Intertidal Algae

Area coverage of red algae (Mazzaella parksii) in two herbivore treatments (herbivores) at two tide levels (height).

Usage

IntertidalAlgae

Format

A data frame with 64 observations on the following 3 variables.

height

a factor with levels low and mid

herbivores

a factor with levels minus and plus

sqrt.area

a numeric vector

Source

Harley, C.D.G. 2003. Individualistic vertical responses of interacting species determine range limits across a horizontal gradient. Ecology 84: 1477-1488.

Examples

str(IntertidalAlgae)
#> 'data.frame':	64 obs. of  3 variables:
#>  $ height    : Factor w/ 2 levels "low","mid": 1 1 1 1 1 1 1 1 1 1 ...
#>  $ herbivores: Factor w/ 2 levels "minus","plus": 1 1 1 1 1 1 1 1 1 1 ...
#>  $ sqrt.area : num  9.41 34.47 46.67 16.64 24.38 ...

# Using * includes the main effects and the interaction
aov.fit <- aov(sqrt.area ~ herbivores * height, data = IntertidalAlgae)
summary(aov.fit)
#>                   Df Sum Sq Mean Sq F value  Pr(>F)   
#> herbivores         1   1512  1512.2   6.358 0.01436 * 
#> height             1     89    89.0   0.374 0.54310   
#> herbivores:height  1   2617  2617.0  11.003 0.00155 **
#> Residuals         60  14271   237.8                   
#> ---
#> Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
lm.fit <- lm(sqrt.area ~ herbivores * height, data = IntertidalAlgae)
anova(lm.fit)
#> Analysis of Variance Table
#> 
#> Response: sqrt.area
#>                   Df  Sum Sq Mean Sq F value   Pr(>F)   
#> herbivores         1  1512.2 1512.18  6.3579 0.014360 * 
#> height             1    89.0   88.97  0.3741 0.543096   
#> herbivores:height  1  2617.0 2616.96 11.0029 0.001549 **
#> Residuals         60 14270.5  237.84                    
#> ---
#> Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1