B. W.J. van Rensburg

Species richness, environmental correlates, and spatial scale: a test using South African birds.

Energy and habitat heterogeneity are important correlates of spatial variation in species richness, though few investigations have sought to determine simultaneously their relative influences. Here we use the South African avifauna to examine the extent to which species richness is related to these variables and how these relationships depend on spatial grain. Taking spatial autocorrelation and area effects into account, we find that primary productivity, precipitation, absolute minimum temperature, and, at coarser resolutions, habitat heterogeneity account for most of the variation in species richness. Species richness and productivity are positively related, whereas the relationship between potential evapotranspiration (PET) and richness is unimodal. This is largely because of the constraining effects of low rainfall on productivity in high‐PET areas. The increase in the importance of vegetation heterogeneity as an explanatory variable is caused largely by an increase in the range of vegetation heterogeneity included at coarse resolutions and is probably also a result of the positive effects of environmental heterogeneity on species richness. Our findings indicate that species richness is correlated with, and hence likely a function of, several variables, that spatial resolution and extent must be taken into account during investigations of these relationships, and that surrogate measures for productivity should be interpreted cautiously.

Melatonin in Chronic Renal Failure

The melatonin status of patients in end-stage chronic renal failure (CRF) was evaluated by the determination of daytime plasma melatonin levels and by the investigation of the circadian rhythmicity of melatonin secretion. A significant increase in plasma melatonin concentration was found in all CRF patient groups investigated, i.e. CRF patients on conservative treatment (CT; n = 48), CRF patients on maintenance haemodialysis treatment (HD; n = 39) and CRF patients on peritoneal dialysis (PD; n = 32). Successful transplantation led to a marked reduction in plasma melatonin levels. The circadian rhythm of melatonin secretion would appear to be suppressed in CRF as the nocturnal secretory surge was absent in all HD patients and in 80% of the posttransplantation patients studied.

Micro-scale heterogeneity of spiders (Arachnida: Araneae) in the Soutpansberg, South Africa : a comparative survey and inventory in representative habitats

ABSTRACT Coarse-scale studies that focus on species distributions and richness neglect heterogeneity that may be present at finer scales. Studies of arthropod assemblage structure at fine (1 × 1 km) scales are rare, but important, because these are the spatial levels at which real world applications are viable. Here we investigate fine-scale variation in spider assemblages, comparing five representative vegetation types in the western Soutpansberg, Limpopo Province, South Africa. We assess these vegetation types in terms of their family and species composition, as well as levels of endemicity, relating these differences with vegetation structure. We inventoried 297 species (49 families) in an area less than 450 ha, as part of South African National Survey of Arachnida. Analysis of the results suggests that endemic taxa are associated with Tall Forest and, to a lesser extent, Woodland. The Woodland had the highest species diversity, and much of the variation observed in spider assemblage structure is explained by these two vegetation types. Based on vegetation structure variables that explained significant variation in spider assemblages, human influence through bush encroachment will result in a change of spider assemblages to that of Short Forest and Mosaic Woodland vegetation types, with implications for biodiversity maintenance and heterogeneity.

Assessing local scale impacts of Opuntia stricta (Cactaceae) invasion on beetle and spider diversity in Kruger National Park, South Africa

There is a paucity of studies examining direct impacts of introduced alien species on biodiversity, a key need for motivating for alien species control in conservation areas. The introduced prickly pear (Opuntia stricta) has invaded some 35 000 ha of Kruger National Park. We investigated the effect of O. stricta on beetle and spider species assemblages in the Skukuza region of Kruger National Park. We used unbaited pitfall traps over a 12-month period in four treatments of varying O. stricta density. Species richness, species density and abundance of beetles and spiders were compared. A total of 72 beetle and 128 spider species were collected. Species richness and species density for beetles and spiders did not differ significantly across the four treatments. Assemblages for spiders did not differ across treatments but beetle assemblages were significantly different from uninvaded control sites. This study suggests that the current density of O. stricta does not significantly affect spider species richness, density or assemblages but that beetle assemblages are significantly affected.

Non-linear analysis of structural steel frames

Abstract Material, geometrical and connection non-linearities could have a significant influence on the forces and moments in a steel structure, especially in sway frames at ultimate load levels. Some structural steel design codes (such as CAN3-S16·1-M89) require that a designer consider second-order moments (i.e. the geometric non-linearities). If the steel members are able to redistribute moments through plastic hinge formation, it makes economic sense to do a plastic design. Certain so-called ‘hinge’-connections do in fact transfer significant moments. It would thus also make the structure more economical if one can take this moment transfer into account. All the above effects could be built into a steel frame analysis program. In this paper, ways of including geometrical, material and connection non-linearities into the matrix stiffness method in a relatively uncomplicated manner will be discussed. A computer program developed by the authors, for design-office use, where the matrix stiffness method has been adjusted to incorporate all these non-linearities is described. The use of the computer program is illustrated by means of an example.

Whole blood serotonin levels in chronic renal failure.

Whole blood serotonin levels were investigated in a control group (n = 35) and in a group of chronic renal failure patients (n = 127) on various treatment regimen i.e. conservative treatment (n = 39), maintenance haemodialysis (n = 35) and after renal transplantation (n = 53). The whole blood serotonin levels, as determined by high performance liquid chromatography, were significantly lower in the chronic renal failure patients than in the control group (p = 0.0001). Whole blood serotonin levels were significantly lower in the white subjects than in the black subjects of the study (p = 0.0001).

Lightweight cold-formed portal frames for developing countries

Abstract Southern Africa is a developing area. In this regard, a severe demand exists for the development of the small to medium industrial sector, as well as provision of low-cost domestic housing. Correspondent to this demand, employment has to be created, mainly for the unskilled labour sector. Pre-manufactured hot-rolled steel sections which are bolted together on site are commonly used in the construction of industrial-type structures. An economical alternative structural concept for low-rise portals is proposed, whereby the total frame is made up of standard cold-formed sections which are cut and welded together on site.

The Effect of Timber Density and Type of Adhesive on the Strength of Finger-joints in S.A. Pine and Eucalyptus grandis

SYNOPSIS It is universally accepted that a finger-joint is a strength reducing feature in timber members that are subjected to tensile stresses. This weakening effect is most pronounced in high density timber such as high grade S.A. Pine and the Eucalyptus species. This study compares the strength of finger-joints manufactured with phenol resorcinol formaldehyde (p.r.f.) to those manufactured with two different epoxy mixtures. The epoxy resins had to provide a stronger finger-joint without sacrificing any of the positive qualities of p.r.f. such as stiffness, durability and minimal creep. All the test specimens were manufactured according to the glue manufacturers instruction sheet on a normal production line as it was felt that test specimens manufactured under laboratory conditions would give a false impression of the strengths that could be expected from commercially prepared finger-joints.

The behaviour of eccentrically restrained I-sections subjected to axial loads

Abstract The axial load capacity of a strut is commonly defined in terms of a slenderness parameter, which is a function of the distance between restraints. Theoretical and experimental investigations into strut behaviour have concentrated on cases where the restraints are placed in such a manner as to prevent displacement of the centroid of the section. In some practical applications, restraints are placed in such a manner as to restrain only part of the cross-section and displacement of the centroid is still possible. Common practical examples of such struts may be found in industrial-type portal frames, where some difference of opinion exists as to the restraining action of the sheeting rails which are attached to one flange only. Existing knowledge of strut behaviour is not directly applicable to such cases Experimental studies were conducted with a view to developing a theoretical model reflecting the behaviour of I-columns where intermediate restraints are attached to one flange only. Cases considered include one, two and three intermediate restraints and two different section sizes were used. Section parameters influencing the behaviour over a range of slenderness ratios are discussed in this paper and comparisons with a theoretical model are made. Some design curves are presented and general observations regarding the behaviour of such struts are indicated.

S A Pine—Load Sharing. Fact or Fiction?

SYNOPSIS Load sharing amongst timber members, that are restrained to the same deflection, has been accepted as a given fact for some time. This paper discusses a simulation method that can be used to determine whether load sharing does in fact exist when S A Pine members are used. Results of tests as well as simulations are presented and discussed. It is concluded that load sharing will not occur when the material behaviour is elastic-brittle. Some form of ductility is required for load sharing to take place.