Disturbance regulates the density–body‐mass relationship of soil fauna

Abstract

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.

Coexistence, Energy, and Trophic Cascade in a Three-Level Food Chain Integrating Body Sizes

“…As a result, we obtain that the equilibrium abundance R * is bounded below and above by body mass-dependent amounts (Damuth, 2001). It should be added that several studies have shown that densities of some species are not proportional to body size in −3/4 and even positive relationships between density and body size have been observed (Russo et al, 2003;Maxwell and Jennings, 2006;van Langevelde et al, 2020). Moreover, these relationships can be generated in a non-linear and polygonal fashion (Leaper and Raffaelli, 1999;Andrew and Hughes, 2008).…”

Collection of human and environmental data on pesticide use in Europe and Argentina: Field study protocol for the SPRINT project

“…Non-target and beneficial insects are known to be negatively affected by PPP, with for example the effects of neonicotinoid insecticides receiving much attention in the last decade [ 21 ]. As insects are susceptible to PPP, insects are considered indicator species to quantify differences in the use of PPP between fields [ 22 , 23 ]. In this study we will collect ground-dwelling and flying insects, in three 21-day cycles (for flying insects the cycles may be slightly longer depending on weather conditions) to assess biodiversity.…”