If we consider land areas that have been largely isolated from each other from a human point of view, but with a similar climate – for example, a part of Europe and a part of Americas with a similar climate before the time of Columbus – generally how different can one expect the flora and fauna to be between the places?
I realize there can be quite different approaches to measuring the biological differences. Not being a biologist, I probably miss some quite important metrics. Some ideas that come to my mind:
- How distinct are the species in each environment? For example, can we expect to see the same ant species? Same grass species? Same bacteria?
- DNA difference based approaches: How much of the DNA material in each environment does not exist in the other one? How large a proportion of organisms in one environment does not have a close relative on the other, given some threshold closeness value?
- Historical approach (probably overlaps the DNA approach quite a bit): How long ago (alternatively: how many generations ago) did the common ancestor of similar organisms in each environment live? Do the organisms share this number, i.e. is the common ancestor of, say, humans in Europe and America as ancient as that of ants and grasses?