Although large evolutionary radiations producing many species have captured the attention of biologists, comparison of the sizes of evolutionary lineages show that unusually small groups with few species are more frequent than one would expect from a model of random speciation and extinction.
Among songbirds (Passeriformes), more than 30 of 106 tribe-level taxonomic groups have five or fewer species, compared to the average size of 54 species and a maximum of more than 10 times that number. The existence of so many small taxa suggests that these lineages must have unusually low rates of speciation and extinction compared to other songbirds. In an earlier analysis, Robert E. Ricklefs suggested that species in these small groups might avoid extinction by competitive exclusion because they are marginal both geographically and ecologically. In this new study, which will appear in the June 2005 issue of The American Naturalist, Ricklefs shows that species in small clades tend to have extreme morphology, in particular relatively long toes, sometimes in contrast with short legs, and small beaks. Such traits are associated with foraging on bark or rock surfaces or feeding from perched positions or in dense, shrubby vegetation. These are unusual habits for typically more active songbirds. How such marginal ecology slows the rates of species formation and extinction remains an open question.
Carrie Olivia Adams | EurekAlert!
Scientists unveil completely human platform for testing age-specific vaccine responses
20.11.2018 | Boston Children's Hospital
From Receptor Structure to New Osteoporosis Drugs
20.11.2018 | Universität Zürich
Researchers at the University of New Hampshire have captured a difficult-to-view singular event involving "magnetic reconnection"--the process by which sparse particles and energy around Earth collide producing a quick but mighty explosion--in the Earth's magnetotail, the magnetic environment that trails behind the planet.
Magnetic reconnection has remained a bit of a mystery to scientists. They know it exists and have documented the effects that the energy explosions can...
Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.
Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...
Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.
In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...
On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.
When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure
Now, a team of Penn Engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square...
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20.11.2018 | Physics and Astronomy