SHIFTING SCALES AND PASSÉ PARADIGMS: alternative spatio-temporal perspectives on environmental heterogeneity and plant community assembly Andrew D. Letten Centre for Ecosystem Science School of Biological, Earth and Environmental Science UNSW Australia Thesis Submitted for the Degree of Doctor of Philosophy July 2015 ii PLEASE TYPE THE UNIVERSITY OF NEW SOUTH WALES Thesis/Dissertation Sheet Surname or Family name: Letten First name: Andrew Other name/s: David Abbreviation for degree as given in the University calendar: PhD School: Biological, Earth, and Environmental Sciences Faculty: Science Title: Shifting scales and passe paradigms: alternative spatio-temporal perspectives on environmental heterogeneity and plant community assembly Abstract 350 words maximum: (PLEASE TYPE) Environmental heterogeneity has been a focal point of ecological research for decades and yet we have tended to stick to comparatively formulaic interpretations of its dimensionality. In this thesis I explore alternative perspectives on the relationship between heterogeneity and plant community assembly in both spatial and temporal dimensions. Beginning with perhaps the most basic property of an ecological community, its taxonomic diversity, in Chapter 2 I investigate the explanatory power of fine-scale spatial heterogeneity in temporal climate variability. Consistent with coexistence theory, the results of this study indicate that climate variability can be a better predictor of richness than more commonly used climatic averages, and highlight the need for ecologists to expand their purview beyond absolutes and averages. Turning to multivariate distance-based descriptors of community structure, in Chapters 3 and 4, I consider the under-explored role of temporal scale and variability on inference in community phylogenetic and trait-dispersion studies. Given a classic Brownian model of trait evolution, in Chapter 3, I show that the expected functional displacement of any two taxa is most parsimoniously represented as a linear function of time's square root. On this basis I argue that existing methods overweight deep time relative to recent time. Taking into account this methodological adjustment, in Chapter 4, I use standard phylogenetic and functional-trait metrics to evaluate the temporal stability of community structure through succession in a fire-prone heathland. Contrary to widely-held assumptions, community structure did not become increasingly functionally and phylogenetically dispersed with time. This contributes to an emerging body of evidence indicating that limits to the similarity of coexisting species are rarely observed at fine-scales. In Chapter 5, I adopt a model-based approach to the analysis of species co-occurrence patterns in response to fine-scale spatial environmental heterogeneity. This study confirms the vital role of hydrological niches for the maintenance of within-community plant diversity. Two primary conclusions emerge from the thematically broad investigations within the thesis: subtle shifts in the scales at which spatial and temporal heterogeneity are examined can yield new insights into community assembly; and reliable mapping of processes from patterns requires the continuous scrutiny of paradigmatic assumptions. Declaration relating to disposition of project thesis/dissertation I hereby grant to the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or in part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act 1968. I retain all property rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the 350 word abstract of my thesis in Dissertation Abstracts International (this is applicable to doctoral theses only). 21/07/15 …………………………………………………………… ……………………………………..……………… ……….……………………...…….… Signature Witness Date The University recognises that there may be exceptional circumstances requiring restrictions on copying or conditions on use. Requests for restriction for a period of up to 2 years must be made in writing. Requests for a longer period of restriction may be considered in exceptional circumstances and require the approval of the Dean of Graduate Research. FOR OFFICE USE ONLY Date of completion of requirements for Award: THIS SHEET IS TO BE GLUED TO THE INSIDE FRONT COVER OF THE THESIS Copyright Statement I hereby grant the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act 1968. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the 350 word abstract of my thesis in Dissertation Abstract International. I have either used no substantial portions of copyright material in my thesis or I have obtained permission to use copyright material; where permission has not been granted I have applied/will apply for a partial restriction of the digital copy of my thesis or dissertation. Signed Date 21/07/15 Authenticity Statement I certify that the Library deposit digital copy is a direct equivalent of the final officially approved version of my thesis. No emendation of content has occurred and if there are any minor variations in formatting, they are the result of the conversion to digital format. Signed Date 21/07/15 Originality Statement I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, or substantial proportions of material which have been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project’s design and conception or in style, presentation and linguistic expression is acknowledged. Signed Date 21/07/15 To Ash et al. Acknowledgements For what has been an incredibly rewarding and wonderfully challenging 45 months I have several people to thank, several times over. David, for being a superb supervisor, whose unstinting zen and benevolent wisdom are a template for academic mentorship. Richard and Will, who both played the role of unofficial supervisors and always left their doors ajar. Sharon, whose gravitational pull kept me (and everyone else) in orbit. Dan, Mick and John for providing valuable advice along the way. Steve and Bill who as panel members took a much appreciated interest in my progression. Cam who provided valuable insights into my original project proposal. Various other fantastic UNSW folk that have contributed to the fun, including in no particular order: Sam, Sylvia, Eve, Mitch, Nick, Evan, Jo, Chris, Ben, Anna, Chantel, Francis, David and the Ecostats crew, Angela, Haba, Rhiannnon and the rest of the Big Ecology lab. The brilliant academics of the UCT Botany Dept, and in particular Jeremy and Tony who as honours supervisors made me think differently, in a really good way. My patient parents who have supported me unconditionally in my every pursuit. My generous brother who amongst many other things has done his best to keep me in fashion. My wonderful wife Shan, a mention in the acknowledgements of my thesis almost makes a mockery of your contribution; you rock like Kilimanjaro. Finally, I thank my amazing little Ash Mae, who makes me stop and smell the roses (and the nappies). viii “Space and Time! Two minor omissions that no one is likely to notice” Isaac Newton in The System of the World by Neal Stephenson Abstract Although environmental heterogeneity has been a focal point of ecological re- search for decades, we have tended to stick to comparatively formulaic inter- pretations of its dimensionality. In this thesis I explore alternative perspectives on the relationship between heterogeneity and plant community assembly in both spatial and temporal dimensions. Beginning with perhaps the most basic property of an ecological community, its taxonomic diversity, in Chapter 2 I investigate the explanatory power of fine-scale spatial heterogeneity in temporal climate variability. Consistent with coexistence theory, the results of this study indicate that climate variability can be a better predictor of richness than more commonly used climatic averages, and highlight the need for ecologists to expand their purview beyond absolutes and averages. Turning to multivariate distance- based descriptors of community structure, in Chapters 3 and 4, I consider the under-explored role of temporal scale and variability on inference in community phylogenetic and trait-dispersion studies. Given a classic Brownian model of trait evolution, in Chapter 3, I show that the expected functional displacement of any two taxa is most parsimoniously represented as a linear function of time’s square root. On this basis I argue that existing methods overweight deep time relative to recent time.