Lack of energetic equivalence in forest soil invertebrates

Abstract

Ecological communities consist of small abundant and large non-abundant species. The energetic equivalence rule is an often-observed pattern that could be explained by equal energy usage among abundant small organisms and non-abundant large organisms. To generate this pattern, metabolism (as an indicator of individual energy use) and abundance have to scale inversely with body mass, and cancel each other out. In contrast, the pattern referred to as biomass equivalence states that the biomass of all species in an area should be constant across the body-mass range. In this study, we investigated forest soil communities with respect to metabolism, abundance, population energy use, and biomass. We focused on four land-use types in three different landscape blocks (Biodiversity Exploratories). The soil samples contained 870 species across 12 phylogenetic groups. Our results indicated positive sublinear metabolic scaling and negative sublinear abundance scaling with species body mass. The relationships varied mainly due to differences among phylogenetic groups or feeding types, and only marginally due to land-use type. However, these scaling relationships were not exactly inverse to each other, resulting in increasing population energy use and biomass with increasing body mass for most combinations of phylogenetic group or feeding type with land-use type. Thus, our results are mostly inconsistent with the classic perception of energetic equivalence, and reject the biomass equivalence hypothesis while documenting a specific and nonrandom pattern of how abundance, energy use, and biomass are distributed across size classes. However, these patterns are consistent with two alternative predictions: the resource-thinning hypothesis, which states that abundance decreases with trophic level, and the allometric degree hypothesis, which states that population energy use should increase with population average body mass, due to correlations with the number of links of consumers and resources. Overall, our results suggest that a synthesis of food web structures with metabolic theory may be most promising for predicting natural patterns of abundance, biomass, and energy use.

Drivers of nitrogen leaching from organic layers in Central European beech forests

“…Lumbricidae were extracted separately in situ with a mustard solution (area = 0.25 m 2 ). Soil fauna was determined to the species level, average weight per species was determined after drying at 60 • C and mass-length regressions and population biomass in mg dry weight m −2 was calculated as detailed in Ehnes et al (2014). For statistical analysis, soil fauna species were aggregated to the functional groups macro detritivores, including the taxonomic groups Coleoptera, Diplopoda, Isopoda, Lumbricidae, and Symphyla, and meso detritivores, including Collembola and Oribatida.…”

Consequences of tropical land use for multitrophic biodiversity and ecosystem functioning

“…First, we investigate the biodiversity value of jungle rubber, conventional rubber and secondary forest compared with oil palm agriculture by comparing observed species richness, density and biomass of litter-associated macroinvertebrate communities across these systems. Second, as a multitrophic measure of the rate of ecosystem processes carried out by these communities, we calculate total solid fresh mass energy flux in a system by incorporating community metabolism27, resource-specific assimilation efficiencies and biomass loss to predation18 into whole-community energy flux equations (Fig. 1).…”

Biotic interactions and trait-based ecosystem functioning in soil

“…This hypothesis is supported by Ehnes et al (2014), who found that phylogenetic groups, more than the effect of land-use type, affected the allometric scaling. This means that there is a trade-off between being able to study and visualize energetic paths of the entire soil food web and keeping the resolution that can be obtained by studying single soil taxonomic groups.…”

“…Finally, it has been suggested by Meehan et al (2006) and Ehnes et al (2014) that allometry could be sensitive to the different estimation techniques required for different taxa.…”

“…The allometric relationships between body mass (M) and population density (N) of organisms are thought to reflect underlying biological and physicochemical constraints in ecosystems (Cohen et al 2003;Ehnes et al 2014;Mulder et al 2005a;Reuman et al 2008;Turnbull et al 2014;Yvon-Durocher et al 2011). Investigations on allometric scaling were mostly performed in aquatic and terrestrial environments, specifically marine, freshwater and aboveground ecosystems, in sharp contrast to soil systems that appear to be a kind of Pandora's Box (Fitter 2005) despite their apparent structural homogeneity.…”