Life history strategies and ecological adaptations of two similar species of shrews (Sorex vagrans vagrans and Sorex obscurus setosus) were examined in southwestern British Columbia in an attempt to understand 1) how they are able to coexist in sympatry, 2) what kinds and degrees of interspecific competition are evident, and 3) how strategic responses to selective pressures differ between species and among habitats. A trap and recapture program allowed the study of population dynamics and individual life histories of the two species in a forest situation where they were sympatric. Standardized snap-trap lines were set through several habitat types to ascertain basic distributional patterns and habitat preferences of each species. Finally, the collection and specimen preparation of extensive series of Sorex vagrans from lowland grassy fields facilitated
examination of seasonal and geographic variation in morphology and reproductive strategy.
Sorex vagrans and Sorex obscurus share a common life history pattern, several features of which were examined in detail with reference to their adaptive significance. Many adaptations were considered in terms of energy limitations. Both intra- and interspecific territoriality were evident in non-breeding (first year) individuals of each species. Home range analysis, using an elliptical model, reflected the abandonment of territoriality in breeding adults as home
range size increased. My conclusions are that strong site attachment and the establishment of territories during the non-breeding time of life serve to ensure the territory holder sufficient food for overwintering.
Species distributions and habitat analyses show that, although the two species overlap geographically, competition is mitigated through, habitat segregation at the microgeographic level, with soil type and the associated soil fauna appearing to be significant factors. Sorex vagrans is competitively superior in the relatively richer soils, while Sorex obscurus has the advantage in the more acidic soils.
Intraspecific comparison of forest- and grassland-inhabiting. Sorex vagrans reveal basic differences in reproductive strategy. The attainment of sexual maturity in first year females is relatively common in lowland grassland habitat, whereas no such case is documented in forest habitat. The shorter generation, time appears to be an adaptive response to a situation where food-is less limiting and the reproductive season is longer.
Ecological strategies and their evolution in forest and grassland populations, and the significance of evolutionary ecology to shrew systematics are discussed in light of the findings. / Science, Faculty of / Zoology, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/19720 |
| Date | January 1975 |
| Creators | Hawes, Myrnal Leong |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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