When Charles Darwin traveled to the Galapagos Islands almost 200 years ago as a gentleman naturalist, he used the power of observation to develop his theory that species evolve over time.
Today, evolutionary biologists Donald Miles, Robert Ricklefs and Jonathan Losos have the advantage of huge data sets and the power of statistical analysis to study how species within a group develop their own unique characteristics and become new species.On Darwin's 1831 journey aboard the HMS Beagle, he collected samples of 18 different species of passerine birds, or birds that perch. These species varied widely in size and had different kinds of beaks based on their diet.
Miles provides the classic examples of how island passerine birds have been used to illustrate the alternate view that adaptive radiations are simply those clades with the greatest ecological and morphological disparity. "We investigated whether celebrated cases of evolutionary radiations of passerine birds on islands have produced exceptional diversity relative to comparable-aged radiations globally," the researchers wrote in their paper.
They also analyzed the distribution of"phenotype disparity" among bird clades. And lastly, they"focused on two factors thought to promote adaptive radiation -- diversification on islands and in the tropics -- and asked whether clades exhibiting these factors are more diverse," they wrote. As part of their statistical analysis, they looked at the exceptional cases,"whether clades observed to exceed the 95th percentile could be considered extreme values.
"Our results may surprise many in that they exhibit little evidence for a set of clades qualitatively distinct from the distribution of all clades, but further analysis using larger morphological datasets and more refined statistical approaches would be welcome next steps," Miles said.
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