Disentangling community functional components in a litter‐macrodetritivore model system reveals the predominance of the mass ratio hypothesis

Abstract

Recent investigations have shown that two components of community trait composition are important for key ecosystem processes: (i) the community-weighted mean trait value (CWM), related to the mass ratio hypothesis and dominant trait values in the community, and (ii) functional diversity (FD), related to the complementarity hypothesis and the divergence of trait values. However, no experiments controlling for the inherent dependence between CWM and FD have been conducted so far. We used a novel experimental framework to disentangle the unique and shared effects of CWM and FD in a leaf litter-macrodetritivore model system. We manipulated isopod assemblages varying in species number, CWM and FD of litter consumption rate to test the relative contribution of these community parameters in the decomposition process. We showed that CWM, but also the combination of CWM and FD, is a main factor controlling litter decomposition. When we tested individual biodiversity components separately, CWM of litter consumption rate showed a significant effect on decomposition, while FD and species richness alone did not. Our study demonstrated that (i) trait composition rather than species diversity drives litter decomposition, (ii) dominant trait values in the community (CWM) play a chief role in driving ecosystem processes, corroborating the mass ratio hypothesis, and (iii) trait dissimilarity can contribute in modulating the overall biodiversity effects. Future challenge is to assess whether the generality of our finding, that is, that dominant trait values (CWM) predominate over trait dissimilarity (FD), holds for other ecosystem processes, environmental conditions and different spatial and temporal scales.

Soil fauna diversity increases CO2 but suppresses N2O emissions from soil

“…Bílá et al () concluded that dominant trait values in the community play a chief role in driving ecosystem processes such as C cycling processes (so corroborating the mass ratio hypothesis); it is yet to be determined whether the generality of their findings also hold true for other ecosystem processes. Here, we find that ecosystem engineers like our two earthworm species indeed possess dominant trait values concerning emissions of N 2 O and CO 2 .…”

Functionally or phylogenetically distinct neighbours turn antagonism among decomposing litter species into synergy

“…These studies found opposite results (Gartner & Cardon, ; Gessner et al., ; Hättenschwiler, Tiunov, & Scheu, ), depending on abiotic conditions (Jonsson & Wardle, ; Santonja, Fernandez, Gauquelin, & Baldy, ), composition and functional properties of mixed litter (Barantal, Schimann, Fromin, & Hattenschwiler, ; Bílá et al., ; Chapman & Koch, ; Pérez Harguindeguy, Blundo, Gurvich, Díaz, & Cuevas, ; Wardle, Yeates, Barker, & Bonner, ), and identity or activity of decomposers (Handa et al., ; Schädler & Brandl, ; Vos, van Ruijven, Berg, Peeters, & Berendse, , ). Many of these studies showed that litter mixtures that are functionally dissimilar decompose synergistically, probably by providing complementary resources needed by generalist decomposers or by multiple specialist decomposers, which have complementary effects on decomposition (Bílá et al., ; Gessner et al., ; Meier & Bowman, ; Tardif & Shipley, ; Vos et al., ). But, other studies showed that trait dissimilarity might also render decomposition antagonistic as a given decomposer or detritivore might find its preferred resources diluted in unpreferred ones (Pan et al., ).…”

“…of decomposers (Handa et al, 2014;Schädler & Brandl, 2005;Vos, van Ruijven, Berg, Peeters, & Berendse, 2011. Many of these studies showed that litter mixtures that are functionally dissimilar decompose synergistically, probably by providing complementary resources needed by generalist decomposers or by multiple specialist decomposers, which have complementary effects on decomposition (Bílá et al, 2014;Gessner et al, 2010;Meier & Bowman, 2008;Tardif & Shipley, 2014;Vos et al, 2013). But, other studies showed that trait dissimilarity might also render decomposition antagonistic as a given decomposer or detritivore might find its preferred resources diluted in unpreferred ones (Pan et al, 2015).…”

Relatively rare root endophytic bacteria drive plant resource allocation patterns and tissue nutrient concentration in unpredictable ways

“…Low‐abundance species are assumed to contribute very little to the functioning of the systems they reside within. The mass–ratio hypothesis (Grime, ) predicts that a species' effect on ecosystem function is proportional to its relative abundance (Bílá et al., ). Numerous examples from plant (Grime, ; Ervin and Wetzel, ; Smith and Knapp, ), plankton (Dayton, ; Norberg, ), and animal (Dangles and Malmqvist, ; Balvanera et al., ; Larsen et al., ; Bílá et al., ; Cárdenas et al., ) communities demonstrate that dominant species shape ecosystem function.…”

“…The mass–ratio hypothesis (Grime, ) predicts that a species' effect on ecosystem function is proportional to its relative abundance (Bílá et al., ). Numerous examples from plant (Grime, ; Ervin and Wetzel, ; Smith and Knapp, ), plankton (Dayton, ; Norberg, ), and animal (Dangles and Malmqvist, ; Balvanera et al., ; Larsen et al., ; Bílá et al., ; Cárdenas et al., ) communities demonstrate that dominant species shape ecosystem function. However, in many systems, low‐abundance (rare) species can exert large effects on ecosystem function (Zavaleta and Hulvey, ; Lyons et al., ; Hol et al., ; Hussa and Goodrich‐Blair, ; Mouillot et al., ; Mariotte, ; Ziegler et al., ).…”