Temporal patterns of energy equivalence in temperate soil invertebrates

Abstract

The question whether total population energy use is invariant to species body size (the energy equivalence hypothesis) is central to metabolic ecology and continues to be controversial. While recent comparative field work and meta-analyses pointed to systematic deviations of the underlying allometric scaling laws from predictions of metabolic theory none of these studies included the variability of metabolic scaling in ecological time. Here we used extensive data on the invertebrate soil fauna of Kampinos National Park (Poland) obtained from six consecutive quantitative sampling seasons to show that phylogenetically corrected species density—body weight and population energy use—body weight relationships across all soil fauna species and within trophic groups and body weight classes were highly variable in time. On average, population energy use tended to increase with species body weight in decomposers and phytophages, but not in predators. Despite these trends, our data do not exclude the possibility that energy equivalence marks the central tendency of energy use in the edaphon. Our results highlight the need for long-term studies on energy use to unequivocally assess predictions of metabolic theory.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-015-3317-3) contains supplementary material, which is available to authorized users.

Size compartmentalization of energy channeling in terrestrial belowground food webs

“…protists that had relatively low density (but see discussion below) and flattened overall abundance -body mass scaling. Correspondingly, macroconsumers had higher biomass and used more energy than is expected by biomass and equivalence rules in our and other published large-scale empirical studies (Ehnes et al 2014, Ulrich et al 2015. The larger energy use by macroconsumers supports allometric degree Accepted Article hypotheses, as they are able to feed on a wider range of food items and thus having access to more energy (Ehnes et al 2014).…”

“…Across all size classes we observed average abundance -body mass scaling of -0.54, which is flatter than the expected scaling of -0.75. Similar large-scale studies across temperate forests in Germany and Poland showed slopes of -0.68 across trophic groups (Ehnes et al 2014) and -0.58 in decomposers (Ulrich et al 2015). Our data are at the lower end of published estimates potentially due to inclusion of wider range of size classes, i.e.…”

“…In particular, non-linear size spectra, which were repeatedly noted in individual-level resolved communities (Fig. 1C; Mulder et al 2008, Reuman et al 2009, Ulrich et al 2015, can support size compartmentalisation of food webs. Different size classes of belowground consumers are living in very different environments (Erktan et al 2020): microconsumers, such as soil microfauna inhabit water films and thus literally represent aquatic compartment within terrestrial food webs; macroconsumers (meso-and macrofauna) colonize various surfaces and live outside water with some being able to burrow through the substrate (e.g.…”

“…The body mass -abundance scaling was indeed shown to be more steep in predators than in detritivores and herbivores (i.e. primary consumers, or 'grazers') in soil (Ehnes et al 2014, Ulrich et al 2015. The dominance of grazers among large consumers implies a negative body mass -trophic level scaling in belowground communities, which contradicts common assumptions (e.g.…”

“…Existing empirical studies across invertebrate size classes showed that larger animals in belowground food webs have systematically higher biomass and use more energy than smaller ones (Mulder et al 2008, 2011, Reuman et al 2009, Ehnes et al 2014, Ulrich et al 2015. This is in contrast to the 'universal' pattern of an even biomass distribution across logarithmic body mass classes (Fig.…”