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Don't stand so close to me: a new view on how species coexist

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-Royal Holloway, University of London
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For immediate release
Friday 1 October 2004

Plants and animals living together in communities don't rub shoulders too closely because evolution has caused them to compromise on key life measures, say ecologists at Imperial College London and Royal Holloway, University of London, writing in the journal Science today (1 October).

The researchers suggest a new basis for explaining how communities of species assemble: they have to give up being good at everything and 'trade off' their life histories.

'Life histories' is ecological jargon for the important measures, shaped by evolution, such as how often you can reproduce; how many children you will have; how long you can live for; and crucially, how good you are at getting food on which to survive.

"You can't be good at doing everything," says Dr Mike Bonsall, a Royal Society University Research Fellow working at Imperial College London, and first author of the paper.

"Most people do one thing really well, another thing fairly well and then aren't very good at anything else. So it is with any other species. Now we know that they coexist precisely because they each have different life histories."

An Asobara wasp standing on apple mush. This parasitoid attacks fruit fly larvae which live in the apple mush.

The London researchers assembled a simple artificial community of parasitoid wasps within a computer model, and then watched what happened over very long periods of time - up to 100,000 generations.

Parasitoid wasps, insects that kill other insects by laying eggs in them, account for a fifth of all known multi-celled species. Their 200,000 species places them approximately next to land plants in terms of diversity.

To their surprise they found that over long periods of time, 'gaps', or differences in their life histories, opened up between the evolving parasitoid wasp species, which are not filled by others. They suggest this may explain the great diversity of wasps seen in nature.

"There is a fixed amount of difference necessary," says Dr Bonsall. "This allows evolution to affect patterns of diversity such as how many similar species we see."

Dr Vincent Jansen, author of the paper from Royal Holloway, University of London, added: "The bottom line of this work is that patterns of diversity are shaped both by ecology and by evolution."

One way of capturing the essence of the new work, he added, is expressed in the concept of the 'Darwinian demon' - a hypothetical species that develops rapidly, reproduces continuously and does not age. Trade offs in life histories are thought to prevent Darwinian demons from evolving. Rather, similar species are allowed to coexist.


For further information, please contact:

Dr Michael Bonsall
Department of Biological Sciences
Imperial College London
Silwood Park campus
Tel: +44 (0)20 7594 2360


Tom Miller
Imperial College London Press Office
Tel: +44 (0)20 7594 6704
Mobile: +44 (0)7803 886 248

Notes to Editors:

The research appears in the 1 October 2004 edition of the journal Science.

Title: 'Life History Trade-Offs Assemble Ecological Guilds'

Authors: Michael Bonsall 1, Vincent Jansen 2, Michael Hasssell 1

1 Imperial College London
2 Royal Holloway, University of London

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