Theory on the density-body-mass (DBM) relationship predicts that the density of animal species decreases by the power of -0.75 per unit increase in their body mass, or by the power of -1 when taxa across trophic levels are studied. This relationship is, however, largely debated, as the slope often deviates from the theoretical predictions. Here, we tested the ability of the DBM relationship to reflect changes in the structure of communities subjected to an anthropogenic disturbance. The slope would become less steep if smaller animals were more impacted by the disturbance than the larger ones, whereas the slope would become steeper if larger animals were more affected than the smaller ones. We tested the changes in the DBM relationship by sampling soil fauna, i.e., nematodes, Collembola, and larger arthropods, from a semiarid grassland before and after spraying diesel fuel as disturbance. We applied three different treatments: a control, a light disturbance, and an intense disturbance. We found that the slopes of the DBM relationships before the disturbance were around -1 as predicted by theory. The slope became more positive (i.e., less steep) just after the disturbance, especially after the intense disturbance as smaller fauna suffered the most and early colonizers had larger body mass. Interestingly, we observed that the slopes converged back to -1 by 2 months post-disturbance. Our findings show that the response of soil fauna communities to anthropogenic disturbances could explain the large variation in observed slopes of the DBM relationships. We experimentally demonstrate that an animal community, when disturbed, shows a temporal pattern of DBM relationships ranging from deviations from the predicted slope to convergence to the predicted slope with time. We recommend that deviations in the DBM relationships after disturbances can provide insights in the trajectory of community recovery, and hence could be used for biomonitoring.

中文翻译：

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干扰调节土壤动物的密度-质量-质量关系。

关于密度-质量-质量（DBM）关系的理论预测，动物物种的密度会因每单位体重增加-0.75的幂而降低，或者在研究整个营养级的分类群时降低-1的幂。然而，由于斜率经常偏离理论预测，因此这种关系受到了很大的争议。在这里，我们测试了DBM关系反映人为干扰的社区结构变化的能力。如果较小的动物比较大的动物受干扰的影响更大，则坡度将变得不那么陡峭；如果较大的动物比较小的动物受到的影响更大，则坡度将变得更陡峭。我们通过取样土壤动物（即线虫，Collembola和大型节肢动物）来测试DBM关系的变化，从半干旱草原喷洒柴油作为干扰前后。我们应用了三种不同的处理方法：控制，轻度干扰和强烈干扰。我们发现，扰动之前的DBM关系的斜率在理论上约为-1。刚发生扰动后，特别是在剧烈扰动之后，斜率就变得更正（即不那么陡峭），这是因为较小的动物区系遭受的最大，早期定居者的体重较大。有趣的是，我们观察到扰动后2个月，斜率收敛到-1。我们的发现表明，土壤动物群落对人为干扰的响应可以解释DBM关系的观察坡度的巨大变化。我们通过实验证明，一个动物群落在受到干扰时，图中显示了DBM关系的时间模式，范围从随时间变化的预测斜率到收敛到预测斜率。我们建议，干扰后DBM关系的偏差可以提供有关社区恢复轨迹的见识，因此可用于生物监测。