The commonly observed negative correlation between the number of species in an ecological community and disease risk, typically referred to as "the dilution effect", has received a substantial amount of attention over the past decade. Attempts to test this relationship experimentally have revealed that, in addition to the mean disease risk decreasing with species number, so too does the variance of disease risk. This is referred to as the "variance reduction effect", and has received relatively little attention in the disease-diversity literature. Here, we set out to clarify and quantify some of these relationships in an idealized model of a randomly assembled multi-species community undergoing an epidemic. We specifically investigate the variance of the community disease reproductive ratio, a multi-species extension of the basic reproductive ratio [Formula: see text], for a family of random-parameter community SIR models, and show how the variance of community [Formula: see text] varies depending on whether transmission is density or frequency-dependent. We finally outline areas of further research on how changes in variance affect transmission dynamics in other systems.

中文翻译：

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关于物种丰富度和流行病严重程度差异的注释。

在过去的十年中，通常观察到的生态群落中物种数量与疾病风险之间的负相关关系（通常称为“稀释效应”）引起了广泛关注。通过实验检验这种关系的尝试表明，除了平均疾病风险随物种数量降低外，疾病风险的方差也是如此。这被称为“减少变异效应”，并且在疾病多样性文献中受到的关注相对较少。在这里，我们着手阐明和量化在流行病的随机组装多物种社区的理想化模型中的某些关系。我们专门调查了社区疾病繁殖率的方差，基本生殖比率的多物种扩展[公式：参见文本]，用于一族随机参数社区SIR模型，并显示群落的方差[公式：参见文本]根据传播是密度还是​​频率而变化-依赖。最后，我们概述了有关方差变化如何影响其他系统中传输动力学的进一步研究领域。