Disentangling an entangled bank: using network theory to understand interactions in plant communities Photo by Ray Blick Ray A.J. Blick Thesis submitted for the degree of Doctor of Philosophy Evolution and Ecology Research Centre School of Biological, Earth and Environmental Sciences University of New South Wales July 2012 PLEASE TYPE THE UNIVERSITY OF NEW SOUTH WALES Thesis/Dissertation Sheet Surname or Family name: Blick First name: Raymond Other name/s: Arthur John Abbreviation for degree as given in the University calendar: School: School of Biological, Earth and Environmental Sciences Evolution and Ecology Research Centre Faculty: Science Title: Disentangling an entangled bank: using network theory to understand interactions in plant communities Abstract 350 words maximum: (PLEASE TYPE) Network analysis can map interactions between entities to reveal complex associations between objects, people or even financial decisions. Recently network theory has been applied to ecological networks, including interactions between plants that live in the canopy of other trees (e.g. mistletoes or vines). In this thesis, I explore plant-plant interactions in greater detail and I test for the first time, a predictive approach that maps unique biological traits across species interactions. In chapter two I used a novel predictive approach to investigate the topology of a mistletoe-host network and evaluate leaf trait similari ties between Lauranthaceaous mistletoes and host trees. Results showed support for negative co-occurrence patterns, web specialisation and strong links between species pairs. However, the deterministic model showed that the observed network topology could not predict network interactions when they were considered to be unique associations in the community. Network analysis has revealed similarities between mistletoe- and vine-host interactions. In this thesis I investigated the role of chance in structuring these interactions. Results showed that mistletoes and vines use host trees in very different ways even though network topology suggest similarities. In chapter three I show that the dispersion of individual mistletoes (i.e., clumping of mistletoe on certain trees) was not dependent on tree availabil ity; however and perhaps more importantly, I show in chapter fi ve that coincidental associations between vines and trees are sufficient to generate similar network patterns to that found in mistletoes. Each of these studies explored untested hypotheses regarding the architecture of plant-plant interactions. (n chapter six I turned to plant-animal interactions to test whether temporal changes influenced network topology. That is, I quantified variability among species interactions and I tested the role of species turnover in structuring a frugivore network spanning six sequential years. Results showed that frugivore interactions (i) changed from year-to-year, (ii) showed inconsistent patterns of nestedness, and (iii) novel interactions occurred even after six years of data collection. In conclusion, a modified approach to the traditional randomisation procedure has allowed me to test explicit factors that determine interactions in plant communities. Network analysis is a useful measure of structure that can depict structural diffe rences among arboreal plant communities in Australian ecosystems. 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 apR !Cable to doctoral theses only). ··· · ···~ ·· · ·· ··· .........V-Y.!? .......... .. ...... Witness Date Date of completion of requirements for Award: THIS SHEET IS TO BE GLUED TO TH E INSIDE FRONT COVER OF THE THESIS ii .. 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 co~tion or in style, presentation and linguistic :~:~::5107<:::::.: ' ............... .. ................... Date ... ...... 9:/s/(~ .............. ......... ...... ........ ........ ii i 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 (this is applicable to doctoral theses only) . 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 dissert tloh.' Signed Date .... .. ?;($/! ~ ....... ..... ..... .... ..... .... ... ................ ... ...... AUTHENTICITY STATEMENT 'I certify that the Library deposit digital copy is a direct equivalent of the final officially approved version of my thesis. No emendation of content has occurred and if there are any minor variations in formatting, they are the result of the conversion to digit rfofmat.' Signed Date ..... 1./$'/(~ ...... ... .... ..... ... ..... ........ ...... .... .. .. .... .... .. Statement of contributions of co-authors and declarations of permission to publish All publishers and co-authors have granted permission for the following publications to be submitted and published as a thesis. No other authors will be submitting this work as part of their thesis submissions. The contribution of each author to the respective publications is stated at the start of each chapter. All photographs were taken by Ray Blick unless stated otherwise. Blick, R.A.J., Burns, K.C. & Moles, A.T. 2012. Predicting network topology of mistletoe-host interactions: do mistletoes really mimic their hosts? Oikos 121: 761-771 [DOI: 10.1111/j.1600-0706.2011.19854.x] Blick, R.A.J., Burns, K.C. & Moles, A.T. In press. Dominant network interactions are not correlated with resource availability: a case study using mistletoe-host interactions. Oikos [DOI: 10.1111/j.1600-0706.2012.20870.x] Reproduced with kind permission from Oikos and Wiley-Blackwell. Oikos grants authors the right to reproduce their article in a new publication of which they are the author, editor or co-editor, including a thesis or dissertation Acknowledgements Many people have been helped me complete this thesis. I express my deepest and sincerest thanks to friends, colleagues and family. First, thanks must go to my supervisor, Angela Moles. I consider my time in the Big Ecology Lab extremely valuable. It has been a vehicle for many excellent conversations, debates and collaborations. I am sure many students will come through these doors and leave as well-rounded scientists with a keen sense of curiosity about the natural world. During my time at UNSW I was given many opportunities to experience the less advertised side of science. For example, science communication in social media was an area of science I had not considered before. I demonstrated six different ecology courses, presented at four internationally recognised conferences, published three peer- reviewed articles and in-turn reviewed 14 articles from eight internationally recognised journals. I believe these activities are important for anyone considering a scientific career and I urge students to pursue these opportunities when they arise. Two researchers shared their hard earned data. Thank you Rachael Gallagher and K.C. Burns, I am extremely grateful to have this opportunity. Such a phenomenal amount of work has been shared by these two researchers with no expectation in return. Thank you so much for your help. I thank many people from UNSW, including co-supervisor Steve, Frank Hemmings, Rob Brooks, Alex Jordan, Terry Ord, Michael Kasumovic, Laura Warmen, Joanna Buswell, and many others. In addition, I thank Keith Leggett for his help at Fowlers Gap Research Station, coincidental barbeques and exceptional advice. FGRS will remain the most memorable part of my PhD. I highly recommend visiting FGRS to everyone. Suzy Evans, you endured the themed motor lodges of Western New South Wales and the endless revamping of my PhD every time I got behind the wheel of a car. There are far too