Individualistic and phylogenetic perspectives on plant community patterns.

摘要

Plant communities have traditionally been viewed as spatially discrete units structured by dominant species, and methods for characterizing community patterns have reflected this perspective. In this dissertation, I adopt an alternative, individualistic community characterization approach that does not assume discreteness or dominant species importance a priori (Chapter 2). This approach was used to characterize plant community patterns and their relationship with environmental variables at Zion National Park, Utah, providing details and insights that were missed or obscure in previous vegetation characterizations of the area.;I also examined community patterns at Zion National Park from a phylogenetic perspective (Chapter 3), under the assumption that species sharing common ancestry should be ecologically similar and hence be co-distributed in predictable ways. I predicted that related species would be aggregated into similar habitats because of phylogenetically-conserved niche affinities, yet segregated into different plots because of competitive interactions. However, I also suspected that these patterns would vary between different lineages and at different levels of the phylogenetic hierarchy (phylogenetic scales). I examined aggregation and segregation in relation to null models for each pair of species within genera and each sister pair of a genus-level vascular plant supertree. Some pairs confirmed predictions, but many others did not, suggesting niche divergence rather than niche conservatism.;In the final chapter, I discuss community characterization from a phylogenetic perspective, exploring the possibility of using phylogenetic units in lieu of species in community analysis. I consider scenarios where species may not be optimal units of analysis, such as broad-scale community studies spanning species range limits. In such scenarios, species sharing common ancestry could potentially be merged and treated as a single unit. I present a method for identifying such species that I developed by adding a phylogenetic dimension to species clustering. This method is demonstrated through an analysis of bog and rock outcrop plant communities of the Southern Appalachian Mountains.