Date of Award
Doctor of Philosophy
Phylogenetic and functional perspectives of community assembly can reveal new insights into how variation within dominant species interact with the local species pool to influence the structure of restored plant communities. Many studies have examined the effect of dominant species and species pools in structuring plant communities, but few have investigated their effects on phylogenetic and functional diversity. This research seeks to determine the effect of intraspecific genetic variation (population sources) and species pools on evolutionary relatedness of coexisting species and ecosystem functioning (such as productivity). The first study examined the importance of incorporating phylogenetic approach into restoration ecology to tease out the effect of population sources and species pools on community phylogenetic diversity (Chapter 2). This study was first study to show consequences of using different seed sources on phylogenetic diversity (PD) in grassland restoration. It showed that population sources had a transitory effect on community phylogenetic structure over time. Local ecotypes decreased the abundance of closely related eudicots, monocots and volunteer species more than cultivars. However, population sources did not affect ecologically conservative species (i.e. species with intermediate-to-poor ecological tolerance and a high degree of fidelity to prairie habitats). Thus, cultivars might have a positive effect on community phylogenetic diversity more than local ecotypes by decreasing the abundance of a phylogenetically diverse community of less closely related volunteer species. Differences in PD of seed mixes were maintained in the community of high-fidelity species, but did not affect PD of the unsown (volunteer) species in the assembling community. The second experiment showed the importance of functional diversity rather than phylogenetic diversity in monitoring population source and species pool effects (as biotic filters) in grassland restoration (Chapter 3). In this experiment, the establishing communities as well as the eudicots, Asteraceae and volunteers established with local ecotypes were functionally more diverse than when established with cultivars. By contrast, the exotic species established with cultivars were functionally more similar than when established with local ecotypes. Thus, local ecotypes might have a positive effect on community FD and species coexistence more so than cultivars. In addition, population sources had more contingent effects (i.e. interaction effects of population sources with species pools) when quantified as FD in eudicots, Asteraceae and volunteers than when measured as PD. Supplemental seeding of a functionally dissimilar species pool after four years led to an increase in FD among coexisting species. Population sources and species pools had more effects on continuous functional traits than on categorical traits. A weak phylogenetic signal in the functional traits and lack of relationship between FD and PD indicates that measuring PD alone without inclusion of functional traits may not adequately address factors affecting species coexistence. The third study investigates the effect of intraspecific trait variation in dominant species of cultivars and local ecotypes on intraspecific trait variability in subordinate species (Chapter 4). This experiment showed that cultivar sources of dominant species as well as some of the subordinate species established with them had higher functional trait values (especially leaf area and leaf nitrogen content) in comparison to when established with local ecotype sources of the dominant species. In addition, the functional relatedness among subordinate species established with local ecotypes was less (more functionally dissimilar) than among subordinate species established with cultivars. This study showed the importance of considering the phenotypic response of subordinate species to intraspecific trait variability of dominant species and species coexistence in community ecology. In addition, using local ecotype could increase form functional and phylogenetic diversity of restored communities more than cultivars. Thus, monitoring functional and phylogenetic diversity are useful tools in restoration ecology to understand the effect of biotic filters on community composition.
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