Species richness
In these data the response is the species richness represented by a count of the number of plant species on plots that have different biomass and three different soil pH levels: low, mid, and high. See Crawley (2007, page 534).
data(richness)
A data frame with 90 rows and 3 variables:
a numeric vector giving the value of the biomass in the plots.
a factor giving the soil pH level in the plots: "low", "mid", and "high".
a numeric vector giving the number of plant species in the plots.
Crawley M.J. (2007) The R Book. John Wiley & Sons, Chichester.
with(richness,{
plot(Biomass, Species,
col=apply(as.matrix(pH),1,function(x) switch(x,"low"="red","mid"="black","high"="blue")),
pch=apply(as.matrix(pH),1,function(x) switch(x,"low"=15,"mid"=16,"high"=17)))
legend(8.5, 50, legend=c("low","mid","high"), col=c("red","black","blue"),
pch=c(15,16,17), bty="n", cex=0.85, y.intersp=0.5, x.intersp=0.3,
title="Soil pH level", title.adj=0.2)
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