Species Interactions Affect the Distribution and Evolution of Multiple Floral Traits in California Native Wildflowers PDF Download

Author: Katherine Elizabeth Eisen
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Languages : en
Pages : 255

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Book Description
Darwin famously identified that species interactions in a "tangled bank" could influence how species evolve. Yet community ecology - the study of species interactions - and evolutionary biology - the study of phenotypic evolution - have been primarily studied in isolation; as a result, we still have limited knowledge of how ecological interactions cause phenotypic change in multiple types of traits, and how the evolutionary effects of these interactions may vary across communities. In flowering plant communities, co-occurring plant species often share pollinators, which can lead to indirect beneficial facilitation or detrimental competition between plant species for pollination. I hypothesized that interactions between co-occurring plant species might affect the composition of and patterns of selection in flowering plant communities. In this dissertation, I conducted field and greenhouse common garden studies using species in the genus Clarkia, which are California-native annual plants that commonly co-occur in multi-species communities and are primarily pollinated by solitary bees that specialize on the genus. In the first chapter, I assessed how interactions among plants that share pollinators might affect communities ecologically, by determining what species can co-occur, and evolutionarily, by affecting ongoing, in situ evolution. I conducted a field survey of species co-occurrence patterns and a greenhouse common garden study of trait variation. Two plant species co-occur more frequently than expected by chance alone, and these species have converged in flowering time and diverged in flower size where they co-occur. In the second chapter, I tested if differences in flowering times observed in Clarkia communities minimize competition for pollination by conducting a phenology manipulation experiment with potted plants. Contrary to the general expectation, my results indicated that staggered flowering in these communities does not minimize competition for pollinators and may result from selection from herbivory or water availability. In the third chapter, I conducted the first test for character displacement-the evolution of trait differences where species co-occur relative to where they occur alone-in a trait that mediates many plant- pollinator interactions, floral scent. I developed high-throughput methods for measuring the floral scent of two species of Clarkia to examine whether the emission rates of floral volatiles varied across communities that contain one, two, or four Clarkia species. I found a pattern consistent with character displacement in the emission rates of eight species-specific compounds, and novel evidence that this evolutionary process can be context-dependent and may occur via multiple pathways in plants. In the fourth chapter, I examined whether interactions between co- occurring plant species in natural communities alter patterns of net- and pollinator-mediated phenotypic selection on floral traits. Across two years, I estimated phenotypic selection on four species and experimentally tested for pollinator-mediated selection on two species in >20 communities that differ in species richness and floral density. Intraspecific competition at high densities and interspecific competition at low densities may affect the evolution of floral traits in these communities. Together, my results indicate that patterns of trait evolution in more species-rich communities are not predictable from simpler communities, and that species interactions can affect the evolution of multiple aspects of a species' phenotype. Because plant-plant interactions could be modifying selection exerted by the abiotic or biotic environment, my results illustrate that species interactions can have wide-ranging effects on species' evolutionary trajectories.