THE CONSERVATION OF WETLANDS

Diplotaxodon limnothrissa is a widely distributed species occurring throughout Lake Malawi and is probably the most abundant cichlid in the pelagic zone of the lake. The species is exploited commercially in the south-east arm of the lake, but since the fishery's inception the resource has never been assessed. Per-recruit analysis indicated that the resource is under-exploited, with current spawner biomass per-recruit between 55% and 74% of pristine levels.     

杀虫剂混用方法——抗性治理的一种策略

本文根据种群遗传学的基本原理,采用计算机数值模拟的方法定量比较了合理混用、轮用、棋盘式使用等用药策略对害虫抗性增长的影响.结果表明,对半显性遗传,两性繁殖的害虫来说,在较有利的条件下合理混用与轮用效果基本一致,而优于棋盘式用药;在条件不利(抗性基因初始频率高,稀释作用小等)时,合理混用的方法明显优于其他两种方法.因此合理混用是一种有希望的抗性治理方法.     

THE USE OF THE ABBOTT-RAWSON TUBE

The Abbott-Rawson tube is a useful device in gastrointestinal surgery, as it obviates intravenous and intramuscular therapy. Jejunal rather than intravenous feedings may be used and the tube may also be used for administration of potassium, antibiotics and vitamins.     

THE DISTRIBUTION OF WETLANDS IN THE SOUTH-WESTERN CAPE PROVINCE,SOUTH AFRICA

Summary

The hydrological and habitat value of wetlands is beginning to be recognised in South Africa, but only in parts of Natal Province has an effort been made to map wetlands and to record their status over large areas. While the most accurate method of mapping wetlands is a combination of photogrammetry and field surveys, this is time-consuming and expensive. An alternative “desktop” method was therefore used to draw up a preliminary distribution of wetlands in the south-western Cape Province, and this approach consisted of summarising the information contained on 1:50 000 topographical survey maps. The summary shows that shallow, vegetated wetlands (vleis) occur mainly in the wetter south and south-west of the region, while the non-perennial wetlands (pans) predominate inland, where the land is dryer and flatter. There are many estuarine wetlands along the coast, resulting from the tendency of river mouths to be blocked by sand-bars. Farming requirements and suitable topography account for the many small artificial wetlands (farm dams) in the central southern parts. Farm dams predominate in the region (15067 were counted), followed by pans (1741), riverine wetlands (261), vleis (216) and estuarine wetlands (15).