How diverse are species in remote, isolated areas on Earth?

Question

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?

Answer 1

This all depends on whether genetic material is shared between these two different environments. A similarity in climate may cause similar stresses on the species, however we will not see the same species if there was never any genetic flow between these two environments.

For example, let's say two islands halfway across the world have two different species of ants. Both these islands have similar climates- let's say they are both hot and dry. Both these species of ants may evolve to be smaller (so they require less water) and more heat resistant (because of the heat), however this will not result in both islands having the same species.

If two ants on one island happened to float across the ocean and survive until they reached the other island, and live and reproduce, then they may evolve in the same way into the same species.