Evolution of new species slows down as number of competitors increases

25 March 2008

The rate at which new species are formed in a group of closely related animals decreases as the total number of different species in that group goes up, according to new research published today (Tuesday 25 March) in PLoS Biology.

The research team believes these findings suggest that new species appear less and less as the number of species in a region approaches the maximum number that it can support.

In order for new species to thrive they need to evolve to occupy their own niche in the ecosystem, relying on certain foods and habitats for survival which are sufficiently different from those of other closely related species.

Competition between closely related species for food and habitat becomes more intense the more species there are, and researchers believe this could be the reason for the drop-off in the appearance of new species over time.

Dr Albert Phillimore, from Imperial College London's NERC Centre for Population Biology, lead author on the paper, explains, "The number of niches in any given region is finite, and our research supports the idea that the rate of speciation slows down as the number of niches begins to run out.

"In essence, it seems like increased competition between species could place limits on the number of species that evolve."

The new study used detailed analysis of the family trees, or phylogenies, of 45 different bird families. By examining the rate at which new species have arisen in each of these trees over a period of millions of years, scientists saw that the rate of appearance of new species seemed to be much higher in the early stages of the family tree, compared to more recent lower rates.

For example, when the researchers examined the phylogeny of tits they found that some 10 million years ago species formed rapidly but this rate has slowed over time to perhaps a quarter of the initial rate.

Further information

Danielle Reeves
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Notes

1. 'Density-dependent Cladogenesis in Birds', PLoS Biology, 25 March 2008.
AB Phillimore (1), TD Price (2)

(1) NERC Centre for Population Biology and Division of Biology, Imperial College London, Silwood park, Ascot, Berkshire, SL5 7PY, UK;
(2) Division of Biological Sciences, University of Chicago, 5801 South Ellis, Chicago, IL 60637, USA

2. Imperial College London - rated the world's fifth best university in the 2007 Times Higher Education Supplement University Rankings - is a science-based institution with a reputation for excellence in teaching and research that attracts 12,000 students and 6,000 staff of the highest international quality. Innovative research at the College explores the interface between science, medicine, engineering and business, delivering practical solutions that improve quality of life and the environment - underpinned by a dynamic enterprise culture.

3. The Natural Environment Research Council (NERC) funds world-class science, in universities and its own research centres, that increases knowledge and understanding of the natural world. It is tackling major environmental issues such as climate change, biodiversity and natural hazards. NERC receives around £400m a year from the government's science budget which is used to provide independent research and training in the environmental sciences.

4. The Centre for Population Biology is hosted by Imperial College London and funded primarily by NERC. It is one of NERC's major collaborative programmes, set up in 1989 to increase knowledge of how ecological systems function.

Evolution of new species slows down as number of competitors increases

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