Can Shrews Avoid Competition When Hutchinson's Ecological Rule Is Disobeyed?

It is established that Hutchinson's ratio of the weights and sizes of the body and foraging organs in similar species is not fully obeyed in shrew species of the genus Sorex. Similarity in the centroid size of the mandible was observed in the large species S. isodon and S. araneus. Differences in the shape of the mandible, which is intensely used in foraging, were detected between the species by geometric morphometrics. Interspecific differences were found in mandibular indices, which reflect trophic specialization and functional features of the mandibles. Shrews can therefore avoid competition even when Hutchinson's rule is violated. The avoidance is due to a transformation and specialization of the mandible and changes in prey capture methods and diet, rather than to changes in size. Hutchinson's ecological rule is thus not mandatory, but is only one of the conditions for reducing competition between closely related species.