Distribution and abundance of terrestrial gastropods on a winter range of bighorn sheep in southwestern Alberta

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Abstract
Living specimens of 15 species of terrestrial gastropods (14 snails and 1 slug) were collected on a series of plots located in a variety of habitats associated with a winter range of bighorn sheep (Ovis canadensis) in southwestern Alberta. Four species of snails (Vertigo gouldi, Discus cronkhitei, Vitrina alaskana, and Euconulus fulvus) constituted ca. 85% of all living specimens recorded in 1979, 1980, and 1981. However, the relative abundance of the last three species changed markedly between years. Based on the size of living individuals recovered over the snow-free season, only one snail (Vitrina alaskana) and the slug (Deroceras laeve) appeared to be annual species; the other common snails appear to live more than 1 year. The distribution of gastropods was correlated with the vegetative cover; maximum abundance was found within forested areas where deciduous tree or shrub growth was a major component of the canopy. The implications of the distribution and abundance of these molluscs for the transmission of lungworms to bighorn sheep is discussed.