Ecological Archives E089-150-A4

Aidan M. Keith, René van der Wal, Rob W. Brooker, Graham H. R. Osler, Stephen J. Chapman, David F. R. P. Burslem, and David A. Elston. 2008. Increasing litter species richness reduces variability in a terrestrial decomposer system. Ecology 89:2657–2664.

Appendix D. Summary statistics for modeling random variation as a function of litter species richness.

TABLE D1. Summary statistics for modeling random variation as a function of litter species richness. Optimal value of b is that which minimised the deviance in the power-law variance parameter model [3) v=a. s^-^b]. P values are derived from chi-squared tests on 4 degrees of freedom comparing deviances between the single-variance parameter and five-variance parameter models [1)-2)], and from chi-squared tests on 1 degree of freedom comparing deviances between the single-variance parameter and power-law variance parameter models [1)-3)]. Significant values at P < 0.05 are in bold.


Variable	Time (days)	Model structure (after block)	Optimal value of b	Model deviances (-2 log-likelihood)			P values from chi-squared test
				1)v	2)v1-v5	3) v=a. s^-^b	1) - 2)	1) - 3)

Mass loss	196	Species richness	1.91	603	537	541	0.003	0.001
Mass loss	564	Species richness	1.63	671	619	620	0.007	<0.001
Mass loss	196	Species composition*	0.55	347	340	342	0.911	0.434
Mass loss	564	Species composition*	0.32	460	458	458	0.233	0.045
Moisture	196	Species richness	1.23	1266	1237	1237	0.106	0.007
Moisture	564	Species richness	0.06	1288	1287	1288	0.728	0.722
Moisture	196	Species composition*	-0.30	913	911	911	0.836	0.341
Moisture	564	Species composition*	-0.16	1072	1070	1071	0.763	0.453
C:N ratio	196	Species richness	1.89	- 299	-367	-364	0.001	<0.001
C:N ratio	564	Species richness	0.66	538	528	529	0.319	0.039
C:N ratio	196	Species composition*	0.65	-337	-348	-344	0.269	0.070
C:N ratio	564	Species composition*	-0.16	438	436	438	0.915	0.646
Microbial biomass	196	Species richness	0.02	-193	-200	-193	0.728	0.964
Microbial biomass	564	Species richness	0.06	-322	-324	-322	0.872	0.794
Microbial biomass	196	Species composition*	-0.39	-189	-200	-191	0.313	0.285
Microbial biomass	564	Species composition*	-0.11	-216	-219	-216	0.667	0.695
Nematode abundance	196	Species richness	0.76	1193	1178	1182	0.182	0.031
Nematode abundance	564	Species richness	0.55	1130	1123	1124	0.375	0.059
Nematode abundance	196	Species composition*	0.13	364	359	363	0.511	0.688
Nematode abundance	564	Species composition*	0.35	363	358	361	0.342	0.190

*Species composition is a categorical variable with 31 levels and hence incorporates species richness as a categorical variable with 5 levels.

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