In addition to its six main chapters, the book includes nineteen essays by regional experts that provide more depth on key issues, as well as six detailed appendixes that present summary data used in the analyses, specific analytical methodologies, and a thorough text description for each of Africa's ninety-three freshwater ecoregions.
Freshwater Ecoregions of Africa and Madagascar provides a blueprint for conservation action and represents an unparalleled guide for investments and activities of conservation agencies and donor organizations.
About the Author
Michele Thieme joined the World Wildlife Fund's Conservation Science Program in 1999 and works to conserve freshwater life in WWF’s priority river and lake basins. Her current research centers on the role of protected areas in conserving freshwater ecosystems, and improving conservation planning in freshwater environments. She leads the Spatial Tools and Analysis Team and is an active member of the Impact Evaluation team.
Robin Abell is a senior freshwater conservation biologist at WWF. She specializes in broad-scale conservation planning to protect freshwater biodiversity.
Dr. Melanie L.J. Stiassny is Axelrod Research Curator at the Department of Ichthyology, American Museum of Natural History.
Paul Skelton is Managing Director Emeritus of the South African Institue for Aquatic Biodiversity.
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Freshwater Ecoregions of Africa and Madagascar
A Conservation Assessment
By Michele L. Thieme, Robin Abell, Melanie L. J. Stiassny, Paul Skelton, Bernhard Lehner, Guy G. Teugels, Eric Dinerstein, Andre Kamdem Toham, Neil Burgess David Olson
ISLAND PRESSCopyright © 2005 World Wildlife Fund
All rights reserved.
From the muddy waters of the Congo River spilling into equatorial swamp forests to the vast floodplains of the Inner Niger Delta, from the deep and shallow lakes of the Rift Valley in eastern Africa to the ephemeral streams of the Namib Desert, the fresh waters of Africa and Madagascar are incredibly diverse. Matching this array of systems is a wondrous diversity of life forms and strategies for survival. Below the surface of nearly every body of water, even the most ephemeral pools, freshwater organisms survive. More than 4,300 described species of freshwater vertebrates and invertebrates (fish, aquatic-dependent mollusks, amphibians and reptiles, and mammals) that live in the continent's waters were included in this conservation assessment. An abundance of new species and communities are yet to be described (Lundberg et al. 2000; Stiassny 2002a).
For hundreds of millions of African people, the health of these freshwater systems and of the diverse communities of organisms that depend on them often is inextricably linked to their own health and survival (Revenga et al. 2000; Jackson et al. 2001; Johnson et al. 2001; Everard and Harper 2002; Directorate of Fisheries – Ghana 2003). As in human communities everywhere, clean freshwater is a daily necessity, and healthy ecosystems are needed for its provision. For example, about one-third of twenty-five large cities in Africa draw their drinking water from forested protected areas (Dudley and Stolton 2003). Fish and other aquatic and amphibious animals are also critical sources of protein for many people in the region. The vital importance of Africa's wetlands in providing food security, tradable products, and cultural and aesthetic values for local communities is clear (Brouwer 2003; Denny 2001; essay 1.1). As recently recognized by the targets set at the World Summit on Sustainable Development, sustainable development in the region will not occur without clean and adequate sources of freshwater (United Nations 2002). The economic value of the ecosystem services that freshwater systems provide is extraordinary; one recent estimate places a global value of US$6.6 trillion annually for the goods, services, biodiversity, and cultural contribution provided by all inland waters and wetlands (Postel and Carpenter 1997; Costanza et al. 1997; Balmford et al. 2002; essay 1.2).
Yet freshwater systems across much of Madagascar and the African continent are under increasing pressures from the combined onslaught of introduced species, pollution from burgeoning populations and industries, dams and water withdrawals, and overall land use change (Cohen et al. 1996; Lévêque 1997; Davies and Day 1998; Chapman and Chapman 2003).
This multitude of threats requires us to establish priorities and to set goals and targets for the conservation of aquatic systems and their rich biodiversity. We need a framework that allows us to take conservation actions based on knowledge of what is important at global, regional, and local scales. This book aims to present an objective plan for large-scale biodiversity conservation in Africa and Madagascar, focusing on the global biodiversity values of the region.
To set priorities for future work, we need first to look backward to examine the evolution and natural diversity of Africa's freshwater systems. In this chapter, we introduce Africa's fresh waters (figure 1.1) and the forces considered responsible for the distribution and concentration of Africa and Madagascar's freshwater biodiversity. We then move to the modern era to review contemporary pressures and threats to African freshwater systems that will dramatically and permanently change the distribution of their biota unless addressed in the coming years.
The Evolution and Diversity of Africa's Freshwater Systems
Africa's river and lake basins are among the oldest in the world, having a much longer history than those in the temperate zone. The breakup of Gondwanan landmasses in the mid- to late Mesozoic (165 – 65 m.y.a.) led to the separation of Madagascar from Africa and India; Madagascar may have been isolated from mainland Africa for as long as 160 m.y. (Rabinowitz et al. 1983; Lourenço 1996). It is unclear whether the freshwater fauna of the island was present at that time or originated later via marine dispersal (see essay 3.6; Krause et al. 1997). The major catchments of mainland Africa, with the exception of the drainage systems of eastern Africa, have existed since before the Miocene (23.8 – 5.3 m.y.a.), although the details of their configuration have changed over time.
The late Miocene marked the end of a long period of tectonic stability across the continent (Beadle 1981). At this time many of the continent's basins, including the Niger, Chad, and Congo, were endorheic (i.e., forming large inland lakes without external drainage) (Roberts 1975). The relief of the continent is also thought to have been low, such that divides between basins were low and faunal barriers between systems were permeable, resulting in a widespread, uniform freshwater fauna (Lévêque 1997). Post-Miocene earth movements marked the beginning of the rifting and uplifting that caused greater separation of basins and promoted speciation. Because of these tectonic activities over the past 20 million years, African rivers generally have many more rapids and waterfalls than other rivers in the world, and none of the rivers have unimpeded access into the interior of the continent (Lévêque 1997). The end of the Miocene also marked the beginning of the rifting and formation of the Rift Valley (Beadle 1981). The Rift Valley divides into the western and eastern portions, with most of the East African lakes lying in the trenches of the rift; Lake Victoria is an exception, lying in a depression between the two rifts (Lévêque 1997).
Climatic changes have also influenced the connections and extent of waterbodies on the continent and on Madagascar. During the Quaternary, humid periods have alternated with droughts, drastically affecting discharge and interbasin connections. A detailed review of these changes is beyond the scope of this book; we refer readers to Lévêque (1997), who details climatic changes and their effects on freshwater systems from the Paleocene through present. At least five climatic zones currently exist across the Afro-Malagasy region, including equatorial (hot and humid with two rainy seasons), tropical (hot with summer rain), subtropical (hot and arid), mediterranean (arid summers and winter rains, with rare frost), and mountain (Denny 1993). These climatic conditions significantly affect discharge patterns and vegetation communities across the continent. The general precipitation pattern is one of highest rainfall near the equator in the Congo Basin and along the Gulf of Guinea, with progressively less at higher latitudes. However, the deserts in the north and south interrupt this general pattern, and the amount of rain and its distribution can vary greatly within Africa. Because of the high rainfall and low evaporation in the Congo Basin, this river and its tributaries, which account for only about 13 percent of the surface area of the continent, carry about 30 percent of the Africa's surface flow (FAO 1995). Arid, semi-arid, and dry subhumid areas (lands with a ratio of precipitation to potential evaporation of 0.05 to 0.65) cover about 43 percent of Africa's surface area (Bjørke 2002), and about 80 percent of the continent's surface waters are estimated to be lost to evaporation (Gleick 1993). Most of Africa's rivers (more than 90 percent) are less than 9 km long, with many flowing only seasonally (Lundberg et al. 2000).
The major basins in Africa are the Niger, Nile, Congo, Orange, Limpopo, and Zambezi rivers and lakes Chad, Malawi, Tanganyika, and Victoria. Africa is divided into High Africa (elevations mainly above 1,000 m) and Low Africa (150 – 600 m, with land above 1,000 m confined to a few peaks and plateaus). The dividing line runs from south of the Cuanza Basin in Angola eastward, then northward along the western boundary of the Congo Basin, then between the Ethiopian Highlands and the lowland portions of the Nile Basin toward the Red Sea (Roberts 1975) (figure 1.2). Low Africa includes the sedimentary basins of the Nile, Chad, Niger, and Congo, all of which contain large, shallow depressions and are separated from one another by low-lying divides. There are only a few mountain ranges in Low Africa; these include the Guinean and Cameroonian Highlands and several mountains in the southern Sahara. The Ethiopian Highlands, the Albertine Highlands, the Eastern Arc, and the Drakensberg and Maloti Highlands all occur in the east in High Africa, creating a system of highland plains and mountains from southern Africa up to the Horn of Africa. The main feature of High Africa is the Central African Plateau, which dominates the interior of southern and eastern Africa with elevations of more than 1,000 m, except at the continent's edge (Kingdon 1989). Associated with the uplifted regions of High Africa is the Great Rift Valley, a geological fault system that extends about 3,000 km from the Red Sea to central Mozambique in eastern Africa. Many small lakes and several large lakes, including lakes Malawi and Turkana, occupy the eastern branch of the Rift Valley, and lakes Tanganyika, Kivu, Edward, and Albert occupy the western branch. Lake Victoria lies not in the Great Rift Valley but in the sunken plain between the two troughs of its eastern and western branches. The two largest river basins in High Africa are the Zambezi, which flows across a plateau at about 1,200 m before descending to its delta at the Indo-Pacific Ocean, and the Orange, with elevations of about 1,800 m in the west and 600 m in the east.
Accompanying this geographic and topographic variety is a diversity of freshwater species assemblages. Tropical communities in general are characterized by greater numbers of species for many taxonomic groups and more complex interactions compared with those in the temperate zone, and Africa's freshwater systems are no exception (Lowe-McConnell 1987). For example, Africa's freshwater fish diversity, at more than 3,000 species, rivals that of Asia (>3,500 species) and South America (>5,000 species) (Kottelat and Whitten 1996; Lundberg et al. 2000). However, Africa's evolutionary phenomena—its diverse species flocks (groups of two or more sister species that are endemic to a lake or river basin; Turner et al. 2001) and relictual "living fossils"—are what make its freshwater fauna particularly distinctive (Brown 1994; Lundberg et al. 2000). Africa has more archaic and phylogenetically isolated freshwater fishes than any other continent and outstanding species radiations among a variety of taxa in both rivers and lakes (Roberts 1975; Lowe-McConnell 1987; Brown 1994). Diverse riverine fish faunas (Upper and Lower Guinean, Nilo-Sudanian, and Congolian), including almost all of the archaic and phylogenetically isolated groups, occur in Low Africa. In contrast, the rivers of High Africa are species-poor for fish. However, this pattern does not hold for amphibians, odonates, and mollusks, with several ecoregions in coastal and highland eastern and southern Africa displaying high richness and endemism (Fjeldså et al. ongoing; LeBerre 1989; Brown 1994; Schiøtz 1999; Clausnitzer 2001) (essay 1.3). Also, High Africa holds the large Rift Valley lakes, which are renowned for their radiations of hundreds of cichlid fishes (Roberts 1975; Stiassny and Meyer 1999).
Based on freshwater fish species assemblages, most of continental Africa falls within the African realm. However, the fauna of the Atlas Mountains in the northwest of the continent has strong affinities with the fauna of the Palearctic zone and therefore is included in the Palearctic realm (figure 1.2) (Roberts 1975; Doadrio 1994; Banarescu 1995). Madagascar sometimes is considered to be a subregion of the African realm, but its fish fauna is not distinctly African (see essay 3.6).
Many of Africa's fresh waters are yet to be explored, and, despite recent advances in our knowledge of their biota, much taxonomic work remains to be completed (Lundberg et al. 2000; Stiassny 2002a). Future studies undoubtedly will reveal new species and relationships between taxa. We stress that this volume provides a synthesis of current knowledge of Africa's freshwater species diversity and distributions, and its results should be considered preliminary, given the lack of data for many waterbodies across the continent and Madagascar.
Increasingly, land and forest degradation, water withdrawals, dams, and pollution threaten Africa and Madagascar's distinctive freshwater systems. About 85 percent of Africa's total water withdrawals are estimated to be directed toward agriculture (FAO 1995), and as of the year 2000, about one-third of its surface area was estimated to be under agricultural land use (FAO 2001a). Runoff of sediments, nutrients, pesticides, and herbicides enters rivers and lakes from these agricultural lands. Pollution from domestic sewage and industrial facilities is also a large problem in many parts of Africa, where sanitation infrastructure often is inadequate and industrial point and non-point source pollution are underregulated (Institute of Marine Sciences et al. 1998; UNEP 1999).
Increasing fishing pressure and introduced aquatic species also have negative effects on the biota of many river and lake systems. Inland fish capture in Africa increased by an average of about 37,000 tons per year, or 2 percent, between 1984 and 1997 (FAO Inland Water Resources and Aquaculture Service: Fishery Resources Division 1999). Africa is now second only to the Asia-Pacific region in total catch of inland fisheries. Most systems are considered to be fished at levels where damage to the assemblages has already occurred (see essay 4.2). The well-known case of the introductions of Nile perch (Lates niloticus ) (Ogutu-Ohwayo 1990) and Nile tilapia (Oreochromis niloticus ) into Lake Victoria and the subsequent loss of many fish taxa is a stark example of the potential effects of introduced species, particularly when introductions occur in concert with habitat disturbance (Harrison and Stiassny 1999). Introduced aquatic plants, such as water hyacinth (Eichhornia crassipes ) and Kariba weed (Salvinia molesta ), are also problems in many river and lake systems, resulting in mounting economic, social, and ecological costs (see essay 4.1).
Not only are freshwater systems across Africa and Madagascar currently facing these threats, but human population growth points toward an increasing intensity of threat in the future. Projections show the population of Africa tripling over the period 1995 to 2050 (from 0.7 billion people in 1995 to 2.0 billion in 2050) (United Nations Population Division 2001). As inhabitants of the poorest continent in the world, many Africans are heavily reliant on natural resources (Economic Commission for Africa 2001). Increasingly, humans and freshwater species are forced into a destructive competition that both probably will lose without intervention. Healthy freshwater systems are vitally important to the survival of Africa's rich biodiversity and to African human communities.
Given the imperative to conserve healthy freshwater systems and the limited resources and time available for doing so, WWF has embarked on a project to identify the freshwater systems of highest conservation value. These are places that are highly distinctive for the numbers and types of species that inhabit them and that are under threat. The results of this prioritization are intended for both WWF and conservation partners throughout Africa and Madagascar.
Structure of the Book
This book is one in a series of continental conservation assessments of freshwater and terrestrial biodiversity and follows a structure similar to those of the previous assessments (Dinerstein et al. 1995; Olson et al. 1998; Ricketts et al. 1999a; Abell et al. 2000; Wikramanayake et al. 2002; Burgess et al. 2004). In chapter 2 we summarize our methods for ecoregion delineation and assessment. The results of the biological distinctiveness and conservation status analyses are presented in chapters 3 and 4, respectively. In chapter 5 we integrate the results of these two indexes to make recommendations for where freshwater conservation work should proceed first in the Afro-Malagasy region. The identification of priorities is not an end in itself, and in chapter 6 we provide examples of visionary efforts that are under way in important freshwater ecoregions across the continent. Throughout the text, each ecoregion is indicated by its name followed by the map code in brackets (e.g., Inner Niger Delta ).
Excerpted from Freshwater Ecoregions of Africa and Madagascar by Michele L. Thieme, Robin Abell, Melanie L. J. Stiassny, Paul Skelton, Bernhard Lehner, Guy G. Teugels, Eric Dinerstein, Andre Kamdem Toham, Neil Burgess David Olson. Copyright © 2005 World Wildlife Fund. Excerpted by permission of ISLAND PRESS.
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Table of Contents
List of Special Essays List of Figures List of Tables List of Boxes Acronyms and Abbreviations Preface Acknowledgments Chapter 1. Introduction -The Evolution and Diversity of Africa's Freshwater -Systems -Threats -Structure of the Book Chapter 2. Approach -Geographic Scope of the Study -Ecoregions and Bioregions -Freshwater Habitat Types -Conceptual Foundations -Elements of Analysis: Biological Distinctiveness and ConservationStatus Indexes -Integrating Biological Distinctiveness andConservation Status Chapter 3. BiologicalDistinctiveness of African Ecoregions -Africa and Madagascar's Fresh Waters: Teeming with Life -Species Biological Values -Combining Species Richness and Endemism: Preliminary BiologicalDistinctiveness -Nonspecies Biological Values -Synthesis of Biological Distinctiveness Data -Conclusions Chapter 4. Reversing the Flow:Conservation Status of Africa's -Freshwater Ecoregions -Snapshot Conservation Status -Future Threat Assessment -Final Conservation Status Chapter 5. Setting Priorities forBiodiversity Conservation among Africa's Freshwater Ecoregions -The Priority-Setting Matrix -Integrating Biological Importance and Conservation Status Indexes:Where to Act First -Priority Ecoregions -Comparison with Other Priority-Setting -Exercises -Summary Chapter 6. Africa'sFreshwater Systems and Their Future -Who's Watching the Water? -Conservation Planning in Ecoregions and River Basins -Visionary Work in Freshwater Ecoregions and River Basins -Challenges to Freshwater Conservation and Sustainable Development inAfrica and Madagascar Appendices A. Methods for Assessing the Biological Distinctiveness of FreshwaterEcoregions B. Methods for Assessing the Conservation Status of FreshwaterEcoregions C. Data on the Species Richness and Endemism of Ecoregions D. Data on the Biological Distinctiveness, Conservation Status, andPriority Class of Ecoregions E. Statistical Analyses of Biological Distinctiveness and ConservationStatus Data F. Ecoregion Descriptions Glossary Literature Cited List of Authors Index