Université de Lyon, Université Lyon 1, UMR5558 Laboratoire de Biométrie et Biologie Evolutive, Villeurbanne, France.
Oecologia. 2011 Nov;167(3):635-46. doi: 10.1007/s00442-011-2018-9. Epub 2011 May 24.
The impact of parasites on population dynamics is well documented, but less is known on how host population density affects parasite spread. This relationship is difficult to assess because of confounding effects of social structure, population density, and environmental conditions that lead to biased among-population comparisons. Here, we analyzed the infestation by two groups of nematodes (gastro-intestinal (GI) strongyles and Trichuris) in the roe deer (Capreolus capreolus) population of Trois Fontaines (France) between 1997 and 2007. During this period, we experimentally manipulated population density through changes in removals. Using measures collected on 297 individuals, we quantified the impact of density on parasite spread after taking into account possible influences of date, age, sex, body mass, and weather conditions. The prevalence and abundance of eggs of both parasites in females were positively related to roe deer density, except Trichuris in adult females. We also found a negative relationship between parasitism and body mass, and strong age and sex-dependent patterns of parasitism. Prime-age adults were less often parasitized and had lower fecal egg counts than fawns or old individuals, and males were more heavily and more often infected than females. Trichuris parasites were not affected by weather, whereas GI strongyles were less present after dry and hot summers. In the range of observed densities, the observed effect of density likely involves a variation of the exposure rate, as opposed to variation in host susceptibility.
寄生虫对种群动态的影响已有大量记载，但宿主种群密度如何影响寄生虫传播的了解较少。由于社会结构、种群密度和环境条件的混杂影响导致种群间比较存在偏差，因此很难评估这种关系。在这里，我们分析了 1997 年至 2007 年期间在法国特罗伊桑斯的马鹿（Capreolus capreolus）种群中两组线虫（胃肠道（GI）强蝇和旋毛虫）的感染情况。在此期间，我们通过改变去除量来实验性地操纵种群密度。利用对 297 只个体进行的测量，我们在考虑了日期、年龄、性别、体重和天气条件的可能影响后，量化了密度对寄生虫传播的影响。除了成年雌鹿中的旋毛虫外，两种寄生虫在雌鹿中的卵的流行率和丰度均与马鹿密度呈正相关。我们还发现寄生虫与体重之间存在负相关，以及寄生虫与年龄和性别之间的强烈依赖性模式。成年个体处于最佳生育年龄时，感染率较低，粪便卵数也低于幼鹿或老年个体，而雄性的感染程度和频率均高于雌性。旋毛虫寄生虫不受天气影响，而 GI 强蝇在干燥和炎热的夏季后则较少出现。在观察到的密度范围内，密度的观察到的影响可能涉及暴露率的变化，而不是宿主易感性的变化。
