The Influences of Conspecific and Heterospecific Residents on Colonization

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Abstract
To determine if dispersing prairie voles, Microtus ochrogaster, are prevented from establishing home ranges in habitat already occupied by conspecifics or potentially competitive species, voles were introduced into enclosed populations of: the same species; southern bog lemmings, Synaptomys cooperi; cotton rats, Sigmodon hispidus; or an empty enclosure. The results indicated that colonization by dispersing voles was negatively affected by resident conspecifics. Introduced females were more strongly affected than males during the vegetative growing season but not during the nongrowing season when reproductive activity is typically low. Resident bog lemmings also negatively affected colonization by dispersing voles. However, both sexes of introduced voles were similarly affected in both seasons. There was no evidence of postcolonization competitive effects, suggesting that interspecific competition does not occur between established resident individuals. Cotton rats, which have only recently become part of the small mammal community in Kansas, did not adversely affect colonization by dispersing voles or have adverse post—colonization effects on their survival and reproduction. The ability of residents to inhibit colonization by another species may facilitate the coexistence of M. ochrogaster and Synaptomys cooperi by retarding the competitive exclusion of either species until annual fluctuations in reproduction and density create an abundance of suitable but unoccupied space. This type of coexistence is similar to the storage effect in lottery models of competitive coexistence.