Scielo RSS http://www.scielo.org.za/rss.php?pid=0038-235320090003&lang=es vol. 105 num. 5-6 lang. es http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000300001&lng=es&nrm=iso&tlng=es http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000300002&lng=es&nrm=iso&tlng=es http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000300003&lng=es&nrm=iso&tlng=es http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000300004&lng=es&nrm=iso&tlng=es http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000300005&lng=es&nrm=iso&tlng=es http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000300006&lng=es&nrm=iso&tlng=es http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000300007&lng=es&nrm=iso&tlng=es http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000300008&lng=es&nrm=iso&tlng=es http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000300009&lng=es&nrm=iso&tlng=es http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000300010&lng=es&nrm=iso&tlng=es http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000300011&lng=es&nrm=iso&tlng=es South Africa was an early leader in multidisciplinary studies of marine resources, particularly with the Benguela Ecology Programme in the 1980s and 1990s and catch records are available for some species dating back more than a century. Resources data have focused on trends in catches, fishing effort and changes in distribution and abundance of harvested resources, which often account for a major part of the structure and functioning of marine ecosystems. Data have been collected by means of fishery-dependent and fishery-independent survey techniques appropriate to each particular stock and analysed using traditional single species stock assessment techniques. The data are complemented by comprehensive information on the environment and top predators and have been analysed using trophodynamic models such as Ecopath with Ecosim. Future approaches include a shift to an ecosystem approach to fisheries monitoring and management, in an attempt to reconcile utilisation and biodiversity conservation objectives. Despite these scientific achievements, the single species approach to the management of most resources still persists, with only limited interactions between competing species or predators and prey being formally taken into account when modelling the stock dynamics and providing management advice to the authorities. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000300012&lng=es&nrm=iso&tlng=es Recent developments in imaging spectroscopy have seen a dramatic improvement in the characterisation of terrestrial features due to the high spectral resolution of the sensors used. For example vegetation species discrimination, stress detection and foliar chemistry mapping can now be achieved using these high spectral resolution sensors, a task that was almost impossible with coarse resolution satellite sensors. In spite of its capabilities, imaging spectroscopy is still in its early stages of development and application in southern Africa. This overview will attempt to briefly describe the science and analysis techniques, as well as review trends and challenges in the South African imaging spectroscopy landscape. It therefore is not intended as a pure research paper, but merely to illustrate the potential of and developments in imaging spectroscopy. This is pertinent to the South African scientific community where the technology is still in its infancy, especially given that the first-ever spaceborne South African imaging spectrometer, the Multi-Sensor Micro-Satellite Imager Satellite (MSMISat) is being developed for launch in the near future. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000300013&lng=es&nrm=iso&tlng=es The precipitation data for some regions in South Africa were studied for the period 1900-1998. From the 11 regions examined, 8 in South Africa had maximum precipitations in the austral summer months (December, January, February, March), while 3 had maxima in autumn and winter. Annual values showed considerable year-to-year fluctuations (50% to 200% of the mean), while five-year running means showed long-term fluctuations (75% to 150% of the mean). A spectrum analysis indicated periodicities in the ranges 2-3 (quasi-biennial oscillation, QBO), 3-4 (quasi-triennial oscillation, QTO), 6-11, 17-21, 23-26, 32-35 and 55-66 years, some common to, and some different in different regions. The QBO and QTO accounted for a substantial fraction (30-50%) of the total variance. In five-year running means, the effects of QBO and QTO were suppressed considerably. The plots showed distinct peaks, but the spacings varied in a wide range, indicating that predictions based on extrapolation of single peaks are not likely to come true even for decadal averages. El Niño effects for the giant event of 1982/83 were as expected but those for 1997/98 were obscure, almost absent. Running means over 21 years did not indicate linear trends, upwards or downwards. Instead, considerable oscillations were seen, with magnitudes different in different regions (5-25%). On average, high values during 1915/16 decreased considerably (5-8%) up to 1935, oscillated upwards thereafter and recouped by 1980, but decreased considerably thereafter. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000300014&lng=es&nrm=iso&tlng=es The relatively recently developed scintillometry method, with a focus on the dual-beam surface layer scintillometer (SLS), allows boundary layer atmospheric turbulence, surface sensible heat and momentum flux to be estimated in real-time. Much of the previous research using the scintillometer method has involved the large aperture scintillometer method, with only a few studies using the SLS method. The SLS method has been mainly used by agrometeorologists, hydrologists and micrometeorologists for atmospheric stability and surface energy balance studies to obtain estimates of sensible heat from which evaporation estimates representing areas of one hectare or larger are possible. Other applications include the use of the SLS method in obtaining crucial input parameters for atmospheric dispersion and turbulence models. The SLS method relies upon optical scintillation of a horizontal laser beam between transmitter and receiver for a separation distance typically between 50 and 250 m caused by refractive index inhomogeneities in the atmosphere that arise from turbulence fluctuations in air temperature and to a much lesser extent the fluctuations in water vapour pressure. Measurements of SLS beam transmission allow turbulence of the atmosphere to be determined, from which sub-hourly, real-time and in situ path-weighted fluxes of sensible heat and momentum may be calculated by application of the Monin-Obukhov similarity theory. Unlike the eddy covariance (EC) method for which corrections for flow distortion and coordinate rotation are applied, no corrections to the SLS measurements, apart from a correction for water vapour pressure, are applied. Also, path-weighted SLS estimates over the propagation path are obtained. The SLS method also offers high temporal measurement resolution and usually greater spatial coverage compared to EC, Bowen ratio energy balance, surface renewal and other sensible heat measurement methods. Applying the shortened surface energy balance, measurements of net irradiance and soil heat as well as SLS estimates of sensible heat allows path-weighted evaporation from the surface to be estimated. Research applications involving the use of the SLS method, as well as the theory on which the method is based, are presented. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000300015&lng=es&nrm=iso&tlng=es Numerous investigations have shown that fumonisin B1 (FB1) is the causal agent in a range of animal toxicities, including leucoencephalomalacia, pulmonary oedema and renal and hepatic cancer in rats and mice. Fumonisin B1 has also been implicated in the aetiology of oesophageal cancer in South Africa. Human data are lacking, however, and the International Agency for Research on Cancer has accordingly classified this mycotoxin as a Type 2B carcinogen. This study investigated the ultrastructural effects of FB1 cytotoxicity on a human oesophageal carcinoma cell line (SNO). The pathological changes induced by FB1 were determined using transmission and scanning electron microscopy. Immunocytochemistry was used to immunolocalise FB1 (monoclonal anti-FB1) within the cells. The results showed marked pathological changes that included enlargement or microsegregation of the nucleus, microsegregation of the nucleolus, and swelling and elongation of mitochondria, as well as signs of membrane damage. These cytotoxic effects were associated with the action of FB1, since the toxin was internalised in nuclei, mitochondria and the cytoplasm of affected cells. This study shows that FB1 may exert its biological effects in SNO cells through binding to cellular macromolecules or membrane components within the affected organelles. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000300016&lng=es&nrm=iso&tlng=es At the end of the Miocene epoch, C4 grasslands began to expand at the expense of tree-, shrub- and forb-dominated C3 ecosystems. While C4 grasses were spreading throughout most regions of the world, C3 grasses may have been spreading along South Africa's southwest coast. Stable isotope analyses of hypsodont fossil ungulates from 'E' Quarry, a well-known Late Miocene/Early Pliocene fossil locality near the town of Langebaanweg, suggest that the local environment might have included a substantial C3 grass component. Besides this indirect evidence, little is known about the evolution, nature and importance of grass in the 'E' Quarry biome. As a preliminary step towards addressing these questions, we initiated a trial investigation to assess whether sediments at the site are conducive to the preservation of phytoliths, an important tool in the reconstruction of palaeohabitats. Results indicate that fossil phytoliths are sufficiently well preserved to allow a comprehensive analysis of the 'E' Quarry phytolith assemblage. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000300017&lng=es&nrm=iso&tlng=es Sixteen years of low-resolution Landsat 5 and 7 satellite images were used to construct Boolean images of snow cover over the Drakensberg through a GIS. Contemporary patterns of snow cover, including altitudinal variations, were determined for individual months and various seasons. The seasonal occurrence and spatial influence of various snow-producing weather systems were determined through remote sensing and the consultation of daily climate data and synoptic charts. A proportional relationship was found between altitude of snow-covered pixels and the number of occurrences that pixels were covered in snow. The highest incidence and most widespread snow cover occurred from June to August; spring snow occurred preferentially in the central and southern Drakensberg regions. Cold fronts and associated cut-off lows accounted for about 80% of snow cover over the Drakensberg. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000300018&lng=es&nrm=iso&tlng=es A whistler is a very low frequency (VLF) phenomenon that acquires its characteristics from dispersive propagation in the magnetosphere. Whistlers are derived from the intense VLF radiation produced in lightning strikes, which can travel great distances within the Earth-ionosphere waveguide (EIWG) before penetrating the ionosphere, and exciting a duct. Field-aligned ducts of enhanced plasma density guide the propagation from one hemisphere to the other. The location of the duct, relative to the strike that causes the whistler, is unknown. Whistler time series from Tihany, Hungary, have been cross-correlated with lightning data obtained from the World Wide Lightning Location Network (WWLLN). The results show that whistlers observed at Tihany originate mainly from lightning strikes in an area with a radius of approximately 1 000 km surrounding the magnetic conjugate point in the Indian Ocean just east of East London, South Africa. A clear diurnal distinction was seen in that the correlation is maximised when the whistler station and the source region are in darkness. This is believed to relate to the diurnal variation of the ionosphere, which becomes more transparent to VLF waves at night. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532009000300019&lng=es&nrm=iso&tlng=es The Afrikaans poet and writer Eugène Marais is well known in South Africa but not elsewhere. The publication of his The Soul of the Ape in 1969 triggered a hard hitting response from the British primatologist Solly Zuckerman, in which he attacked Marais' writings and rejected him as a legitimate scientist. The two never met and Marais had been dead for nearly 40 years when Zuckerman's attack took place. This paper examines the basis for Zuckerman's attack and looks at the context of both men, especially in the light of Zuckerman's combativeness and Marais' naivety and lack of scientific rigour.