ResearchOnline@JCU This file is part of the following reference: Brandl, Simon Johannes (2016) Functional niche partitioning in herbivorous coral reef fishes. PhD thesis, James Cook University. Access to this file is available from: http://researchonline.jcu.edu.au/45253/ The author has certified to JCU that they have made a reasonable effort to gain permission and acknowledge the owner of any third party copyright material included in this document. If you believe that this is not the case, please contact [email protected] and quote http://researchonline.jcu.edu.au/45253/ Functional niche partitioning in herbivorous coral reef fishes Thesis submitted by: Simon Johannes Brandl January 2016 For the degree: Doctor of Philosophy College of Marine and Environmental Sciences ARC Centre of Excellence for Coral Reef Studies James Cook University i Acknowledgements I am deeply indebted to my supervisor, David Bellwood, whose invaluable intellectual and emotional support has been the cornerstone of my degree. His outstanding guidance, astute feedback, incredible generosity, and tremendous patience cannot be credited adequately within the scope of this acknowledgements section. Besides his supervisory contribution to my degree, I am grateful for the countless hours full of cheerful negotiations, curly remarks, philosophical debates, humorous chitchat, and priceless counselling. I also thank everybody who has helped me in the field: Jordan Casey, Christopher Goatley, Jennifer Hodge, James Kerry, Michael Kramer, Katia Nicolet, Justin Welsh, and the entire staff of Lizard Island Research Station. I am especially grateful for Christopher Mirbach’s help, commitment, and loyalty throughout many weeks of fieldwork. This thesis would have been impossible without his dedication and enthusiasm for marine fieldwork. Further, I have great appreciation for all individuals who have assisted me during my daily struggles within the university, namely Savita Francis, Debbie Berry, Diane Bailey, Sue Reilly, Phil Osmond, Gordon Bailey, Jane Webb, Alanna Newman, Angela Rachel, Tammy Walsh as well as JCU IT support and Wayne Mallett from the HPC unit. In addition, I would like to thank everybody who has intellectually contributed to this thesis in one way or the other. This includes Orpha Bellwood, Brock Bergseth, Shane Blowes, Andrew Baird, Culum Brown, Sean Connolly, Howard Choat, Jordan Casey, Peter Cowman, Jenn Cowman, Rebecca Fox, Christopher Goatley, Jennifer Hodge, Andrew Hoey, Mia Hoogenboom, Rhondda Jones, Michael Kramer, Joanna Khan, Justin Marshall, David Mouillot, Valeriano Parravicini, Douglas Rasher, Justin Rizzari, Dominique Roche, Will Robbins, Theresa Rueger, Jodie Rummer, Sébastien Villéger, Brett Taylor, Sterling Tebbett, Alex Vail, Mathew Vickers, and Justin Welsh. A special thanks to all inhabitants of the tin box, who had to endure the circadian announcement of coffee time, operatic music ii accompanied by the deafening staccato of keyboard strokes, and several other atrocities that came with my sustained presence. Finally, my deepest gratitude goes out to people around the world, who have patiently tolerated and overwhelmingly supported me as a son, brother, brother-in-law, friend, or partner, with special thanks to Benedikt Gebrande and my pch-pals, who have never complained about my long absence. A special mention also belongs to Monika Lohmaier, who has fought a battle much harder than mine. I especially thank my parents, Alfons and Katharina, who have sponsored and supported all of my educational escapades with their endless love and kindness. I thank my sister, Veronika Klein, for her steadfast care for her little brother, and my brother-in-law, Thomas Klein, for being awesome. Finally, I thank my partner, Jordan Casey, for being my silent sounding board in all circumstances. Her love and patience have turned this arduous journey into a wonderful saunter beneath the tree of life. iii Statement of the Contribution of Others This thesis was supported by funds provided by the Australian Research Council to David Bellwood (ARC Discovery and ARC Centre of Excellence grants), and funds provided to me by the James Cook University Graduate Research Scheme and the Great Barrier Reef Foundation. During the course of my degree, I was supported by a James Cook University International Postgraduate Research Scholarship. The thesis was conducted under the supervision of David Bellwood and all of its chapters have been completed in collaboration with him. For Chapter 6, William Robbins provided additional data and editorial assistance. For Chapter 7, Andrew Hoey gave conceptual advice and provided editorial assistance. Detailed contributions of all authors to each chapter are found below: Chapter 2: • Simon Brandl: concept of study, data collection, writing of manuscript • David Bellwood: concept of study, writing of manuscript Chapter 3: • Simon Brandl: concept of study, data collection, data analysis, writing of manuscript • David Bellwood: concept of study, writing of manuscript Chapter 4: • Simon Brandl: concept of study, data collection, data analysis, writing of manuscript • David Bellwood: concept of study, writing of manuscript Chapter 5: • Simon Brandl: concept of study, data collection, data analysis, writing of manuscript • David Bellwood: concept of study, writing of manuscript Chapter 6: iv • Simon Brandl: concept of study, data collection, data analysis, writing of manuscript • William Robbins: data collection, writing of manuscript • David Bellwood: concept of study, writing of manuscript Chapter 7: • Simon Brandl: concept of study, data collection, data analysis, writing of manuscript • Andrew Hoey: writing of manuscript • David Bellwood: concept of study, writing of manuscript Chapter 8: • Simon Brandl: concept of study, data collection, data analysis, writing of manuscript • David Bellwood: concept of study, writing of manuscript All work reported in this thesis was carried out under Great Barrier Reef Marine Park Authorization Permits No. G12/34955 and No. G14/36625.1 and JCU Ethics Approvals No. A503, A504, A1641, A1700, and A2086. v Abstract Ecological niche theory predicts that the diversity of life hinges on differences in the ways in which species exploit available resources, i.e. their ecological niche. An organism’s niche can be divided into the fundamental and the realized niche. The fundamental niche refers to a species’ inherent potential capabilities (based on, for instance, its morphology), while the realized niche represents a species’ behaviour when it can interact with the biotic and abiotic components of its environment. Tropical coral reefs stand out as one of the most diverse ecosystems on Earth, but patterns of niche partitioning among coral reef organisms are poorly understood. Herbivorous coral reef fishes are frequently considered to perform one of the most critical ecosystem processes on coral reefs, the removal of algal and detrital material from the reef substratum. However, while several classification schemes have previously been employed to characterize the functional role of different herbivores, detailed holistic investigations of niche differences among herbivore species are rare. Therefore, in this thesis, I use social, morphological, behavioural, and environmental factors to disentangle the functional niches of herbivorous fishes on coral reefs. One of the most prominent social systems in animals is the association between two individuals, commonly termed a ‘pair’. However, given that sexual reproduction in higher animals commonly requires the association between two partners, reproductive connotations frequently override the social-ecological benefits that a partner can provide and thus, the potential effects of pairing on an animal’s functional niche. In teleost fishes, pairing is common but little is known about the potential drivers and consequences of this behaviour. My first objective, therefore, was to quantify the extent of pair-formation in coral reef fishes and to examine potential ecological/reproductive correlates of pair-formation. Of a total of 1,981 species of Indo-Pacific reef fishes, 341 (17.2%) are reported to form pairs, with pair- forming species being particularly common (more than 50% of species) in five families. Pair- vi forming species had few commonalities with regards to their reproductive strategies. Instead, two ecological traits appear to be prevalent in pairing species: 1) the consumption of small, benthic, and relatively immobile prey items, and 2) the maintenance of permanent burrows. Based on these results, I conclude that pairing may have important ecological benefits in coral reef fishes. To further explore this hypothesis, I performed an ecomorphological assessment of pair-forming fishes, evaluating whether pairing fishes are also morphologically similar. Using a suite of six morphological traits, predominantly describing the cranial region and overall body shape of reef fishes, I demonstrate that morphology can accurately predict the prevalence of pairing behaviour in 47 species of benthos-feeding, reef fishes and that there is a strong relationship between morphology and pairing behaviour in three common families of reef fishes, the Acanthuridae, Chaetodontidae, and Siganidae. Basically, pair-forming fishes are characterized by concave foreheads, pointed snouts, deep bodies, and large eyes, attributes that relate to the feeding on small prey in topographically complex environments. I then sought to examine specific benefits of pair-forming