Randolph S E
Department of Zoology, University of Oxford, U.K.
Med Vet Entomol. 1997 Jan;11(1):25-37. doi: 10.1111/j.1365-2915.1997.tb00286.x.
The creation of a generic population model for the tick Rhipicephalus appendiculatus requires a detailed, quantified understanding of the interactions of these ticks with their biotic and abiotic environment in the different parts of their range, from the tropical regions of East Africa to the temperate regions of South Africa. The much greater seasonal variation in climatic conditions, particularly temperature, further from the equator introduces variable development rates and diapause into the life cycle. Estimates of natural temperature-dependent interstadial development periods, derived from a combination of published laboratory and field data, were applied to published data on the seasonal abundance of R.appendiculatus on three farms in the Eastern Cape Province of South Africa. This enabled an assessment of which ticks of one stage give rise to which ticks of the next stage, from which (a) the onset and duration of diapause in unfed adults, and (b) seasonal interstadial mortality indices in the form of k-values, could be estimated. The contribution of biotic (tick density) and abiotic (climatic) factors as predictors of mortality at each life stage was investigated by step-wise multiple regression. Density-independent mortality at the female-to-larval stage is correlated with geographically variable climatic factors, minimum temperature at two farms and minimum relative humidity at the third. The other two stages are governed by density-dependent mortality, which, it is argued, may be caused largely by the hosts' acquired resistance to ticks. As expected on theoretical grounds, this density dependence is weaker nearer to the edge of the tick's range and for the more vulnerable immature stages.
要创建一个适用于微小扇头蜱的通用种群模型，需要详细、定量地了解这些蜱在其分布范围的不同区域（从东非的热带地区到南非的温带地区）与其生物和非生物环境之间的相互作用。离赤道越远，气候条件（尤其是温度）的季节性变化就越大，这会使生命周期中的发育速率和滞育情况产生变化。结合已发表的实验室和野外数据得出的自然温度依赖型龄期间发育时间估计值，被应用于南非东开普省三个农场已发表的微小扇头蜱季节性丰度数据。这使得能够评估一个阶段的哪些蜱会产生下一阶段的哪些蜱，由此可以估计（a）未进食成虫滞育的开始时间和持续时间，以及（b）以k值形式表示的季节性龄期间死亡率指数。通过逐步多元回归研究了生物因素（蜱密度）和非生物因素（气候）作为每个生命阶段死亡率预测指标的作用。从雌性到幼虫阶段与密度无关的死亡率与地理上不同的气候因素相关，在两个农场是最低温度，在第三个农场是最低相对湿度。其他两个阶段则受密度依赖型死亡率的控制，据认为这可能主要是由宿主对蜱产生的获得性抗性引起的。正如理论上所预期的那样，这种密度依赖性在蜱分布范围的边缘附近以及对于更脆弱的未成熟阶段较弱。
