Dissertation Research: Regional/historical Influences and Top-down vs. Bottom-up Processes in Arthropod Community Structure

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0073055TaylorEvidence of strong direct effects of predators ("top-down") and resources ("bottom-up") are emerging from mathematical models and simplified assemblages. Data from natural communities are necessary to improve our understanding of their combined effects over multiple scales. Using large-scale surveys combined with manipulative field experiments at a single site, this project examines the trophic interactions of avian predators and arthropod assemblages of the Hawaiian myrtaceous tree Metrosideros polymorpha. Across a four million-year gradient of volcanic substrate age, nutrient availability varies in a unimodal fashion. Arthropod densities on Metrosideros track this relationship across the island chain, suggesting a strong influence of resources to the system. Species diversity accumulates with geological age and is independent of density. These relationships will be evaluated on a young basaltic lava flow (120 y.o.) where Metrosideros plant communities are nutrient limited and respond to fertilization with a tenfold increase in productivity. Vertebrate predators (birds) are to be excluded and large plots will be fertilized in a completely crossed well-replicated design. The proposed research program combines the scales and perspectives of observational data on natural patterns with controlled field experiments, thereby expanding the scope of inference from either approach alone.