Appendix D. Spatial variance components for periphyton.
TABLE D1. Spatial variance components for ln(periphyton density), standard error of the variance component, stratum variances, effective degrees of freedom (brackets indicate the randomeffects model that includes the reach stratum), P values for the variance components, and the percentage contribution of each scale to the total observed spatial variation.
Strata (scale)
_{}
SE
Strat. Var
df
P
% Var ^{†}
Stream
0.0043
0.0436
1.7319
1
0.50
0.63
Reach
0 ^{‡}


(4)
0.86
0.00
Site
0.1006
0.0997
1.4783
18 (14)
0.0004
14.72
Plot
0.1360
0.1087
0.9034
19.98
0.0169
19.89
Rock
0.1483
0.0952
0.5003
38.57
0.1183
21.69
Sample
0.2944
0.0671
0.2944
38.46
43.07
† , where i indexes scales (Underwood and Chapman 1996).
‡ The estimated variance component at the reach scale was 0.033. This small, negative variance component was assumed equal to zero (difference from 0, P = 0.86, likelihood ratio test) and all the variance components in the table were estimated omitting the reach term from the randomeffects model (Payne 2002).LITERATURE CITED
Payne, R. W. 2002. The Guide to Genstat, Part 2 Statistics. VSN International, Oxford, UK.
Underwood, A. J. 1996. Spatial patterns of variance in density of intertidal populations. Pages 369–389 in R. B. Floyd, A. W. Sheppard, and P. J. De Barro, editors. Frontiers of Population Ecology. CSIRO Publishing, Melbourne, Australia.