Antelope Conservation: From Diagnosis to Action

1

Our Antelope Heritage – Why the Fuss?

Jakob Bro‐Jørgensen

Mammalian Behaviour and Evolution Group, Department of Evolution, Ecology and Behaviour, Institute of Integrative Biology, University of Liverpool, United Kingdom

Introduction

Why a book dedicated to antelope conservation? Our planet has witnessed a decrease of more than 50% in its vertebrate populations since 1970, and this drastic decline has hit antelopes particularly hard, according to the Living Planet Index (BBC, 2008; McLellan, 2014; see also Craigie et al., 2010). Many will agree that antelopes constitute an outstanding aspect of the world’s biodiversity and that the prospect of losing this heritage is a concern in its own right. A savanna bereft of flickering herds of gazelles (Figure 1) or a rainforest where duikers no longer lurk in the understorey may be likened to bodies that have lost their souls. But leaving subjective sentiments aside, antelopes are also of fundamental importance for the functioning of many ecosystems across Africa and Asia. They have important roles as architects of habitats, as dispersers of seed, as the prey base for endangered carnivores and indeed in nutrient cycling in general (Sinclair & Arcese, 1995; Sinclair et al., 2008; Gallagher, 2013). Maintaining healthy antelope populations is therefore vital for the management of many ecosystems, and the motivation for this book comes from an urgent concern not only at the species level but also relating to wider repercussions at the ecosystem level.

Figure 1 Thomson gazelles and impalas in Maasai Mara National Reserve, Kenya

(© Jakob Bro‐Jørgensen).

Antelopes moreover provide a well‐suited model to obtain insights into the operation of threat processes affecting wildlife populations more generally. Because they share the same basic biology, yet display a striking variation in habitats and threats, this species‐rich group presents an extraordinary opportunity to pinpoint how human impact on wildlife populations depends on the interaction between threats and specific species traits. Many of the issues facing antelopes are central to the current conservation debate, including the sustainable use of wildlife (for meat and trophies), protection of migratory as well as highly habitat‐specific species in a world of climate change and habitat fragmentation, and the coexistence of wildlife with people and their livestock without conflict. Typically, antelope conservation takes place in developing countries with growing human populations and severely under‐resourced wildlife authorities, which brings the issue of how to integrate conservation and development to the forefront. Valuable long‐term data sets are present for several antelope species, placing them in a strong position to provide some general lessons for conservation biology, especially in relation to the particular challenge of preserving large mammals (MacDonald et al., 2013).

However, following a surge in pioneering field studies of many antelope species in the 1960s and 1970s, the reality is that antelope research seems to have lost its general appeal, and the attention from the general public is modest compared to that received by many of their mammalian relatives, such as carnivores and primates, which are widely seen as more charismatic. This book is intended to reinvigorate the interest in antelope research and give a deeper understanding of the threat drivers facing antelopes today, thereby providing a basis for reflection on common best practices in conservation. As a background, this introductory chapter will first take an evolutionary perspective to understanding the ecological importance of global antelope biodiversity and then outline the current conservation status of this world heritage.

Antelopes – an evolutionary success story … so far

A green world presents a tremendous opportunity for the evolution of efficient plant‐eaters, and here antelopes have been an extraordinary success story. A major evolutionary breakthrough took place in the Eocene some 50 Myrs BP when the compartmentalized ruminant stomach evolved (Fernández & Vrba, 2005). This enabled a more efficient breakdown of fibrous plant material by chewing cud and using microbial symbionts to digest cellulose. The antelopes are members of the ruminant family Bovidae, characterized by permanent horns consisting of a bone core covered by a sheath of keratin. The first known bovid fossil, Eotragus, dates back to the early Miocene some 20 Myrs BP (Gentry, 2000; Fernandez & Vrba, 2005), and since then, an astonishing adaptive radiation has taken place as bovid species have evolved to occupy a wide range of ecological niches. The majority of these species are antelopes: 88 extant species are represented by 14 species in Asia and 75 species in their main stronghold in Africa, with only the dorcas gazelle (Gazella dorcas) found on both continents. Antelopes vary in size from the 1.5 kg of a royal antelope (Neotragus pygmaeus) (Plate 3) to nearly a ton in a full‐grown giant eland bull (Tragelaphus derbianus) (cover).

So what distinguishes antelopes? Treating antelopes as a group is questionable from a strict evolutionary perspective because it violates the ideal of keeping together all species descending from a given distinctive ancestor. The group is created by cutting off two distinct monophyletic branches from the bovid tree: (i) the wild oxen Bovini, characterized by their heavier build and water‐dependence, and (ii) the wild goats and sheep Caprinae, characterized by their extreme adaptation to rocky habitats (Figure 2). However, antelopes are not defined only by what they are not (i.e., as a bovid that is neither an oxen nor a goat). They can be succinctly described as horned ruminants lightly built for swift movement in habitats with predominantly even ground. This has resulted in a characteristic graceful and elegant morphology, often adorned with spectacular ornaments and weapons due to strong sexual selection in the more social species (Stoner et al., 2003; Bro‐Jørgensen, 2007).

Figure 2 The evolution within Bovidae since the divergence from deer 32 million years ago (for common names, see the Appendix). Bar indicates one million years.

Based on Fernández & Vrba 2005; drawn in Dendroscope, Huson & Scornavacca 2012.

The broad array of ecological adaptations in antelopes is apparent when considering the variety between the 12 tribes (Plates 1, 2, & 3). The spiral‐horned antelopes of Africa Tragelaphini (elands, kudus, nyalas and allies), together with their Asian relatives Pseudorygini (saola Pseudoryx nghetinhensis) and Boselaphini (nilgai Boselaphus tragocamelus, four‐horned antelope Tetracerus quadricornis), represent a highly diverse ancient line from within which the wild oxen descended. Except for the browsing saola, they are mixed feeders; that is, feeding on both browse and grass. They vary more than tenfold in size and are found from dense forests (bongo Tragelaphus eurycerus, saola) to semi‐deserts (common eland Tragelaphus oryx), and from swamps (sitatunga Tragelaphus spekii) to mountains (mountain nyala Tragelaphus buxtoni). Other mixed feeders include the arid‐adapted gazelles Antilopini which span from hot to rather cold regions, and the horse antelopes Hippotragini, which predominantly graze and occur from relatively moist savannas (roan Hippotragus equinus and sable antelope Hippotragus niger) to semi‐deserts (oryxes) and deserts (addax Addax nasomaculatus). Both the latter tribes have representatives in Africa as well as Asia. Also mixed‐feeders, the African impala (Aepyceros melampus) and rhebok (Pelea capreolus) are the only living representatives of the tribes Aepycerotini and Peleini respectively. The grazing tribes include the reduncines Reduncini (lechwes, reedbucks and allies), adapted to relatively moist savannas and wetlands, and the alcelaphines Alcelaphini (wildebeests and allies), adapted to drier savannas; both are exclusively African. The Tibetan antelope (Pantholops hodgsonii), the only representative of the caprine‐related Pantholopini, also feeds on grass, as well as herbs, on the often snowy steppes of the Tibetan Plateau. Smaller antelopes include the duikers Cephalophini, which are adapted to the ecology of African forests, where they feed on high‐quality browse and fruits, and the dwarf antelopes Neotragini which are ecologically diverse, mainly browsers and frugivores, but some also feeding on grass (notably the oribi Ourebia ourebi), and inhabiting a wide range of habitats spanning from forests (royal antelope) and thickets (suni Neotragus moschatus, dik‐diks), to rocky outcrops (klipspringer Oreotragus oreotragus, beira Dorcatragus megalotis) and fairly open savannas (oribi); several neotragines are actually likely to be more closely related to gazelles than to the genus Neotragus. In contrast to the gregarious species of the open land, the smaller species in dense habitats are usually solitary or found in groups of minimal size (Jarman, 1974; Brashares et al., 2000).

Antelopes as an integral part of the structure and function of ecosystems

In an evolutionary and ecological sense, antelopes have thus been an immensely successful group, occupying a remarkable range of habitats. Moreover, within each habitat, a proliferation of species often occupies distinct niches in terms of their diet and antipredator behaviour. For example, 16 species coexist alongside each other in the Serengeti‐Mara ecosystem. Throughout Africa and Asia, antelopes often dominate the community of larger herbivores in undisturbed wilderness areas. Their numerical abundance – at least historically – combined with their long period of coevolution with plants and predators means that they are intrinsically linked to the function of the ecosystems they inhabit. Some of their ecological roles are fairly obvious whereas other important links are more subtle and indirect and some dynamics undoubtedly still await discovery.

Antelopes have a major impact on both the structure and function of the plant community. In some cases, the loss of antelope populations may even cause wilderness areas to switch from one biome to another. For example, the grazing pressure from the great migration of wildebeest in Serengeti‐Mara is crucial for maintaining the open landscape to which the wider savanna community is adapted. In the absence of wildebeest, thickets proliferate, and the whole system could eventually reach an ecological tipping point where the habitat becomes unfavourable for today’s rich community of grazers and gravitates towards an alternative, more wooded state (Sinclair et al., 2007). Antelopes may also have important effects on the vegetation that are less conspicuous. For example, impala distribute themselves in a ‘landscape of fear’ as they avoid areas of thick cover due to high predation risk from leopards and hunting dogs (Ford et al., 2014). As a consequence, impala browsing pressure on acacia is highest in open habitats, and this gives acacia species protected by thorns a competitive advantage in such areas. In this way, browsing by impala has been shown to shape the spatial structure of the woody community of African savannas (Ford et al., 2014).

Antelopes can also have a profound effect on the vegetation by acting as seed dispersers. Frugivores in forest habitats, such as the duikers, are highly important in this regard (Jordano, 2013). They act as vectors of seeds, and seed germination may even depend on being passed through the gut of an antelope consumer. In tropical forests, many of the most carbon‐rich hardwood trees rely on animals such as forest antelopes for their dispersal, and loss of seed‐dispersers through bushmeat hunting has been linked to a reduction in hardwoods (Brodie & Gibbs, 2009). Because hardwoods are particularly important in sequestering CO2, this could compromise the role of the forest as a carbon sink, which in turn reduces its potential to mitigate the adverse effects of climate change.

Antelopes are of crucial importance also as a prey base for larger predators: without thriving antelope populations, efforts to preserve carnivores will often make little sense. From a management perspective, it is important to recognize the intricate relationships between predators and their prey. Predator species show marked differences in their prey preference profiles. For instance, lions (Panthera leo) prefer large, relatively slow prey species that are not suitable prey for smaller predators (Sinclair et al., 2003). In turn, cheetahs (Acinonyx jubatus) prefer smaller, but fast prey species that are less preferred by lions (Hayward et al., 2006b), while leopards (Panthera pardus), ambush predators, also prefer smaller, but slower prey (Hayward et al., 2006a). Such relationships are the result of long‐term coevolutionary processes (Bro‐Jørgensen, 2013), and it is unreasonable to expect that different prey species can readily substitute for each other. A decline in the population size of one species can have knock‐on effects on others, and to maintain natural ecosystem dynamics the full breadth of species diversity within both predator and prey communities requires conservation.

Threats facing antelopes today

As a key component of natural ecosystems, antelopes are an integral part of global life support systems. In areas of poverty, they can directly benefit human livelihoods as sources of food for subsistence or sale and through other income‐generating activities such as ecotourism and trophy hunting. The physiological efficiency and high productivity of bovids is shown by the fact that the taxon includes the ancestors of the most important domesticated livestock: that is, cattle, sheep and goats. Yet, the evolutionary potential of antelopes and the ecosystem services they provide are usually grossly undervalued in the formal economy, and human development therefore takes place without the relevant costs from squandering areas of wilderness being integrated into land use planning.

Consequentially, human activities are rapidly decimating many of the remaining antelope populations: 31% (27/88) of the extant antelope species assessed by the IUCN Red List are now formally categorized as threatened (including 64% [9/14] of the Asian species) and a further 9% (8/88) as near‐threatened (IUCN 2015). The extinction in the wild of the scimitar‐horned oryx (Oryx dammah) in year 2000, and the global extinction of the bluebuck (Hippotragus leucophaeus) in 1800, and probably also the kouprey (Bos sauveli) in recent years, clearly point to the serious danger that further bovid extinctions are imminent. Particular hot spots of highly threatened species include the desert regions of North Africa, the horn of Africa, the West African rainforests and the Asian steppes. Taxonomically, species with high threat status are dispersed throughout the phylogeny. Conservation concerns are not limited to red‐listed species: the population trend is decreasing for 64% (54/84) of all the species assessed, stable for 33% (28/84) and increasing for only 2% (2/84) (i.e., the springbok Antidorcas marsupialis and black wildebeest Connochaetes gnou in Southern Africa). As many as 76% (67/88) of all species are threatened by exploitation through hunting and trapping primarily for meat, but also for horns (used predominantly as trophies and in traditional medicine), hides and – specifically in the Tibetan antelope – underfur (‘shahtoosh’) used for shawls. Various human land‐use changes affect 69% (61/88) of species, practically all of which are simultaneously affected by exploitation; specifically, 45% (40/88) are affected by livestock farming and ranching, and 48% (42/88) are affected by encroaching human settlements. In addition, 13% (11/88) of species are threatened by war or other civil unrest; half of these are in the Horn of Africa and also the Sudano‐Sahelian savannas belt is severely affected. Currently, 18% (16/88) of species are referred to as affected by climate change, but our knowledge in this area is still limited, and the figure may rise as more information becomes available (Akçakaya et al., 2014; Payne & Bro‐Jørgensen, 2016).

Outline of this book

In summary:

Antelopes are a high conservation priority of significant ecological importance

Multiple threats face this ecologically diverse set of species

Conservation generally takes place in developing economies with growing human populations so social sustainability of any conservation action is a priority

Given these conditions, which approaches can most effectively secure antelope populations into the future? The chapters in this book seek a deeper understanding of the key threat processes facing antelopes today and critically evaluate the various options for action. Whereas a broad consensus emerges on several issues, a diversity of opinion also manifests itself on certain points, reflecting the varied experience of the authors. To begin with, Chapter 2 provides an overview of ecosystem functioning and conservation challenges pertaining to savannas, a habitat of vital importance for antelope biodiversity. Chapter 3 goes on to present a conceptual framework for understanding what regulates antelope populations in natural ecosystems and uses this insight to explore the potential impact of climate change alongside other threat drivers. Following on from this, Chapter 4 focuses specifically on interspecific interactions over resources and provides a critical review of the current evidence that competition and facilitation significantly affect antelope population performance. Chapter 5 reviews the role of disease in antelope ecology, both as part of natural systems and as a threat associated with human activities.

In Chapter 6, attention turns to human exploitation of antelope populations with a review of the conservation impact of subsistence hunting of antelopes for meat, emphasising forest systems. Next, Chapter 7 examines the potential of trophy hunting to contribute to antelope conservation. Considering a broader set of management interventions, Chapter 8 takes its outset in the South African context and discusses the usefulness of a range of options to promote antelope conservation. Chapter 9 in turn outlines ways in which molecular techniques can be applied to inform antelope conservation; and Chapter 10 focuses specifically on the application of landscape genetics as a tool in conservation. Chapter 11 introduces another novel conservation technique, the use of camera‐trapping in population monitoring. Chapter 12 provides a review of the use of reintroduction in antelope conservation, and Chapters 13 and 14, by concentrating on the critical conservation status of Sahelo‐Saharan desert antelopes, stresses the urgent need for action to preserve the most threatened antelopes. Rounding off, Chapter 15 reflects, based on experience from saiga (Saiga tatarica) conservation, on the factors that can create opportunities and present obstacles when it comes to safeguarding antelope populations in practice. Finally in Chapter 16, key challenges facing antelope conservation over the next century are summarized in a synthesis.

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2

Conservation Challenges Facing African Savanna Ecosystems

Adam T. Ford¹, John M. Fryxell¹, and Anthony R. E. Sinclair²

1 Department of Integrative Biology, University of Guelph, Canada

2 Biodiversity Research Centre, University of British Columbia, Canada

People evolved in African savannas and rapidly spread across the rest of the globe, assuming a defining role in the acquisition of space, energy, and other resources. Despite an epoch of co‐existence with wildlife, the tides are shifting towards an increasingly troubled future for antelope in these ancient landscapes. In this chapter, we review the biophysical characteristics of savannas, some of the key interactions that define how savannas function, and how people are changing this functionality. We end by highlighting conservation efforts that can help maintain ecosystem function in an increasingly human‐dominated world. Within this context, we focus on issues relating to large herbivores in general and in particular the antelopes that often dominate the ecology of many savannas.

Key characteristics of savanna systems

At the global scale, savannas occur between grasslands and forests, typically where rainfall ranges between 50 and 130 cm per year and where average temperatures rarely fall below 20°C (Sankaran et al., 2005; Lehmann et al., 2014). At the landscape scale, savannas are defined by pronounced heterogeneity in vegetation cover, manifesting itself as a discontinuous overstory of woody cover, interspersed with herbaceous understorey and bare ground. Indeed, it is the co‐domination of trees and grasses that most clearly distinguishes a savanna ecosystem from that of forest or grasslands. Over time, the relative composition of tree and grass cover changes in a shifting mosaic largely determined by the interaction of bottom‐up factors – rainfall, fire, soil nutrients – and top‐down factors – herbivory and, indirectly, via predation and pathogens.

The temporal pattern of rainfall underlies ecological interactions in savannas. Savanna ecosystems typically experience a period of four or more months of very low rainfall, coupled with one or more periods of high rainfall. Marked seasonality results in dramatic pulses in vegetation growth in both understorey and overstory plants. In these low rainfall environments, soil moisture is often the major limiting factor for plant growth (Breman & de Wit, 1983; McNaughton, 1985). As such, when sufficient rainfall occurs, a carpet of nutritious new grass‐shoots rapidly emerge, either from the seed bank in the case of annuals or from root or crown reserves in the case of perennial grasses.

As with rainfall, both the frequency and intensity of fire affects the composition and spatial patterning of tree‐grass cover in savannas. In landscapes where fires are frequent, fires tend to be less severe, and cover tends to be dominated by grasses. Within days (Green et al., 2015) to years (Sensenig, Demment et al., 2010) after a fire, nutrient release increases the quality of forage, which then attracts smaller and medium‐sized ungulates. Fire also reduces the accumulation of plant biomass and increases visibility, thereby enhancing the ability of medium and larger‐sized antelope to detect and avoid their predators. Thus, recently burned areas may offer both forage and antipredator benefits to antelope.

The biomass potential of vegetation communities in African savannas is also underlain by soil fertility. Concentrations of key nutrients for plant growth depend on geological materials and the degree of weathering, erosion, and leaching that has taken place (Hopcraft et al., 2010). Over time, soils may become weathered and consequently low in crucial minerals. In other places, volcanism, such as that associated with the African rift, is responsible for deposition of nutrient‐rich ash that can be highly productive. The distribution of nutrient‐rich and poor soils can be highly patchy relative to the movements of large mammalian herbivores (Goheen & Palmer, 2010), further adding to the spatial heterogeneity of savanna vegetation. At the patch scale, ‘hotspots’ of nutrients provide access to high‐quality forage, attract grazers, and keep grasses in a state of high productivity (Anderson et al., 2010). These hotspots can be derived through natural variation in nutrient availability or through human sources, such as abandoned cattle corrals (Augustine, 2003; Augustine et al., 2003; Augustine, 2004).

One of the most conspicuous top‐down forces in African savannas is herbivory by the species‐rich and abundant populations of ungulates. For example, the biomass of large herbivores in Laikipia, Kenya, is 1.74 t/km² among 9 species (Georgiadis et al., 2007), and 0.94 t/km² among 31 species in the Serengeti‐Mara ecosystem (Frank et al., 1998). Conversely, in temperate systems, such as Yellowstone National Park in the United States, there are 0.37 t/km² of grazer among eight species (Frank et al., 1998). The composition of antelope communities varies widely among different vegetation types and land uses in Africa. Landscapes with higher tree cover tend to support a great abundance of browsers, while grassier areas are dominated by grazers. Within these broad diet types, there exists a pronounced diversity of feeding styles, body sizes, and digestive strategies that confer differential use of forage resources (Jarman, 1974; Demment & Van Soest, 1985). For example, impala (Aepyceros melampus) tend to browse more in the dry season when grasses are rank, but will switch to grass in the wet season (Augustine, 2010). Dik‐dik (Madoqua spp.) eat a diversity of browse species year‐round and rarely consume grasses (Manser & Brotherton, 1995). Buffalo (Syncerus caffer), zebra (Equus quagga), and wildebeest (Connochaetes taurinus) compete with smaller antelope like Thomson’s gazelle (Eudorcas thomsonii) for the same plant species, but each consumes different parts of grasses to maximize intake of biomass (for larger species) or nutrient‐dense forage (for smaller species) (Jarman, 1974; Demment & Van Soest, 1985; Cerling et al., 2003).

Because of the pronounced environmental heterogeneity borne out over large (landscape) and fine (patch) scales, many antelopes are highly mobile, both within their home ranges (Augustine, 2010) and via seasonal migrations (Fryxell & Sinclair, 1988; Holdo et al., 2009). The abundance, diversity, and mobility of African antelope enable them to effectively exploit forage that can vary widely in quality, quantity, and palatability (Fryxell et al., 2005). Together, both small and large herbivores alter shrub cover (Prins & Vanderjeugd, 1993; Augustine & McNaughton, 2004; Sankaran et al., 2005; Bond, 2008; Goheen et al., 2013; Pringle et al., 2014) and the distribution of grass biomass (du Toit & Olff, 2014). Consequently, factors influencing the movement and abundance of antelope can profoundly affect the vegetation structure of African savannas.

In addition to resources (e.g., water, forage), the distribution and abundance of African antelope is also driven by pathogens and predators. For example, rinderpest caused widespread declines in antelope in the Serengeti prior to the 1950s. With the loss of herbivory, grass biomass accumulated, prompting a series of intense fires that carried into the canopy and reduced the amount of woody cover (Holdo et al., 2009). On smaller and closed systems, such as the game reserves of South Africa, tuberculosis can spread among antelope and spill over into the livestock herds on neighbouring range lands (Michel et al., 2006). Indeed, species diversity in reserves increases risk of infection for impala, as does decreasing reserve size (Ezenwa, 2004). Thus, the characteristic mobility and diversity of antelope assemblages mediates the extent to which pathogens shape savanna ecosystem function.

Predation can powerfully shape both the abundance and distribution of antelope. Smaller species (<100 kg) are more vulnerable to predators than larger species, which are more vulnerable to starvation (Sinclair et al., 2003). This allometric relationship arises because larger species are better able to defend themselves, and because there is a greater diversity, dietary overlap, and abundance of smaller predators than larger ones (Sinclair et al., 2003). Spatial variation in predation is also linked to the patchy habitat structure of savannas. Lions (Panthera leo), for example, prefer to hunt in areas with greater cover (Hopcraft et al., 2005), as do wild dogs and leopards (P. pardus) (Ford et al., 2014). As a result, landscapes characterized by greater cover may have stronger top‐down effects than more open areas (Hopcraft et al., 2010). Likewise, homogenization of this structure can heighten top‐down regulation of predators on antelope (Beale et al., 2013). In addition, the behaviour (Underwood, 1982) and movement patterns (Thaker et al., 2011) of antelope are shaped by the perceived risk of predation relative to foraging gains, with many species acting more vigilant and more cryptic, or altogether avoiding areas with dense cover. Temporal variation in predator activity is seemingly influenced by both prey vulnerability and thermoregulatory demands. Savanna carnivores are typically more active at night, during crepuscular periods, and on full (or new) moons (Packer et al., 2011; Cozzi et al., 2012). As result, antelope like impala (Ford et al., 2014) and dik‐dik (Ford & Goheen, in press), shift between habitats with dense cover in the day to more open habitats at night.

People and the function of savannas: salient conservation issues for antelopes

Of all terrestrial biomes, African savannas may be the ecosystem with the longest history of human occupancy, and it is difficult to separate how these landscapes would have evolved in the absence of human activity. However, there is little doubt that human population growth here as elsewhere has been implicated in much of the loss of biodiversity that has occurred over the past 200 years (Vitousek et al., 1997; McKee et al., 2004). In 1800, the world supported 1 billion humans. That number doubled by the middle of the 20th century and is currently slightly higher than 7 billion. This growth occurred despite profound changes in human demographic rates across the globe, commonly termed the ‘demographic transition' (Bongaarts, 2009). As countries develop, initial drops in mortality rate due to improved health care drive rapid growth. This typically slows down as fertility rates more slowly equilibrate with mortality rates, but human populations continue to grow at a decelerating rate throughout that socio‐economic transition period and indeed for several decades more, as the population converges on a new stable configuration. These patterns are well in place across much of the globe, but even optimistic forecasts call for a human population of 9 billion by the time humans approach zero population growth. In other words, we can anticipate further demands on all natural resources simply to meet the minimal demands of a larger population of humans, let alone cope with rising economic expectations and consumption patterns as development proceeds. This will further accentuate the already pronounced demand by humans (Vitousek et al., 1997) for freshwater supplies, arable land, and wood fibre for fuel and home construction as well as implying increased loading of nitrogen and siltation in watercourses.

Next, we consider how global shifts in climate, human population growth, and the changing structure of socio‐economic systems in Africa are changing the structure and function of savanna ecosystems, and along with it, the distribution and viability of antelope populations. We then review how, along with these large‐scale changes, savannas are being transformed by local changes in livestock utilization, disease, fire management, invasive species, abundance of predators, consumption by people, and habitat loss.

Climate change.

Climate change is altering rainfall and temperature patterns throughout the savannas of eastern and southern Africa. Climate models suggest that while the total amount of rainfall is expected to increase slightly, variation in rainfall intensity is predicted to increase dramatically (Hulme et al., 2001). This means that droughts are drier, or last longer, and that rainy seasons are wetter. Such changes may impact antelope in a number of ways; for example, extended droughts may reduce the availability of forage, increase fire frequency, and increase the prevalence of grasses vs. trees (Bond, 2008). Furthermore, temperature increases (Hulme et al., 2001) may reduce the hunting effort of some carnivores, like African wild dogs (Lycaon pictus) (Woodroffe, 2011), potentially reducing overall predation on antelope prey like dik‐dik and impala. Surface water availability may also be reduced because of climate change (De Wit & Stankiewicz, 2006), and should have a greater impact on larger, water‐dependent antelope (e.g., topi, Damaliscus lunatus) than smaller species (e.g., dik‐dik) (Georgiadis et al., 2007; Augustine, 2010). Many large herbivores require water on a daily basis, thereby limiting spatial distribution at certain times of year to areas adjacent to permanent water sources (Redfern et al., 2003; Hopcraft et al., 2012).

Variation in weather caused by the El Niño/Southern Oscillation (ENSO) can further exacerbate changes in savanna ecology. Years with strongly positive ENSO scores typically experience less rainfall in the wet season, but more rainfall in the dry season, than occurs on average. Some antelope, such as Serengeti wildebeest, have highly synchronized breeding, timed to coincide with the latter part of the wet season. As a consequence, the survival of young is highly dependent on food conditions over the dry season; hence positive ENSO years lead to higher food availability and improved offspring recruitment in wildebeest (Sinclair et al., 2013). However, other species of Serengeti herbivores breed throughout the year and so experience little benefit from positive ENSO events. Top carnivores, such as lions, benefit in turn from improved numbers of young prey, which form the bulk of their diet, so leading to improved cub recruitment (Mosser et al., 2009; Sinclair et al., 2013). Because ENSO‐like events are predicted to increase in frequency with climate change (Timmermann et al., 1999), uncertainty in top‐down and bottom‐up forcing for antelope will likely increase.

Human population growth.

The growth of the human population is having an adverse impact on antelope populations by fomenting conflict over scarce resources, altering land‐use to more intensive production methods, and redistributing people to more agriculturally marginal areas that are often adjacent to protected areas. Indeed, human populations at the margins of such protected areas are growing even faster than those in other comparable rural landscapes (Wittemyer et al., 2008). This might reflect the economic advantages of living close to protected areas, which receive external funding not available to communities in other rural areas. Therefore, the human footprint around protected areas is likely to increase in the near future. Of particular concern is competition for scarce water supplies in semi‐arid environments and declines (e.g., for charcoal production) or increases (e.g., because of over‐grazing) in woody vegetation to meet the needs of a growing human population (Wittemyer et al., 2008). For example, models suggest profound changes to the Serengeti ecosystem may accompany increased usage of permanent water supplies, such as the Mara River (Gereta et al., 2002). Such speculation is not unreasonable, given the rapid population growth that has been well documented around the Mara Reserve and Serengeti National Park (Ogutu et al., 2009; Ogutu et al., 2011; Bhola et al., 2012). These same economic forces will also increase pressure for access to scarce grasslands within protected areas to feed livestock as well as suitable sites for raising cereal crops, such as wheat.

Economic development.

Since World War 2, economic linkages between European‐based colonial administrations and African countries have been supplemented by stronger ties between Africa and the emerging economies of the Middle East and Asia. These new economic partnerships are transforming patterns of development in savanna ecosystems (Cotula, 2009). For example, Kenya and China announced a USD $5 billion deal involving Chinese investment in Kenya transportation and energy; foreign investment in Ethiopia’s biofuel sector is concentrated in areas where livestock grazing predominates land use, one of the few land‐uses that are compatible with wild populations of antelope (Vermeulen & Cotula, 2010). Throughout 2004–2009, over 2.5 million ha were approved as foreign land allocation in Ethiopia, Ghana, Madagascar, Mali, and Sudan (Cotula, 2009). This systematic shifting of land‐use and economic valuation of uncultivated land may further erode the habitat available for antelope in areas outside of protected areas.

Livestock.

In addition to these global drivers of change, local variation in human activity can have pronounced effects on antelope in African savannas. Where people and antelope co‐exist, livestock and ranching are the primary means of livelihood. In many areas, wildlife and livestock readily co‐exist – and have for millennia. Indeed, wild grazers facilitate forage availability for cattle in some seasons (Odadi et al., 2011), while traditional ranching practices facilitate safety for impala (Ford et al., 2014). In other areas, high stocking densities deplete forage reserves for wild herbivores (Georgiadis et al., 2007; Georgiadis et al., 2007; Kinnaird & O'Brien, 2012), and cause shrub encroachment into grassy areas (Roques et al., 2001; Sankaran et al., 2005; Ward, 2005). Shrub encroachment has been implicated in the declines of species preferring more open habitats, such as the critically endangered hirola (Beatragus hunteri) (Dahiye, 2009).

Pastoralism and more recently, commercial ranching, re‐create some of the processes driven by wild herbivores, though their impacts on vegetation are not entirely interchangeable. Unlike many antelope populations, livestock often are supplemented with artificial mineral, water, and forage resources. Livestock are also defended by herders from most predation, and their movement is determined largely by access to forage and water, rather than risk avoidance. Unless there is catastrophic drought, these adjuncts (forage resources, safety) allow livestock to acquire forage that wild antelope are reluctant to use and, as such, may occur at biomass densities much greater than that of wild herbivores (Ottichilo et al., 2000; Georgiadis et al., 2007; Kinnaird & O'Brien, 2012). Indeed, livestock can alter the distribution of woody cover, especially at high stocking densities, leading to shrub encroachment and a reduction in palatable grasses (Joubert et al., 2008; Eldridge et al., 2011). Understanding the dynamic coupling of people, their livestock, and savanna ecology is a critical gap in our knowledge of antelope conservation in human‐occupied‐areas.

While there is some indication that cattle and zebra may facilitate one another (Odadi et al., 2011), it is less clear how most species of antelope and livestock interact. In some of the pastoralist and commercial ranching properties of central Kenya, abandoned cattle corrals provide access to nutrient‐enriched grasses (Augustine, 2004) that also facilitate predator‐avoidance for impala (Ford et al., 2014). This suggests that cattle ranching may facilitate large, grazing antelope that exploit both the forage and safety benefits accruing from the open spaces. However, predators may preferentially hunt in these abandoned cattle corrals, potentially contributing to apparent competition between abundant grazers (e.g., zebra) and rarer antelope (e.g., roan (Hippotragus equinus), sable (H. niger), tsessebe (Damaliscus lunatus lunatus)) that aggregate together (Owen‐Smith & Mills, 2006).

The type of livestock also bears on the question of how people and wildlife interact. For example, in parts of East Africa, camel ranching is becoming increasingly more common as a means to buffer against catastrophic droughts that more greatly threaten cattle husbandry. Moreover, camels and goats consume browse, whereas cattle and sheep forage on grasses. Thus, species composition of livestock herds determines the extent to which wild and domesticated herbivores compete or facilitate one another. While there is a tendency for antelope and other wild herbivores to occur at lower – and declining – densities as livestock density increases (Georgiadis et al., 2007a; Georgiadis et al., 2007b), pastoralism is only one of many anthropogenic factors that are changing the function of savanna ecosystems and the abundance of antelope.

Disease.

Livestock can also serve as a reservoir for disease transmission to wild antelope (Prins & Weyerhaeuser, 1987; Mbise et al., 1991; Prins & Vanderjeugd, 1993; Holdo et al., 2009). Diseases such as malignant catarrhal fever, rinderpest, and brucellosis are shared across wild and domesticated ungulates. Rinderpest transmission from cattle caused massive declines in many wild ungulates in the early 20th century, such