Showing papers by "University of Nairobi published in 1979"

The distribution of C3 and C4 grasses and carbon isotope discrimination along an altitudinal and moisture gradient in Kenya

Abstract: More than 500 species of the Poaceae are found in Kenya, East Africa. Eighteen of twenty-seven tribes are exclusively (except the Paniceae and Danthonieae) of the C3 photosynthetic type. A floristic analysis of low altitude grasslands suggests that nearly all species at these low altitudes are of the C4 photosynthetic type. At high altitudes, however, nearly all grasses are of the C3 photosynthetic type. Open grassland vegetation was sampled along a transect from arid low altitude sites to the top of Mt. Kenya in an attempt to document the general distributions of the photosynthetic types.

Allometry of the limb bones of mammals from shrews (Sorex) to elephant (Loxodonta)

Abstract: Measurements have been made of the principal leg bones of 37 species representing almost the full range of sizes of terrestrial mammals. The lengths of corresponding bones tend to be proportional to (body mass)0·35 and the diameters to (body mass)0·36, except in the family Bovidae in which the exponents for length are much nearer the value of 0·25 predicted by McMahon's (1973) theory of elastic similarity. Comparisons are made between mammals of similar size belonging to different orders.

Use of δ13C values to determine vegetation selectivity in East African herbivores.

Abstract: The quantitative plant species composition of the rumen contents of a large number of individuals from eight East African herbivores was determined by direct visual analysis. All plant species were classified as either C3 or C4, and an estimated δ13C for the rumen sample was calculated. This estimated value was compared to a measured value determined directly from rumen subsample. The two methods of determining quantitative C3 and C4 composition differed by less than 1%, and the isotopic analysis has the advantage of being rapid and totally objective.

Mechanical stresses in fast locomotion of buffalo (Syncews coffer) and elephant (Loxodonta africana)

Abstract: Films of buffalo and elephant running, and detailed measurements on dissected legs, have been used to estimate the maximum stresses which occur in locomotion, in certain muscles, tendons and bones. These stresses are similar to stresses previously determined for some other, smaller mammals.

Mechanics of running of the ostrich (Struthio camelus)

Abstract: Ostriches have been filmed running fast in their natural habitat. A female ostrich has been dissected and the principal bones, muscles and tendons in a leg have been measured. It is calculated that stresses up to 240 kN m−2 and 40 MN m−2, respectively, act in the digital flexor muscles and their tendons during running. Tensile and compressive stresses up to about 70MNm−2 and 110 MNm−2 act in the tibiotarsus. A large proportion of the energy which would otherwise be required for running is probably saved by elastic storage in tendons. Comparisons are made with the legs of flying birds and of antelopes.

Environmental Aspects of Settlement Site Decisions Among Pastoral Maasai

Abstract: Maasai settlements in Amboseli are distributed in a pattern which reflects various physical and biological characteristics of the landscape. The settlements avoid hillslope gradients exceeding 0.08, and the lower sections of long hillsides, which receive large amounts of runoff. Long, relatively high hillslopes are difficult for exhausted cattle to climb at the end of the dry season, and even the welldrained sites at the upper ends of these slopes are not commonly used. Deep, poorly drained, and light-colored soils are avoided because they affect the comfort of humans, and especially the milk production of cattle. The settlements are located away from dense tree and bush vegetation because of the danger of predators, but during occupation of the site important changes in the vegetation are wrought by the use of trees for settlement construction and firewood. The reasons for the pattern were elucidated by making a set of systematic measurements of settlement distributions and various environmental factors. The conclusions of this analysis were then checked and extended through conversations with Maasai elders. These latter exhibited a sophisticated knowledge of environmental characteristics and processes which is reflected in their choice of settlement sites. Such knowledge has commonly been overlooked by other writers on the subject of pastoralism.

Allometry of the legs of running birds

Abstract: The principal bones, muscles and tendons of the legs have been measured in a selection of running birds, ranging in size from 0–1 kg quail to 40 kg ostrich. Maximum stride frequencies of the same species have been determined from films. Allometric equations have been derived. Most of the exponents agree well with McMahon's (1973, 1975a) theory of elastic similarity, which is discussed.

Rainfall Variability in Africa

Abstract: Time series of annual rainfall for 69 stations in Africa were analyzed for trends and periodicities. Trend analysis showed that most of the annual series indicate some forms of oscillations rather than any particular trend. Use of binomial coefficients to smooth the series indicated positive or negative trends in recent years in 20 series, but only four of these were statistically significant judging by the Spearman rank correlation test. These four stations were geographically distributed within those showing no significant trends. Assuming the generating process to be purely random, the prominent cycles revealed by the spectral analysis were 2.0–2.5 years and 2.7–3.3 years. In general, the larger observed cycles (3.5–4.4 years, 5.0 years, 6.0–6.5 years, 7.0–8.0 years and 10.0 years) were weak at the 0.05 significance level.

The erodibility of two soils from Kenya.

Abstract: Summary A portable rainfall simulator was used to measure the runoff rates and soil losses from a freshly ploughed luvisol at Katumani, and a nitosol at Kabete, on a 6° slope at varying rainfall intensities. The soil losses from storms of 50 and 100 mm/h intensities, in which a total of SO mm rain was applied to plots in the wet moisture state, varied from 0.8 to 1.4 metric tons/ha at Kabete and 8.5 to 13.9 metric tons/ha at Katumani. The percentage runoff from these storms was 15 to 17 per cent at Kabete and 67 to 71 per cent at Katumani. The much greater runoff rates from the Katumani soils were shown to be due to surface capping caused by degradation of the surface structure. It has been proposed that soil credibility K factors of 0.4 and 0.04 could be used for the Katumani and Kabete soils respectively in the Universal Soil Loss Equation

Studies in Mixed Cropping. III. Further Results with Maize-Bean Mixtures

Abstract: In contrast to earlier results, a clear advantage from mixed cropping of maize and beans (Phaseolus vulgaris) was found in the long-rain seasons (March to September) of 1976 and 1977. Pure stand yields were low due to drought in 1976 and excessive rainfall in 1977. These and other results for long-rain seasons in Kenya suggest that mixtures are more efficient where pure stand yield levels are low, but there is little difference between cropping systems where levels are high. Light interception by maize leaves was quite small until late in the life of the bean crop.

Potassium fixation in some kenyan soils

Abstract: Summary Potassium fixation was measured for 13 Kenyan soils with a range of applied potassium (0 to 1000 mg kg−1). The fixed potassium was measured, and hence is defined in this study, by the difference between the amount of applied K and the increase in the extractable K after equilibration, using a single ‘equilibrium’ extraction procedure with 0. 25 M Cad, as the extractant. At application rates of 50 and 1000 mg kg−1 the fixed potassium varied from −52% to 64% and 7% to 39% respectively. A correlation was found between the K fixation and % clay content at the 1000 mg kg1 application rate. Estimates of the % fixation by the clay fractions gave 53 to 80% for montmorillonites, 48 to 66% for amorphous clays and 19 to 32% for kaolinites. It is suggested that the amorphous clays may fix potassium by a ‘sieve’ mechanism.

Recent archaeological findings at the Sterkfontein site

Abstract: UNTIL the present decade it was thought that the Early Stone Age of Africa consisted of two industrial complexes, the Oldowan and the Acheulian, the latter succeeding the former after a transitional phase. Well excavated and well dated Oldowan sites are known only from Eastern Africa, although Oldowan sites are reported from North and South Africa, and all known examples are older than 1.5 Myr (refs 1–4). The earliest manifestations of the Acheulian appear approximately 1.5 Myr BP (refs 5, 6) and continue until the Last Interglacial. Leakey has challenged the idea that the Acheulian represents a continuous development of the Oldowan in East Africa1,7,8. At Olduvai in Bed II she recognises two industrial complexes, which are said to represent two distinct cultural traditions, possibly produced by two different hominid taxa. These industries are the Acheulian and the Developed Oldowan. The criteria for defining the Developed Oldowan B have recently been revised and Leakey7 now states that the morphology and technical features of manufacture of bifaces are the principal distinguishing characters between the two industries. The main technological distinction is that the Acheulian biface makers knew how to detach large flakes (>10 cm) while the Developed Oldowan hominids did not. As a result of this revised definition some of the assemblages at Olduvai originally defined as Developed Oldowan B have been reclassified as Acheulian by Leakey7. The problem of the Acheulian and Developed Oldowan can be stated as two alternative hypotheses. (1) Two cultural traditions began in East Africa approximately 1.5 Myr BP, each associated with a distinct social population over an immense span of time; possibly they were of different hominid taxa. Or (2), there was only one cultural tradition (industry), the Acheulian Industrial Complex, beginning about 1.5 Myr BP and marked by highly variable bifacial tools and relative frequency of artefact types; only one hominid taxon during any given period was involved. I have now made a comparative study of the Sterkfontein and Olduvai Gorge Bed II assemblages, which suggests that the Developed Oldowan B industry falls within the Acheulian Industrial Complex and therefore serious consideration should be given to dropping the former term.

O2-uptake, thermoregulation and heart rate in the springhare (Pedetes capensis)

Abstract: 1. O2-consumption (O2), rectal temperature (Tre) and heart rate were measured in two adult springhares (♂,♀; body mass 2.2–2.4 kg) at ambient temperatures (Ta) from 6–35 °C. Abdominal temperature in the female and heart rate in both animals were determined by telemetry. 2. AtTa's from 23–28 °C rectal temperature in both animals ranged between 35.5–36.3 °C. This range was well maintained at lowTa's. Exposure to highTa's, however, led to a considerable rise of the rectal temperature (to above 39 °C atTa=35 °C). 3. The lowest oxygen uptake (0.32–0.37 ml O2·g−1·h−1) was found between 23–33 °C. This is only 65–75% of the predicted value in similar sized mammals. Below 23 °C O2-consumption increased rapidly up to approximately 2,5 times (6–7 °C) the value in the thermoneutral zone (23–33 °C). AtTa's above 33 °C the heat dissipating capacities of the springhares proved to be inadequate and consequentlyTre rose steadily. 4. Basal heart rate (75–85 beats·min−1) was about 30% below the standard value for similar sized mammals. During exposure to cold the heart rate sometimes exceeded 200 beats·min−1. 5. The measured parameters are discussed with special regard to the extent of the springhare's adaptation to arid conditions. It is concluded that these rodents are physiologically adapted to fossorial habits rather than to life in desert environments and are thus restricted to semi-arid areas.

Density and Shrinkage of Old Wood

Abstract: Density and shrinkage were measured in samples of old wood preserved in a glacier, burial grounds, house settlements, harbour installations and ships sunk in the sea. Time of exposure ranged from about 300 to 100,000 years. Density was found reduced in most cases and shrinkage increased. In oak, density was reduced up to 0.13 gr/cm3 (at 12% m.c.) and a tangential shrinkage value of 62.16% was measured. Irrespective of time of exposure and loss of material, old wood retains its gross structural characteristics as long as it remains waterlogged.

The sources of atmospheric gravity waves.

Abstract: The gravity wave theory has been very successful in the interpretation of various upper atmospheric phenomena. This article offers a review of the present state of knowledge about the various sources of atmospheric gravity waves, particularly those which give rise to different types of travelling ionospheric disturbance. Some specific case studies are discussed.

Aquatic Weeds in African Man-Made Lakes

Abstract: There is a pattern of succession of weeds in man-made African lakes. Each phase of succession differs in each lake depending on the local environment. Floating weeds develop first, followed by sudd, a later decrease in floating weeds, an increase in submerged weeds, and finally an emergent drawdown flora. The stages in this sequence may be very pronounced in some lakes, or may be virtually absent in others.

Dynamic ecology of Aldabran seabird communities

Abstract: The characteristics of the present seabird community of Aldabra are described, and compared briefly with others in the tropics. By comparison with Pacific Ocean communities, Aldabra is deficient especially in petrels and shearwaters, which are poorly represented in the western Indian Ocean generally and are absent probably for zoogeographic reasons. Ground-nesting species are also scarce, especially pelagic feeders that form large colonies, and this is attributed partly to their extermination by rats and partly to the proximity of Assumption, and perhaps Cosmoledo, that offer better nesting sites to these species. Inshore-feeding terns are also scarce on Aldabra, probably owing to insufficient areas of shallow water nearby. Relative population sizes are roughly in agreement with those that would be predicted, except for the fairy tern whose population may have been reduced in the past by barn owls. Almost all Aldabran seabirds nest either in mangroves or on small lagoon islets, the habitats in which birds are least vulnerable to introduced rats, which appear to have had a major effect on nesting distribution. The seabird community is made up of two different trophic guilds, the pelagic feeders which bring in nutrients entirely from outside the ecosystem, and the inshore feeders which cycle nutrients between the intertidal and inshore parts of the system and the terrestrial part. Both result in a net input of nutrients, in the form of bird droppings, to the terrestrial ecosystem. It is estimated that about 1680 t of food are removed from the sea per year, most of the 105 t of guano resulting being channelled into the intertidal, rather than the terrestrial, parts of the ecosystem. The seabird communities likely to have occupied Aldabra in the past are reconstructed on the basis of the known changes in the atoll’s size and structure during the Pleistocene. At most times there would have been more species of seabird using Aldabra than now, and more of their guano would have passed into the terrestrial ecosystem. Probably the most significant event in the recent history of the atoll was the arrival of rats, which exterminated probably quite considerable colonies of ground-nesting seabirds and drove the survivors into the only places where the rats could not survive - the tall mangroves and the tiny lagoon islets. In so doing, the rats destroyed a significant source of nutrient input to the terrestrial ecosystem, with major consequences for the ecology of the atoll as a whole.

Some effects of irrigation and plant density on the water relations of high density coffee (Coffea arabica L.) in Kenya

Abstract: SummaryMeasurements were made of xylem water potentials, stomatal apertures, shoot growth, yield and yield components in two-to four-year-old trees of Coffea arabica growing at a range of high planting densities, and in one experiment given irrigation for different periods during the year. Irrigation greatly increased lateral extension growth and node production but, as node numbers were negatively correlated with fruits per node, fruit yield was relatively little affected. In trees irrigated only once during a very dry period, lateral growth rate, node production and stomatal apertures were generally higher at around 8000 plants ha−1 than at 5000 and at even higher densities either remained constant or declined. Midday xylem water potentials were lowest, not at the times of greatest soil water deficit, but a few days after irrigation or rain showers. The relationship of water potential to plant density was variable but on days when potentials were below −16·5 bar, the highest potentials were found in the...

A palaeomagnetic study of lower Proterozoic granites from Western Kenya

Abstract: Summary This paper reports a palaeomagnetic study of the lower Proterozoic granites, exposed in the western part of Kenya and dated at 2530 ± 50 Ma (λRb= 1.39 × 10−11 yr−1). Ten sites out of 13 have yielded stable palaeomagnetic directions which are believed to be primary. Polished section and thermomagnetic analyses indicate titanomagnetite grains as the main carrier of the primary component of the natural remanence. The mean palaeomagnetic north pole is calculated at 210.7° E, 60.9° N with A95= 13.5°.