The Role of Waterbirds in the Dispersal of Aquatic
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THE ROLE OF WATERBIRDS IN THE DISPERSAL OF AQUATIC ORGANISMS IN SOUTHERN AFRICA Chevonne Reynolds Supervisor: Professor Graeme S. Cumming University of Cape Town The Percy FitzPatrick Institute of African Ornithology Department of Biological Sciences University of Cape Town Thesis presented for the degree of Doctor of Philosophy May 2016 The copyright of this thesis vests in the author. No quotation from it or information derived from it is to be published without full acknowledgement of the source. The thesis is to be used for private study or non- commercial research purposes only. Published by the University of Cape Town (UCT) in terms of the non-exclusive license granted to UCT by the author. University of Cape Town The copyright of this thesis vests in the author. No quotation from it or information derived from it is to be published without full acknowledgement of the source. The thesis is to be used for private study or non-commercial research purposes only. Published by the University of Cape Town (UCT) in terms of the non-exclusive license granted to UCT by the author. This thesis should be cited as: Reynolds C. (2016) The role of waterbirds in the dispersal of aquatic organisms in southern Africa. PhD thesis. University of Cape Town, South Africa. ii “I think it would be an inexplicable circumstance if water-birds did not transport the seeds of freshwater plants to unstocked ponds and streams, situated at very distant points. The same agency may have come into play with the eggs of some of the smaller fresh-water animals” Charles Darwin, 1859 iii DECLARATION I, Chevonne Reynolds, hereby declare that the work on which this thesis is based is my original work (except where acknowledgements indicate otherwise) and that neither the whole work nor any part of it has been, is being, or is to be submitted for another degree in this or any other university. I authorise the University to reproduce for the purpose of research either the whole or any portion of the contents in any manner whatsoever. In accordance with the guidelines outlined by the Doctoral Degrees Board, this thesis is does not exceed 80 000 words. Signature: ___ _________ Date: _________03/05/2016____________ iv PLAGIARISM DECLARATION 1. I know that plagiarism is a serious form of academic dishonesty. 2. I have read the document about avoiding plagiarism, am familiar with its contents and have avoided all forms of plagiarism mentioned there. 3. Where I have used the words of others, I have indicated this by the use of quotation marks. 4. I have referenced all quotations and properly acknowledged other ideas borrowed from others. 5. I have not and shall not allow others to plagiarise my work. 6. I declare that this is my own work. 7. I am attaching the summary of the Turnitin match overview (when required to do so). Signature: v ABSTRACT Dispersal is a fundamental process with far-reaching ecological and evolutionary consequences. Not all organisms are capable of dispersing on their own and instead produce propagules that must be transported to new habitat by a vector. Propagule dispersal by frugivorous bird species is well researched, but only very recently has the capacity of highly mobile waterbirds to disperse aquatic organisms received similar attention in the dispersal literature. Dispersal is important for the organisation of communities, and therefore understanding the frequency and scale of waterbird-mediated dispersal provides insight into the structure of wetland communities. Additionally, the study of waterbird-mediated dispersal in arid southern Africa provides an opportunity to expand our knowledge on the persistence of populations of aquatic organisms in heterogeneous environments. Recently, field and laboratory studies have demonstrated the remarkable ability of waterbirds to disperse the propagules of both plants and aquatic invertebrates. However, these studies have largely been based in the northern hemisphere and many have focussed on long-distance dispersal by migratory waterbirds. Therefore, it is difficult to generalise how waterbird-mediated dispersal plays out in different landscapes and throughout the annual cycle. Furthermore, there is still little knowledge of the spatial patterns of propagule dispersal and the mechanisms that cause these patterns to vary in space and over time. This thesis aims to addresses several of these knowledge gaps in waterbird-mediated dispersal and presents the first detailed study of propagule dispersal by waterbirds anywhere in Africa. In Chapters 2 – 5, I adopt a field- and experimental-based approach to develop a general understanding of waterbird-mediated dispersal in southern Africa. Firstly, making use of faecal samples and feather brushings collected from several waterfowl (duck) species at three locations in South Africa, I determine the quantity and viability of propagules transported via endozoochory and ectozoochory. I then assess the relative contributions of each dispersal mode to the dispersal of plants and aquatic invertebrates in the field. I show that endozoochory is the dominant dispersal mechanism, but it may be complementary to ectozoochory as different propagules are transported via this mode. Secondly, by making use of an experimental feeding trial with two captive waterfowl species, Egyptian Goose and Red-billed Teal, I explore how seed traits mediate a trade-off in recoverability and germinability against gut retention times. I show that small, hard-seeded species are retained vi for longer and therefore may be dispersed further. Thirdly, I incorporate gut retention time data and Egyptian Goose and Red-billed Teal movement data, acquired from GPS satellite transmitters across five study populations in southern Africa, into a mechanistic model to explore spatial patterns of seed dispersal. The model demonstrates that waterfowl generally facilitate dispersal on the local scale of below 5 km, but on occasion can transport seeds as far as 500 km from a seed source. There was variation in dispersal distances between the vectors and across the study populations and the results indicate that dispersal is affected by both intrinsic and extrinsic drivers of animal movement. In Chapters 6 and 7, I apply the concept of waterbird-mediated dispersal more broadly to address (1) the role of waterbirds in the dispersal of aquatic invaders; and (2) the determination of seed dispersal functional groups amongst a waterfowl community. I conducted a literature review to objectively describe the role of waterbirds in the dispersal of aquatic weeds. Waterbirds are important vectors of aquatic invasive species and consideration of the spatially explicit manner in which birds move is imperative to our understanding of invasive spread. In the second case, I used diet data from the 16 waterfowl species indigenous to southern Africa to explore whether finer level seed dispersal functional groups were evident. I found support for several functional groups of seed disperser based on unique plant families in the diet and suggest that important functional differences do occur between groups of waterfowl species. The results of this thesis have shown that waterbirds in the region take up a variety of different propagules, including exotic and terrestrial propagule species, move them over multiple spatial scales and are capable of depositing good numbers of viable propagules in suitable habitat. Furthermore, dispersal is a complicated interaction between the disperser and the vector, and I have shown that both differences in propagule characteristics and vector traits affect spatial patterns of dispersal. I conclude that despite their apparent isolation, important ecological connections exist between wetlands. Waterbirds play an important role in connecting wetlands through dispersal and in doing so influence aquatic community organisation and provide a means of recolonisation in ephemeral habitats. Waterbird- mediated dispersal is thus a significant and perhaps poorly considered mechanism of resilience in aquatic ecosystems. vii ACKNOWLEDGEMENTS Firstly, I would like to thank my supervisor Prof. Graeme Cumming for the amazing opportunity of undertaking a PhD at the Fitz and for supporting my research over the past three years. I am very grateful for all your hard work, the hours spent correcting drafts and for the stimulating ideas and chats. Working with you has been a privilege, and I have learnt an incredible amount and been thoroughly challenged. I look forward to our future projects! A big thank you to the Fitz family! I could not have imagined a better place to spend three years and I have been so spoilt by having such amazing colleagues. To the Fitz support staff – you guys are the absolute kindest, most efficient, patient and awesome bunch. Hilary Buchanan, you are everyone’s second mom and I must thank you for all the life chats and support during this time. Also, a big thank you for tackling UCT admin on my behalf and dealing with all my funding issues. Anthea Links, thank you for always finding a car for me even if I booked last minute. And thanks, to both you and Chris Tobler, for not giving me too many hassles when the cars came back with some dents. Anthea, you are a wonderful, kind person and I am glad that there is still one familiar face in the admin offices! Tania Jansen, the office is a lot quieter now that you are over in the maths department, but since you left morning coffee breaks don’t have their same appeal. Thanks so much for dealing with all the admin over the last three years; it was such a breeze with your guidance. Chris Tobler, a big thank you for being so patient with me and helping me get through the field work, I know that every time I drove off in one of the Fitz cars you cringed a little. Dr. Rob Little, thanks for your continued support of me, and for solid advice when needed. To Margaret Koopman, your absence at the Fitz is felt, but I am happy you are doing so well at SAEON.