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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