High dimensionality of stoichiometric niches in soil fauna

Abstract

The ecological niche is a fundamental concept to understand species' coexistence in natural communities. The recently developed framework of the multidimensional stoichiometric niche (MSN) characterizes species' niches using chemical elements in living organisms. Despite the fact that living organisms are composed of multiple elements, stoichiometric studies have so far mostly focused on carbon (C), nitrogen (N), and phosphorus (P), and therefore a quantitative analysis of the dimensionality of the MSN in living organisms is still lacking, particularly for animals. Here we quantified 10 elements composing the biomass of nine soil animal taxa (958 individuals) from three trophic groups.We found that all 10 elements exhibited large variation among taxa, which was partially explained by their phylogeny. Overlaps of MSNs among the nine soil animal taxa were relatively smaller based on 10 elements, compared with those based on only C, N, and P. Discriminant analysis using all 10 elements successfully differentiated among the nine taxa (accuracy: 90%), whereas that using only C, N, and P resulted in a lower accuracy (60%). Our findings provide new evidence for MSN differentiation in soil fauna and demonstrate the high dimensionality of organismal stoichiometric niches beyond C, N, and P.

Multidimensional stoichiometric mismatch explains differences in detritivore biomass across three forest types

“…Combined, these results refute the argument that invertebrates at lower trophic levels contain low N and/or P contents due to low quality of detritus food resources (Fagan et al, 2002;González et al, 2011;Woods et al, 2004). The stable stoichiometric niches revealed here provides additional justifications for the framework of MSN in soil fauna (González et al, 2017;Zhang, Chen, Deng, Li, González, et al, 2022), which regards the elemental contents of soil organisms as taxonspecific characteristics and confined mainly by taxonomy and phylogeny. We note, however, that individuals within each detritivore taxon do vary considerably in their body elemental contents (see Appendix S1, Table S2), possibly accounted for by different species and sexes.…”

“…Plantation‐induced changes in litter C:X ratios have been reported to affect soil animal species richness, but these effects were taxon dependent (Jochum, Barnes, Weigelt, et al, 2017; Mueller et al, 2016). Different soil animal taxa have recently been shown to occupy distinct MSNs, that is, multiple body elemental compositions (Zhang, Chen, Deng, Li, González, et al, 2022). Our analyses support our first hypothesis by showing that the two detritivore taxa differed in their MSNs and thus experience different stoichiometric mismatches (TSR values).…”

“…These studies interpreted the stoichiometric limitations based on different hypotheses, for example, limitation by N and Ca from the structural elements hypothesis, and limitation by P and Na from the secondary productivity and sodium shortage hypotheses. However, due to the lack of stoichiometric data of soil animals, these conclusions remain speculative and may have underestimated the explanatory power of the structural element hypothesis (González et al, 2017; Zhang, Chen, Deng, Li, González, et al, 2022). By revealing the elemental contents of two detritivore taxa and their litter resources, we found that P and Na—even though low in absolute body contents—might also influence detritivore biomass and density due to high TSR values.…”

“…Such differences in the C:X ratios result in high TSR values between resources and consumers, especially between herbivores and plants or between detritivores and litters, which have been shown to colimit the growth, development and feeding strategies of various invertebrate taxa, as well as the decomposition rates and primary productivity of ecosystems (Filipiak et al, 2017; Filipiak & Weiner, 2017a, 2017b; Kaspari & Powers, 2016; Sobczyk et al, 2020). Recently, the framework of multidimensional stoichiometric niche (MSN) has been proposed to characterize species niches based on the multiple elements composing animals (González et al, 2017; Zhang, Chen, Deng, Li, González, et al, 2022). Revealing the MSN may therefore help to depict trophic niche differentiations across taxa and clarify which elements in food resources represent the major restriction on consumer populations.…”

“…Specifically, we quantified the elemental contents of C, N, Na, magnesium (Mg), P, potassium (K), calcium (Ca), Zn, manganese (Mn) and Cu of the litter and the two detritivore taxa among the three forest types, calculated the trophic stoichiometric mismatch (represented by overall TSR values) between litter and detritivores, and examined how such mismatch might affect detritivore population size. Recent studies revealed that earthworms and millipedes occupy distinct MSNs (Zhang, Chen, Deng, Li, González, et al, 2022), and their population sizes were constrained by different elements (see also Ott et al, 2014). Therefore, we hypothesized that (1) forest plantations generated different stoichiometric mismatch patterns (TSR values) for earthworms and millipedes due to their distinct MSNs, (2) earthworms and millipedes retained their stoichiometric compositions in the face of stoichiometric mismatch and had smaller population sizes in forest types with lower litter quality.…”