Ecology and Evolutionary Biology, University of Colorado, Boulder, Colorado 80309, USA.
Ecology. 2012 Jan;93(1):56-64. doi: 10.1890/11-0636.1.
With growing interest in the effects of biodiversity on disease, there is a critical need for studies that empirically identify the mechanisms underlying the diversity-disease relationship. Here, we combined wetland surveys of host community structure with mechanistic experiments involving a multi-host parasite to evaluate competing explanations for the dilution effect. Sampling of 320 wetlands in California indicated that snail host communities were strongly nested, with competent hosts for the trematode Ribeiroia ondatrae predominating in low-richness assemblages and unsuitable hosts increasingly present in more diverse communities. Moreover, competent host density was negatively associated with increases in snail species richness. These patterns in host community assembly support a key prerequisite underlying the dilution effect. Results of multigenerational mesocosm experiments designed to mimic field-observed community assemblages allowed us to evaluate the relative importance of host density and diversity in influencing parasite infection success. Increases in snail species richness (from one to four species) had sharply negative effects on the density of infected hosts (-90% reduction). However, this effect was indirect; competition associated with non-host species led to a 95% reduction in host density (susceptible host regulation), owing primarily to a reduction in host reproduction. Among susceptible hosts, there were no differences in infection prevalence as a function of community structure, indicating a lack of support for a direct effect of diversity on infection (encounter reduction). In monospecific conditions, higher initial host densities increased infection among adult hosts; however, compensatory reproduction in the low-density treatments equalized the final number of infected hosts by the next generation, underscoring the relevance of multigenerational studies in understanding the dilution effect. These findings highlight the role of interspecific competition in mediating the relationship between species richness and parasite infection and emphasize the importance of field-informed experimental research in understanding mechanisms underlying the diversity-disease relationship.
随着人们对生物多样性对疾病影响的兴趣日益浓厚，迫切需要进行研究，从实证角度确定多样性与疾病关系的潜在机制。在这里，我们将宿主群落结构的湿地调查与涉及多宿主寄生虫的机制实验相结合，以评估稀释效应的竞争解释。在加利福尼亚州对 320 个湿地的采样表明，蜗牛宿主群落具有强烈的嵌套性，具有吸虫 Ribeiroia ondatrae 能力的宿主在低丰富度组合中占主导地位，而不合适的宿主在更多样化的群落中越来越多。此外，有能力的宿主密度与蜗牛物种丰富度的增加呈负相关。这些宿主群落组装模式支持稀释效应的一个关键前提。设计用于模拟现场观察到的群落组装的多代中观实验的结果使我们能够评估宿主密度和多样性对寄生虫感染成功率的相对重要性。蜗牛物种丰富度的增加（从一个物种增加到四个物种）对感染宿主的密度产生了明显的负面影响（减少 90%）。然而，这种影响是间接的；与非宿主物种相关的竞争导致宿主密度降低了 95%（易感宿主调节），主要是由于宿主繁殖减少。在易感宿主中，群落结构与感染率之间没有差异，表明多样性对感染没有直接影响（遭遇减少）。在单一种群条件下，较高的初始宿主密度会增加成年宿主的感染率；然而，低密度处理中的代偿性繁殖使下一代受感染宿主的最终数量相等，这凸显了多代研究在理解稀释效应中的重要性。这些发现强调了种间竞争在调节物种丰富度和寄生虫感染之间关系中的作用，并强调了基于实地的实验研究在理解多样性与疾病关系的潜在机制方面的重要性。
