Institute of Biodiversity, Animal Health and Comparative Medicine, Graham Kerr Building, University of Glasgow, 82 Hillhead St, Glasgow, G12 8QQ, Scotland, UK.
Scottish Centre for Ecology and the Natural Environment, Rowardennan, Glasgow, G63 0AW, Scotland, UK.
Parasit Vectors. 2020 Sep 29;13(1):493. doi: 10.1186/s13071-020-04369-8.
The relationship between environmentally transmitted tick parasites, Ixodes spp., and their main reproductive host, deer, is generally thought to be positive. However, measuring host abundance and density directly can be challenging and indirect methods are often used. The observed relationship between the parasite and host may be affected by sampling scale and season, which could lead to different inferences being made. Here, we aimed to test the effect of sampling scale and season on the relationship between density of deer and the density of questing Ixodes ricinus nymphs.
The density of deer (primarily Dama dama) was estimated using line transect distance sampling of deer dung quantified in different seasons (winter and summer) and measured at three different nested scales (site, transect and observation level). Questing nymph density was measured using blanket drag methods and estimates were calculated at the same scales as deer density estimates. General linear models were used to evaluate the relationship between questing nymphs, deer density and other environmental variables at each sampling scale and each season deer density was measured at.
While a positive relationship between deer density and questing nymph density was detected at the site and transect scale, no relationship was apparent at the observation level. This was likely due to increased variation and reduced precision of deer dung counts at the finest sampling scale. Seasonal changes in deer populations were observed likely reflecting seasonal shifts in habitat usage. The summer estimates of deer density explained questing nymph density whereas winter estimates did not.
Our results show that the scale of sampling can affect the detectability of the positive association between host and vector species. Furthermore, such associations can be obscured if hosts exhibit seasonal changes in habitat use. Thus, both sampling scale and season are important to consider when investigating the relationship between host and vector species.
通常认为，环境传播的蜱寄生虫，如硬蜱属（Ixodes spp.）与它们的主要繁殖宿主鹿之间存在正相关关系。然而，直接测量宿主的丰度和密度可能具有挑战性，因此通常采用间接方法。寄生虫与宿主之间的观察到的关系可能会受到采样规模和季节的影响，这可能导致得出不同的推断。在这里，我们旨在测试采样规模和季节对鹿密度与寄生的硬蜱属若虫密度之间关系的影响。
使用不同季节（冬季和夏季）量化的鹿粪便的线截距距离抽样法估计鹿（主要是鹿属（Dama dama））的密度，并在三个不同嵌套的尺度（地点、截距和观测水平）下进行测量。采用覆盖拖曳法测量寄生的硬蜱属若虫密度，并在与鹿密度估计相同的尺度下计算估计值。使用一般线性模型评估在每个采样规模和每个季节测量的鹿密度时，寄生的硬蜱属若虫、鹿密度和其他环境变量之间的关系。
虽然在地点和截距尺度上检测到鹿密度与寄生的硬蜱属若虫密度之间存在正相关关系，但在观测水平上没有表现出这种关系。这可能是由于在最精细的采样尺度上，鹿粪便的计数增加了变异性且降低了精度。观察到鹿种群的季节性变化可能反映了季节性栖息地利用的变化。夏季的鹿密度估计值解释了寄生的硬蜱属若虫密度，而冬季的则没有。
我们的结果表明，采样规模会影响宿主和媒介物种之间正相关关系的可检测性。此外，如果宿主的栖息地利用发生季节性变化，这种关联可能会被掩盖。因此，在研究宿主和媒介物种之间的关系时，采样规模和季节都很重要。
