Data from: Population density, not host competence, drives patterns of disease in an invaded community

Generalist parasites can strongly influence interactions between native and invasive species. Host competence can be used to predict how an invasive species will affect community disease dynamics; the addition of a highly competent, invasive host is predicted to increase disease. However, densities of invasive and native species can also influence the impacts of invasive species on community disease dynamics. We examined whether information on host competence alone could be used to accurately predict the effects of an invasive host on disease in native hosts. We first characterized the relative competence of an invasive species and a native host species to a native parasite. Next, we manipulated species composition in mesocosms and found that host competence results did not accurately predict community dynamics. While the invasive host was more competent than the native, the presence of the native (lower competence) host increased disease in the invasive (higher competence) host. To identify potential mechanisms driving these patterns, we analyzed a two-host, one-parasite model parameterized for our system. Our results demonstrate that patterns of disease were primarily driven by relative population densities, mediated by asymmetry in intra- and interspecific competition. Thus, information on host competence alone may not accurately predict how an invasive species will influence disease in native species.广食性寄生虫（generalist parasite）可显著影响本地物种与入侵物种之间的相互作用。宿主感染能力（host competence）可用于预测入侵物种如何影响群落疾病动态；学界普遍预测，引入高感染能力的入侵宿主会加剧疾病传播。然而，入侵物种与本地物种的种群密度同样会调控入侵物种对群落疾病动态的影响强度。本研究旨在探究仅依靠宿主感染能力数据，能否精准预测入侵宿主对本地宿主疾病水平的影响。我们首先针对一种本地寄生虫，分别测定了某入侵宿主物种与某本地宿主物种的相对感染能力。随后，我们通过调控中型实验生态系统（mesocosms）中的物种组成开展实验，结果发现仅基于宿主感染能力的预测结果无法准确反映群落疾病动态。尽管该入侵宿主的感染能力高于本地宿主，但本地（低感染能力）宿主的存在反而提升了入侵（高感染能力）宿主的疾病感染水平。为解析驱动该实验现象的潜在机制，我们针对本研究体系构建了双宿主-单寄生虫模型并完成参数化分析。研究结果表明，群落疾病动态主要由种群相对密度决定，而种内与种间竞争的不对称性会对该过程产生调控作用。因此，仅依靠宿主感染能力数据，可能无法精准预测入侵物种对本地物种疾病水平的影响。