Borgsteede F H
DLO-Institute for Animal Science and Health (ID-DLO), Department of Pathobiology and Epidemiology, Lelystad, The Netherland.
Vet Q. 1996;18 Suppl 3:S138-40.
Populations of animals which live in the wild are regulated by many biotic and abiotic factors. Parasites are one of the biotic factors. Parasites may influence their hosts in different ways. They may cause the death of the host due to a direct lethal effect or an indirect effect. Direct lethal effects may occur if killing is a part of the life cycle of the parasite or if hosts and parasites have not developed an equilibrium. The introduction of hosts or parasites into a new environment with suitable hosts or parasites is an example. Death by parasitism may also be caused by a combination of the emaciating effects of parasites combined with factors such as bad weather conditions, environmental pollution or human handling. Parasites may also influence the behaviour of their hosts. If the hosts are intermediate hosts in the life cycle of the parasites, the alterations in behaviour may make them an easier prey for their predators, the final hosts. Parasites may also influence the reproductive success of the hosts. In this respect the relationship between the red grouse (Lagopus lagopus scoticus) and the caecal nematode Trichostrongylus tenuis has been well worked out.
生活在野外的动物种群受到许多生物和非生物因素的调节。寄生虫是生物因素之一。寄生虫可能以不同方式影响其宿主。它们可能由于直接致死效应或间接效应导致宿主死亡。如果杀戮是寄生虫生命周期的一部分，或者宿主和寄生虫尚未形成平衡，就可能发生直接致死效应。将宿主或寄生虫引入具有合适宿主或寄生虫的新环境就是一个例子。寄生虫寄生导致的死亡也可能是寄生虫消瘦效应与恶劣天气条件、环境污染或人为处理等因素共同作用的结果。寄生虫还可能影响其宿主的行为。如果宿主是寄生虫生命周期中的中间宿主，行为的改变可能使它们更容易成为其捕食者（终末宿主）的猎物。寄生虫也可能影响宿主的繁殖成功率。在这方面，红松鸡（Lagopus lagopus scoticus）与盲肠线虫细颈三齿线虫（Trichostrongylus tenuis）之间的关系已经得到了充分研究。
