鈥淓ACH new variety or species, during the progress of its formation, will generally press hardest on its nearest kindred, and tend to exterminate them.鈥�
So said Charles Darwin in On the Origin of Species, when he was describing how competition for resources between species drives some to extinction. It now turns out that Darwin could have been wrong. Researchers in the US have shown that in some situations, the more strongly animals compete with each other, the more species can coexist.
The first hint that Darwin鈥檚 maxim might be flawed came from biologists studying saltwater plankton. They noticed that many species coexist quite happily, even though they all rely on the same basic nutrients.
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This apparent paradox was resolved in 1999 by Jef Huisman of the University of Amsterdam and Franjo Weissing. The answer is simply that every species relies slightly more on one nutrient than on the others. The complex interrelations between species also make the system behave chaotically, with populations crashing and blossoming in unpredictable patterns.
However, Huisman and Weissing only showed this is true for simple systems where creatures depend on non-living nutrients like iron. Now researchers in the US have redone the maths for ecological systems where different species of predators prey on live animals.
John Vandermeer and a team from the University of Michigan at Ann Arbor found the predators also interact in a chaotic way, with tiny changes in the numbers of one species having huge impacts on the others. As expected, species crashed to extinction if they all ate exactly the same food, and systems could support extra species as long as they had completely different diets.
But if predators had diets that overlapped to a certain degree, then the more they competed, the greater the number of species that survived (Proceedings of the National Academy of Sciences, vol 99, p 8731).
鈥淭his is really surprising,鈥� says Huisman, who says he is impressed by the work. Although Vandermeer can鈥檛 yet explain the counterintuitive result, it seems to provide a new explanation for how some species diversify.
Huisman speculates that might also be true for competing herbivorous species that ate different plants: 鈥淚n the savannah, there are a lot of different kinds of antelope. This could be part of the reason why.鈥�