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Environment Southwest: Africa The Central Namib Desert 'Iext and photographs by David K. Faulkner Department of Entomology San Diego Natural History Museum All deserts are the same. All deserts are different. 'TWoseemingly contradic- tory statements, yet to a certain extent both are correct. In early 1988 I was given the opportunity to discover just how similar and different a desert in southwestern Africa, the Namib, was from xeric regions of the southwestern United States and northwestern Mexico. From January to March, during the southern hemisphere's summer months, areas of the central Namib Desert were scale researched by an international group of I I entomologists from South Africa, west- ern Europe, and North America. The primary reason for choosing Namibia BOTSWANA was to study its unique insect fauna, especially the Neuroptera-nerve-winged insects-which attain a high degree of endemism and diversity in this part of the African subcontinent. Atlantic Ocean Extending 1,250 miles south from Angola to the Olifants River of South Africa's northern Cape Province, the Namib Desert is one ofthe driest regions CAPE PROVIDENCE on earth. It lies between the south Atlan- tic Ocean to the west and what is termed the great western escarpment to the east, averaging 125 miles in width. The east- Map inset shows the western Namibian desert of the African subcontinent. ern boundary is also delineated by the Tile Namib Desert Research Institute is located at Gobabeb. 3.9- inch rainfall line which increases to the east and is almost nonexistent along the western coast. the Benguela Current, which developed than permanent. The Kuiseb River, It is believed by many that the Namib 5 million years ago and pushes cold which flows by the Central Namib Desert represents one of the oldest deserts in Antarctic water along the western coast, Research Station at Gobabeb, originates existence, continually alternating which in turn creates an inversion layer from rain falling hundreds of miles to the between arid and semi-arid conditions that prevents cloud formation. east, and only sporadically flows to the for the last 80 million years. Influencing Only a few rivers cross the Namib coast. However, despite its unpredictable and maintaining the present climate is and most of these are intermittent rather nature, this water source supports a per- manent stand of large trees and smaller shrubs that in turn allow a limited nondesertic fauna to survive. 10 the east and north of the river extends the seem- ingly endless gravel plains, while to the west is the dune "sea" that characterizes much of the Namib. The dune fields extending southwest from the research station are parallel, linear dunes that can reach a height of about 300 feet and average two-thirds of a mile apart. Despite their inert appear- ance, they are actually dynamic systems that have evolved as a result of wind movements, sand accumulation, and the presence of vegetation. Each dune system varies in color, shape, and com- plexity. Different parts of a dune support Looking soutll from dune crest in tile direction of tile research station and the unique insect faunas. The dune base Kuiseb River. contains coarse sand grains that trap a Left: Mylabris blister beetle feeds on tile fleslly petals of tile endemic cucurbit nara. ENVIRONMENT SOUTHWEST 9 considerable amount of detritus on Right: Prominent female which many ground beetle scavengers cones of the endemic depend. The second part of the dune, Namibian plant the dune slope, has an incline of about Welwitschiamirabilis. 14degrees, which remains constant and Below: Centuries-old supports a minimum of insect species. male specimen of Finally, the actively changing slip-face, Welwitschiaare with a slope between 32 and 34 degrees, examined for pollinators maintains much of the diversity in the by Florida entomologist dune, including many endemic moths Lionel Stange. and beetles. The unique character of the linear dunes is perpetuated by the exist- ing winds which reverse their direction during the year, thus reversing the slip-faces. Although deserts are known for their irregular and undependable rainfall, there are other sources of water in the Namib, the most important being fog. Condensing on west-facing surfaces, fog supports a variety of succulent vegeta- tion. Many insects, especially certain tenebrionid beetles (see ESW #518), depend on this resource for most of their water requirements. Besides lapping up droplets of liquid from vegetation and rock surfaces, certain beetles have mod- ified their behavior in a way that increases their ability to accumulate water. One group of tenebrionids, similar in appearance to "stink beetles" of the southwestern United States, employs a head-standing or "fog-basking" behavior. While the insect is in this posi- tion, the dorsal region serves as a con- densation surface from which water drips downward to the mouth where it is sucked in. An individual beetle's body One of the many endemic dune asso- Welwitschia is truly the strangest weight can increase by 40 percent in a ciate plants is nara, Acanthosicyos hor- endemicofthe region.The plants possess single morning. Another beetle genus, rida, a spiny member of the cucumber only two leaves that grow continually Lepidochora, has evolved a system of family first described by Friedrich Wel- from the trunk, twisting, fraying, and fog-trapping wherein the flattened witsch in the 1800s. This plant is abun- splitting endlessly from the terminal insects construct narrow trenches dant along water courses and dune bases ends. Being dioecious, the Welwitschia perpendicular to the wind direction. and relies on a tap root to reach available has male cones on some plants and These furrows collect more fog water ground water. Leavesare greatly reduced female cones on the others. Research on than the surrounding sand and allow for how the plants are pollinated is still a more efficient extraction of dew and and modified and the stems are respon- sible for most of the plant's photosyn- inconclusive; however the male cones water. It is not known whether similar thetic activity.The plant produces a fruit attract a variety of pompilid and vespid adaptations have evolved for North (melon), which along with the male and wasps that easily transport the sticky American species, particularily in the female flowers, is an important nutri- pollen from one plant to another. The more recently developed dune systems tional resource for insects, such as the Welwitschia bug, Probergrothius sex- of Baja California. There are definitely blister beetle genus Mylabris, and for punctatis, which is restricted to this prospects for future research in this two- and four-legged vertebrates. host, may also play an important role in region. Of all the plants on the Namib, none pollination. is more bizarre in appearance than Wel- One other aspect of the Welwitschia witschia mirabilis. Classifiedsomewhere plant is its longevity. The few "middle- between pine trees and club mosses, aged" specimens that have been carbon dated were estimated to be 1,000 years old. This is indeed one of the best adapted organisms to be found in any desert. 10 AUTUMN 1988 Indigenous dune ant, Camponotus detritus, on stems of the Stipagrostis grass. less is known of their adult stages. Lar- val resource partitioning-the explana- tion for how certain insects can exist in the same habitats and use the same resources, yet not out-compete or dis- place one another-as well as desert sur- vival strategies still remain mostly a mystery, but current studies are reveal- ing more complex and specialized behaviors than were originally thought to exist. Larvae of a number of species were collected by sifting sand through gradu- ated sieves and waiting a few minutes for the antlions to move. Well-adapted for desert existence, the larvae have evolved Dune-inhabiting numerous specialized structures for tenebrionid beetle feeding dune and sand dwelling. Modified setae, on windblown detritus. or hairs, face forward, which allow the insect to pull prey underground while restricting the prey from dragging the larvae to the surface. However, this adap- tation also prevents the antlion from moving in a forward direction. A variety of plant and animal life is potential predators and slow moving Almost nothing is known of adult supported by the dunes and associated entomologists. antlion biology though gut content analy- habitats near Gobabeb. A dune grass, At the base of dune grass can be sis has revealed that certain species feed Stipagrostis sabulicola, which is also found antlions, the predaceous larvae of on soft bodied insects and pollen. One dependent on fog condensation for sur- a family of neuropteroid insects. southern African species specializes in vival, provides a suitable environment Although they are recognized by the con- the nocturnal capture of other antlion for a number of insect species. Feeding ical pits they construct in the soil, it adults, snaring them in flight and land- on fluids derived from the plants's should be mentioned that only a few ing on vegetation to devour their meal. tissues are scale insects and aphids genera have evolved this behavior, while Much work remains to be done on which are in turn tended by the abun- the majority of species prefer to lie the insects in this region as well as the dant carpenter ant, Camponotus motionless below the soil. Upon coming southwestern United States. The oppor- detritus. Unlike its nocturnal North into direct contact with a prey species the tunities for extended research are pres- American counterpart, this dune ant, antlion quickly impales the insect on its ent and with the continued efforts of about two-thirds of an inch long, is curved mandibles, pulls the victim scientists and observant naturalists distinctively marked and is active dur- under the ground, and sucks it dry.

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