This example was used to illustrate phylogenetic diversity in Faith and Richards (2012).
faith_treefaith_tree is a phylogenetic tree with five tips, labeled
a-e. It was created with the ape library.
In the paper, they give the total branch length as 41, but they
don't assign a length to the branch leading to species "b" and "c". Looking
at the figure, we estimated that the length should be 4. For that reason,
the total branch length of faith_tree is 45, rather than 41.