top-down influence of root herbivores. While root herbivores can influence plant community structure, the extent to which they influence ecosystem-scale factors such as net primary production is unclear. In addition, little is known regarding root herbivore foraging behaviors and, more importantly, whether these foraging behaviors can actually influence species interactions. In this dissertation, I present a conceptual model of soil-root-herbivore interactions in which soil resource heterogeneity structures both root dynamics and the abundance and influence of root herbivores. I conducted two field and one greenhouse experiment examining this proposed model. The dissertation includes an introductory chapter (Chapter 1), a field study examining root responses to manipulations of soil fertility and root herbivory (Chapter 2), a greenhouse study that used plant species responses to heterogeneity to develop predictions about the role of root herbivores in mixed-species neighborhoods (Chapter 3), and a field study of planted communities examining soil fertility and fauna effects on above- and belowground structure and function (Chapter 4). In all cases, there were significant effects of root herbivores on community structure and components of net primary production. Resource distribution had a strong effect in studies conducted in sandy, nutrient-poor soils (Chapter 2 and 3), but had a reduced effect in the study conducted at Kentland Farm in loamy soils (Chapter 4). Interactions between resource availability and root herbivory were common. These results support the theory that the potential benefit of resource-rich patches may be constrained by root herbivores. This research complements recent findings that demonstrate other potential costs of species foraging behaviors (such as exposure to soil anoxia and increased drought stress), as well as potential effects of root herbivores and other soil fauna on plant diversity.
- Doctoral Dissertations