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Ecology of certain terrestrial snails and their relationship to the lungworm of Bighorn sheep Reid, Kenneth Walter

Abstract

The distribution and abundance of terrestrial snails which inhabit the Rocky Mountain bighorn sheep (Ovis canadensis Canadensis Shaw) ranges in the East Kootenay region of British Columbia were related to edaphic and climatic factors. Emphasis was placed upon those snail species which have been implicated as intermediate hosts of the sheep lungworm, Protestrongylus stilesi Dikmans. Retinella electrina (Gould), Euconulus fulvus (Muller), and Vitrina alaskana Dall were found to be widely distributed on all ranges and were present in all but the driest plant communities. On low elevation ranges, Euconulus is the most abundant but Retinellai.is the most widely distributed. In alpine regions, however, Vitrina is the dominant species. These hydrophilic species were found mainly on organic soils under leaf litter or logs in aspen and coniferous forest communities where moisture conditions were suitable. The relatively xerophilic species, Vallonia cyclophorella (Sterki), Gastrocopta holzingeri Sterki, and Pupilla muscorum (L.) are restricted to the dry, sandy soils of the bunchgrass communities, where they live under rocks. Of these species, Vallonia is the most abundant, but on the Columbia Lake range, Pupilla, which is restricted to this range, is almost as numerous. The clay and silt soils of the bitterbrush communities appear to be unsuitable for the survival of any snails. Wide temperature and moisture fluctuations, resulting in part from soil texture, appear to be the main factors limiting the occurrence of snails in these sites. With the possible exception of Vitrina and Pupilla, the distribution and abundance of snails on the East Kootenay sheep ranges can not be explained by variations in soil calcium, even though calcium was shown to affect reproductive and growth rates. Vallonia and Pupilla appear to be the most suitable intermediate hosts for sheep lungworm. However, no infected snails were found on any of the ranges and it was established that snails live in a habitat which is inaccessible to sheep. This indicates that terrestrial snails may not play a role in the life cycle of sheep lungworm in the East Kootenay region of B.C.

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