Patterns And Ecological Consequences Of Aboveground And Belowground Herbivory
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Terrestrial plants are embedded in a complex biological network consisting of microorganisms, plants, and animals at several trophic levels. Because plant mass is roughly equally divided above- and belowground, plants function as a key link between the two subsystems. Thus, our understanding of how communities are structured and function may be advanced by considering above- and belowground ecological interactions in tandem. As a model for understanding above-belowground dynamics, this dissertation focuses on the interactions between common milkweed (Asclepias syriaca), a perennial plant native to Eastern North America, and the red milkweed beetle (Tetraopes tetraophthalmus), a monophagous herbivore that feeds aboveground as an adult and belowground as a larva. The broad aims of this dissertation are to 1) characterize biotic interactions in the rhizosphere of A. syriaca; 2) investigate the individual and community-wide effects of above- and belowground herbivory by T. tetraophthalmus; and 3) examine the extent to which A. syriaca growth, defense, and ecophysiological traits are genetically correlated in expression, and how these traits affect the performance of T. tetraophthalmus adults and larvae. Soil-dwelling insects commonly co-occur and feed simultaneously on belowground plant parts, yet patterns of damage and consequences for plant and insect performance remain poorly characterized. Chapter 1 addresses how two root-feeding insects, T. tetraophthalmus and wireworms, affect the performance of A. syriaca and the mass and survival of both conspecific and heterospecific insects. Initial herbivory and induced plant responses have the potential to shape patterns of subsequent insect attack above- and belowground. When different life stages of the same herbivore species damage different plant parts sequentially, there is especially strong potential for induced responses because the sequence of attack is predictable. Chapter 2 characterizes induced responses of A. syriaca following aboveground herbivory by adult, and belowground herbivory by larval, T. tetraophthalmus and then tests for changes in the performance of insects that subsequently interact with shoot- and root-damaged plants. Because many ecological interactions are mediated by plant phenotype, characterizing shoot and root traits is critical for understanding broader scale interactions. Chapter 3 describes above- and belowground plant traits in terms of heritability, evolvability, pairwise correlations, and clusters and tests for associated impacts on T. tetraophthalmus performance.
Plant-insect interactions; Tetraopes tetraophthalmus; Asclepias syriaca
Geber, Monica Ann; Sparks, Jed P.
Ph. D., Ecology
Doctor of Philosophy
dissertation or thesis