TALES FROM THE SWAMP
The Biodiversity Crisis In Microcosm
Tucked away in the northern reaches of Botswana--a landlocked country about the size of France seated just to the north of South Africa--lies the closest thing to Eden left on the planet, the Okavango Delta. Here rich droves of wildlife still roam the grasslands, surrounded by beds of reeds and papyrus and stands of majestic gallery forest that line the myriad riverine channels braiding their way through the delta. It is a scene right out of Olduvai Gorge 2.5 million years ago, and a remnant of the stage on which our own species, Homo sapiens, evolved in the most recent act of the human evolutionary drama, played out in Africa about 125,000 years ago.
If ever a place deserved our attention, even our reverence, it is the Okavango Delta. The most recent extension of the famed East African Rift Valley system, where so many ancient hominid fossils have been found, the delta tells us precisely what our ancient homeland--the environment in which we evolved and, in a cultural sense, grew up--was like. To know the Okavango is to know ourselves, where we came from, how we have come to be what we are, what our relation to the natural world was, is, and most likely will be in the future.
But there is trouble in Eden. The Okavango stands imperiled by the same basic roster of threats faced by ecosystems throughout the world: overdevelopment and overuse by humans, coupled with the more usual vicissitudes of climatic change. Of these, by far the strongest threat comes from ourselves, as we poise on the brink of destroying our very birthplace. The humans responsible are not the local hunter-gathering San (Bushmen), who had until very recently been living in small bands in a rhythmic harmony with the dynamics of the local ecosystems of the delta and its drier surrounds, the scrub and grasslands of the Kalahari. Indeed, the San are as threatened with extinction--culturally as well as biologically--as are the other species of the region.
Rather, the threat comes from the pastoral peoples--initially black African Bantu-derived tribes immigrating southward, followed soon after by European colonists coming up from the Cape region of what is now South Africa. Above all else, it is modern technology--expressed in agricultural practice, water control technology, hunting weaponry, and even the planes and cars transporting tourists eager for a glimpse of the Okavango's bounties--that threatens this last vestige of Eden. It is as if our species, striking out from Africa 100,000 years ago, wending our way around the world and only recently showing up in numbers back in our birth land--now equipped with all the knowledge and technology of the modern world--has forgotten utterly how to live in the very place where we grew up.
The stories of the Okavango are our stories: Our beginnings, to be sure, but also where we are right now, what we are doing to Earth right now, and what that means for our own future. Together, the tales of the Okavango are a microcosm of the human experience, from the dim reaches of time over 2.5 million years ago, right on up past the now and across the millennial divide. I can think of no better way to begin our examination of the global issues of mounting species loss, environmental degradation, and what they mean for the human future than the specifics of the modern Botswana story. All the glories and all the perils faced by the living world appear in microcosm in these tales from the swamp, tales of life hanging in the balance.
THE PHYSICAL SETTING The Okavango Delta is a bit of a geographic oddity. Rising in the highlands of western Angola to the northwest, the Cubango River first flows south, then strikes a southeastern course. Leaving Angola, what is by now called the Okavango River traverses the Caprivi Strip, itself a modern geopolitical oddity. When the Germans controlled the colony they called German Southwest Africa (today's Namibia), they insisted on access to both the Atlantic and Indian Oceans. Namibia fronts on the Atlantic, but to reach the Indian Ocean on the other side of the southern African continent, the Germans annexed a narrow right-of-way, the Caprivi Strip, to reach the Zambezi River. The Zambezi flows out to the Indian Ocean via Mozambique, after forming the Zimbabwe-Zambia border. That the Zambezi cascades over Victoria Falls--a drop of over 90 meters--didn't seem to faze the German colonialists of the day.
It is what happens next to the Okavango that is so unusual. Entering Botswana and continuing to flow southeastward, the river flows through a 10-kilometer wide, reed and papyrus-choked flatland surrounded in places by lush grasslands, where the river's floodplain meets the surrounding drylands. Then, after some 100 kilometers, the river divides into several branches, defining the Okavango Delta proper: a fan-shaped system of waterways, grasslands, scrublands and riverine forest some 170 kilometers wide and 140 kilometers long. On all sides, there is nothing but dry scrublands and grasslands. The Okavango Delta is in reality a gigantic oasis. [Figure 1] At its bottom lies Maun, by far the most substantial settlement of the region and the jumping off point for all who would venture into the delta itself.
Say "delta," and most people think of the Mississippi, the Danube, Rhine or the Nile: Deltas form where mighty rivers meet the sea, dumping vast quantities of mud and silt eroded from the continental interiors that these rivers drain. Here, in northern Botswana, we have something very different: A river that never reaches the sea; a river that simply stops, emptying into the sands of the Kalahari. Some of its waters percolate into the subsurface (though how much is a bone of contention). Most of it evaporates into the air that stays so dry for most of the year in this region of southern Africa. When the rains fall in Angola, swift currents reach all the way down to Maun, and the main channels--home to hippos, crocodiles, tiger fish and bream--can be up to 3 or 4 meters deep. The water is crystal clear, fresh in every sense of the word. A tenderfoot Western-world visitor can drink it straight, with little fear of contracting even the otherwise ubiquitous bacterial strains of childhood diarrhea that regularly fell adult travelers to foreign climes. The reason: The waters of the Okavango Delta are filtered through its bottom sands, and human population density is still sufficiently low in the delta that transmission of human disease pathogens is correspondingly curtailed--at least so far.
What's going on? Most of the world's other interior basins--the Great Salt Lake, the Aral, Caspian, Black, and Dead Seas--are saltier than the oceans. To stay fresh, lakes must flow. Why isn't the Okavango also salty, and why, for that matter, is it mostly drylands and wetlands bordering on fast-moving streams? The answer lies in the delicate balance between the tilt of Earth's surface, which keeps the streams running, and the dry climate, which insures that the moving waters evaporate before they get a chance to form a stagnant, and thus salty, pool.
Visitors to the delta are invariably shocked to learn that the region experiences, on average, one hefty earthquake every day. The scene is so placid, so calm, and you cannot actually feel the deep-seated tremors, cushioned as they are by the thick pile of sand and mud lying below the delta's surface. There are none of the telltale signs of active seismic (earthquake) activity. Go to California, and the fresh, jagged look to many of the hills literally screams out the constant upheaval of the landscape. Nor are there any volcanoes remotely near the delta, even though volcanoes and earthquakes typically go hand-in-hand. Nonetheless, the ground under the delta is constantly moving, sinking a bit every day. And although there are no volcanoes there now, volcanoes definitely lie in the deltas future. It may take a few million years, but the delta is destined to look like the East African Rift Valley system, with huge volcanoes like Mt. Kenya and Mt. Kilimanjaro overlooking open savannas.
The Okavango Delta, it seems, is the newest part of that thousands-of-miles long crack that starts in Ethiopia, running in from the sea and down the eastern region of the African continent. Until recently, geologists thought that the crack died out somewhere in Mozambique, but sensitive seismographs began monitoring the earthquakes of northern Botswana, and we now know that the Rift Valley system takes a sharp westward turn, running through the region of Victoria Falls and continuing to the present site of the Okavango Delta.
The African Rift Valley system is plate tectonics in action: Africa is being torn apart, as the East African crust (plate) begins to separate from the main crustal core of the African continent. As the plates move apart, the region between them drops down, forming a slowly widening chasm. The end result: Oceanic waters will flood the African interior (as they are in Ethiopia, where the crack began); what is now dry land will become an oceanic deep, and what has been for billions of years a single massive structure will become two smaller continents.
Nor is this the first such event to strike Africa. Only 160 million years ago (only!), Africa was part of an enormous single continental structure, Gondwanaland (meaning "Land of the Gonds," an indigenous Indian people living in the region where the early convincing evidence of the existence of the supercontinent was discovered). Gondwanaland once included Africa, South America, Antarctica, Madagascar, and India, conjoined into a single mega-continent. The events of the African Rift Valley system over the past 20 million years simply continue this complex process of fragmentation of the old supercontinent, and the Okavango Delta is merely the youngest manifestation of its effects.
The Okavango Delta is framed by faults: one on its northern edge, where the river divides and begins fanning out over the landscape, and the other in the south, forming the southern edge of the delta. The delta is there because the land between these faults is submerging, bit by bit, with those daily jolts. The faults have been active, and the land has been sinking, for only some 5,000 years, but already 3,000 meters of sediment lie below the surface. As the landscape sinks, the rivers bring in new supplies of sand and mud, keeping the surface level of the delta up just about to the height of the surrounding Kalahari surface--another equilibrial balance between river and landscape that helps make the Okavango Delta system so utterly unique.
Five thousand years ago the Okavango Delta didn't exist. In its place--but extending much farther south--was a real lake, an enormous expanse of inland waterway that did in fact eventually empty out to the sea. Feeding it were several rivers: the Okavango, naturally enough, but also the Chobe and Zambezi Rivers to the east of the Okavango. The lake's outlet was to the south, along the present day Limpopo River (which Rudyard Kipling called the "great grey green greasy Limpopo River," where the elephant, you may recall, got his trunk). The structural movements in the southern African crust that have led to the formation of the present-day delta simply raised what is now southern Botswana, preventing the outflow of water from the lake from reaching the Limpopo drainage. The block faulting activity that led to the formation of the Okavango Delta diverted the Chobe and Zambezi Rivers, forcing them to make dramatic right-angle turns, eventually merge, flow over Victoria Falls, and find the sea hundreds of miles farther north than the Limpopo. The lake grew salty and eventually dried up.
Evidence of that ancient lake is everywhere in northern Botswana, just below the delta itself. Old shorelines stick out. Vast expanses of salt flats--reminiscent of the Bonneville Salt Flats in Utah, themselves relicts of an Ice Age lake (Lake Bonneville) many times the size of the present Great Salt Lake--lie as mute testimony to this once great body of water. The most extensive of these are the Makgadikgadi Pans, which still hold water in the rainy season, attracting what is left of the once great herds of wildebeest and zebra of the Botswanan Kalahari. Humans--our ancestors and ourselves--have lived in the region for at least 300,000 years, leaving a sequence of old, middle, and new Stone Age tools in and around the pans.
Another dramatic sign of this ancient lake and drainage system comes, oddly enough, from the discovery of diamonds in Botswana. South Africa's diamond industry was established in the mid-1800s, with the first diamonds coming from the farm of a Mr. DeBeers at Kimberley. By 1914, the "Big Hole" had already played out, though South Africa until recently remained the world's largest producer of diamonds. It now ranks fifth, while Botswana has moved into first position.
Three diamonds were all that had turned up for all the initial prospecting in Botswana, three diamonds recovered from a tributary of the Limpopo, which forms the southeastern boundary between Botswana and South Africa. Efforts to find the Kimberlite pipe--the actual source of the diamonds--had all failed because all the early prospectors had, naturally enough, assumed that the source pipe must lie somewhere within the existing Limpopo drainage.
They were wrong, but it wasn't until the mid-1960s, when Gavin Lamont, a seasoned DeBeers Consolidated Mining Company field geologist, tackled the job and solved the problem of the missing diamonds. Lamont, the story goes, had been much impressed by the theories of South African geologist Alex DuToit, one of the earliest and foremost exponents of continental drift--the forerunner of our modern theory of plate tectonics--the notion that, over the eons, continents had changed their positions vis-a-vis one another. In the early decades of the twentieth century, continental drift was taken seriously by only a handful of prominent geologists (DuToit and the German Alfred Wegener chief among them) and was generally laughed off as a schoolboy's fantasy inspired by the evident fit of the coastlines of western Africa and eastern South America. How little the experts knew!
Not only did Lamont sympathize with DuToit's vision of a restless Earth, but he also took quite seriously DuToit's conclusion that the southern African crust had been "warped" along a line extending from Zimbabwe (Rhodesia to DuToit) down through southern Botswana some 20 million years ago. If DuToit was right, thought Gavin Lamont, the basic configuration of the drainage of all of Botswana must have changed drastically. In a move that epitomizes the very best scientific procedure, Lamont then predicted that he would discover the source of the diamonds much farther north than anyone had so far looked. It took several years of painstaking, arduous field exploration, compiling bag after bag of sand, each of which had to be sifted and examined for telltale minerals that would give away the presence of the mother lode, the long-sought Kimberlite pipe. Patience was rewarded in 1967 at a site named Orapa, on the southern edge of the Makgadikgadi Pans far to the north of the Limpopo.
Seldom has theory, coupled with keen field work and observation, yielded such fantastic economic rewards. Lamont discovered a second Botswanan diamond source in 1971--this time with the aid of termites, which had brought the telltale mineral grains up from several hundred feet below the surface (this is not the last we shall hear of the impact of termites on the Kalahari-Okavango systems). When the British Protectorate of Bechuanaland gained its independence, becoming Botswana in 1966, its 330,000 inhabitants ranked among the poorest in the world. More than anything else, the discovery of diamonds has sharply raised the per capita income in Botswana. DeBeers splits its proceeds, retaining 25%, while the Botswanan government receives 75%. More graphic a confirmation of a scientific theory--and the former existence of that giant lake and its outlets to the south through the Limpopo system--would be hard to imagine.
DYNAMICS OF THE KALAHARI AND OKAVANGO ECOSYSTEMS The game or life is played out in the local ecosystems in each and every corner of the globe, from the Arctic tundra to the tropical rain forests, from sandy beaches to the reaches of the oceanic deep. Everywhere energy flows through the system, as plants convert solar energy to sugars, to be eaten by an army of insects and other invertebrates, on up through the great herbivorous mammals who, 65 million years ago, inherited their plant-eating niche from the now-defunct dinosaurs. Then there are the carnivores, the animals that prey on the plant eaters. Africa is virtually synonymous with the "big hairies," including herbivorous buffalo and elephants, to be sure, but especially conjuring up images of the big carnivores: wild dog, cheetah, leopard, and especially lion. Smaller carnivores abound as well; birds, lizards, and prodigious numbers of snakes, spiders, scorpions, and insects also are busily engaged consuming other kinds of animals. Lastly, but most crucially, come the humble agents of decay: fungi, bacteria, and protozoans, essential to the critical task of recycling organic debris and adding nutrients to the mix so that the game of life can continue, endlessly, generation after generation.
The Okavango-Kalahari ecosystems are a quilt-work of intersecting habitats. Flying north from Gaborone, Botswana's capital near the South African border, at an altitude of 300 meters, the acacia scrublands and grasslands of the southern and central regions immediately hove into view. Here, in its easternmost expression, the Kalahari is technically not a true desert at all, receiving (depending on locality) anywhere from 150 to 500 millimeters of rain a year (true deserts receive less than 100 millimeters). Farther to the west, primarily in Namibia, the climate is drier, and the land conforms more closely to more conventional, stereotypical images of true deserts.
Botswana's Kalahari environment is itself a patchwork of habitats, with plenty of open grasslands supporting--until very recently--huge herds of wildebeest, hartebeest (a related species of antelope), and zebra, with lesser numbers of other antelope, giraffe, warthog, jackal, hyena, and various cats, most certainly including lion. Several species of thorny acacia (a species of which was called "fever tree" by early European settlers because they mark the southern limits of the African malarial regions) form stands in the grasslands, creating a scrubland ideal for both grazers and browsing species. Giraffes are particularly fond of acacias, finding the prodigious thorns no obstacle at all. Other species, such as the ubiquitous impala, can also browse these trees. Impalas, which are antelopes, are the quintessential ecological generalists--jacks-of-all-trades that browse and graze a wide variety of grasses, shrubs, and low trees, and that are consequently equally at home in open grasslands, scrublands, open woodlands, and dense stands of forest. They do require water more than some desert-adapted species (such as the springbok, the southern African equivalent of East Africa's Thomson's gazelle, and, as such, the only true gazelle in the region). With plenty to eat, but with water a limiting factor, impala are more numerous in the wetter regions to the north, in and around the Okavango Delta, than in the drier regions of the central Kalahari.
Approaching Maun in our Kalahari flyover, the salt pans of the Magkadikgadi loom off to the right. Directly below, dense stands of Mopane woodland appear. Mopane is an important tree in southern African ecosystems: Its leaves, which close up along a fold line, have an extremely high protein content, making them the favored food of elephants, baboons, and many other species. The wood is very hard and tough and is the slow-burning fuel of choice for the traditional African cooking fire, which consists of two or three logs burning on end, radiating away from the flames.
With plenty of moisture in the soil, the mopane leaves are green, and the forest is alive with birds and an abundance of larger game. Arnot's chat, a sprightly black and white bird ever on the lookout for insects, is a common denizen, as are woodpeckers, several species of hornbills, warblers, and dozens of other bird species. Outside the delta, though, the dry season turns the green mopane leaves a coppery color; the leaves collect on the ground below the trees, and from the air these dry mopane woodlands are a desolate sight. You can walk, even drive, for hours through these dry mopane woodlands without catching a glimpse of a single mammal, or hearing the call of a single bird. It is as if these mini-ecosystems shut down, hibernating through the dry season in wait of the next burst of rains to bring life teeming back once again to their midst.
Approaching Maun, the Boteti River hoves into view. The Boteti used to flow year-round, the single outlet of the Okavango Delta that reached its end, finally, at the Mopipi Pan, a small salt pan just southwest of the Makgadikgadi, now used as a reservoir to slake the water needs of the diamond operation at Orapa. The Boteti hasn't run for several years, since the onset of the present drought in the late 1980s, but there is always, nonetheless, some pooled water present here and there--vital for the needs of wildlife and, in recent years, for the cattle that have effectively replaced antelope along the Boteti's course.
Approaching Maun, still at 300 meters in the air, the rondavel huts and bomas (corrals) of local Botswanans appear, and in addition to the usual signs of civilization, there are the unmistakable barren dusty signs of overgrazing by domestic livestock. Dry as the region just outside the delta may be, it would still be covered with grasses, yellowish in the dry season, verdant in the wet. Instead, light gray soil, a fine-grained clayey silt, is all that meets the eye.
Once past Maun, the scene once again changes dramatically, for we have entered the complex of habitats and vegetation zones that together form the Okavango Delta environment. The grasslands are intact, and look greener--even in the dry season--than they did in the Kalahari. Water springs into view, as a welter of lagoons, streams, and side channels develop. Along their sides, trees appear, forming gallery forests that ring the margins of the main channels. There are 80 common tree species in the Okavango Delta. Among them are jackal berry trees, whose fruit appeals to elephants, baboons, and humans. The sausage tree--so named for its half-meter-long seedpods that dangle from thin stringy stalks--produces a chemical substance recently shown to be an effective agent against some forms of skin cancer. There are also two species of palm tree, including the "real fan palm," which bears a tennis ball-sized "ivory" fruit much beloved by elephants and humans alike. This species, together with the wild date palm, are often home to the African palm swift, the red-necked falcon, and several other species of breeding birds.
Islands abound in the southern reaches of the Delta. The largest ones, with Chief's Island by far the dominant, house the greatest variety of habitat. Typically, reed beds fringe the shores of the streams, but majestic gallery forest also comes to the water's edge on the larger islands. The forests house a rich assortment of birds, most notably Pel's fishing owl, a magnificent large brown bird that takes its prey by plunging feetfirst to the very bottom of the pools flanking the forest's edge. [Figure 2] The beautiful, small chobe bushbuck hides in these dense forests.
Farther inland, more open mopane woodlands (typically green the year around because of the continual presence of water) and acacia scrubland are occasionally present. Invariably, though, there are open grassland savannas, sometimes approaching quite close to the water's edge and generally extending onto and covering the interiors of the islands.
It is on these islands that the closest setting to the primordial African--meaning the primordial human--ecosystem persists. Here the ancient rhythms of life are still being played to their fullest. The sheer variety of mammal species in itself tells the tale. Near the water's edge, large herds of red lechwe, a medium-sized, tawny antelope adapted to grazing riverine grasses and escaping wild dogs and lions by dashing through the lagoons and reed beds on toes well-adapted for marsh muck, are the most common sight. [Figure 3] Reed buck, a smaller, tanner species, form smaller groups that haunt the taller grasses, again not too far from the open water. Larger waterbuck, a gray species with prominent white rings around their derrieres--a species whose flesh is sometimes said to be repugnant to both man and beast--also, as their name implies, like the water, though they can also be seen ranging farther inland than red lechwes and reed bucks.
Impala are everywhere. Their distant cousins, the tsessebes, however, are more specialized, preferring the open grasslands and tree-dotted savanna grasslands of the island interiors (there are plenty of water holes that persist virtually year-round on these islands). Tsessebes (the same species, Damaliscus lunatus, as eastern Africa's topi) are ungainly beasts, and it usually surprises safari-goers to hear that they are the fastest antelope species in Africa. A grayish-brown, tsessebes cluster around the grasslands in generally smallish groups of 5 to 10 individuals.
Blue wildebeest (the same species, Connochaetes taurinus, as the East African gnu that everywhere forms such huge, migratory herds) are close relatives of the tsessebes. They abound on the grasslands of the Okavango, almost always within sight of small herds of Burchell's zebra. Specializing on different grasses, the intimate association of wildebeest and zebra reflects the mutual benefit each derives from their differing abilities to detect predators.
The list of antelope species is long: little steenboks and slightly larger gray duiker fall on the smaller end of the size spectrum, while the magnificent kudu (the horns of the male are used as natural trumpets by local tribesmen) are among the larger of all antelopes. [Figure 4] Rarer, but spectacularly beautiful, are the two species of "horse antelope" present in the delta, the roan and the even more spectacular sable antelope. [Figure 5]
Antelopes are members of the cattle family, and their closest relatives on the Okavango savannas are African buffalo, which occur in herds that often exceed 1,000 individuals. The older breeding bulls are systematically excluded from thebreeding herds, forming small knots of testy has-beens that are the most serious threat to unarmed, unwary foot travelers on the Okavango grasslands.
Giraffes, favored food of lions in the Okavango, are abundant and grace the woodland margins and open plains in small herds. Both species of rhino (black and white) are scarce--virtually gone to the poachers, who still take their horns to feed the insatiable Asian aphrodisiac market. In sharp contrast to the plight of the rhinos, though, elephants are undergoing a population explosion in the delta, as we will discover in greater detail below.
Hippos thrive in the delta's waterways. Lurking in the deep channels, sometimes rearing up suddenly to challenge a fast-moving motor boat laden with tourists, hippos tend to accumulate in larger herds in the more open waters of the side channels, adjacent to the interior grasslands of the islands. There they share space with the ubiquitous Nile crocodile--more or less at peace with one another, though crocs will take young hippos, and adult hippos will kill even large crocs when threatened.
Warthogs are all over the place; their cousins, the bushpigs, are harder to find, preferring dense cover and, in any case, being primarily nocturnal creatures. Three large rodents finally round out the long list of mammalian herbivores: the African porcupine, the tree squirrel, and a large hopping rodent called the springhare, rarely seen by day, but out in droves at night.
The list of carnivores is almost as long as that of the herbivores. Six species of cats run the gamut from the house-cat-sized African wildcat (probable ancestor of modern domestic cats) up through lions. Servals are slightly larger, spotted cats; caracals are the equivalent of the North American lynx. Cheetahs come next in size; predators of the open plains that chase down their prey in wind sprints, cheetahs nonetheless hold their own in the smaller expanses of grasslands of the delta. Leopards, true ecological generalists like impalas, are at home in deserts, mountain ranges, and tropical rain forests. No surprise, then, that leopards are also abundant in the Okavango. At the top of the heap, of course, are the lions that likewise thrive in goodly numbers on the region's savannas and scrublands.
Hyenas and civets are close relatives of cats. Spotted hyenas are common, often bringing their maniacal laugh into camp at night. Much harder to find are the smaller brown hyenas, as are aardwolfs, hyena relatives that eat only termites. The African civet and small spotted genet round out the roster of catlike mammalian carnivores. Not to forget the three species of mongoose, weasellike carnivores that nonetheless are more closely related to the civet branch of the mammalian carnivores.
But there's still more: Four species from the dog family roam the savannas and marginal woodlands. Smallest is the bat-eared fox, followed by two species of jackal (black-backed and side-striped). Surprisingly common is one of Africa's most endangered species, the wild dog [Figure 6]. Recent research in the Okavango has shown a tendency for the wild dogs there to hunt singly, rather than in packs that dominate wildlife films from East Africa.
There is also a species of otter in the waterways, and, back in the grasslands, the honey badger, a rough customer known to have attacked even elephants, with a reputation of going for the groin when provoked. The skunk-like striped polecat finally exhausts the list of mammalian carnivores.
African anteaters include the antbear and the scaly pangolin. Both species stick out like sore thumbs in an evolutionary sense: Neither has any other close living relatives. They are "living fossils," whose closest kin lie buried deep in the fossil record of earliest mammalian history.
Which, with the conspicuous exception of the many species of mice and bats, leaves only the primates, our closest kin. Aside from ourselves, three primate species live in the Okavango ecosystems. Vervet monkeys occur in small bands, eating an omnivorous diet of fruits and insects. More conspicuous are the troops of chacma baboons. Omnivorous, like vervets, baboons will take small antelope to supplement their diet of scorpions, insects, and, of course, fruit. Least conspicuous are the nocturnal lesser bushbabies, a species of lower primates that can jump over 10 meters seemingly effortlessly.
That's just a lightning-quick tour of the commonly encountered mammals alone. All told, there are 164 mammalian species known from the delta. Add to them, 38 species of amphibians (frogs and salamanders), 157 species of reptiles (snakes and lizards, including the meter-long monitor living along the waterways), and the great wealth of bird life (540 species), and you have a very rich set of players in the Okavango ecosystems indeed.
And that's just for starters. The insects are incredibly diverse (at least 5,000 species!), as are the spiders, scorpions, and sunspiders. Butterflies, walking sticks, grasshoppers, and beetles abound. Ants are very diverse. Then there are the termites, in many ways the backbone of the Okavango's terrestrial ecosystems, whose story is so complex, it is told as a microcosm of ecosystem dynamics below. Add to this melange of animal life, the 100 or so species of trees, many additional species of grasses--all told, at least 3,000 species of plants--plus the microbes in animal intestines, in plant tissues, and free-living in the soil, and the total riot of life in the Okavango emerges, adding up to churning ecosystems whose vibrancy is somehow greater than the sum of their parts and that cannot be done justice by simply listing all the species found there.
If the savannas, woodlands, and scrublands of the delta's islands are the consummate vestiges of primordial Africa, there is still more to the complete picture of the Okavango habitats. Forsaking a plane for a motorboat, a cruise along the main channels northward into the heart of the delta yields a very different picture from that seen in a flyover. For one thing, in the eastern reaches at least, the main watercourses are lined with tall reeds, peppered with small stands of papyrus. Even standing in the boat, you cannot see beyond the thick wall of grasses and papyrus, except in places where the watercourse widens, or where there has been a recent fire. As you go northward, the papyrus increases in frequency, until it is the dominant and, ultimately, the only plant lining the waterways. This plant, with its long, tough green stem and frizzy top knot, has given us the very word "paper."
The Gcodikwe heronry, on one reed-and-papyrus-choked island in the very heart of the delta, is perhaps the largest of all the many breeding sites for the Okavango's herons, egrets, ibises, storks, cormorants, and darters. Here, fiercely ugly marabou storks share space with much more comely yellow-billed storks. The saddle-billed stork, largest of the region, is one of the most beautiful birds in the world.
Traveling farther north, the islands eventually all but disappear, and the entire delta is one vast papyrus wetland. Here is where the most elusive of all antelopes is most common: the sitatunga, an animal whose hooves are splayed even more than the red lechwe's, enabling it to live virtually its entire existence in the reed beds and papyrus swamps.
Turning the boat around and returning southward along the western side of the delta, there is one new twist to the landscape: Gone, for the most part, are the dense stands of tall papyrus and reeds that line the channels to the east. The grasslands come right down to the banks, allowing an unimpeded view of the wildlife and an opportunity for larger crocodiles to sun themselves at the river's edge.
Despite the illusions of casual Western visitors that they are in some kind of a game park, and despite all the damage already done by human encroachment, the Okavango's ecosystems are astonishingly intact, incredibly complex, yet at the same time evincing a kind of simplicity that only systems as old, as well broken in, can possibly show. The Okavango is the real thing.
TERMITES IN THE OKAVANGO SCHEME OF THINGS it is difficult to capture the dynamism of local ecosystems simply by listing the species, the players in the ecological game of life. The intricate web of energy flow and matter exchange starts with plants trapping sunlight, storing the energy in sugars that they--and those that eat them--then utilize to grow, maintain their bodies, and reproduce. Focusing on one intermediate step in this energy web--the role that a singlo species plays in the Okavango grasslands and scrublands--helps capture the complex interdependence of all living components of the ecosystem.
Consider the role that termites play, especially in the arid Tropics where they are so abundant. Without termites in these ecosystems, there simply would be no decay of cellulose, the predominant component of plant tissue. Without decay, the system would rather quickly grind to a halt, as nutrients would remain forever trapped in dead wood and stems, and a thick carpet of dead plants would quickly begin to clog the landscape. Termites, as all homeowners know, can eat and digest cellulose, though how they do so is in itself an interesting ecological story. Termites themselves cannot digest cellulose directly. Just as we depend on a rich flora of microbes in our stomachs and intestines for complete digestion and absorption of nutrients, termites house, in their hindgut, a truly amazing array of microbes, including various bacteria and protozoans. These microbes actually convert the cellulose to utilizable energy--an example of ecological mutualism beneficial to host and microbe alike, but with vast implications for the ecosystem at large.
As if the digestion of cellulose itself were not a sufficiently monumental service paid to the ecosystem, it has recently been discovered that the microbial ecosystem of the termite hindgut also "fixes" nitrogen, extracting and storing it in a form usable by other organisms. All animals require nitrogen to manufacture proteins and DNA and have no means to derive the substance from the inorganic world, even though nitrogen forms 79% of the air that we breathe. For years it was thought that only the bacteria living in association with the roots of leguminous plants (such as peas) performed this absolutely critical task of nitrogen fixation, but now it seems that nitrogen also enters the organic cycle through the efforts of the microbial microecosystem developed in the hindgut of termites.
Macrotermes michaelseni is the most conspicuous termite in the Okavango region--not that the insects are themselves usually seen except when swarming to fly off to found other colonies. Rather, it is their enormous mounds dotting the landscape virtually everywhere that are so conspicuous. [Figure 7] The mounds are often over 3 meters high, and function, so far as the termites are concerned, as air conditioning structures and essential protection from their many enemies.
These termites are loaded with fats and proteins, and many species find them delicious. African peoples have consumed termites for millennia. School kids, finding a fresh termite swarm, will fall on them and gorge themselves before going off to tell their friends of their discovery (or so a Ugandan college roommate of mine once told me--at the same time professing disgust at the mere thought of anyone eating shrimp, crabs, or lobsters; chacun a son gout!).
Termites are on the menus of many other species as well. Their most persistent and formidable enemies are driver ants, which is why termites labor so intensively to keep their gray-clay mounds impervious to even the smallest of invaders. But they also are beloved by many larger animal species, especially aardwolves and aardvarks, as well as many omnivorous species, including certainly chacma baboons and vervet monkeys, that happen to chance on them.
So much is fairly typical--if dramatically so--of the role of a single species in an ecosystem: Macrotermes michaelseni is important because of what it eats, how it cycles nutrients through the system, and because of what eats it. (Unlike other termites, cellulose digestion in Macrotermes michaelseni colonies is actually handled by cultivation of fungal farms inside the mound itself rather than by microbes living in their hindguts). But position in the food chain-energy web hardly exhausts the importance of these termites in the Okavango scheme of things. For these termites are literally master builders, and their mounds far transcend their original purpose of providing shelter for their builders.
To begin with, unused termite mounds provide homes to other species; aardvarks, hyenas, and many others seek out tunnels in termite mounds. Holes in sides of termite mounds cut through as they lay exposed on river banks are nesting sites for swallows and whitefronted bee eaters, and the deadly black mamba is a frequent denizen, as it seeks out small rodents hiding in the abandoned channels.
But termite mounds play even larger roles than providing shelter for other species. What little topographic relief exists in the Okavango is crucial to the maintenance of its complexity. The main river courses have, of course, the deepest beds. They are flanked by shallow marshlands and wetlands. When the floods come, though, the waters overstep their banks and flood low-lying grasslands, greatly reducing, for a time, the space open to the dryland browsers and grazers. Many tree species, too, cannot tolerate periodic inundation. Thus, without some higher ground to provide year-round refuge from the floodwaters, the Okavango ecosystem complex would not be as rich as it is. Once again, we look to termites--especially Macrotermes michaelseni--to understand why there is any high and dry ground whatsoever in the delta.
Termite mounds frequently have trees growing out of them--trees dependent on both the slightly higher ground that a termite mound automatically creates, and perhaps as well the moisture that termites bring up from the depths. Bring in a tree, and the accumulation of leaves, seeds, dust, and animal droppings starts an accumulation of soil. Termite mounds are the very cores of small islands sticking out among the floodwaters, islands that will grow with the addition of more trees and shrubs. The islands grow by accretion, and termites play a critical role in the very creation of permanently dry grassland, scrubland, and woodland habitat in the Okavango.
Warthogs play an equivalent, if opposite role: The shallow excavations warthogs make while rolling in a mud puddle is often expanded when elephants seize the opportunity to mud bathe there, too. Enough elephant wallowing and pretty soon there is a large depression, hardened and clay-lined as it bakes in the sun during the dry season, forming a perfect cachement basin when the waters return. Thus, small wallows can quickly grow to sizable ponds--perhaps eventually with permanent water--homes for crocodiles waiting for the antelope to come to drink. Though it is easy to see how animal species are adapted to their environments, it is less obvious how these species act to create that environment in the first place.
The interplay between species in systems like the Okavango far transcends who eats whom. That the daily routine of humble little termites eventually determines where elephants, buffalo and lions will roam gives us some handle on what the complex interplay between species in tropical ecosystems is really like. No matter how we look at the Okavango and its surrounding Kalahari systems, we see that, up until now at least, these systems are healthy, vibrant, alive. So much is clear--but how do we really know the delta resembles Eden, the environment from which we originally came?
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