Not Kept Apart by Competition

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Science  17 Oct 2008:
Vol. 322, Issue 5900, pp. 348
DOI: 10.1126/science.322.5900.348a

According to the theory of limiting similarity, in order to minimize competition, species coexisting in the same habitat must differ enough in size, shape, or other variables. Ecologists and paleontologists have reported such differences in a wide range of organisms in modern environments or time-averaged deposits. To provide a temporal context, Huntley et al. examined the size and shape of Quaternary endemic land snails from the Canary Islands through the past 42,500 years. They considered two types of limiting similarity: ecological character displacement (differences between two closely related species are greater when speciation is ongoing in the same location) and community-wide character displacement (particularly large size or morphology variation among potentially competing species). The data showed that the two most abundant species of the pulmonate gastropod Theba exhibited a parallel reduction in size, but when one went extinct the other did not show convergence (a shift toward the other) or release (increased variation). Thus, limiting similarity appears to be a transient ecological phenomenon rather than a long-term evolutionary process. — SJS

Paleobiology 34, 378 (2008).

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