Resource Overlap Within a Guild of Browsing Ungulates Inasouth African Savanna

RESOURCE OVERLAP WITHIN A GUILD OF BROWSING UNGULATES INASOUTH AFRICAN SAVANNA by Lorene Breebaart submitted in partial fulfilment ofthe requirements for the degree of MASTER OF SCIENCE In Range and Forage Resources School ofApplied Environmental Sciences Faculty ofScience and Agriculture University ofNatal PIETERMARITZBURG December 2000 11 ABSTRACT Food selection by free-ranging black rhinoceros, eland, giraffe and kudu as well as the utilisation ofvegetation types by the latter three browsers were investigated over an entire seasonal cycle, from June 1998 to July 1999, at Weenen Nature Reserve, KwaZulu-Natal. The study was aimed at determining the extent ofresource overlap within this browser guild. Feeding habits ofeland, giraffe and kudu were studied by direct observations, while a plant-based technique was used for black rhinoceros. Dung counts were conducted to monitor selection for vegetation types. Overlap was estimated by measuring the similarities in resource utilisation patterns. Giraffe were exclusively browsers, feeding mostly on woody foliage, over the complete seasonal cycle. The bulk ofthe annual diet ofkudu also consisted ofwoody browse, although forbs were important and their use increased from early summer to winter. The annual diet of eland consisted ofapproximately equal proportions ofgrass and browse, with pods making up almost a third ofthe diet. Similar to kudu, forbs were more prominent in the winter diet, while grass use decreased. During winter, overlap in forage types generally increased and was considerable because the browsers did not resort to distinct forage 'refuges'. Overlap in the utilisation of woody plant species, however, decreased as animals diversified their diets. Nonetheless, overlap was extensive, primarily owing to the mutual utilisation ofAcacia karroa and Acacia nilatica. The quantity ofwoody foliage decreased during winter, as indicated by phenological differences, but numerous individual plants still carried leaves. Based on current evidence, food quality was assumed to decline. Under prevailing conditions, eland, giraffe and black rhinoceros suffered no mortalities indicating that they were not food limited, possibly owing to the nutritional advantages conferred by their large body size, and that competition among them was unlikely. By comparison, kudu mortalities were great which may signify that they were constrained by food supply and that the larger browsers exerted a pronounced competitive effect on them. Based on the current study it is hypothesised that during periods of resource scarcity the abundance ofhigh quality foods are limited and ifinterspecific competition does prevail, which will further limit the availability ofthese resources, it is the smaller bodied herbivores that will be most affected and suffer the greatest mortalities. Consequences ofcompetitive interactions among these browsers have important management implications, especially in small reserves, which are a key stone for the conservation ofmammalian herbivores. 111 DECLARATION I, Lorene Breebaart, declare that the research reported in this thesis is the result of my own investigations, except where acknowledged. It has not, in its entirety or in part, been submitted previously for any degree or examination at any other university. 8th day ofDecember 2000 IV ACKNOWLEDGMENTS I wish to extend my thanks and appreciation to the following people: Prof T. O'Connor, my supervisor, without whom this thesis would not have been possible and from whose knowledge and academic standard I benefitted greatly; Mr H. Dicks for assistance and advice with statistical analyses, with respect to selection for vegetation types; Mr C. Moris for assistance with the classification of vegetation types and his never ending kindness; KwaZulu-Natal Nature Conservation Service (KZNNCS) and Mr J. Llewellyn, Officer in Charge, Weenen Nature Reserve, in particular, for allowing me to work at Weenen Nature Reserve and providing me with accommodation and field assistance; Mr I. Rushworth of KZNNCS for assistance with locality and vegetation maps, and general encouragement; The ,field rangers ofWeenen Nature Reserve, especially Inok, for assisting me with my field work and insuring my safety; Xolani and Chonco ofWeenen Nature Reserve for their friendship; Mrs M. Goddard for secretarial assistance and Mr J. Naiken for logistic assistance; The National Research Foundation for financial support; Friends, especially Carol, and family for continuous support and encouragement; and lastly, Leon who was always there for me. v TABLE OF CONTENTS INTRODUCTION 1 INTRODUCTION 2 AIM AND OBJECTIVES 5 LITERATURE REVIEW 8 INTRODUCTION 9 DIET COMPOSITION 9 ASSESSING DIET COMPOSITION 9 Faecal and Ingesta Analysis 9 Animal-based Methods 11 Plant-based Methods 12 QUANTIFYING DIET COMPOSITION 13 Frequency ofUtilisation 14 Feeding Time 14 Enumeration ofBites 15 Amount or Volume ofBrowse 15 Difference Techniques 16 Post-browse Techniques 16 Bite Size and Intake Rate 18 FOOD PREFERENCES 21 ASSESSING FOOD AVAILABILITY 22 FOOD PREFERENCE INDICES 24 HABITAT UTILISATION 28 ASSESSING THE UTILISATION OF HABITATS 28 HABITAT PREFERENCE INDICES 30 RESOURCE OVERLAP AND PARTITIONING 31 MEASURES OF OVERLAP OR SIMILARITY 32 MEASURES OF RESOURCE PARTITIONING 33 RESOURCE PARTITIONING, OVERLAP AND COMPETITION 34 ECOLOGICAL SEPARATION 35 VI BROWSERS AT WEENEN 37 KUDU 38 GTIRAFFE 38 ELA~ 39 BLACK RHINOCEROS 40 OVERLAP IN RESOURCE USE BETWEEN BROWSER PAffiS 41 Kudu and Eland 41 Kudu and Giraffe 41 Kudu and Black Rhinoceros 42 I, Eland and Black Rhinoceros 42 Giraffe and Black Rhinoceros 43 Giraffe and Eland 43 STUDY AREA 44 INTRODUCTION 45 LOCATION AND SIZE 45 TOPOGRAPHY AND GEOLOGY 45 CLIMATE 47 FAUNA 50 VEGETATION 53 INTRODUCTION 53 VEGETATION SAMPLING 53 VEGETATION CLASSIFICATION 54 VEGETATION DESCRIPTION 54 Thornveld 54 Open Woodland 57 Riverine Thornveld 57 Mixed Veld 57 Bushveld 58 Valley Bushveld 58 FEEDING PATTERNS 60 INTRODUCTION 61 DIET COMPOSITION 61 vu SPECIES RICHNESS AND DIETARY DIVERSITY 62 DIETARY PREFERENCES 62 RESOURCE OVERLAP 63 ECOLOGICAL SEPARATION 64 METHODOLOGY - DATA COLLECTION 65 DIET COMPOSITION 65 Black Rhinoceros 66 Other Browsers 67 AVAILABLE BROWSE 69 Black Rhinoceros 69 Other Browsers 70 METHODOLOGY - DATA ANALYSIS 71 PHENOLOGY OF AVAILABLE WOODY PLANT SPECIES 71 DIET COMPOSITION 71 SPECIES RICHNESS, DIETARY DIVERSITY AND EVENNESS 73 FEEDING HEIGHT 75 DIETARY OVERLAP 76 Diet Composition Overlap 76 Feeding Height Overlap 76 Total Dietary Overlap 77 DIETARY PREFERENCES 77 Food Preferences 77 Feeding Height Preferences 79 RESOURCE PARTITIONING 79 RESULTS 79 PHENOWGY OF AVAILABLE WOODY PLANT SPECIES 79 Fruit and Flowers 80 Leaves 81 DIET COMPOSITION 94 Forage Types 94 Woody Plant Species 96 Kudu 98 Eland 102 Giraffe 104 Vlll Black Rhinoceros 106 SPECIES RICHNESS, DIETARY DIVERSITY AND EVENNESS 109 Forage Types 109 Woody Plant Species 110 FEEDING HEIGHT 113 Forage Types 113 Woody Plant Species 116 DIETARY OVERLAP 120 Diet Composition Overlap 120 Forage Types 120 Woody Plant Species 122 Feeding Height Overlap 122 Forage Types 122 Woody Plant Species 123 Total Dietary Overlap 125 Forage Types 125 Woody Plant Species 125 DIETARY PREFERENCES 128 Food Preferences 128 Kudu 129 Eland 135 Giraffe 136 Black Rhinoceros 140 Feeding Height Preferences 145 RESOURCE PARTITIONING 148 Diet Composition Similarities 148 Feeding Height Similarities 148 Total Dietary Similarities 150 DISCUSSION 151 DIET COMPOSmON 151 Forage Types 151 Woody Plant Species 156 IX THE GUILD AND INTERSPECIFIC COMPETITION 160 Dietary Diversity and Overlap 160 Overlap Avoidance or Reduction 161 Food Limitation 163 SELECTION FOR VEGETATION TYPES 165 IN1RODUCTION 166 METHODOLOGY - DATA COLLECTION 167 METHODOLOGY - DATA ANALYSIS 169 UTILISATION OF VEGETATION TYPES 169 ASSOCIATION 170 RESULTS 170 UTILISATION OF VEGETATION TYPES 171 Kudu 171 Eland 173 Giraffe 175 ASSOCIATION 177 DISCUSSION 179 UTILISATION OF VEGETATION TYPES 179 ASSOCIATION 181 CONCLUSION 183 LIMITATIONS OF STUDY 184 INTERSPECIFIC COMPETITION 184 RESOURCE PARTITIONING 187 MANAGEMENT RECOMMENDATIONS 187 REFERENCES 189 APPENDICES 206 1. Revised names ofthe six vegetation types ofWeenen Nature Reserve, as in publication to be submitted 206 x 2. An indication ofthe independence offeeding events for each animal species per season considering (a) one event per observation and (b) successive individuals ofdifferent plant species as a percentage (%) ofthe total number offeeding events 206 3. Annual and seasonal overlap in diets, considering all forage types, between species pairs as calculated by Pianka's overlap index 207 4. Annual and seasonal overlap in diets, in terms ofwoody plant species, between species pairs as calculated by Pianka's overlap index 207 5. Annual and seasonal overlap in feeding heights, considering all forage types, between species pairs as calculated by Pianka's overlap index 207 6. Annual and seasonal overlap in feeding heights, in terms ofwoody plant species, between species pairs as calculated by Pianka's overlap index 208 7. Annual and seasonal total dietary overlap, as a product ofdiet composition and feeding height based on the utilisation ofall forage types, between species pairs as calculated by Pianka's overlap index 208 8. Annual and seasonal total dietary overlap, as a product ofdiet composition and browsing height based on the utilisation ofwoody plant species, between species pairs as calculated by Pianka's overlap index 208 9. Logistic regression output for kudu 209 10. Logistic regression output for

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