Habitat Partitioning, and an Assessment of Habitat Suitability Using Presence Data, of a Large Herbivore Community on a Zimbabwean Private Wildlife Reserve
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Habitat partitioning, and an assessment of habitat suitability using presence data, of a large herbivore community on a Zimbabwean private wildlife reserve. Lochran Traill Thesis presented in partial fulfilment of the requirements for the degree of Master of Forestry at the University of Stellenbosch Promoter: Professor R.C. Bigalke March 2003 i Declaration I, the undersigned, hereby declare that the work contained in this thesis is my own original work and that I have not previously in its entirety or in part submitted it to any University for a degree. …….…..……………………………. 01/05/2003 Lochran Traill ii Abstract The factors determining habitat selection of large herbivores, on a private wildlife reserve in semi-arid southeastern Zimbabwe, were investigated. Gross vegetative structure, herbaceous composition and topographic features thought to determine herbivore distribution were measured. Seasonal variation in resource distribution was considered, and research therefore extended over an entire year. Herbivore distribution and ecological niche separation was explained through several important environmental variables, and potential for inter-specific competition inferred. Additionally, predictive habitat suitability models were designed for each of the grazing species in the critical dry season. Herbivores showed a large degree of niche overlap in both the hot- wet season and the cool-dry season, when food resources were more plentiful. Niche separation between grazers was pronounced in the hot-dry season. Herbivore distribution was associated most closely with distance to water, grass sward height, time since burn, woody plant density and by the presence of predominant grasses, these being Urochloa mossambicensis, Panicum maximum, Heteropogon contortus and Digitaria eriantha. Ecological separation of herbivores by the grasses P. maximum, H. contortus and D. eriantha was more indicative of associated environmental variables than feeding niche separation. A GIS-based analysis, using species presence data and quantitative coverages of environmental variables, produced maps of gradations of habitat suitability for grazing species during the dry season. Results of both analyses were integrated and gave a better understanding of ecological separation, and possible competitive interactions, among the large herbivore community on Malilangwe Estate. Recommendations were made based on the interpretation of findings, within the context of available management options. iii Opsomming Die bepalende faktore van habitat seleksie by groot herbivore op ‘n privaat wildreservaat in semi-dorre suidoos Zimbabwe is ondersoek. Globale plantegroei stuktuur, kruidagtige samestelling en topografiese eienskappe wat glo herbivoor verspreiding bepaal, is gemeet. Seisoenale variasie in hulpbronverspreiding is in ag geneem en dus het navorsing oor ‘n hele jaar gestrek. Herbivoor verspreiding en ekologiese nisskeiding is verduidelik deur verskeie belangrike omgewingsveranderlikes en die potensiaal vir interspesifieke kompetisie is afgelei. Boonop is voorspellende habitat-geskiktheidsmodelle ontwerp vir elk van die weidingspesies in die krities droë seisoen. Herbivore toon ‘n hoë graad van nis oorvleueling in sowel die warm, nat seisoen as die koel, droë seisoen wanneer voedingsbronne meer volop is. Nis verdeling tussen weidiere was duidelik herkenbaar in die warm, droë seisoen. Herbivoor verspreiding is meestal geassosieer met die afstand na die water, die grasveld hoogte, tydperk sedert ‘n brand, digtheid van houtagtige plantsoorte en met die teenwoordigheid van die oorheersende grasse, Urochloa mossambicensis, Panicum maximum, Heteropogon contortus en Digitaria eriantha. Die ekologiese skeiding van herbivore deur die grasse P. maximum, H. contortus en D. eriantha het meer gedui op geassosieerde omgewingsveranderlikes as op skeiding van voedingsnisse. ‘n GIS-gebaseerde analise wat spesie-teenwoordigheidsdata en kwantitatiewe dekking van omgewingsveranderlikes gebruik, het klassifikasiekaarte geproduseer van habitatgeskiktheid vir weidiere tydens die droë seisoen. Resultate van beide analises is geïntegreer en het ‘n beter begrip van ekologiese skeiding en moontlike kompeterende interaksies tussen die groot herbivore gemeenskap op Malilangwe Estate tot gevolg gehad. Aanbevelings is gemaak, gebaseer op die interpretasie van bevindinge, binne die konteks van beskikbare bestuursopsies. iv Acknowledgements I am indebted to all those that have guided me through this study. I owe the profound personal growth that I’ve experienced to these people: The late Professor Rudi Bigalke and Professor David Ward: who were always patient, helpful and particularly, constructively critical. Dr Pete Goodman and Bruce and Sarah Clegg: for their invaluable assistance and guidance. These three individuals were my greatest source of inspiration through this project. Paul Tudor Jones, who through his great generosity made this entire project possible. Derek de la Harpe who not only believed in me, but who at all times treated me as a mature and self-reliant individual, thus making my field work a pleasure. Colin Wenham who also allowed me to ‘get on with the job’ and was the greatest fitness partner I ever had, and will have. Gavin Young for vehicle and logistical support and particularly, Sue Young who acted as a trusted confidant during some trying times. The research technicians: Julius Shimbani, Cryson Chinondo and Pandeni Chitimele for the hours of commitment put into challenging and oftentimes tedious field work. These technicians were not only closely trusted guides in potentially dangerous situations, but simply the best companions I could have asked for in the bush. Lastly, my mother who gave me the complete and unfailing support that only mothers are capable of. This thesis is dedicated to the late Professor R. C. Bigalke. v Contents Declaration................................................................................................ ii Abstract................................................................................................... iii Opsomming.............................................................................................. iv Acknowledgements..................................................................................... v Contents .................................................................................................. vi Figures ..................................................................................................... x Tables .....................................................................................................xii CHAPTER 1: INTRODUCTION ....................................................................1 CHAPTER 2: THEORETICAL BACKGROUND ................................................4 2.1 Introduction ......................................................................................... 4 2.2 Habitat selection and ecological separation ............................................... 4 2.3 Competition ......................................................................................... 8 2.3.1 Intraspecific competition .............................................................................9 2.3.2 Interspecific competition ........................................................................... 10 2.3.2.1 Niche ............................................................................................ 13 2.3.3 Facilitation. ............................................................................................. 15 2.4 Adaptive management......................................................................... 15 2.4.1 Water provision........................................................................................ 16 2.4.2 Veld burning............................................................................................ 19 2.4.3 Harvesting .............................................................................................. 21 2.5 Summary of review............................................................................. 24 CHAPTER 3: STUDY AREA .......................................................................25 3.1 Location ............................................................................................ 25 3.2 History .............................................................................................. 26 3.3 Climate ............................................................................................. 27 3.4 Geology and soils................................................................................ 29 3.5 Vegetation communities ...................................................................... 31 3.6 Fire regime ........................................................................................ 36 3.7 Surface water provision ....................................................................... 38 3.8 Herbivore populations.......................................................................... 42 CHAPTER 4: HERBIVORE/HABITAT RELATIONSHIPS..............................45 4.1 Introduction ....................................................................................... 45 4.2 Methods ............................................................................................ 46 vi 4.2.1 Study design and data collection ................................................................ 48 4.2.1.1 Statement of problem ..................................................................... 48 4.2.1.2