life, species, organism.... all are leaky abstractions.

[There's a "species" that spread around the Andes and eventually reached itself on the other side---and could no longer breeed with "itself". Genes could still in theory travel all the way around and back to the discontinuous point, however.]

edit: http://i.stack.imgur.com/4VsFW.png will make this less confusing, and quite unintentionally :).