Key Factors Driving the Foraging Ecology of Oribi: Fear, Cattle and the Quality and Quantity of Food
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KEY FACTORS DRIVING THE FORAGING ECOLOGY OF ORIBI: FEAR, CATTLE AND THE QUALITY AND QUANTITY OF FOOD Keenan Stears Submitted in fulfilment of the academic requirements for the degree of Doctor of Philosophy In the Discipline of Ecology School of Life Sciences College of Agriculture, Engineering, and Science University of KwaZulu-Natal Pietermaritzburg, South Africa As the candidate’s supervisor, I have approved this thesis for submission. Supervisor: Dr. Adrian M. Shrader Signed: _ __ Name: ____ Date: _____________ March 2015 ii ABSTRACT Body size and digestive physiology are two factors that influence herbivores foraging behaviour, habitat use and potential to compete with other animals. The aim of this study was to determine how seasonal changes in grass quality, interactions with cattle, and perceived predation risk influenced oribi (Ourebia ourebi) foraging and landscape use. Oribi are one of the smallest pure grazing ruminants. As a result, they should select high quality vegetation. In line with this, I found that throughout the study oribi fed selectively over multiple spatial scales ranging from plant parts to habitats. By focussing on green grass within these different scales, oribi were able to maintain their crude protein intake needed for maintenance. Throughout South Africa, oribi frequently interact with cattle. Due to their differences in body size and nutritional requirements, there should be sufficient resource partitioning to avoid competition. However, I found that the nature of the interspecific interactions (i.e. competition or facilitation) between these species depended on season and cattle stocking rates. During the wet season, cattle facilitated oribi by providing high quality regrowth. However, at high stocking rates, cattle indirectly competed with oribi during the dry season via the impacts of their wet season grazing. Specifically, intense wet season grazing by cattle reduced the availability of high quality grass for oribi in the dry season. This was not the case at low and intermediate stocking rates. Differences in food availability and predation risk across habitats can influence how herbivores utilise landscapes. I found that predation risk greatly affected oribi foraging behaviour, with oribi preferring to feed in safer rather than riskier habitats. However, when food availability increased in these risky habitats, oribi increased their risk-taking behaviour at both small- and large-scales within these risky areas. Ultimately, this suggests that oribi trade-off between predation risk and food iii availability. Finally, to link my results to the management and conservation of this vulnerable antelope, I applied the knowledge I gained from the above research to a case study. iv Male oribi antelope (Ourebia ourebi) This project was funded by: v COLLEGE OF AGRICULTURE, ENGINEERING AND SCIENCE DECLARATION I, Keenan Stears, declare that (i) The research reported in this dissertation/thesis, except where otherwise indicated, is my original research (ii) This dissertation/thesis has not been submitted for any degree or examination at any other university (iii) This dissertation/thesis does not contain other persons’ data, pictures, graphs or other information, unless specifically acknowledged as being sourced from other persons. (iv) This dissertation/thesis does not contain other peoples’ writing, unless specifically acknowledged as being sourced from other researchers. Where other written sources have been quoted, then: a) Their words have been re-written but the general information attributed to them has been referenced; b) Where their exact words have been used, their writing has been placed inside quotation marks and referenced. v) Where I have reproduced a publication of which I am author, co-author or editor, I have indicated in detail which part of the publication was actually written by myself alone and have fully referenced such publications. ……………………… Keenan Stears December 2014 vi PREFACE The work described in this thesis was carried out at the School of Life Sciences, University of KwaZulu-Natal, Pietermaritzburg, South Africa, from January 2012 to December 2014, under the supervision of Dr. Adrian Morgan Shrader. This thesis, submitted for the degree of Doctor of Philosophy in the College of Agriculture, Engineering and Science, University of KwaZulu-Natal, Pietermaritzburg, represents original work by the authors and has not been submitted in any form to another university. Where use of other work was made, it has been acknowledged in the document All work was approved by the University of KwaZulu-Natal’s Animal Ethics Committee and permits were obtained from Ezemvelo KZN-Wildlife for working in protected areas. ___________________ Keenan Stears Student ___________________ Dr Adrian M. Shrader Supervisor vii ACKNOWLEDGEMENTS I am grateful to my supervisor, Dr Adrian Shrader, who approached me towards the end of my Master’s Degree with a potential PhD project working on oribi. At the time, not much research had been done on oribi, so we started putting together a few ideas that eventually led to this project. From the beginning Adrian always said that this would not be an easy project because of the difficulties in gathering field observations from such a small antelope. It was probably this warning that always pushed me to do whatever was needed to get the data. I refused to come back from the field and say “it’s too difficult to collect data”. So, thank you for those words that fortified me throughout this project. Without your valuable contributions, continued support and encouragement this project would not be what it is today. This research would not have been possible without the funding provided by the Rufford Small Grant Foundation. Although the grants you offer are considered “small,” it funded this entire project and will make a huge contribution to oribi conservation. Additional funding was also provided by the University of KwaZulu-Natal and the Gay Langmuir Scholarship. A key aspect of using giving up densities as a measure of patch use in relation to predation risk is to know what animal is feeding from your food patches. I would like to thank Idea Wild for providing six trail cameras to ensure I was measuring the giving up density of oribi and not a grey duiker. Throughout the last three years I have interacted with the Oribi Working Group, who are determined to help with conservation of oribi. Many of the ideas that are included in this research started as discussions in this group. My first challenge was to find suitable field sites to conduct my research. Without the Oribi Working Group I would not have known where to start. Thank you to the following members Dr. Athol viii Marchant, Dr. Iain Little, Brent Coverdale, Mo Lister, Cliff Walton and the rest of the group for all your help. The majority of my field work was done at Chelmsford Dam. I would like to thank Ezemvelo KZN Wildlife, especially Kim Zungu and Nokwazi Nzimande for providing me with accommodation during the eight months that I was there. I would also like to thank Petros Ngwenya for providing me with the animal count numbers for Chelmsford Dam. The rest of my field work would not have been possible without the hospitality of Hugh Humphries, who allowed me to work on his farm and provided accommodation. I thoroughly enjoyed staying on your property as well as the chats we had about the oribi on your property. Those oribi are in good hands. I would like to give a big thank you to Ian and Gwen Watson for providing me with accommodation while I was in Fort Nottingham. Gwen, those home cooked meals were a life saver after walking many kilometres of transects during the day. A special thanks to Roy Tabernor, the Chairman of the Lions Bush Conservancy, for showing such interest in my research at Fort Nottingham and for always making time for a trip to the commonage to share everything you know about the oribi up there. I would also like to thank my two field vehicles The Satisfaction and The Red Dragon for safely transporting me to and from my field sites with no hassles at all. Without these vehicles I would not have been able to collect my data for this project. A major component of my research was to determine the nutritional quality of hundreds of grass samples that I collected. A special thank you to Dr. Virginie Decruyenaere from the Wallon Agricultural Research Centre in Belgium who interpreted the NIRS output spectra to determine the nutritional values of each sample. This saved me a huge amount of time. I would also like to thank Richard Burgdorff who ix showed me how to use the University of KwaZulu-Natal’s NIRS machine. I would also like to thank Gareth Boothway for his help making the GIS maps. To my fellow lab/office mates Melissa Schmitt, Tamanna Patel, Steph Lyle, Mark Summers, David and Courtney Marneweck thank you for all the discussion about statistics, rugby and the many beers we had after long days in the office. You guys really made the long days of entering data a lot better. I am sure a few names have slipped through the cracks and have not been mentioned, but a huge thank you to my family mom, dad, Bren, Robyn, Russ, Sally and my wife, Melissa. The endless support and many hours of discussions about work and the field trips you took to come and see my oribi have made this work possible. Melissa, thank you for holding my hand and supporting me through this crazy journey, which has consisted of two years of field work, many hours of screaming at my stats program and the late nights of writing. The strong G&Ts that you ensured were poured at the end of the day made everything better. x TABLE OF CONTENTS ABSTRACT ..................................................................................................................... ii DECLARATION: ............................................................................................................. v PREFACE .......................................................................................................................