Thesis Title

Species interactions and the formation of novel annual plant communities following rapid environmental change Claire Elizabeth Wainwright MSc A thesis submitted for the degree of Doctor of Philosophy at The University of Queensland in 2015 School of Biological Sciences Abstract Recent environmental change associated with human activities has given rise to ecological communities that have no historical counterpart. In particular, introductions of non-native plant species have in many cases altered the structure and functioning of resident plant communities through changes in species composition and the surrounding environment within which species interact. As a result, new combinations of species are forming “novel” communities across an increasingly large portion of the earth’s land surface. Because novel plant communities differ in configuration from original native-dominated communities, they present unique challenges to management, restoration, and conservation efforts. Thus, there is a growing need to understand how novel communities function differently from the original communities they replace. In this thesis, I investigate a variety of interactions in original and novel plant communities. Using a diverse annual plant system that persists within a fragmented agricultural landscape in Western Australia, I focus on the role of local-scale species interactions, an important biotic component of plant community assembly. I explore the complexities of local-scale interactions between native and non-native invasive species in light of coexistence theory, community assembly, and conservation of native floral diversity. This thesis comprises seven chapters. The first chapter serves as a general introduction which places the thesis within the larger context of multispecies coexistence in novel plant communities. The second chapter serves as a description of the York gum (Eucalyptus loxophleba subsp. loxophleba) – jam (Acacia acuminata) woodland annual flora, the study system for the data chapters (3 – 6) which are based on laboratory and field experiments. Chapters 3 and 4 are experimental evaluations of frequency-dependent and density-dependent performance of native and invasive species that co- occur in York gum-jam annual plant communities. Chapter 5 reports on a field experiment, which investigates the performance of common native and non-native invasive annuals experiencing inter- and intraspecific competition in natural York gum-jam annual assemblages. Chapter 5 also assesses changes in community-level functioning due to compositional differences by evaluating diversity effects in novel and original annual communities. The final data chapter, Chapter 6, experimentally investigates how local-scale environmental gradients and a non-native invasive annual grass impacts annual plant community structure in the field. Finally, I conclude with a discussion of my results in Chapter 7, which unites the previous chapters, addresses limitations of the thesis, and presents suggestions for future research. ii Overall, my results suggest that the local-scale impacts of non-native invasive species on native species may be more variable than those often reported in the literature on plant invasions (i.e. competitive exclusion). Consistent with previous studies, I did indeed observe negative interactions among invasive non-native and native annual plant species in field and laboratory settings. Specifically, I found that some species of invasive annual grass have the potential to negatively impact native populations over very short timescales through direct competition as well as interference from litter. These negative interactions, however, were not representative of interactions in novel communities as a whole. Notably, I found interactions between native annual forbs and an invasive non-native annual grass that ranged from neutral to positive. The direction and magnitude of invader impacts were highly dependent on species identity and the composition of the community, but were generally consistent across community densities and natural environmental gradients. Species interactions play a potentially complex role in the assembly of annual plant communities post-invasion. My results lend empirical support to the notion that species in these novel communities should be considered according to their impacts rather than their origins. These studies serve as some of the first investigations into the processes that stabilize interactions among native and invasive non-native species and contribute to novel community formation and maintenance. When considered alongside large-scale patterns from observational studies, my findings demonstrate that interactions that occur over small spatial and temporal scales have the potential to influence large-scale plant community dynamics. In total, this thesis represents a valuable contribution to the community ecology and biological invasions literature, and has the potential to inform future restoration and conservation efforts in this threatened woodland ecosystem and beyond. iii Declaration by author This thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis. I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have carried out since the commencement of my research higher degree candidature and does not include a substantial part of work that has been submitted to qualify for the award of any other degree or diploma in any university or other tertiary institution. I have clearly stated which parts of my thesis, if any, have been submitted to qualify for another award. I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the policy and procedures of The University of Queensland, the thesis be made available for research and study in accordance with the Copyright Act 1968 unless a period of embargo has been approved by the Dean of the Graduate School. I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this thesis. iv Publications during candidature Conference abstracts: Wainwright, C.E., Hobbs, R.J., Buckley, Y.M., Dwyer, J.M., Mayfield, M.M. “Positive interactions in a novel annual plant community”. Ecological Society of Australia/New Zealand Ecological Society Joint Annual Meeting, Auckland, New Zealand, 2013. Wainwright, C.E., Hobbs, R.J., Buckley, Y.M., Dwyer, J.M., Mayfield, M.M. “Biotic interactions among annual plant species in a novel ecosystem” Ecological Society of Australia Annual Meeting, Melbourne, Australia, 2012 Peer-reviewed paper relevant to the thesis, but not forming part of it: Dwyer, J.M., Hobbs, R.J., Wainwright, C.E., Mayfield, M.M. Climate moderates release from nutrient limitation in natural annual plant communities. Global Ecology and Biogeography 24.5: 549-561. Publications included in this thesis No publications included. v Contributions by others to the thesis All experiments (Chapters 3 – 6) were conceived of by the candidate and advisors Dr. Margaret Mayfield, Dr. Richard Hobbs, and Dr. John Dwyer unless otherwise stated below. Data collection and analysis was carried out by the candidate with input from advisors described below. All writing of the thesis was done by the candidate, and underwent revision by all advisors. The larger research project which this PhD contributed to was designed by Dr. Mayfield and Dr. Hobbs, and was funded by a grant from the Australian Research Council (DP1094413) awarded to Dr. Mayfield and Dr. Hobbs. All field soil samples were analysed by CSBP Limited. Chapters 1, 2, and 7 were written by the candidate with improvements to drafts made by all advisors. Chapter 3 was conceived of by the candidate and Dr. Mayfield. Data collection and analysis was carried out by the candidate with guidance from Dr. Dwyer. The manuscript was written by the candidate with editorial input by Dr. Mayfield, Dr. Hobbs, and Dr. Dwyer. Chapter 4 was designed by the candidate with input from Dr. Mayfield and Dr. Dwyer. The candidate collected all field data and the majority of the data at UQ, the remainder of which was collected by volunteers (see Acknowledgments). Analysis was carried about by the candidate with advice from Dr. Dwyer. The manuscript was written by the candidate with editorial input from all advisors. The community-level component of Chapter 5 was conceptualized by Dr. Mayfield and Dr. Hobbs in ARC grant DP1094413 and modified by the candidate in the field. Data was collected primarily by the candidate with help from field volunteers (see Acknowledgments), and analysed by the candidate with input from Dr. Dwyer. The neighbourhood-level component was conceptualized by Dr. Mayfield and Dr. Janneke HilleRisLambers and data was collected by the candidate, Hao Ran Lai, Dr. Mayfield, and Dr. HilleRisLambers. The manuscript was written by the candidate with input from all advisors. Chapter 6 was conceptualized by the candidate and Dr. Mayfield,

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