Non-random patterns of vegetation clearing and potential biases in studies of habitat area effects     

Jeremy S. Simmonds  Berndt J. van Rensburg  Martine Maron 《Landscape Ecology》2017,32(4):729-743

  相似文献   

Schistosoma mattheei--an ovum containing twin miracidia     

Van Rensburg LJ  Van Wyk JA 《The Onderstepoort journal of veterinary research》2003,70(1):69-71

A large Schistosoma mettheei ovum containing two miracidia was recovered from a squash preparation of the liver of an experimentally infected hamster. When observed, the miracidia were motile and facing in opposite directions.  相似文献   

Description and classification of abnormal cercariae of Schistosoma mattheei and a method of concentration and collection     

Van Wyk JA  Van Rensburg LJ 《The Onderstepoort journal of veterinary research》2003,70(2):121-129

Over a period of about 12 years, 30 abnormal Schistosoma mattheei cercariae were found among a total of approximately 2.8 million examined. Initially seven were recovered from about 1.02 million (0.0007%), which were examined individually while being counted with the aid of a stereoscopic microscope. Subsequently, on the strength of relatively high percentages of abnormal individuals recovered when counting cercariae that failed to penetrate into oxen, it appeared that the morphologically abnormal cercariae were unable to swim and would mostly sediment out of a suspension while most of the normal cercariae would remain swimming. This surmise is supported by recovery of 23 morphologically abnormal cercariae (0.001%) from about 1.8 million, by examining the sediment after the cercarial suspension had been left standing undisturbed in glass measuring cylinders. The abnormalities ranged from aberrant tails only (e.g. an underdeveloped tail, or different degrees of schism) or aberrant heads only, to abnormalities of both the heads and tails. A suggested schematic classification of abnormal cercariae is presented. A young, adult hamster was exposed to eight S. mattheei cercariae with complete schism of the shaft of the tail, by pipetting the cercariae onto the shaved abdominal skin of the anaesthetised animal. Two underdeveloped females were subsequently encountered in squash preparations of the liver when the hamster was killed for worm recovery 10 weeks after infection, thus showing that some of the abnormal cercariae were viable. A method is also described for killing and fixing cercariae while retaining some of the shining brilliance of live cercariae, without them becoming shrivelled, granular and semi-opaque, as occurs when cercariae die spontaneously or are killed with heat. This is apparently the first report of abnormal cercariae of S. mattheei. In addition, a method of concentrating abnormal cercariae after emergence from a snail, a schematic classification of abnormal cercariae and a method for killing and fixing cercariae while retaining much of the shiny brilliance of live cercariae are also reported for the first time as far as is known.  相似文献   

Yield and seasonal water productivity of sunflower as affected by tillage and cropping systems under dryland conditions in the Limpopo Province of South Africa     

J. Mzezewa  E.T. GwataL.D. van Rensburg 《Agricultural Water Management》2011,98(10):1641-1648

Sustainable food production in semi-arid tropical countries can be achieved through efficient utilization of rainwater. A field experiment to assess the grain yield, seasonal water use (WU), water use efficiency (WUE) and precipitation use efficiency (PUE) of sunflower (Helianthus annuus L.) intercropped with cowpea (Vigna unguiculata L.) on two tillage systems was conducted during the 2007/2008 and 2008/2009 cropping seasons at the University of Venda (22°58′ S, 30°26′ E at 596 m above sea level). The experiment was configured as a 2 × 2 × 2 factorial design with three replications. The tillage treatments were conventional tillage (CT) (control) and in-field rainwater harvesting (IRWH) system. The IRWH is a special crop production technique that promotes runoff on 2.0-m wide no-till strip between crop rows and collects the runoff water in basins where it infiltrates into the soil profile. The treatments in the cropping system (CS) consisted of a sole crop (sunflower or cowpea) and an intercrop (sunflower × cowpea). Results of the experiment revealed that IRWH led to a significant (P < 0.05) increase in sunflower grain yield in the second season but cowpea grain yield was not influenced by tillage systems. IRWH resulted in significantly higher WU, WUE and PUE of both crops compared to CT system in the second season. The CS had significant effects on sunflower grain yield in both seasons but none on the cowpea grain yield. WU was significantly higher in intercrops than in sole cowpea and sole sunflower in the first and second season, respectively. WUE and PUE were significantly greater in sole sunflower than in the intercrops but less in the sole cowpea than in the intercrops.  相似文献   

Selection of yeast starter culture strains for the production of marula fruit wines and distillates     

Fundira M  Blom M  Pretorius IS  van Rensburg P 《Journal of agricultural and food chemistry》2002,50(6):1535-1542

Juice of the Sclerocarya birrea subsp. caffra (marula) fruit was fermented by indigenous microflora and different commercial Saccharomyces cerevisiae yeast strains at different temperatures, namely, 15 and 30 degrees C. Volatile acids, esters, and higher alcohols were quantified in the wine and distillates, and the results were interpreted using a multivariate analysis of variance and an average linkage cluster analysis. Significant differences between 15 and 30 degrees C and also among yeasts with respect to volatile compounds were observed. Yeast strains VIN7 and FC consistently produced wines and final distillates significantly different from the other strains. A panel of tasters and marula and brandy producers was asked to select wines and distillates that had an acceptable and typical marula "nose". They were also asked to detect the differences among wines and distillates fermented with the same yeast strain at different temperatures.  相似文献   

Soil Microbial Community Structure of Coal Mine Discard Under Rehabilitation     

S. Claassens  P. J. Jansen Van Rensburg  L. Van Rensburg 《Water, air, and soil pollution》2006,174(1-4):355-366

Assessment of soil microbial diversity, in terms of the actively growing population, may be a sensitive indicator of ecological stress and restoration processes. During this study, the relationship between microbial community structure; vegetation cover; and physical and chemical characteristics of topsoil covers at seven coal discard rehabilitation sites in South Africa were evaluated. A positive association was observed between the microbial biomass, vegetation cover and the organic carbon, ammonium, nitrate and phosphorus contents. Although the seven coal discard sites had different rehabilitation ages (1–8 years), there was no statistically significant difference between these sites based on physical and chemical characteristics. The various rehabilitation sites could be differentiated based on the microbial community structure. The Hendrina site was characterised by the highest viable biomass, monounsaturated fatty acids, and high ground cover. Bethal and Ermelo sites were the youngest sites (1 and 3 years) in terms rehabilitation age. Both these sites were associated with higher abundances of fungi and Actinomycetes than the other sites. Ratios of trans- to cis-monoenoic fatty acids and cyclopropyl fatty acids to their monoenoic precursors indicated stress in all sites sampled.  相似文献   

Corneal anatomical differences in the aetiology of chronic superficial keratitis     

S. W. Petrick  I. B. J. Van Rensburg 《The Journal of small animal practice》1989,30(8):449-453

The apparently normal corneas of 14 diseased eyes of German shepherd dogs (GSDs) were shown to possess very thin epithelial layers on microscopy. Normal corneas of 38 GSDs and 113 dogs of various breeds and crossbred animals were compared for epithelial thickness, structure of corneal stroma and corneal strength. Due to lower values for these criteria found in the GSDs they are considered to play an important role in the aetiology of chronic superficial keratitis.  相似文献   

An ultrastructural study of the development of Babesia occultans in the salivary glands of adult Hyalomma marginatum rufipes     

E F Blouin  L van Rensburg 《The Onderstepoort journal of veterinary research》1988,55(2):93-100

The development of Babesia occultans in the salivary glands of adult Hyalomma marginatum rufipes was studied with the electron microscope. Sporogony involved a process of multiple fission in which sporozoites formed from the periphery of a polymorphous sporont. Different stages of development were found concurrently in individual acini as well as within individual acinar cells. Mature sporozoites were found on Day 3 post-tick attachment and measures 3.0-3.5 X 1.5 micron. The apical complex consisted of a polar ring and 4-6 rhoptries. Micronemes were concentrated anteriorly and 1 or 2 spherical bodies were identified in each sporozoite. The general pattern of development was similar to that described in several other Babesia spp. but distinct morphologic differences were noted.  相似文献   

Malnutrition of the foetus as a cause of abortion     

S J van Rensburg 《Journal of the South African Veterinary Medical Association》1971,42(4):305-308

  相似文献   

The significance of the cytoplasmic droplet in the disintegration of semen in Guernsey bulls     

S W van Rensburg  S J van Rensburg  W H de Vos 《The Onderstepoort journal of veterinary research》1966,33(1):169-184

  相似文献