THE POPULATION ECOLOGY AND ENERGETICS OF MACROTERMES BELLICOSUS ISMEATHMANY(ISOPTERA) by NICHOLAS MARK COLLINS B.A. A thesis submitted for the degree of Doctor of Philosophy of the University of London and for the Diploma of Imperial College. JUNE 1977 Dept. of Zoology and Applied Entomology, Imperial College Field Station, Silwood Park, Sunninghill, Ascot, Berkshire. 2 ABSTRACT This thesis is an enquiry into the ecology of a litter-feeding termite, Macrotermes bellicosus, which builds large mounds in the savanna zones of tropical Africa. The study was carried out in Southern Guinea savanna at Mokwa, Nigeria (9°18'N, 5°04'E). In the preliminary section the climatic, edaphic and vegetational features of the area are described. The second section is concerned with plant litter dynamics; esti- mates of litter production, accumulation and decomposition are given. Termites removed 60.1% of wood-fall and 2.9% of leaf-fall while fire destroyed 0.9% and 49.1% respectively. Of the 25.9% of total litter production removed by termites, 95.2% was taken by the Macrotermitinae, a group in which the faeces (fungus combs) are degraded by a symbiotic basidiomycete fungus, Termitomyces sp., prior to reingestion. The ability of the Macrotermitinae to feed on fresh litter is considered to be an important element in the high turnover rate of litter and distinguishes decomposition processes in savanna from the essentially fungal and microbial based patterns found in equatorial and temperate regions. The third section is concerned with the energetics of Macrotermes bellicosus. A new type of nest is described and colony populations and densities discussed. Data on colony growth, caste composition, biomass and survivorship are given. Field consumption measurements were checked using isolated colonies and faeces production was calculated from fungus comb biomass and turnover rate. Respiration rates were measured using Gilson respirometers and extrapolated to the field population. Produc- tion was calculated from alate production, larval populations and larval turnover rate. 3 It is concluded that the fungal symbiont Termitomyces sp. concen- trates nutrients in the combs by respiration of organic carbon. The heat evolved is used in maintaining an optimal homoeostatic microclimate by the construction of a highly complex nest. The high quality diet permits a high termite production to biomass ratio, which renders the termite-fungus symbiosis an important link in the nutrient flux from plant litter to the consumer food chain. Note: A brief review of the quantitative data may be found in the summary. 4 FRONTISPIECE The above-ground portion of a nest of Macrotermes bellicosus, ,(Macrotermitinae : Isoptera). This exceptionally tall example was over 7 m high. The mound is hollow and constructed in such a way that it helps to maintain an optimal microclimate within the main nursery, which is below ground level. The size and complexity of these nests is largely the result of co-adaptation between the termites and their fungal nest symbiont, Termitomyces sp. .^ ^ 5 CONTENTS PAGE ABSTRACT 2 FRONTISPIECE 4 CONTENTS 5 LIST OF FIGURES 9 LIST OF TABLES 11 GENERAL INTRODUCTION 15 SECTION ONE: CLIMATIC, EDAPHIC AND VEGETATIONAL FEATURES, WITH AN INVENTORY OF TERMITE SPECIES AND A DESCRIPTION OF THE STUDY AREA. 18 1.1 CLIMATE 19 1.2 SOILS 22 1.3 VEGETATION 27 1.4 LAYOUT OF THE STUDY AREA 31 1.5 SPECIES OF TERMITES AND THEIR HABITS 35 1.5.1 Species found on the study area 35 1.5.2 Summary of the habits of each species 37 1.5.3 Discussion 40 SECTION TWO: LITTER DYNAMICS AND THE ROLE OF TERMITES IN LITTER DECOMPOSITION. 43 2.1 ANNUAL WOOD AND LEAF FALL 44 2.1.1 Methods 44 2.1.2 Results 45 2.1.2.1 Wood fall 45 2.1.2.2 Leaf fall 47 2.1.3 Discussion 53 2.1.3.1 Seasonal variation in litter fall 53 2.1.3.2 Litter production and latitude 55 2.1.3.3 Litter production and environmental factors 59 2.2 THE STANDING CROPS OF WOOD AND LEAF LITTER 61 2.2.1 Methods 61 2.2.1.1 Wood litter 61 2.2.1.2 Leaf litter 62 6 2.2.2 Results 63 2.2.2.1 Wood litter 63 2.2.2.2 Leaf litter 68 2.2.2.3 Calorific values 68 2.2.3 Discussion 71 2.2.3.1 Seasonal variation in standing crops 71 2.2.3.2 Standing crop, litter fall and calculated decomposition rates 71 2.2.3.3 Effects of annual bush fires on the termite community 72 2.3 DECOMPOSITION OF WOOD AND LEAVES WITH SPECIAL REFERENCE TO TERMITES 76 2.3.1 Introduction ' 76 2.3.2 Methods 77 2.3.2.1 Wood 77 2.3.2.2 Leaves 78 2.3.3 Results 78 2.3.3.1 Wood 78 2.3.3.2 Leaves 88 2.3.4 Discussion 92 2.4 CONSUMPTION BY WOOD-FEEDING TERMITES 94 2.4.1 Introduction 94 2.4.2 Methods 101 2.4.3 Results 103 2.4.3.1 Calculation of consumption by termites 103 2.4.3.2 Assessment of assumptions used in the baiting experiments 112 2.4.4 Discussion 122 2.4.4.1 Consumption estimates in relation to feeding habits 122 2.4.4.2 Seasonality of foraging 123 2.5 DISCUSSION AND CONCLUSIONS - 130 2.5.1 k-Values 130 2.5.2 Major determinants of the decomposition constant (k) 130 2.5.3 Termites and decomposition processes in Southern Guinea savanna 133 7 SECTION THREE: THE NEST STRUCTURE, POPULATIONS AND ENERGETICS OF MACROTERMES BELLICOSUS 137 3.1 THE NEST OF MACROTERMES BnLICOSUS 138 3.1.1 Introduction 138 3.1.2 Macrotermes bellicosus nests 141 3.1.2.1 M. bellicosus nest with a spiral base plate 141 3.1.2.2 M. bellicosus nest without a spiral base plate 146 3.1.3 Nest structure and microclimatic stability 149 3.2 POPULATIONS OF MACROTERMES BELLICOSUS 160 3.2.1 Introduction 160 3.2.2 Methods 161 3.2.3 Results and discussions 165 3.2.3.1 The abundance and distribution of M. bellicosus colonies 165 3.2.3.2 Mound size and colony age distribution for Macrotermes bellicosus 175 3.2.3.3 Populations of Macrotermes bellicosus colonies 187 3.2.3.4 Total population density of Macrotermes bellicosus 195 3.2.3.5 Caste composition in Macrotermes bellicosus colonies 200 3.2.3.6 Biomass of M. bellicosus castes, total biomass estimates for the colonies sampled and estimates of area-specific biomass 205 3.2.3.7 Food stores 211 3.2.3.8 Calorific values for individuals of each caste and estimates of calorific equivalents of populations 215 ' 3.2.4 Conclusions 218 3.3 CONSUMPTION STUDIES IN ISOLATION TANKS 225 3.3.1 Introduction 225 3.3.2 Methods 226 3.3.3 Results 227 3.3.4 Discussion 233 8 3.3.4.1 Isolation tanks consumption results 233 3.3.4.2 Synthesis of consumption data for Macrotermes bellicosus 233 3.4 FAECES PRODUCTION BY MACROTERMES BFILICOSUS: THE FUNGUS COMBS' 236 3.4.1 Introduction 236 3.4.2 Methods 238 3.4.3 Results 239 3.4.4 Discussion 243 3.5 RESPIROMETRY 250 3.5.1 Introduction 250 3.5.2 Methods 250 3.5.3 Results and discussion 251 3.5.3.1 The effect of temperature on respiratory rate 252 3.5.3.2 The effect of body weight on respiratory rate 253 3.5.3.3 Population respiration calculations and the relationship between fungus comb and termite respiration within colonies 262 3.6 PRODUCTION 267 3.6.1 Introduction 267 3.6.2 Methods 269 3.6.3 Results 269 3.6.4 Discussion 274 SECTION FOUR: SYNTHESIS 278 4.1 DISCUSSIONS 279 4.1.1 Energetic equations and assessment of experi- mental errors 279 4.1.2 Ecological efficiencies and a consideration of the role of the fungus combs 282 4.2 FINAL CONCLUSIONS 290 SUMMARY 293 ACKNOWLEDGEMENTS 298 APPENDIX FOR SECTION TWO 301 APPENDIX FOR SECTION THREE 305 REFERENCES 318 PLATES 335 9 LIST OF FIGURES PAGE Legends have been abbreviated in many cases. 1.1.1 Nigeria with vegetation zones. 20 1.3.1 Profile diagram of common trees in S. Guinea Savanna. 30 1.4.1 Map showing position of study area. 33 1.4.2 The layout of the study area. 34 2.1.1 Seasonal distribution of litter fall. 54 2.1.2 Litter production in relation to latitude. 58 2.1.3 Litter production in relation to rainfall. 60 2.2.1 The standing crop of wood and leaf litter. 74 2.3.1 The decomposition of logs and twigs during 1975. 85 2.4.1 Bait consumption data represented by pie diagrams. 108 2.4.2 Monthly bait discovery and bait consumption data. 127 2.4.3 Monthly bait discovery and bait consumption data. 128 2.5.1 Flow diagram summarising data from Section 2. 136 3.1.1 Nest of Macrotermes bellicosus with a spiral base plate. 145 3.1.2 Nest of Macrotermes bellicosus without a spiral base plate. 148 3.1.3 The design of protected thermistor probes. 153 3.1.4 Temperature profiles from an M. bellicosus mound, height 2.6m. 155 3.1.5 Temperature profiles from an M. bellicosus mound, height 1.6m. 156 3.1.6 Temperature profiles from an M. bellicosus mound and surrounding soil. 157 3.2.1 Distribution of M. bellicosus mounds in March 1974. 171 3.2.2 Distribution of M. bellicosus mounds in February 1975.