# Recall that you can exclude objects using "!" 
# We can analyze a subset of this data using this subset command in lm() 
lm3 <- lm(logMaxAbund ~ logMass, data=bird, subset =! bird$Aquatic) # removing the Aquatic birds

# or equivalently
lm3 <- lm(logMaxAbund ~ logMass, data=bird, subset=bird$Aquatic == 0)

# Examine the model
opar <- par(mfrow=c(2,2))
plot(lm3, pch=19, col=rgb(33,33,33,100,maxColorValue=225))
summary(lm3)
par(opar)

# Compare the two datasets
opar <- par(mfrow=c(1,2))
plot(logMaxAbund ~ logMass, data=bird, main="All birds", ylab = expression("log"[10]*"(Maximum Abundance)"), 
     xlab = expression("log"[10]*"(Mass)"))
abline(lm2,lwd=2)

plot(logMaxAbund ~ logMass, data=bird, subset=!bird$Aquatic, main="Terrestrial birds",
     ylab = expression("log"[10]*"(Maximum Abundance)"), xlab = expression("log"[10]*"(Mass)"))
abline(lm3,lwd=2)
opar(par)