Abstract: In natural ecosystems, different trophic levels can have a profound impact on ecosystem stability and population by trait-mediated indirect effects (TMIEs). However, at present, experimental studies on TMIEs are more common in invertebrates, fish, amphibians and reptiles. In this study, root voles (Microtus oeconomus) were used as experimental animals to establish two treatment populationsin field enclosures :: one in which predation was prevented and one in which predation was allowed to oocurWe then systematically examined thetypes of intestinal parasites, parasitic infection prevalence and intensity of infection by a modified McMaster method.. Phytohemagglutinin (PHA) response and white blood cell count were used to test the individual immunities of the different treatment populations to analyze the infection effect of predation risk on intestinal parasites in root voles. The results showed that the PHA response, leukocyte counts and lymphocyte counts of root voles exposed to predation treatment was significantly decreased compared to voles in which predation was prevented, while infection prevalence and intensity of infection of E. wenrichi were significantly increased. However, there were no significant changes in infection prevalence and intensity of infection of cestodes and nematodes and three other coccidias. It shows that predators can indirectly affect the intestinal parasites of prey by mediating the immune system and validated the hypothesis that the predation risk can increase the intestinal parasitic infection by decrease the immunocompetence of root voles.

Key words: Coccidia, Immunocompetence, Predation, Root voles, Trait-mediated indirect effects

摘要： 在自然生态系统中，不同营养级物种可通过特征介导间接效应对生态系统的稳定及种群产生深刻的影响。但目前有关特征介导间接效应的实验研究多见于无脊椎动物、鱼类和两爬类。本研究以根田鼠为对象，在野外围栏内建立预防捕食者和未预防捕食者两种实验处理种群，并通过采用麦克马斯特法测定两种处理种群实验个体肠道寄生物感染种类及感染率和感染强度，采用PHA（phytohemagglutinin）反应和白细胞分类计数测定不同处理种群实验个体免疫能力，以分析捕食风险对根田鼠肠道寄生物的感染效应。结果表明，未预防捕食者处理组根田鼠PHA反应、白细胞计数和淋巴细胞计数较预防捕食者处理组实验个体显著降低，而球虫 E. wenrichi 的感染率和感染强度则显著增加，但绦虫和线虫以及其他3种球虫的感染率和感染强度无显著差异。结果表明，捕食者可通过介导猎物免疫力特征而间接影响猎物肠道寄生物的感染，验证了本项提出的捕食风险可通过降低根田鼠的免疫能力而增加其肠道寄生物感染的假设。

关键词: 捕食, 根田鼠, 免疫能力, 球虫, 特征介导间接效应