The influence of predator-prey relationships and. managerial actions on ungulate population dynamics in. Madikwe Game Reserve

Transcription

1 The influence of predator-prey relationships and managerial actions on ungulate population dynamics in Madikwe Game Reserve by Anne-Marie Elizabeth Stewart Submitted in partial fulfillment of the requirements for the degree of Magister Technologiae: Nature Conservation In the Department of Nature Conservation FACULTY OF AGRICULTURAL SCIENCES TSHWANE UNIVERSITY OF TECHNOLOGY Supervisor: Dr PJ Funston July 2006

2 DECLARATION BY CANDIDATE I hereby declare that the dissertation submitted for the degree, M Tech: Nature Conservation, at Tshwane University of Technology is my own original work and has not previously been submitted to any other institution. This dissertation consists of a series of manuscripts that are to be submitted to various scientific journals. As a result, styles vary between chapters of the dissertation. I testify that the work in this dissertation is my own, although it benefited greatly from comments by my supervisor and referees. Anne-Marie Elizabeth Stewart Pretoria, July 2006 Copyright Tshwane University of Technology ii

3 ACKNOWLEDGEMENTS There are numerous people that contributed in so many ways to the successful completion of this project. I would like to extend a huge thank you to all of them, as without their assistance, I doubt very much whether there would be a finished Masters today. My parents, Bruce and Marie Stewart, for their encouragement and support, not only during the completion of my Master s, but throughout my studies. My supervisor, Dr Paul Funston, for his guidance and seemingly endless enthusiasm for this project, and for instilling in me an appreciation for good research. Prof Tony Starfield, for his invaluable assistance and guidance with the modelling process. The Tshwane University of Technology for their generous granting of a Masters bursary. The National Research Foundation for financial support in the form of a bursary during my studies. North West Parks and Tourism Board for allowing me to use Madikwe as a case study for this project, and in particular Mr Steven Dell, for the assistance he gave and the huge desire he expressed to see this project go ahead. Ms Louise Viljoen, for her tireless help and assistance with administrative duties during these past few years. iii

4 André Badenhorst and his family, for their kindness and support during my two years in Pretoria. My peers at the University who were there to provide comic relief when the going got tough, and my friends elsewhere who, although they often didn t know what I was talking about, always showed interest and listened attentively when I rambled on about predators and prey. Particular thanks are due to Chris Gordon for his encouragement, input, and for cracking the whip! To all of you, thank you so much. I could not have done it without you. iv

5 ABSTRACT African savanna ecosystems involve complex multi-species predator-prey systems that can be further complicated by extreme fluctuations in environmental conditions. Much of the mortality in ungulate populations is attributable to predation, and possibly most populations are limited in this way. Although an understanding of the relationships between large carnivores and their prey is crucial, relatively little attention has been given to these aspects in the smaller conservation areas (< 1000 km²) and game ranches that have reintroduced large carnivores. This research project makes use of ecological modelling to highlight the need for reserve managers to clearly define their objectives with regards to carnivore and ungulate population management. The models can also be used to determine more general theoretical expectations of the outcome of large carnivore re-introductions into smaller game reserves, information that is currently lacking in southern Africa. The project was conducted in Madikwe Game Reserve, which stocks the five larger carnivores and a variety of ungulate species. The reserve had experienced a sharp decline in its ungulate population numbers, and needed a decision-analysis tool to assist them in determining how best to deal with these low populations. The question was also posed as to why these populations had experienced such a drop in numbers. A modelling approach was seen as the most effective way of determining the causes of this decline in the ungulate populations, and would also allow management to predict the outcome of different courses of action. Four multi-species predator-prey models were constructed for Madikwe, using both predicted predation information gathered during a literature review, and Madikwe predation information collected in the field. These v

6 models clearly illustrated the value of good data collection and the subsequent use of these data to assist managers with decision-making and wildlife management. Through the modeling exercise, Madikwe Game Reserve was able to pinpoint where they were lacking in their monitoring and data collection. Constructing the models also clearly highlighted the prey requirements of the different predators, a factor that management had definitely underestimated to begin with. The result of this project and the modelling exercise was the development of a model that managers of smaller, enclosed reserves can easily implement, and that will clearly show future trends in their ungulate populations. Once managers can look at projected trends in the populations in their reserves before any managerial interference takes place, they will be able to make more informed decisions when it comes to manipulating both carnivore and ungulate populations to achieve their required management objectives. vi

7 CONTENTS ACKNOWLEDGEMENTS ABSTRACT CONTENTS LIST OF TABLES LIST OF FIGURES Page iii v vii ix x CHAPTER 1 INTRODUCTION 1 CHAPTER 2 PREY SELECTION OF LARGE AFRICAN CARNIVORES 2.1 Introduction Results and discussion Lions Leopards Cheetah Spotted Hyaenas Wild dogs Conclusions 35 CHAPTER 3 THE PREDATOR-PREY MODEL 3.1 Introduction Study area The modelling process Modelling with Predicted Predation Scenarios Modelling with Madikwe Predation Scenarios Incorporating Management Actions into the Models Sensitivity Analysis 54 vii

8 CHAPTER 4 RESULTS AND DISCUSSION 4.1 Comparison of prey selection data Comparison of model outputs Modelling without Removals Modelling with Removals Comparing Model Outputs with Census Data Sensitivity analysis and model manipulations 77 CHAPTER 5 CONCLUSIONS 88 REFERENCES 91 viii

9 LIST OF TABLES Page Table 2.1 Prey selection of the five larger carnivores 34 Table 2.2 Percentage occurrence of size and age classes of selected prey in the diets of the five larger carnivores 35 Table 2.3 Percentage occurrence of size and age classes in the diets of four of the larger carnivores 36 Table 3.1 Ungulate and predator figures used to construct the model for MGR 43 Table 3.2 Percentage occurrence of size and age classes in the diets of the five larger carnivores, using data from the literature 49 Table 3.3 Percentage occurrence of size and age classes in the diets of the five larger carnivores, using data from Madikwe 52 Table 3.4 Removals of the five selected ungulate species since Table 3.5 The life history parameters of the five ungulates 57 ix

10 LIST OF FIGURES Page Figure 4.1 Prey selection of the five larger carnivores using data from the literature 59 Figure 4.2 Prey selection of the five larger carnivores using data from MGR 60 Figure 4.3 Zebra population trends under four modelling scenarios 64 Figure 4.4 Wildebeest population trends under four modelling scenarios 64 Figure 4.5 Kudu population trends under four modelling scenarios 65 Figure 4.6 Eland population trends under four modelling scenarios 65 Figure 4.7 Impala population trends under four modelling scenarios 66 Figure 4.8 Comparison of zebra population trends from three data sources 74 Figure 4.9 Comparison of wildebeest population trends from three data sources 74 Figure 4.10 Comparison of impala population trends from three data sources 75 Figure 4.11 Changes in zebra population trends with manipulations of adult fecundity 80 Figure 4.12 Changes in zebra population trends with manipulations of juvenile fecundity 80 x

11 Figure 4.13 Changes in zebra population trends with manipulations of adult survival 81 Figure 4.14 Changes in zebra population trends with manipulations of juvenile survival 81 Figure 4.15 Zebra population trends under different management scenarios 84 Figure 4.16 Wildebeest population trends under different management scenarios 84 Figure 4.17 Zebra population graph showing new projection from adjusted selection data 87 xi

12 CHAPTER 1 INTRODUCTION African savanna ecosystems involve complex multi-species predator-prey systems (Mills & Shenk, 1992), which are further complicated by often extreme fluctuations in environmental conditions (Gertenbach, 1980). For reserve managers, an understanding of the relationships between large carnivores and ungulate species is crucial, especially in smaller reserves that traditionally receive more intensive management. It is important for wildlife managers to be aware that the dynamics of specific animal populations cannot be separated from those of associated populations or from the environment as a whole (Smuts, 1978). Predation by large carnivores on ungulates is influenced by many physical and biotic environmental factors, with management practices usually serving to compound these already complex relationships (Peel & Montagu, 1999). To date relatively little attention has been given to these aspects in the smaller conservation areas (< 1000 km²) and game ranches that started reintroducing large carnivores in the early 1990 s (Hunter, 1998; Peel & Montagu, 1999). In any savanna ecosystem much of the mortality in ungulate populations is attributable to predation, and possibly most populations are limited in this way, especially those that are both resident and at occur at low densities (Caro & Fitzgibbon, 1992; Mills & Shenk, 1992). It would seem that only large populations of migratory ungulates escape the population regulation imparted by 1

13 large carnivores. In certain cases the effects of predation are exacerbated by inappropriate managerial actions, especially in conjunction with extreme environmental variations or perturbations (Peel & Montagu, 1999; Grant et al., 2002). The research project reported on here was conducted in Madikwe Game Reserve (MGR), and was undertaken to unravel the differential effects of predator-prey relationships and various management interventions, on the population dynamics of selected resident ungulates. The aim of the project was, twofold; to develop a general framework of understanding on how Africa s large predators select for their savanna ungulate prey, and to determine whether this knowledge of the parameters involved in predator-prey interactions can be used in an ecological modelling process to accurately predict ungulate population trends. The development of mathematical models is one of the most frequently used methods to study population dynamics (Norton, 1994), with researchers attempting to model and predict population trends in wildlife areas so as to allow for a better understanding of population dynamics. Some of these studies have been carried out on ungulate populations in smaller (< 1000 km²), closed (fenced) reserves, focusing on the influence of environmental conditions and management actions, such as culling or harvesting, on these species (Starfield, Owen-Smith & Bleloch et al., 1976; Hilborn & Sinclair, 1979; Berry, 1981; Peel & Montagu, 1999). Other research has concentrated on the effect of predation on ungulate populations in open systems such as the Serengeti (Hilborn & Sinclair, 1979; Caro & Fitzgibbon, 1992; Caughley & Sinclair, 1994), as well as in large, closed, actively managed areas (Hirst, 1969; Smuts, 1978; Mills & Shenk, 1992; Mills & 2

14 Biggs, 1993). A number of general deductions concerning predator-prey interactions can be made from these studies. Predator and prey populations can coexist, with prey either being held at a low density by predator regulation, or at high densities by intraspecific competition for food, where the effect of predation is depensatory (Caughley & Sinclair, 1994). However, as Caughley and Sinclair (1994) point out, there are situations where the prey population may decline and indeed become extinct. This takes place when the prey population is reduced below a certain number, with predation mortality then being greater than net prey recruitment. The conditions for this situation occur when there is no switching by predators, there is no refuge for prey at low densities, and predators have an alternative prey source to maintain their population when the first prey species is in low numbers (Caughley & Sinclair, 1994). Low densities of the primary prey species could result from reduction of habitat, from hunting or through live game removals. This sort of theoretical explanation is believed to explain much of the situation leading to the decline of roan antelope (Hippotragus equinus) in the Kruger National Park (Grant et al., 2002). Mills and Shenk (1992) showed that lion predation affected resident low-density wildebeest populations more so than semi-migratory higher-density zebra populations in the Kruger National Park, with this effect being more pronounced during periods of above-average rainfall (Funston & Mills, 2006). Smuts (1978) mentions the importance of a buffer high-density prey species, in this case impala in Kruger National Park, which may reduce the impact of predation on other less 3

15 abundant ungulate populations. Theoretically, should impala numbers decline drastically, the predators in question would have to find an alternative source of food, thereby having an impact on other ungulate populations. Hunter (1998) explored the effect of lion introductions in Phinda Game Reserve (considered a relatively small game reserve) on the population size and diversity of ungulates. Declines in preferred prey species were recorded, as well as modified vigilance behaviour by ungulates following the introductions (Hunter, 1998). Hunter (1998) predicted that the possibility for less abundant prey species to become extinct in smaller reserves with re-introduced large carnivores is substantially increased. Peel and Montagu (1999) showed that a declining blue wildebeest population exposed to intense lion predation and a live game removal program would continue to decrease under this management regime unless all removal was halted and the re-introduced lion numbers were reduced to a certain level. There are thus many factors to be considered when planning for the management of wildlife populations in closed reserves. As Smuts (1978) states, the management of large carnivores and their prey populations still remains a highly complex and controversial issue, which has been corroborated by more recent studies (Mills & Shenk, 1992). This can be ascribed primarily to a lack of knowledge of the basic factors influencing interactions between these predators and their prey. Thus, in reserves that are not self-regulating, where large carnivores could be potentially disruptive, there is an urgent need for sound managerial guidelines. 4

16 To obtain an accurate estimate of the impact of predation on ungulate populations in a given area, it is necessary to know whether predators kill those individuals that would contribute to the population s growth, or those that would contribute little to its increase. Species, age, condition and amount of prey consumed are important considerations, as well as the factors that influence this choice. Kill frequencies of predators have been calculated, but Viljoen (1997) cautioned that estimates of the number of prey animals killed per year and kill frequency might be of little practical value due to the large differences in body mass of prey animals killed in different regions. The estimated amount of food consumed, in weight, provides a better basis for comparison between different areas (Viljoen, 1997) and also allows for easier estimation of the number of predators a prey population in a certain area can support. Mills and Biggs (1993) indicated that the extent to which predators impact on their prey and compete with one another is not only a function of their diets, but is also influenced by the number of prey available, and the relative numbers of predators. Factors influencing the dynamics of the prey population such as fecundity, survival rates, age and sex structure of the population, and causes of mortality other than predation are also important parameters that need to be considered (Mills & Shenk, 1992). Ecologists and reserve managers often emphasize the importance of thinking holistically and are conscious of the fact that they are dealing with a complex system with many interactions (Pellew, 1983; Starfield & Bleloch, 1991). However, at the decision-making level, this holistic way of thinking is sometimes 5

17 lost and attention becomes focused on a specific problem. Starfield and Bleloch (1991) suggest that the process of building models helps to highlight and direct attention to those aspects of the system that are vital for the decision-making process. Models can be described as any representation or abstraction of a system or process (Starfield & Bleloch, 1991). They are intellectual tools that allow for the definition and organization of problems and an understanding of data. Models also test this understanding and allow one to make predictions (van Rooyen, 1994). The resolution of a model depends on the amount of accurate data available. When a large amount of data is available to feed into the model, the result is a model of high resolution. The effectiveness and value of a model should not be ignored, however, when data is lacking and reasonable assumptions have to be made in the construction of the model. Collecting data can take time and money, resources that managers often don t have. Exact figures to feed into a model are not too important; it is the trends that the model shows that are really useful. Working models should be built making use of the best available data at that time, and that can be readily updated when new data is available or a better understanding of the existing data is achieved. This approach emphasizes the adaptive management school of thought (Holling, 1978). Thus, in essence, the purpose of a model is not to mimic nature, but to enable one to think usefully about a problem (Starfield & Bleloch, 1991). A model is not, ultimately, concerned with numbers; the numbers are merely a vehicle for the logic. Ecological models are built for a number of reasons. However, the two purposes that are of importance to this project are those of prediction, and the understanding of a system. Using the model to predict how a population may react 6

18 under different management strategies allows for the experimentation of population processes without incurring the great cost or damage to ecological systems that would result from such experimentation with real populations (Caughley, 1981; Norton, 1994). MGR follows an ecological management strategy that focuses on restoring the reserve to its former state, promoting sound ecological functioning while depending on wildlife-based tourism and live game sales to remain economically viable. Currently objectives may be too broadly focused leading to a conflict in management strategies regarding conservation and management of low-density, expensive ungulate species while at the same time supporting satisfactory large carnivore and high-density ungulate species to meet important eco-tourist objectives. Through the use of ecological modelling, this project aimed to highlight the need for reserve managers to clearly define their objectives with regards to carnivore and ungulate population management. Furthermore, the results obtained from the modelling process may be used to determine more general theoretical expectations of the outcome of large carnivore re-introductions into smaller game reserves. This information is currently lacking in southern Africa. The desired result of this project and the modelling exercise will be the development of a model that managers of smaller, enclosed reserves can easily implement, and that will clearly show future trends in their ungulate populations. Once managers can look at projected trends in the populations in their reserves before any managerial interference takes place, they will be able to make more 7

19 informed decisions when it comes to manipulating both carnivore and ungulate populations to achieve their required management objectives. 8

20 CHAPTER 2 PREY SELECTION OF LARGE AFRICAN CARNIVORES 2.1 INTRODUCTION Food habits of carnivores are central to the ecological niche they occupy and play a fundamental role in explaining their social systems, behaviour, and factors affecting their population density (Mills, 1992). These habits may also have important consequences in the life histories of their prey, and are therefore important considerations when formulating species and ecosystem management strategies. With regards to the feeding habits of predators, it is important to consider both what species of prey are being eaten, as well as how many are eaten. By determining prey selection, one is able to establish the effects of predation both qualitatively and quantitatively on the different prey species, and predict the effects on the predator of changes in the number of prey species (Bertram, 1979). Feeding rate, or how many animals are killed per predator during a specific time period, is best determined through direct observations (Bertram, 1979; Mills, 1992; Caro & Fitzgibbon, 1992). Such methods provide the most accurate measurements of prey selection, killing frequency and consumption rates, and compensate for the biases arising from the fact that large kills take much longer to be eaten whereas small prey animals are eaten far more quickly and completely, and are therefore likely to be overlooked by other methods (Mills, 1984; Caro & 9

21 Fitzgibbon, 1992). However, it is not always practical or possible to follow predators in this way, and the method employed is usually dependant on habitat and ease of observation. Carnivore habits are also obviously an important consideration. It is often suggested that the population sizes in many interacting communities are stabilized by predation, in that it acts to prevent large fluctuations or extinctions of prey populations (Oaten & Murdoch, 1975). Schaller (1972) adds that predators constitute an important check on ungulate populations. Predation allows for a dampening of the tendency of populations to increase beyond the carrying capacity of their range, an effect that curbs severe oscillations. Predation works in conjunction with other factors, such as disease and malnutrition, but according to Schaller (1972), as the intensity of predation increases so the incidence of disease decreases. It might then be concluded that when predation holds species below their carrying capacity, it holds them below a level at which disease, starvation, and other population reducing forces associated with poor nutrition can take effect. To obtain an accurate estimate of the impact of predation on ungulate populations in a given area it is necessary to know whether predators kill those individuals that would contribute to the population s growth or mostly those that would contribute little to its increase. Species, age, condition and amount of prey consumed are important considerations, as well as the factors that influence this choice. Classical optimal foraging models presume that animals maximize energy intake per unit time (Caro & Fitzgibbon, 1992). Accordingly, three factors are vital in 10

22 determining selection between two types of prey: (i) the relative energy gained from the two sorts of prey; (ii) the time to find them; and (iii) their handling time (time taken from the hunt till they are eaten) (Caro & Fitzgibbon, 1992). Many studies have been directed at determining whether predators do select prey by comparing the relative frequencies of different prey types in the predators diet with their relative frequencies in the environment, and various different measures of preference have been proposed (Caro & Fitzgibbon, 1992; Power, 2002). In the Kruger National Park, Pienaar (1969) recorded the relative frequencies of prey species in all kills made by the larger mammalian carnivores, as well as the relative frequencies of prey animals. He was able to derive a preference rating of a prey species for a particular predator: Preference rating = Kill frequency of prey Relative abundance of prey Accordingly, these preference ratings provide a true indication of the real food preferences of a particular predator irrespective of the density of its various prey species. Caughley and Sinclair (1994) refer to a type of predator behaviour known as switching. This implies that the predator will focus its attacks disproportionately on the more abundant prey species in an area. There are several mechanisms that might result in switching, one of which is referred to as conditioning. This concept is based on the possibility that the predator s preference for a particular 11

23 species is affected by its experience, especially of the recent past (Oaten & Murdoch, 1975). There are several ways by which such an effect might result in the predator preferring the more abundant prey. Most of these ways involve the predator s rejecting (consciously or not) some available prey, and this rejection rate increasing as the relative density of the prey decreases. It might be that catching, killing and eating require practice (and therefore an abundance of a particular prey type), or that the predator develops a taste for the species he eats more often (Oaten & Murdoch, 1975). According to Radloff and Du Toit (2004), the relationship between predator and prey body size in African savannas indicates that larger predators have wider predatory options than smaller predators, rather than specializing on differentsized prey to their smaller counterparts. If the larger members of the predator guild were removed, Radloff and Du Toit (2004) hypothesize that the next members in size would respond by increasing their prey size range. Not all predators from a particular population necessarily select a particular profile of prey, and diet may differ between individual predators for a number of reasons (Caro & Fitzgibbon, 1992). In sexually dimorphic carnivores, males can take larger prey than females, while younger animals that rely on experience to capture prey effectively often take different prey than do adults of the species (Funston et al., 1998). Reproductive status also influences prey choice mothers with dependant offspring have been shown to hunt different prey than females without young (Caro & Fitzgibbon, 1992). Predator population structure may 12

24 therefore be an important consideration when determining the factors that influence the impact of predators on prey populations. Is predation merely compensatory in that only those individuals that would contribute little to the growth of the population are selected? Do predators target substandard individuals, old or young prey, or males of the species? The diet of the larger predators is generally opportunistic and is determined to a large extent by what food is available, with the size of the prey being taken usually increasing with predator size or hunting group (Bothma, 1997). Various attempts have been made to establish whether predators select substandard individuals, or animals in poor condition, from a population (Caro & Fitzgibbon, 1992). High selectivity, in this sense, would mean that the predator is taking prey that would add little to the population growth, and would be likely to die soon anyway. Low selectivity would imply that the predator is removing those animals that would contribute significantly to the population. It has been shown that high selectivity is displayed for prey difficult to capture, with pursuit predators like cheetahs, Acinonyx jubatus, lions, Panthera leo, and African wild dogs, Lycaon pictus, testing the condition of their prey and showing strong selectivity. It can be concluded that predators differ in their selection of sick individuals according to their hunting technique (coursing predators vs. stalkers), availability of alternative prey, and their own health and hunting abilities (Caro & Fitzgibbon, 1992). There have been various arguments as to whether predation has a greater effect on a population if older or younger individuals are selected. According to Fitzgibbon and Fanshawe (1989) younger animals do suffer heavier predation and are more 13

25 likely to be chosen by predators as they are easier to catch, are slower and have lower stamina, and may not be able to recognize predators. This predation on young animals may have less impact on the prey population than the removal of mature animals due to the fact that younger individuals can be replaced quickly while mature individuals may also still contribute significantly to the reproductive output of the population (Caro & Fitzgibbon, 1992; Mills & Shenk, 1992). Males of a population are usually more likely to be preyed upon than females (Caro & Fitzgibbon, 1992; Bailey, 1993; Broomhall, 2001). Although this is not always the case (Pienaar, 1969), males do expose themselves to a greater risk of predation as they generally seek less safe environments, are often found alone defending territories, and may be more vulnerable after exhausting themselves competing for females. In monogamous species, however, this risk of predation may be equal for males and females, as the benefits of group living do not apply. Should males be selected over females, the impact of predation on the population would be lessened, as males do not contribute as much to recruitment in the population as do females. One might therefore conclude that predators take prey on the basis of its health, age and sex. The term selection might be used when referring to the particular species or population group within an area on which the predator preys, but should perhaps not be used so loosely when referring to particular individuals within that population. Predators might be seen to choose predominantly males or young animals from a group, but this could merely be a function of their vulnerability within the group, or the ease with which they might be caught. In 14

26 other words, any animal that makes itself vulnerable within a population, regardless of age or sex, could become first choice for predators. Kill frequencies of predators have often been calculated but according to Viljoen (1997), estimates of the number of prey animals killed per year and kill frequency are of little practical value due to the large differences in body mass of prey animals killed in different regions. The estimated amount of food consumed, in weight, provides a better basis for comparison between different areas (Viljoen, 1997) and also allows for easier estimation of the number of predators a prey population in a certain area can support. Kruuk and Turner (1967) provided a useful method for roughly calculating the average killing rate of a predator. Briefly, the percentage of each species in the kill sample is multiplied by a common factor that is derived by dividing the total weight of prey in the sample into the average weight of prey killed by the predator. The aim of this chapter is to provide a thorough overview of the literature available on the food habits of the five larger carnivores found in African savanna ecosystems. The information gathered through the review of this literature will be vital in contributing to a framework of understanding of how these larger carnivores select for prey species, and the effect this selection has on the dynamics of predator-prey systems in enclosed reserves. For purposes of standardization, prey referred to in this report has been divided into certain size classes depending on their adult weight; large (> 300 kg, average adult mass of 810kg); medium ( kg, average adult mass of 280kg); small (30 100kg, 15

27 average adult mass of 41kg); and very small (<30 kg, average adult mass of 14kg). 2.2 RESULTS AND DISCUSSION A number of studies on hunting and behavioural aspects of Africa s large carnivores have provided much information on the food habits and bionomics of numerous predators, including the lion (Schaller, 1972; Eloff, 1973; Scheel, 1993; Funston et al., 1998, 2001), leopard, Panthera pardus, (Bailey, 1993), spotted hyaena, Crocuta crocuta (Kruuk, 1972; Henschel, 1986; Mills, 1990), wild dog (Estes & Goddard, 1967; Fuller & Kat, 1990; Creel & Creel, 1995) and cheetah (Caro, 1994; Broomhall, 2001; Marker et al., 2003). Felids are generally the most carnivorous of the Carnivora and show a high degree of dependence on vertebrate food (Bothma, 1997). Carnivores usually prey on animals more or less the same weight as themselves, avoiding animals that are much smaller and lighter in weight (Radloff & Du Toit, 2004). Only predators that hunt in organized groups, like the lion and wild dog, tend to take animals much larger than themselves (Radloff & Du Toit, 2004; Schaller, 1972). However, although opportunistic in prey choice, the modal prey mass of large felids is usually less than that of the predator, although this relationship does vary between regions (Sunquist & Sunquist, 1989). 16

28 Lions Schaller (1972) states that lions are catholic in their tastes. Serengeti lions have been shown to eat 18 kinds of mammals and 4 kinds of birds. Lions can obviously eat whatever they can catch, food habits being most noticeably influenced by four factors: (i) size of prey, with usual prey size ranging between 15 to 1000kg. Prey that is over 1000kg is thus safe from predation, while at the other extreme small animals are generally also not taken, as the energy expended in trying to subsist on these animals is not compensated for by the energy gained in eating them; (ii) availability; (iii) density, with more abundant species more likely to fall prey to lions; and (iv) scavenging. Species and availability of prey for lions differs throughout the regions in which these carnivores have been comprehensively studied. For this reason, the results of the literature survey presented below are discussed by region, which makes for a simpler comparison between findings. Kalahari Mills (1984) and Eloff (1973, 1984) conducted the most thorough studies thus far regarding the foraging ecology of lions in the Kalahari. Lions were either followed over varying periods so that kills could be directly observed (Eloff 1973, 1984) or information on kills was gathered through carcass examination (Mills 1984). Eloff s (1973, 1984) method ensured that all kills, regardless of size, were recorded, which would explain the much higher preponderance of small and juvenile mammal kills in this data. Eloff (1973) found that small and juvenile mammals together make up more than 50% of known lion kills in the Kalahari, with porcupines, Hystrix africaeaustralis, alone comprising between 25% and 33% of lion kills recorded. Although small mammals are not important in terms of 17

29 biomass, Eloff (1973, 1984) states that they may fulfil a vital role as maintenance diet during lean times. Amongst the larger ungulates Mills (1984) recorded a much higher proportion of adult animals killed during his study, and in contrast to Eloff (1973, 1984) concluded that adults formed the bulk of lion kills (75.1%). This could also be ascribed to the method of data collection, larger carcasses being more readily found. Gemsbok, Oryx gazella, are important in the diet of Kalahari lions, and represented 25% of all kills (Eloff, 1973, 1984). Mills (1984) found blue wildebeest, Connochaetes taurinus, (37.0%) and gemsbok (32.4%) to be the dominant food of lions, contributing 69.2% of all carcasses they fed on, the vast majority of which were kills. The proportions in which gemsbok kills were represented in the different age classes were similar in the studies of both Mills (1984) and Eloff (1984). Lions showed a preference for the males of the different prey species, excluding wildebeest and ostriches, Struthio camelus, where males and females were selected equally. Because so many small animals are caught, a Kalahari lion may make as many as 50 kills per year, significantly more than anywhere else in Africa (Eloff, 1973, 1984). The daily food consumption as determined by Eloff (1973, 1984) was 4.7 kg for a female and 7.2 kg for a male. Kruger In the Kruger National Park (KNP) lions were followed for extended periods by Mills and Shenk (1992), and Funston et al. (1998, 2001), while Smuts (1979) used 18

30 the analysis of stomach contents to assess the diet of lions in KNP. Pienaar (1969) and Mills and Biggs (1993) based their studies on carcasses located by rangers. In the southern area of the park, Mills (1992) recorded that impala, Aepyceros melampus, and then zebra, Equus burchelli, and wildebeest were the most common species killed by pride females. Mills et al. (1995) on the northern plains, however, produced predation data that was significantly different from the southern district, in that zebra were found to be the most important prey species, making up 83% of lion kills, followed by impala (10%). This could be explained by differences in the relative numbers of prey species, with zebra comprising a much higher percentage of available prey on the northern plains. Lions on both the northern and southern plains showed a selection for zebra foals over adults, with Pienaar (1969) noting during his study that both sexes were killed equally often. Smuts (1979) collected specimens for examination in the Central district, and found that impala (29.4%), followed by wildebeest (24.3%), contributed the most to the diet of lions in that area. In the south, lion predation appears to be particularly heavy on the resident wildebeest population (Mills & Shenk, 1992; Mills & Biggs, 1993) with lions estimated to remove up to 42% of the available biomass annually. There was no difference in the frequency with which adults and juveniles were killed and the observed population age structure (Mills & Shenk, 1992). Apart from regional variation in predation of the major prey species there was also variation that could be ascribed to rainfall regimes and differing selection of 19

31 prey by males and females. Lions in the KNP thus showed clear switches in prey selection between wet and dry cycles, with zebra and wildebeest being preyed upon at higher rates during average rainfall periods, and less so in moderate rainfall periods, with the converse occurring with buffalo, Syncerus caffer (Mills & Biggs, 1993). The largest impact on buffalo was during drought conditions when they were particularly susceptible to predation. However, even under favourable ecological conditions the main prey species of male lion groups, particularly subadults and nonterritorial males, was buffalo, although impala and warthog, Phacochoerus aethiopicus, were also of importance (Funston et al., 1998). Males killed significantly less frequently than females: on average, pride females made a kill every 1.8 nights, while males killed only once every 3.2 nights (Funston et al., 1998). Females and territorial males consumed meat according to their estimated minimum daily requirement (estimated at 5.3 kg for adult females and 8.1 kg for adult males), whereas nonterritorial males tended to consume significantly more (Funston et al., 1998). Serengeti On the Serengeti Plains, Scheel (1993) made a number of conclusions regarding lion predation, which compare favourably with earlier findings of Schaller (1972). Both found that wildebeest, gazelle (Gazella granti and Gazella thomsoni), and zebra were more likely to be encountered by lions and also more likely to be preyed upon. Schaller (1972) also noted the importance of buffalo in the diet of Serengeti lions, while Scheel (1993) concluded that warthog were one of the preferred species during his study, based mainly on following pride females. Male 20

32 and female wildebeest yearlings were preyed upon in more or less equal proportions, while there was a definite tendency for lions to select males from the adult segment of the population (Schaller, 1972). This can be attributed, however, to the greater vulnerability of males owing to their social behaviour, as discussed previously (Schaller, 1972). With zebra, the sexes were taken in relation to their availability in the population (Schaller, 1972). The more abundant sex suffered higher predation rates. Schaller (1972) found that lions killed buffalo of all ages. Among subadult and young buffalo, the sexes were killed in equal proportions, while among the older animals noticeably more males than females were killed (Schaller, 1972). Once again, this can be related to the increased vulnerability of older bulls that are rarely found in large herds. Lions took animals of the abovementioned species that were in poor condition, more so in wildebeest than with the other species, but sick individuals did not contribute to a significantly high percentage of all kills made (Schaller, 1972). Using the method suggested by Kruuk and Turner (1967), Schaller (1972) calculated that the kill rate for lions in the Serengeti ranges from about 32 prey animals per year in the Seronera and Masai areas, to 16 animals per lion per year at the edge of the woodlands, where larger prey animals such as zebra are represented to a greater proportion in the diet. Botswana Viljoen s (1993) study in the Savuti region of Chobe National Park in Botswana noted the differences in prey selection of lions between the rainy and dry seasons. Daily meat intake was higher for the rainy season (7.6 kg per female equivalent) 21

33 than for the dry season (4.6 kg per female equivalent), with no significant difference in the killing rate between seasons. Female equivalents are a measure used to standardise consumption rates, in that kilograms eaten are compared to that consumed by an average female lion (Van Orsdol, 1981). Males and cubs, therefore, could be converted to female equivalents. Males equate to 1.5 female equivalents, with large cubs (two to three years) 0.75 female equivalents, and small cubs eating 0.75 and 0.25 times as much as a female respectively. This difference in meat intake between seasons was attributed to the different type and size of prey (migratory and non-migratory) taken in the dry versus the rainy season. Warthog, tsessebe, Damaliscus lunatus, and buffalo were killed most frequently during the dry season, while zebra and buffalo formed the bulk of the lions diet in the rainy season. In this area Viljoen (1993) estimated that buffalo were the most important contributor to the lions annual meat requirements. In the younger age classes, female buffalo were selected significantly more so than males, but more bulls of an advanced age were taken (Viljoen, 1993). More impala females than males were killed, with no apparent selection for any of the age classes. Juvenile zebra were preyed upon more frequently than adults (Viljoen, 1993), while the opposite was true for warthogs. Average daily meat intake was calculated at 5.6 kg per female equivalent (Viljoen, 1993) Leopards The leopard s feeding behaviour is not as well known as those of the larger, more visible African carnivores such as the lion, cheetah and spotted hyaena, but their versatile feeding habits are still one of the more thoroughly documented attributes 22

34 of their ecology (Bailey, 1993). Numerous conclusions have been reached with regards to the leopard s feeding strategies: (1) mammals are the most important class of prey in their diet, (2) ungulates are the most important mammals in their diet, and (3) leopards are opportunistic feeders and will take any prey that is available (Bailey, 1993). Leopards take prey of a specific size class rather than a specific species (Bothma, 1997), and although it varies between different individuals and regions, tends to be in the 20kg to 80kg size class (Bailey, 1993; Bothma, 1997). Schaller (1972) mentions an upper limit of about 150 kg, two to three times the weight of the leopard itself. Leopards seldom kill large prey (Bailey, 1993), and when species killed do fall under the large-size class, it inevitably includes calf or juvenile ungulates. For example, it was found that all eland and wildebeest kills reported from Zimbabwe were calves (Grobler & Wilson, 1972) and similarly all gemsbok, hartebeest and wildebeest killed by leopards in the southern Kalahari were calves (Mills, 1984). In a sample of kills of both male and female Kalahari leopards, most of the prey weighed less than 30 kg and many kills were of animals weighing not much more than 5 kg (Bothma & Le Riche, 1986). Leopards in the KNP are known to prey on at least 31 species (Pienaar, 1969), while Schaller (1972) documented leopards feeding on at least 24 species in the Serengeti National Park. Bailey s (1993) study in the KNP assumed the biomass of leopard prey included (1) only the young of medium-sized ungulates, (2) all small ungulates, (3) all smaller mammals, and (4) game birds. Large ungulates were absent from their diet, with 77% of all leopard kills in the KNP being impala 23

35 (Bailey, 1993), as well as 83% and 92% in similar habitats (Sabi Sands and Timbavati respectively). This high frequency of impala in the leopard s diet is probably related to the high abundance of impala in these areas. In the savanna region of East Africa, where Thompson s gazelle are abundant, they were the leopard s most frequently taken prey (Kruuk & Turner, 1967). Other important ungulate prey of leopards in KNP according to Bailey (1993) was, in decreasing order of magnitude, common duiker Sylvicapra grimmia, steenbok Raphicerus campestris, warthog, and bushbuck Tragelaphus scriptus. Pienaar (1969) also found impala to be the main prey of leopard in the KNP. The second most important group of prey to leopards was small mammals, such as baboon Papio ursinus, porcupine and vervet monkey Cercopithecus aethiops (Bailey, 1993). Bailey (1993) found that leopards did not selectively kill impala according to sex; males and females were killed according to their occurrence in the population. In the Serengeti, where leopards killed proportionately more male than female Thomson s gazelle, Schaller (1972) found that males were more vulnerable to predation than females because nonterritorial males used riparian habitats where leopards often hunted. In the Kalahari, springbok were the most important ungulate prey species, with a relatively strong selection for adult males (Mills, 1984; Bothma & Le Riche, 1986). Red hartebeest calves, Alcelaphus buselaphus, steenbok, gemsbok calves, and duiker were also selected for (Mills, 1984). Size of prey influences the kill rates of leopards (Bailey, 1993). In the Serengeti, where gazelle formed the bulk of the leopards diet, a period of five to six days elapsed between kills (Schaller, 1972). Pienaar (1969) calculated an upper limit in 24

36 the KNP of one kill every 7.3 days, which corresponds to that found in Bailey s (1993) study areas. No significant difference was found between the kill rates of healthy male (once every 7.2 days) and female (once every 7.5 days) leopards. In the KNP, adult male leopards killed an average of 5.0 kg/day and consumed 3.5kg/day, while adult female leopards were estimated to kill and consume an average of 4.0 kg and 2.8 kg/day, respectively (Bailey, 1993). In the Serengeti, leopards killed only 2.7 to 3.3 kg/day (Schaller, 1972), with Bailey (1993) attributing the higher consumption rates of the southern African leopards to their larger size and the cooler temperatures of the more southern regions Cheetahs The majority of studies concerning the feeding ecology of cheetahs have been conducted on the open grassland plains of East Africa (Kruuk & Turner, 1967; Schaller, 1972; Caro, 1994). One of the reasons for this is the ease with which cheetahs can be observed and followed in this area, and the suitability of this environment for their hunting methods (Purchase & Du Toit, 2000). Opportunistic and direct observation of kills is the predominant method used for diet estimation of cheetahs in the open habitats of East and South Africa, but is impractical in the dense bush of Namibia (Marker et al., 2003). Scat analysis and the quantification of undigested prey remains is used in these areas to determine prey preference of cheetahs, with information on kills also being obtained, where possible, from radio-tracking flights and farmers (Marker et al., 2003). The cheetah is an opportunistic predator whose prey varies in size from rodents to adult ungulates (Marker et al., 2003). Although they are known to kill a wide 25

37 variety of prey, they tend to specialize on one species in a specific area (Mills, 1991). Thomson s gazelle was the prey of choice for cheetahs in the Serengeti, comprising over 91% of prey animals recorded (Kruuk and Turner, 1967; Schaller, 1972). In the KNP, Pienaar (1969) recorded 24 food items eaten by cheetahs, with impala comprising 68% of all kills reported. Broomhall (2001) confirms that impala were the dominant prey chosen by cheetah in the KNP. Purchase and du Toit (2000) showed that impala were also the preferred prey of cheetahs in Matusadona National Park, while in the southern Kalahari, cheetahs killed prey ranging from bat-eared foxes (Otocyon megalotis) to blue wildebeest, with springbok being the favoured species (Mills, 1984). Cheetahs on Namibian farmlands were found to select steenbok and hares, as well as the calves of kudu, eland and hartebeest (Marker et al., 2003). Size of prey also plays a large role in its selection (Schaller, 1972). Broomhall (2001) and Marker et al. (2003) state that cheetahs predominantly kill small-sized antelope, with Schaller (1972) noting that all species of larger prey taken in the Serengeti were less than two months old. Any adult prey animals that were taken, such as impala, Grant s and Thomson s gazelle, and reedbuck, all weighed less than 60 kg. However, cheetahs may attack larger prey, especially if two or more cheetahs hunt together (Schaller, 1972). Caro (1994) recorded an increase in weights of prey attempted with male group size, with Broomhall (2001) noting that solitary females hunted smaller prey animals such as steenbok, while male coalitions took larger prey such as kudu and zebra. Hofmeyr and Van Dyk (1998) report on the incidence of cheetahs using fences to help them bring down large 26