University of Vermont, Department of Biology, 109 Carrigan Drive, Burlington, Vermont 05401.
J Parasitol. 2024 Dec 1;110(6):577-589. doi: 10.1645/23-51.
The range of hosts a parasite can successfully occupy is partially determined by the niche breadth, that is, the set of environmental conditions necessary to maintain a stable population. Niche breadth is often quantified using host specificity, which encompasses the number of host species a parasite can exploit and the parasite's distribution among its hosts. Parasites with a wider niche breadth can potentially occupy more host species and are often more evenly distributed among hosts than parasites with a narrower niche breadth. However, parasites interact with potential hosts within the context of a geographic locality and the set of environmental characteristics associated with it. The extent to which environmental filters associated with host individuals and the geographic context explain variation in occupancy of parasites, and the extent to which variation in occupancy is associated with host range and specificity, is poorly understood. Using data from small mammals and ectoparasites in Vermont, I used a multiscale, multispecies occupancy model (MSOM) to (1) estimate ectoparasite occupancy at 10 geographic sites and on individual hosts within each site, (2) quantify the variation in occupancy explained by the site and host levels of the model using Bayesian R2, and (3) evaluate associations between explained variation and host range of ectoparasites. For ectoparasites collected from at least 4 different host species, I calculated structural specificity to determine the distribution of these parasites across the hosts, and β-specificity to evaluate changes in host use across habitats. Host range was significantly associated with host-level Bayesian R2: generalist parasites had more variation in occupancy explained by host-level covariates than specialist parasites. This result may be explained by differences in structural specificity: many generalists disproportionally occurred on a single-host species, suggesting that host characteristics act as habitat filters for these parasites. There were no significant associations between site-level Bayesian R2 and host specificity. However, some generalists demonstrated high β-specificity, suggesting these parasites may "switch" hosts, depending on host availability. These results highlight that the terms specialist and generalist are context dependent and may not accurately describe the niche breadth of parasite taxa. Understanding variation in host specificity as it pertains to potential habitat filters may be important for predicting which parasites can bypass host filters and "jump" to a novel host, which has implications for the surveillance and management of vector-borne diseases.
寄生虫可以成功占据的宿主范围部分取决于生态位宽度，即维持稳定种群所需的环境条件集。生态位宽度通常使用宿主特异性来量化，它包括寄生虫可以利用的宿主物种数量以及寄生虫在其宿主中的分布。生态位较宽的寄生虫可能潜在地占据更多的宿主物种，并且通常比生态位较窄的寄生虫在宿主中分布更均匀。然而，寄生虫在地理区域和与之相关的环境特征的背景下与潜在宿主相互作用。与宿主个体和地理背景相关的环境过滤器在多大程度上解释了寄生虫的占有变化，以及占有变化在多大程度上与宿主范围和特异性相关，这一点了解甚少。使用佛蒙特州小型哺乳动物和外寄生虫的数据，我使用多尺度、多物种占有模型 (MSOM) 来：(1) 在 10 个地理地点和每个地点的个体宿主上估计外寄生虫的占有情况；(2) 使用贝叶斯 R2 量化模型的地点和宿主水平解释的占有变化；(3) 评估解释的变化与外寄生虫宿主范围之间的关系。对于从至少 4 种不同宿主物种收集的外寄生虫，我计算了结构特异性，以确定这些寄生虫在宿主中的分布，并计算了β特异性，以评估跨栖息地的宿主利用变化。宿主范围与宿主水平贝叶斯 R2 显著相关：广宿主寄生虫的宿主水平协变量解释的占有变化比专性寄生虫更多。这一结果可能是由于结构特异性的差异：许多广宿主不成比例地出现在单一宿主物种上，这表明宿主特征对外寄生虫起到了栖息地过滤器的作用。地点水平贝叶斯 R2 与宿主特异性之间没有显著关联。然而，一些广宿主表现出较高的β特异性，这表明这些寄生虫可能会“切换”宿主，这取决于宿主的可用性。这些结果表明，专家和广宿主的术语是依赖于上下文的，并且可能无法准确描述寄生虫类群的生态位宽度。了解宿主特异性的变化，因为它与潜在的栖息地过滤器有关，可能对预测哪些寄生虫可以绕过宿主过滤器并“跳跃”到新的宿主，这对传染病媒介监测和管理具有重要意义。
