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Matthew C. Stevens Phd Thesis View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by St Andrews Research Repository LIFE HISTORY TRADE-OFFS BETWEEN SURVIVAL, MOULT AND BREEDING IN A TROPICAL SEASON ENVIRONMENT Matthew C. Stevens A Thesis Submitted for the Degree of PhD at the University of St. Andrews 2011 Full metadata for this item is available in Research@StAndrews:FullText at: http://research-repository.st-andrews.ac.uk/ Please use this identifier to cite or link to this item: http://hdl.handle.net/10023/1857 This item is protected by original copyright Life history trade-offs between survival, moult and breeding in a tropical season environment By Matthew C. Stevens Submitted for the degree of Doctor of Philosophy to the University of St Andrews Thesis Supervisor: February 2010 Dr Will Cresswell School of Biology University of St Andrews I, Matthew Stevens, hereby certify that this thesis, which is approximately 60,000 words in length, has been written by me, that it is the record of work carried out by me and that it has not been submitted in any previous application for a higher degree. Date 16 October 2010 signature of candidate I was admitted as a research student in February 2006 and as a candidate for the degree of Doctor of Philosophy in February 2007; the higher study for which this is a record was carried out in the University of St Andrews between 2006 and 2010. Date 16 October 2010 signature of candidate I hereby certify that the candidate has fulfilled the conditions of the Resolution and Regulations appropriate for the degree of Doctor of Philosophy in the University of St Andrews and that the candidate is qualified to submit this thesis in application for that degree. Date 17/1/2011 signature of supervisor In submitting this thesis to the University of St Andrews we understand that we are giving permission for it to be made available for use in accordance with the regulations of the University Library for the time being in force, subject to any copyright vested in the work not being affected thereby. We also understand that the title and the abstract will be published, and that a copy of the work may be made and supplied to any bona fide library or research worker, that my thesis will be electronically accessible for personal or research use unless exempt by award of an embargo as requested below, and that the library has the right to migrate my thesis into new electronic forms as required to ensure continued access to the thesis. We have obtained any third-party copyright permissions that may be required in order to allow such access and migration, or have requested the appropriate embargo below. The following is an agreed request by candidate and supervisor regarding the electronic publication of this thesis: No embargo required : Access to printed copy and electronic publication of thesis through the University of St Andrews. Date 16 October 2010 signature of candidate Date 17/1/2011 signature of supervisor for Colin & Julie Abstract The trade-off between current and future investment in reproduction lies at the heart of life history theory. The need to differentially allocate resources between these two options arises generally as a result of environmental pressures. Higher risk of mortality in adults is linked with increased investment in current reproduction, whereas the opposite is true where adults are long-lived (the r- K selection paradigm). Perhaps the most obvious factors influencing the environment stem from seasonality of the climate, since rainfall and temperature affect food availability, resulting in a higher risk of mortality. The available trade-offs that an organism can make will therefore be constrained by environmental variability potentially resulting in general adaptation and so ultimately influencing evolution of biome-specific life-history traits. In this thesis, I examine how the seasonality of a West African tropical savannah environment influences moult and breeding timing and duration, and survival in West African tropical savannah bird species. I show that moult in tropical birds follows the same basic descendant pattern through the wing feathers, but is a much lengthier process than for temperate species (mean = 131 ± 11 days, N = 29 species), and that it frequently overlaps with breeding activities. This suggests either that either the feathers of tropical species take longer to grow; that it is a relatively low-cost activity and has little influence on life history trade-offs; or that individuals further aim to reduce mortality risk by attempting to maintain high flight capability at all times. Breeding also occurred over a longer season than for temperate species, although an obvious peak in occurrence was identified to coincide with the food-abundant period of the late rains and early dry season. Lengthy breeding seasons may indicate an increased tendency to renest (possibly as a result of higher nest predation levels), and we also identified a prolonged immature plumage phase – potentially indicating an extended duration of parental care. Survival rates were calculated from mark-recapture models based on mist-netting data. Previous work has focussed on the use of incorporating mark-resighting data alongside that obtained by standard mark-recapture techniques. Here, I assess the models applied in those methods, identify problems associated with over-paramaterisation, goodness of fit and the generation of biologically unrealistic estimates, and so provide suggestions on how to improve the protocol. Average survival from my study (40 species: 0.63 ± 0.02) was higher than previous estimates obtained from this site and were comparable with estimates from other Afrotropical and Neotropical areas, although rates varied greatly between species. Juvenile survival (13 species) was similar or possibly lower than adult survival. I then used my empirically derived estimates of moult, breeding and survival life history traits to identify potential trade-offs between traits. Overall I was unable to identify significant relationships between any of the life history trait estimates, other than between adult survival and clutch size. In this, the results followed those of previous researchers in identifying a pattern of lower investment in current reproduction (clutch size) and maximisation of adult survival in tropical species. My study, however, demonstrates for the first time how moult and breeding duration are likely to be less constrained in tropical environments. i Acknowledgements There have been innumerable people involved in inspiring, pushing, driving and dragging me to completion of this thesis and I apologise in advance if I omit any by accident. First of all though I owe a huge debt to my supervisor, Will Cresswell who gave me the opportunity in the first place, not just of undertaking this work, but also numerous other opportunities to see and work in different parts of Nigeria. Alongside his tireless help and encouragement he always managed to help me work out the things that I was struggling with, as well as providing lots of laughs – truly a zoologist one can trust. Tasso Leventis was extraordinarily generous in making this research possible and Phil Hall was incredibly helpful in organising everything in Nigeria. The staff of the A.P. Leventis Ornithological Research Institute in Nigeria, in particular Dr Georgina Mwansat, Prof. Gus Ezealor, Addams, Ellie, Rhoda, Gabriel, Azi and the field assistants John, Chris, Martha and the indefatigable Afan, made my time in Nigeria one of happiness and provided me with pretty much everything that I asked for. Alongside these, Mohammed kept the place going with his knowledge of generators and ‘fix-it’ skills, and Joseph, Esther and Rosemary kept me in unexpected African comfort. I owe Chris Otata Odey a huge debt for transporting me safely around the country. He really was the man in the know; expert with his Toyota Hi-Lux and capable of finding the road through the desert, bush and forest even when there really shouldn’t have been one. Dr Oskar Brattström kept me (mostly) sane in the forests of Cross River and, whilst at APLORI, it was Drs Peter Jones, Shiiwua Manu and Ulf Ottosson who were the friends and mentors who made life a laugh and taught me so much about West African life and birds. In the UK, my colleagues Miriam Brandt, Dan Cox, Mark Hulme, Alex Sansom and Mark Boyd helped me enormously. Above all though, the person who provided me with the impetus for seeing this through, who gave me most support, boundless love and continual encouragement was Karin. Much of this is down to her. Thank you. This studentship was funded by the Leventis Conservation Foundation ii Table of Contents Abstract ...........................................................................................................i Acknowledgements .......................................................................................ii Table of Contents...........................................................................................1 Chapter 1: General Introduction...................................................................6 Life history theory.............................................................................................6 Life history trade-offs .......................................................................................7 Influence of environment..................................................................................8 Avian life histories..........................................................................................10
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