Islands speed up evolution

[spuriousmonkey]

It's been long thought that species on islands evolve faster than on the mainland but it has never really been proven.

Dramatic evolutionary changes occur in species isolated on islands, but it is not known if the rate of evolution is accelerated on islands relative to the mainland. Based on an extensive review of the literature, I used the fossil record combined with data from living species to test the hypothesis of an accelerated morphological evolution among island mammals. I demonstrate that rates of morphological evolution are significantly greater—up to a factor of 3.1—for islands than for mainland mammal populations. The tendency for faster evolution on islands holds over relatively short time scales—from a few decades up to several thousands of years—but not over larger ones—up to 12 million y. These analyses form the first empirical test of the long held supposition of accelerated evolution among island mammals. Moreover, this result shows that mammal species have the intrinsic capacity to evolve faster when confronted with a rapid change in their environment. This finding is relevant to our understanding of species' responses to isolation and destruction of natural habitats within the current context of rapid climate warming.

Since it is published in PloS Biology it is an open access article so we all can read it!
http://biology.plosjournals.org/perlserv?request=get-document&doi=10.1371/journal.pbio.0040321

See for instance the rate of evolution (in Darwins) compared to timescale in the figure below:

Open circles are mainland species, closed circles island species. The island species all group together at one end of the figure. Faster evolutionary rates.

discussion:

The difference in tempo of evolution between island and mainland species also appears to be larger for shorter time intervals. These results appear to conform to the theory by which island mammals adapt to their new environment rapidly following isolation (Figure 4), through conspicuous changes in size and morphology [5,16]. Evolution seems to happen so rapidly that in most cases we do not see the intermediate between the mainland ancestor and the island endemics in the fossil record; the small likelihood of fossilisation of these intermediate forms may also be due in part to the small size of the founding population.

So fast evolution in a very short time scale.


The closing comment was quite interesting:

For example, this result demonstrates that most mammal species found today on the mainland have the intrinsic capacity to evolve more rapidly. This insight suggests that the study of island species can improve our understanding of the adaptation of species to changing environmental conditions. The principal result shows that mammal species may increase their rate of morphological change by up to a factor of 3 within a few decades of dramatic and rapid change in their environment. Most species are currently confronted with an extensive deterioration and fragmentation of natural habitats. Moreover, these habitat changes are accentuated by accelerated change in the global climate [35,36]. The quantification of the rates at which species are able to evolve in response to environmental change is thus an empirical question of considerable basic and applied importance.

Since mainland species have the intrinsic capability to evolve faster they could in theory be capabable of adapting to the current major changes in the environment. The question being of course if the changes do not occur too fast for evolution to keep up.

I guess the authors assume that island evolution shows the fastest rate of evolution possible. Is that really the case? island colonizers end up in an environment they can cope with and they change to cope with it better. Could a rapidly changing environment induce more adaptive pressure even than an island environment?

 

[John99]

Since when does growing mushrooms in your closet make you a scientist. LOL

 

[valich]

I used the fossil record combined with data from living species to test the hypothesis of an accelerated morphological evolution among island mammals. I demonstrate that rates of morphological evolution are significantly greater—up to a factor of 3.1—for islands than for mainland mammal populations. The tendency for faster evolution on islands holds over relatively short time scales—from a few decades up to several thousands of years—but not over larger ones—up to 12 million y. These analyses form the first empirical test of the long held supposition of accelerated evolution among island mammals. Moreover, this result shows that mammal species have the intrinsic capacity to evolve faster when confronted with a rapid change in their environment. This finding is relevant to our understanding of species' responses to isolation and destruction of natural habitats within the current context of rapid climate warming.

I've been taught this many times and of course Darwin proved it, but as the author states: "faster evolution on islands holds over relatively short time scales." I think evolution is initially a function of density, but then once that density factor becomes saturated, you have to spread out geographically to increase diversity into different ecosystems.

To me, the author seems to go off on a tangent in his concluding remarks. I don't understand how this "is relevant to our understanding of species' responses to isolation and destruction of natural habitats within the current context of rapid climate warming"? What do you conclude from this? Yes, there is a similarity between a destruction of habitat, leading to a fragmentation or isolation of the species habitat, but does this lead to faster evolution? No. In today's destruction of habitat it leads to extinction because the destruction is in the short term and the species has no time to evolve to adapt to it. Given that, I do not see how this study is of any relevance - or of any help? - to the destruction of natural habitats within the current context of rapid climate warming?

Great post!