Darwin’s finches reach their limits on Galápagos

Brett Smith for redOrbit.com – @ParkstBrett

Darwin’s finches are a group of 15 different bird species that Charles Darwin famously based his theories of evolution on. However, there’s no more room on the island for the development of new species.

Most species of birds are still diversifying, but according to a new report – Darwin’s finches have reached a state of equilibrium in which a new species will not appear until a current one becomes extinct.

Published in the journal Ecology Letters, the new report backs a recently developed tenet of evolutionary theory claiming that as species diversity rises, more and more ecological niches become filled. This has an adverse effect on immigration to the ecosystem and the development of new species.

“However, this has never been tested in detail, for lack of data and the right analytical tools,” said study author Rampal Etienne, associate professor of evolutionary ecology at the University of Groningen in the Netherlands.

Now, researchers have developed a mathematical model with phylogenetic data on living species called Dynamic Assembly of Islands by Speciation, Immigration and Extinction (DAISIE) to simulate evolutionary dynamics.

Using phylogenetic trees of existing bird species on the Galápagos Islands, DAISIE calculated the limits of species diversity and rates of immigration, new species creation, and extinction for each bird pedigree.

Finch diversity has negative effect

“The analysis shows that for the finches, diversity does indeed have a negative effect,” Etienne said. “There is no more room for new species, unless one of the existing species becomes extinct, so the islands are saturated regarding finch-type species.”

Etienne emphasized that the study does not mean the diversity of species is static in the Galápagos.

“We found that the rates of both evolution and extinction are very high for Darwin’s finches,” he said. “That is probably why these birds have reached an equilibrium.”

The study team noted mockingbirds and other birds have not yet reached equilibrium, meaning oceanic islands as a whole are not at equilibrium. They added that in a million years or so, unfamiliar mockingbird species might appear, despite conditions on the islands staying the same.

“Our data shows that they are evolving more slowly and are still diversifying,” Etienne said.

The study team has made DAISIE publicly available as a tool to be used by other researchers and plans to apply it to other archipelagoes around the world.

“In the longer term, our plan is to apply the model to over 30 archipelagos and islands worldwide,” study author Luis Valente, an evolutionary biologist from University of Potsdam in Germany, told redOrbit via email. “The aim is to be able to get a general overview of the importance of equilibrium dynamics on islands on a global scale.”

“If we find that islands are generally at equilibrium, this suggests that there are processes that limit and regulate biodiversity,” Valente continued. “If we find that the number of bird species is not at equilibrium, this suggest that controls on diversity may be relaxed, meaning that we can expect increases or decreases in biodiversity in the future.”


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