Microbe 'Cage Matches' Pass Darwin's Test
by Sarah C.P. Williams on 17 June 2011, 2:10 PM | Permanent Link
Stick two species of microorganisms in a Petri dish, and you won't see hand-to-hand combat with your naked eye. But under the microscope, a turf war is under way. If the organisms rely on the same food source and the same space to thrive, there will be intense competition to drive each other to extinction. Scientists studying how different species compete with one another have long relied on an assumption first made in Charles Darwin's 1859 book On the Origin of Species. The more closely related two species are, he wrote, the harder they'll compete. After all, closely related species are more likely to rely on the same food and habitat.
Ecologist Lin Jiang of the Georgia Institute of Technology in Atlanta has now turned to one-celled microorganisms to determine, once and for all, whether Darwin's competition hypothesis was correct. "You could look at a larger ecosystem," Jiang says, "but in the field, there's always confounding factors, and whether two species can coexist depends on so many things." A predator, for example, could enter the mix, knocking one of the species out of the equation. So he created a simple system in the lab using protists, one-celled organisms that naturally thrive in pond scum and feed on bacteria.
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Phylogenetic limiting similarity and competitive exclusion
Cyrille Violle1,2,3,*, Diana R Nemergut4,5, Zhichao Pu1, Lin Jiang1
Article first published online: 14 JUN 2011
DOI: 10.1111/j.1461-0248.2011.01644.x
Ecology Letters
Early View (Online Version of Record published before inclusion in an issue)
Keywords: Community phylogenetics; competitive ability; functional trait; interspecific competition; niche conservatism; niche difference; phylogenetic dispersion; phylogenetic relatedness; species coexistence; species extinction
Ecology Letters (2011)
Abstract
One of the oldest ecological hypotheses, proposed by Darwin, suggests that the struggle for existence is stronger between more closely related species. Despite its long history, the validity of this phylogenetic limiting similarity hypothesis has rarely been examined. Here we provided a formal experimental test of the hypothesis using pairs of bacterivorous protist species in a multigenerational experiment. Consistent with the hypothesis, both the frequency and tempo of competitive exclusion, and the reduction in the abundance of inferior competitors, increased with increasing phylogenetic relatedness of the competing species. These results were linked to protist mouth size, a trait potentially related to resource use, exhibiting a significant phylogenetic signal. The likelihood of coexistence, however, was better predicted by phylogenetic relatedness than trait similarity of the competing species. Our results support phylogenetic relatedness as a useful predictor of the outcomes of competitive interactions in ecological communities.
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