More Proof For Competitive Exclusion

Phylogenetic limiting similarity and competitive exclusion. 2011. C. Violle, et al. Ecology Letters

Metal Men © DC Comics

A new study provides support for Darwin's hypothesis that the struggle for existence is stronger between more closely related species than those distantly related. While ecologists generally accept the premise, this new study contains the strongest direct experimental evidence yet to support its validity.

"We found that species extinction occurred more frequently and more rapidly between species of microorganisms that were more closely related, providing strong support for Darwin's theory, which we call the phylogenetic limiting similarity hypothesis," said Lin Jiang.

The researchers set up 165 microcosms that contained either an individual bacterivorous protist species or a pairing of two species, along with three types of bacteria for the organisms to eat.

The study results showed that all species survived until the end of the experiment when alone in a microcosm. However, in more than half of the experiments in which protists were paired together, one of the two species dominated, leading to the extinction of the other species.

The researchers found that the frequency and speed of this extinction process -- called competitive exclusion -- was significantly greater between species that were more closely related. In addition, in microcosms where both competitors coexisted for the duration of the experiment, the abundance of the inferior competitor was reduced more as the phylogenetic relatedness between the two competitors increased. link