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CHAPTER 1. GENERAL INTRODUCTION 1.1. Introduction This thesis describes the ecology of desert-dwelling giraffe Giraffa camelopardalis in the northern Namib Desert, north-western Namibia. It assesses the genetic architecture of the giraffe in the study region and in the nearby Etosha National Park in light of subspecies variation within the genus. From this starting point, the research focuses on the structure and dynamics of the desert population and the behavioural and foraging adaptations of giraffe associated with survival at the extreme edge of the species’ range. In this chapter I briefly describe desert environments and in particular the Namib Desert, followed by general adaptations of biota to deserts. I then discuss the taxonomy, distribution of subspecies and conservation status of giraffe throughout the species’ extant range, and the status, historical distribution and population structure of giraffe in Namibia. Finally, I focus on the key research questions addressed in this study. 1.2. Deserts Deserts comprise one of the most extensive environments on Earth. Occurring on all continents, deserts occupy up to 40% of the land surface (Crawford, 1981; Allan, 1993). Deserts vary markedly in size, climate, soils and diversity, with hot deserts located between latitudes 20° and 35° north and south of the equator, and cold deserts between latitudes 65° and 90° (Degen, 1997). Different disciplines describe deserts based on different structures or processes: ecologists use vegetation biomass and structure, climatologists use rainfall and atmospheric moisture, and geomorphologists focus on soil structure, landforms or surface hydrology (e.g. Giess, 1971; White, 1983; Shmida, 1985; Whitford, 2002). As an example, Koppen deserts are described as having sparse vegetation, high temperatures, annual rainfall less than 254 mm, and conditions where more water is lost through evaporation than is gained from precipitation (Larson, 1970; Lovegrove, 1993). Chapter 1. General Introduction 1 Temperate to hot deserts comprise the majority of the world’s deserts and are generally characterised by low and unpredictable precipitation, low relative humidity, desiccating winds and high temperatures (e.g. Brown, 1974; Allan, 1993; Rundel & Gibson, 1996; Degen, 1997; Dickman et al., 1999a). The United Nations Educational, Scientific and Cultural Organization (UNESCO) describes three different desert zones or types: semi-arid (<600 mm rain/year), arid (<200 mm rain/year) and hyper-arid (<25 mm rain/year) (Allan, 1993). 1.2.1. Namib Desert Located in the driest country south of the Sahara, the Namib Desert lies in the latitudinal range of 18° to 30° S (Lovegrove, 1993). It extends almost 2 000 km north to south along Africa’s southwestern seaboard and it is predominantly less than 200 km wide (Louw & Seely, 1982; Seely, 1987; Lovegrove, 1993). Temperatures range from below zero during the cold-dry winter months to above 45°C in the hot-dry summer; rainfall is highly variable with a mean of 5-85 mm per annum at different locations, although prolonged years of no rainfall are not uncommon (Louw & Seely, 1982; Lovegrove, 1993). Precipitation from fog is an important lifeline of the Namib Desert, particularly due to the region’s low and highly variable rainfall (Lancaster et al., 1984; Pietruszka & Seely, 1985; Henschel et al., 1998; Seely & Henschel, 1998). Fog provides essential sustenance for both plants and animals, enabling them to flourish in an otherwise waterless environment. The desert landscape has undergone continuous change over the millennia due to the influence of episodic climatic events (Armstrong, 1990). As one of the most ancient deserts in the world—it is between 50 and 80 million years old—the Namib Desert is typified by a mass of mobile sand dunes (Seely, 1987; Lovegrove, 1993; Barnard 1998). The Namib Desert is bordered by the Atlantic Ocean to the west, while to the east the ‘sand sea’ opens up into gravel plains that are dotted with inselbergs (Seely, 1987; Lovegrove, 1993; Barnard, 1998). The Great Western Escarpment to the east of the northern Namib Desert is categorised by the Etendeka lava field and associated mountain ranges, and separates the coastal desert Chapter 1. General Introduction 2 from the eastern hinterland (Seely, 1987; Rice & Gibson, 2001). Large ‘sand’, or ephemeral rivers dissect the arid landscape of the northern Namib Desert, providing a refuge for one of the region’s most striking vegetative features—the riparian woodlands (Jacobson et al., 1995). Subterranean waters flow beneath the surface of the sand rivers, creating linear oases. Precipitation in the eastern escarpment zone provides valuable water flows along the river courses, providing life to the riparian woodlands. These features consequently form important refugia that provide shelter, food and water for humans and animals alike (Lovegrove, 1993; 2000). The Namib Desert has remarkably diverse animal life for such an arid environment. Much is owed to the seasonal fog, rather than the limited rainfall, and to the high diversity of succulent plant species (Von Willert et al., 1992; Lovegrove, 1993). Both plants and animals exhibit high levels of endemism and adaptations to the arid conditions of the Namib Desert. From Welwitschia mirabilis to the head-standing beetle Onymacris unguicularis, and Gray’s lark Ammomanes grayi to the golden mole Eremitalpa namibiensis, the Namib Desert is home to a wide array of endemic or near-endemic species, including more than 25 species of reptiles, six birds, two bats, gerbils, invertebrates, lichens and plants (Louw & Holme, 1972; White, 1983; Wessels, 1989; Barnard et al., 1998; Branch, 1998; Maggs et al., 1998; Seymour et al., 1998; Griffin, 1999; Hilton-Taylor, 2000; J. Lalley, unpublished data). 1.2.2. Desert adaptations The diversity of animal species in desert environments is predominantly dependent on rainfall, but is shaped also by the high and fluctuating temperatures and availability of vegetative cover (Seely, 1987; Broyles, 1995; Rundel & Gibson, 1996). The driest deserts thus contain fewer species than more temperate deserts. Desert plant species, commonly known as xerophytes, show many adaptations for survival, including the following (e.g. Brown, 1974; von Willert et al., 1992; Maggs et al., 1998): • perennial forbs and herbs that germinate rapidly and mature when sufficient moisture is available; • succulent species that retain moisture; Chapter 1. General Introduction 3 • deciduous, sclerophyllous shrubs that drop leaves during dry periods; • geophytes that have most of their biomass underground; • many taxa with small leaves, waterproofed to limit water loss; and • grey-green leaves that reflect light and reduce heat absorption. Both plants and animals obtain heat directly through radiation as well as indirectly via convection from the air and conduction from the substrate, however, plants are often less susceptible to extremes of temperature than animals because of their insulative woody tissues and bark (e.g. Seely, 1978; Louw & Seely, 1982; Louw, 1993; Broyles, 1995; Jacobson et al., 1995; Cloudsley-Thompson, 1996; Wickens, 1998; Kitchen et al., 2000). Desert animals have developed a range of strategies and have evolved morphological, physiological and behavioural adaptations that enable them to respond to the high temperature variability and fluctuating resource availability that typify deserts. Although some adaptations differ between small and large mammals, reptiles, birds, and other taxa, most serve to conserve water and regulate heat. Behavioural adaptations vary, from simply avoiding extreme climatic conditions to increasing nutrient and moisture intake during the brief periods when food and water are abundant (e.g. Schmidt-Nielson, 1964; Joubert, 1974; Louw & Seely, 1982; Scheepers, 1992; Bradshaw, 1997; Degen, 1997; Bothma, 1998; Dickman et al., 1999a & b; Le Pendu & Ciofolo, 1999; Hudson & Haigh, 2002). Examples include: • seasonal migrations; • biphasic, nocturnal or crepuscular activity; • burrowing, estivation, hibernation, dormancy or torpor; • orientation of body away from sun; • urohydrosis; • selection of moisture-rich forage; and • collection of fog precipitation from plants and substrate. Physiological adaptations, such as those listed below, revolve around the ability to overcome the paucity of water in deserts (e.g. Scholander et al., 1950; Joubert, 1974; Langman et al., 1978; Langman, 1985; Seely, 1987; Louw, 1993; Lovegrove, 1993; MacLean, 1996; Lovegrove, 2000): Chapter 1. General Introduction 4 • concentration of urea; • excretion of uric acid; • expiration of unsaturated breath; • heterothermy; • ability to manufacture water metabolically from food sources; and • nasal heat exchange. Various morphological adaptations allow avoidance of excessive heat loads (e.g. Miller & Stebbens, 1964; Rundel & Gibson, 1996; Schmidt-Nielsen, 1998; Hudson & Haigh, 2002): • reflective pelage (coat), feathers and scales that act as barriers to heat transfer or reduce water loss; and • longer or larger appendage sizes that allow dissipation of body heat. It is unlikely that all of these responses to arid conditions evolved as adaptations only to aridity (see Gould & Lewontin, 1979). For example, mammalian hair or avian feathers may have been selected for under cooler, non-arid conditions, but provided benefits subsequently when aridity prevailed. Hence, I use the term ‘adaptation’ loosely here to describe the range of responses exhibited by biota in desert environments. Adaptations

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