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UBC Theses and Dissertations

Novel approaches to evaluating compositional heterogeneity : a case study using grazing exclosures in alpine meadow communities Ensing, David John


Despite a long history, accurately quantifying biological diversity remains a priority for ecologists and the continuing development of novel tools and approaches has identified areas that require further investigation. Currently, the quantification of evolutionary diversity (phylogenetic diversity) is receiving intense and critical interest, but few have attempted to quantify among sample phylogenetic variation (beta diversity) and fewer still have measured the influence of grazing on the phylogenetic diversity of plant communities. Novel partitions of beta diversity, which quantify the independent influence of richness differences and species replacement, may better clarify how heterogeneity is structured within a system, but such metrics have not yet been developed for phylogenetic diversity or applied to grazing investigations. Furthermore, it has recently been re-emphasized that, when measuring within-community heterogeneity, the only appropriate approaches that facilitate the concurrent measurement of partitioned beta diversity are ‘multiple site beta diversity’ metrics. To date ‘multiple site’ heterogeneity metrics do not exist for phylogenetic diversity. Drawing on previously published derivations of pairwise beta diversity partitions and their phylogenetic analogs, I developed novel multiple site beta diversity tools for taxonomic and phylogenetic diversity that may better quantify community heterogeneity and suggest how these new tools may be useful for the practicing community ecologist. Using long term grazing exclosures, I combined novel beta diversity tools with paired plots across the exclosure fence and appropriate null models to test the influence of grazing on herbaceous alpine plant community heterogeneity. I show that (i) taxonomic and phylogenetic diversity provide differing results, (ii) that grazing influences within community heterogeneity of herbaceous plant communities, but that the response may be site dependent, and (iii) that richness and replacement metrics of beta diversity exhibit different responses to grazing. Novel metrics of partitioned taxonomic and phylogenetic beta diversity therefore provide useful insight into the structuring of herbaceous alpine plant communities. As such, within-community heterogeneity as measured by ‘multiple site beta diversity’ is an important attribute of any ecosystem and efforts aimed at quantifying and preserving biodiversity for ecosystem management or conservation should include it in their goals.

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