Ecological Archives E086-125-A2

Susan L. Williams and Megan N. Dethier. 2005. High and dry: variation in net photosynthesis of the intertidal seaweed Fucus gardneri. Ecology 86:2373–2379.

Appendix B. Data analysis procedures for net photosynthetic rates (NPP) of Fucus gardneri and results of analysis of variance.

We analyzed variance in rates of NPP averaged over all thalli at each tidal height in a randomized block design with each tidal height represented in each block (= site), using SYSTAT (1999). Interactions between site and tidal height were evaluated with a Tukey’s test for non-addivitiy (Snedecor and Cochran 1967, Underwood 1997, Mead 1988). Because size is an important determinant of plant performance and typically varies across the intertidal habitat, the variance in NPR attributable to thallus mass (g dry mass) was tested at each site in an analysis of covariance, after first testing for the assumption of homogeneity of regression slopes (Huitema 1980). Where P < 0.05, the least squares mean rate was adjusted for the covariate. Mass was an obvious measure of size and a good proxy for photosynthetic surface area; the r2 of linear regressions of surface area (estimated by digitizing thalli) vs. mass were 0.77 (n = 155 thalli) and 0.89 (n = 251) in summer and winter, respectively.  

Results of randomized block analysis of variance for NPR (log + 1 transformed). SS = Sum of Squares. NA = Non-additivitiy in Tukey’s test. Degrees of freedom for Tukey’s F test = 1, 12 (summer) and 1, 6 (winter).

Source of Variation
(Season/Medium)

SS

df

F

P

         

Summer/ Water

       

Site

0.4240

13

1.7448

0.1640

Tidal Height

0.0012

1

0.0650

0.8027

Error
     NA

0.2430
0.0122

13
12

0.3534

>0.250

 
 
 
 
 

Summer/Air

 
 
 
 

Site

2.9985

13

2.4117

0.0626

Tidal Height

0.2393

1

2.5018

0.1377

Error
     NA

1.2433
0.0024

13
12

0.0657

>0.250

 
 
 
 
 

Winter/Water

 
 
 
 

Site

1.4655

7

5.4839

0.0195

Tidal Height

0.0387

1

1.0140

0.3475

Error
     NA

0.2672
0.0048

7
6

0.1007

0.05 < P < 0.10

 
 
 
 
 

Winter/Air

 
 
 
 

Site

1.9364

7

5.2659

0.0218

Height

0.00002

1

0.0004

0.9850

Error
     NA

0.3677
0.0793

7
6

1.6506

>0.250

 

LITERATURE CITED

Huitema, B. E. 1980. The analysis of covariance and alternatives. John Wiley and Sons, Inc., New York , New York , USA .

Mead, R. 1988. The design of experiment. Cambridge University Press, Cambridge, UK.

Snedecor, G. W., and W. G. Cochran. 1967. Statistical methods. The Iowa State University Press, Ames , Iowa , USA .

Underwood, A. J. 1997. Experiments in ecology: their logical design and interpretation using analysis of variance. Cambridge University Press, Cambridge, United Kingdom.



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