As a follow-up to the post I wrote yesterday about visually annotating a plotted tree with discrete states at the tips, the original poster asked how to apply the same approach to show presence absence from a geographic region. The following is my attempt at this.

First, I'm going to simulate some imaginary biogeographic data. These I will make simulate under a super-simple island model in which a species can occupy at most two regions, and to get from (say) region A to B, it must first go through A+B. This simulation looks as follows:

```
library(phytools)
## regions A:L
regions<-LETTERS[1:12]
states<-vector()
ind<-1
for(i in 1:length(regions)){
states[ind]<-regions[i]
if(i!=length(regions)){
states[ind+1]<-paste(regions[i],"&",regions[i+1],sep="")
ind<-ind+2
}
}
Q<-matrix(0,length(states),length(states),dimnames=list(states,states))
for(i in 1:(length(states)-1)){
Q[i,i+1]<-0.5
Q[i+1,i]<-0.5
}
tree<-pbtree(n=80,scale=60)
x<-sim.Mk(tree,Q)
X<-sapply(regions,function(r,x,zeros){
zeros[grep(r,x)]<-1
zeros },x=x,zeros=rep(0,Ntip(tree)))
rownames(X)<-tree$tip.label
```

More importantly, here is what the data look like:

```
tree
```

```
##
## Phylogenetic tree with 80 tips and 79 internal nodes.
##
## Tip labels:
## t1, t21, t22, t6, t10, t11, ...
##
## Rooted; includes branch lengths.
```

```
head(X)
```

```
## A B C D E F G H I J K L
## t1 0 0 0 0 0 0 0 1 1 0 0 0
## t21 0 0 1 1 0 0 0 0 0 0 0 0
## t22 0 0 0 0 1 0 0 0 0 0 0 0
## t6 0 0 0 0 0 0 0 1 1 0 0 0
## t10 0 0 0 0 0 0 0 0 0 0 1 0
## t11 0 0 0 0 0 0 0 0 1 1 0 0
```

in which `X`

is a numeric 0/1 presence/absence matrix for my 12 regions.

Now we're ready to plot. For this I will simply adapt what I posted yesterday:

```
tree<-reorder(tree,"cladewise")
X<-X[tree$tip.label,]
plotTree(tree,plot=FALSE)
obj<-get("last_plot.phylo",envir=.PlotPhyloEnv)
plotTree(tree,lwd=1,ylim=c(0,obj$y.lim[2]*1.05),xlim=c(0,obj$x.lim[2]*1.2),
ftype="off")
obj<-get("last_plot.phylo",envir=.PlotPhyloEnv)
h<-max(obj$xx)
fsize<-0.6
for(i in 1:Ntip(tree)){
lines(c(obj$xx[i],h),rep(obj$yy[i],2),lty="dotted")
text(h,obj$yy[i],tree$tip.label[i],cex=fsize,pos=4,font=3,offset=0.1)
}
s<-max(fsize*strwidth(tree$tip.label))
start.x<-1.05*h+s
cols<-setNames(c("white","blue"),0:1)
for(i in 1:ncol(X)){
text(start.x,max(obj$yy)+1,paste("Region",colnames(X)[i]),pos=4,srt=90,
cex=0.7,offset=0)
for(j in 1:nrow(X)){
xy<-c(start.x,obj$yy[j])
y<-c(xy[2]-0.5,xy[2]+0.5,xy[2]+0.5,xy[2]-0.5)
asp<-(par()$usr[2]-par()$usr[1])/(par()$usr[4]-par()$usr[3])*
par()$pin[2]/par()$pin[1]
x<-c(xy[1]-0.5*asp,xy[1]-0.5*asp,xy[1]+0.5*asp,xy[1]+0.5*asp)
polygon(x,y,col=cols[as.character(X[j,i])])
}
start.x<-start.x+asp
}
```

That's all there is to it.

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