The Role of Aardvarks (Orycteropus Afer)
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CORE Metadata, citation and similar papers at core.ac.uk Provided by South East Academic Libraries System (SEALS) THE ROLE OF AARDVARKS ( ORYCTEROPUS AFER ) AS ECOSYSTEM ENGINEERS IN ARID AND SEMI-ARID LANDSCAPES OF SOUTH AFRICA A thesis submitted in fulfilment of the requirements for the degree of MASTER OF SCIENCE of RHODES UNIVERSITY By Gareth Morgan Whittington-Jones December 2006 ABSTRACT Arid and semi arid environments are characterised by extreme fluctuations in temperature and low rainfall which present significant challenges to the animals inhabiting these areas. Mammals, such as aardvarks ( Orycteropus afer , Pallas 1766), excavate burrows in order to avoid predators and climatic extremes and are termed “ecosystem engineers” as they physically modify their environment and in doing so create new habitats and alter the availability of resources to other species. In this study I assessed the microhabitat conditions (maximum and minimum temperature, relative humidity and seed abundance) of aardvark burrows in relation to paired control sites. In addition, I evaluated the use of aardvark burrows by other vertebrate and invertebrate species and investigated the impact of aardvark burrow mounds on landscape scale floristic diversity. Maximum temperatures were significantly lower (p < 0.05) and minimum temperatures and midday humidity were significantly higher (p < 0.05) inside the burrows at the three study sites, Kwandwe Private Game Reserve (Kwandwe), Mountain Zebra National Park (MZNP) and Tswalu Kalahari Reserve (Tswalu). There were no significant differences between the concentration of seeds, the average numbers of unique individual small mammals, trap success or small mammal species richness recorded inside the burrows compared to outside (p > 0.05). At all three sites, small mammal species diversity was higher in the burrows but this result was also not significant (p > 0.05 for all). Trap success and the number of individuals captured was higher at Tswalu than the other two sites (p < 0.05 for both). The different methods i used in this study revealed a total of 25 mammal, seven bird, one amphibian and six reptile species utilising aardvark burrows. There were significant differences in insect community assemblages between the burrows and open control areas at Kwandwe and Tswalu (p < 0.05 for both) but not at MZNP (p > 0.05). The parasitic guild was more prominent inside the burrows than outside but their abundance was not as high as anticipated, possibly due to the placement of traps closer to the burrow entrances than the sleeping chambers. The complex structure of the burrows prevented the placement of traps in close proximity to the sleeping chambers. As expected, the amount of bare earth was significantly higher on active and recently abandoned burrow mounds compared to the old burrow mounds and reference plots at all three sites (p < 0.05 for all), with the exception of the active burrows at Tswalu. Overall, the different plot types were characterised by significantly different plant communities during all the seasons at MZNP, during three of the seasons at Kwandwe and only during winter at Tswalu. The total species richness recorded on the reference plots was higher than on the burrow mounds at all three sites. However, species diversity on the reference plots was not significantly higher than the burrows at any of the sites (p > 0.05 for all sites). Although the results were not significant, the overall species diversity at a site level was greater than the reference patches at Kwandwe and Tswalu (p > 0.05 for both). Aardvarks fulfil the criteria of a significant ecosystem engineer and their presence in arid and semi-arid environments is likely to be critical to the survival of other ii individual organisms and species, particularly when alternative burrowing animals are either absent or restricted in their activities. Thus, aardvark populations should be considered a conservation priority in arid and semi-arid ecosystems. iii TABLE OF CONTENTS ABSTRACT ii LIST OF TABLES vii LIST OF FIGURES xiii ACKNOWLEDGEMENTS xviii CHAPTER 1: GENERAL INTRODUCTION 1 1.1 THE BIOLOGY OF THE AARDVARK 1 1.1.1 Taxonomy and phylogeny 1 1.1.2 Physical Characteristics 1 1.1.3 Distribution and habitat 2 1.1.4 Diet 3 1.1.5 Behaviour and habits 3 1.1.6 Reproduction 4 1.2 CONSERVATION STATUS 4 1.3 ECOSYSTEM ENGINEERING 5 1.4 BROAD MOTIVATION 8 CHAPTER 2: GENERAL DESCRIPTION OF THE STUDY SITES 9 2.1 LOCATION 9 2.2 KWANDWE PRIVATE GAME RESERVE 9 2.2.1 Site description and history 9 2.2.2 Climate 10 2.2.3 Vegetation 11 2.2.4 Topography and geology 12 2.3 MOUNTAIN ZEBRA NATIONAL PARK 12 2.3.1 Site description and history 12 2.3.2 Climate 13 2.3.3 Vegetation 14 2.3.4 Topography and geology 15 iv 2.4 TSWALU KALAHARI RESERVE 15 2.4.1 Site description and history 15 2.4.2. Climate 16 2.4.3 Vegetation 17 2.4.4 Topography and geology 18 2.5 SOIL HARDNESS 19 2.6 BURROW DENSITY 19 2.7 TABLES AND FIGURES 20 CHAPTER 3: MICROHABITAT OF AARDVARK BURROWS 30 3.1 INTRODUCTION 30 3.2 METHODS AND MATERIALS 35 3.2.1 Burrow location 35 3.2.2 Temperature recordings 35 3.2.3 Humidity 35 3.2.4 Seed concentration 36 3.2.5 Burrow orientation 36 3.2.6 Burrow entrance size 37 3.2.7 Data analysis 37 3.3 RESULTS 38 3.4 DISCUSSION 43 3.5 TABLES AND FIGURES 51 CHAPTER 4: COMMENSAL FAUNA OF AARDVARK BURROWS 62 4.1 INTRODUCTION 62 4.2 METHODS AND MATERIALS 67 4.2.1 Small mammal trapping 67 4.2.2 Burrow surveys and opportunistic sightings 68 4.2.3 Questionnaires 69 4.2.4 Insect sampling 69 4.2.5 Data analysis 72 4.3 RESULTS 74 4.3.1 Small mammal community 74 4.3.2 Burrow surveys, opportunistic sightings and questionnaires 76 4.3.3 Insects 78 4.4 DISCUSSION 81 v 4.5 TABLES AND FIGURES 91 CHAPTER 5: THE IMPACT OF AARDVARK BURROWS ON FLORISTIC DIVERSITY 110 5.1 INTRODUCTION 110 5.2 METHODS AND MATERIALS 113 5.2.1 Vegetation sampling 113 5.2.2 Data Analysis 114 5.3 RESULTS 115 5.4 DISCUSSION 120 5.5 TABLES AND FIGURES 126 CHAPTER 6: GENERAL DISCUSSION 153 CHAPTER 7: REFERENCES 158 APPENDIX A: The covering letter and first page of the questionnaire requesting information regarding the utilisation of aardvark burrows by other vertebrate species. 177 APPENDIX B: Common and species names of vertebrates recorded using burrows during this study. Data was obtained from personal sightings, records of tracks and signs and from the questionnaires. 179 APPENDIX C: List of birds recorded using aardvark burrows (Hockey et al ., 2005). 180 APPENDIX D: List of mammals recorded using aardvark burrows (Skinner & Smithers, 1990). 181 vi LIST OF TABLES Table 4.1 SIMPER analysis breakdown of average dissimilarity between recently active burrow mounds and reference plots into contributions from the 10 most influential species at Tswalu during spring. Percentage cover was used as a surrogate for abundance. Table 4.2 The species richness, diversity and evenness values inside and outside of the burrows at all the sites during the four seasons. Table 4.3 The effect of site (the reserves) and position (burrows or open areas) on the numbers of unique individuals and species of small mammals trapped. Data are means of the four seasonal values ± 1 SD with total numbers in parentheses. Common names are listed in Appendix B. Table 4.4 The R and p values for the regression analyses between trap success and the number of unique individuals caught, and the combined biomass of the monocotyledonous and dicotyledonous seeds removed from the soil samples inside and outside of the burrows. Table 4.5 Vertebrate species observed using burrows during the course of this study. Infrequent observations are considered to be less than ten sightings. The purpose of burrow use is denoted either by “+” or “-“. “?” is used when the purpose of burrow use is unknown. Common names are listed in Appendix B. Table 4.6 Tracks and signs of vertebrate species using aardvark burrows. Infrequent observations are considered to be less than ten sightings. Common names are listed in Appendix B. vii Table 4.7 List of vertebrates observed using aardvark burrows according to information derived from questionnaires. The purpose of burrow use is denoted either by “+” or “-“. “?” is used when the purpose of burrow use is unknown. Common names are listed in Appendix B. Table 4.8 The richness, abundance and guild allocations of insect morphospecies inside and outside of burrows. Phyt = phytophagous, Pred/hem = predatory/hematophagous, Fungi = fungivorous, Det/sap = detritivorous/saprophagous and para = parasitic. Table 4.9 SIMPER analysis breakdown of average dissimilarity between burrows and control areas into contributions from the most influential morphospecies at Kwandwe. Table 4.10 SIMPER analysis breakdown of average dissimilarity between burrows and control areas into contributions from the most influential morphospecies at MZNP. Table 4.11 SIMPER analysis breakdown of average dissimilarity between burrows and control areas into contributions from the most influential morphospecies at Tswalu. Table 4.12 Average daily (means ± 1 SD) and total morphospecies diversity and evenness with formicidae included at each site. Table 4.13 Average daily (means ± 1 SD) and total morphospecies diversity and evenness with formicidae excluded at each site. Table 4.14 Average daily (means ± 1 SD) and total morphospecies richness, Michaelis-Menten species richness estimate and the total number morphospecies common to the burrows and controls at each site. viii Table 5.1 Species, family and growth form of plants present on burrow mounds and on reference plots at Kwandwe.