Antoine Tardif1, Bill Shipley. 1. Département de Biologie, Université de Sherbrooke, Sherbrooke, QC, J1K 2R1, Canada.
Abstract
BACKGROUND AND AIMS: A test is made of the acceptability of the biomass-ratio hypothesis (BMRH), operationalized as community-weighted means (CWMs), and of a new hypothesis (idiosyncratic annulment), for predicting the decomposition of multispecies litter mixtures. Specifically, (1) does the BMRH based on monoculture decomposition rates introduce systematic over- or underestimation of rates in mixtures? and (2) does the degree of variability of these rates decrease with increasing species richness (SR) beyond that expected from purely mathematical causes? METHODS: Decomposition rates (mg g(-1) d(-1)) of litter from six tree species in microcosms were measured under controlled conditions during 18 weeks of incubation, alone and in all possible combinations of two, three, five and six species. Observed mixture decomposition rates were compared with those predicted by the BMRH using CWMs calculated from the monoculture rates, and the variability of the differences were compared with the SR of the mixture. KEY RESULTS: Both positive and negative deviations from expectation occurred at all levels of SR. The average differences between observed rates of mixtures and those predicted were approximately zero. Although variability in the prediction errors was independent of the SR, this variability between different mixtures having the same number of species decreased with increasing SR such that mixtures with the most species converged on the predicted values. This decrease in variance was not due to idiosyncratic annulment of higher order interactions between species. CONCLUSIONS: The BMRH described the average response of litter mixtures. The decrease in variance and the convergence to the predicted values based on CWMs was not due to the 'idiosyncratic annulment' of species interactions but was a mathematical consequence of CWMs being sums of random variables. Since convergence occurs with increasing SR and since SR increases with increasing spatial scale, the spatial scale will be a determinant in the prediction of ecosystem processes, such as litter decomposition rates.
BACKGROUND AND AIMS: A test is made of the acceptability of the biomass-ratio hypothesis (BMRH), operationalized as community-weighted means (CWMs), and of a new hypothesis (idiosyncratic annulment), for predicting the decomposition of multispecies litter mixtures. Specifically, (1) does the BMRH based on monoculture decomposition rates introduce systematic over- or underestimation of rates in mixtures? and (2) does the degree of variability of these rates decrease with increasing species richness (SR) beyond that expected from purely mathematical causes? METHODS: Decomposition rates (mg g(-1) d(-1)) of litter from six tree species in microcosms were measured under controlled conditions during 18 weeks of incubation, alone and in all possible combinations of two, three, five and six species. Observed mixture decomposition rates were compared with those predicted by the BMRH using CWMs calculated from the monoculture rates, and the variability of the differences were compared with the SR of the mixture. KEY RESULTS: Both positive and negative deviations from expectation occurred at all levels of SR. The average differences between observed rates of mixtures and those predicted were approximately zero. Although variability in the prediction errors was independent of the SR, this variability between different mixtures having the same number of species decreased with increasing SR such that mixtures with the most species converged on the predicted values. This decrease in variance was not due to idiosyncratic annulment of higher order interactions between species. CONCLUSIONS: The BMRH described the average response of litter mixtures. The decrease in variance and the convergence to the predicted values based on CWMs was not due to the 'idiosyncratic annulment' of species interactions but was a mathematical consequence of CWMs being sums of random variables. Since convergence occurs with increasing SR and since SR increases with increasing spatial scale, the spatial scale will be a determinant in the prediction of ecosystem processes, such as litter decomposition rates.
Authors: J G Hodgson; G Montserrat-Martí; M Charles; G Jones; P Wilson; B Shipley; M Sharafi; B E L Cerabolini; J H C Cornelissen; S R Band; A Bogard; P Castro-Díez; J Guerrero-Campo; C Palmer; M C Pérez-Rontomé; G Carter; A Hynd; A Romo-Díez; L de Torres Espuny; F Royo Pla Journal: Ann Bot Date: 2011-09-21 Impact factor: 4.357
Authors: Eric Garnier; Sandra Lavorel; Pauline Ansquer; Helena Castro; Pablo Cruz; Jiri Dolezal; Ove Eriksson; Claire Fortunel; Helena Freitas; Carly Golodets; Karl Grigulis; Claire Jouany; Elena Kazakou; Jaime Kigel; Michael Kleyer; Veiko Lehsten; Jan Leps; Tonia Meier; Robin Pakeman; Maria Papadimitriou; Vasilios P Papanastasis; Helen Quested; Fabien Quétier; Matt Robson; Catherine Roumet; Graciela Rusch; Christina Skarpe; Marcelo Sternberg; Jean-Pierre Theau; Aurélie Thébault; Denis Vile; Maria P Zarovali Journal: Ann Bot Date: 2006-11-03 Impact factor: 4.357
Authors: Sandra Díaz; Sandra Lavorel; Francesco de Bello; Fabien Quétier; Karl Grigulis; T Matthew Robson Journal: Proc Natl Acad Sci U S A Date: 2007-12-19 Impact factor: 11.205
Authors: Claire Fortunel; Eric Garnier; Richard Joffre; Elena Kazakou; Helen Quested; Karl Grigulis; Sandra Lavorel; Pauline Ansquer; Helena Castro; Pablo Cruz; Jirí Dolezal; Ove Eriksson; Helena Freitas; Carly Golodets; Claire Jouany; Jaime Kigel; Michael Kleyer; Veiko Lehsten; Jan Leps; Tonia Meier; Robin Pakeman; Maria Papadimitriou; Vasilios P Papanastasis; Fabien Quétier; Matt Robson; Marcelo Sternberg; Jean-Pierre Theau; Aurélie Thébault; Maria Zarovali Journal: Ecology Date: 2009-03 Impact factor: 5.499
Authors: Aidan M Keith; René Van der Wal; Rob W Brooker; Graham H R Osler; Stephen J Chapman; David F R P Burslem; David A Elston Journal: Ecology Date: 2008-09 Impact factor: 5.499