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UBC Theses and Dissertations

Fates of disappearing individuals in fluctuating populations of Microtus townsendi Hilborn, Ray William


Fates of disappearing individuals were determined for two natural populations of Microtus townsendi by live-trapping evacuated areas and marginal habitat, and by marking individuals with radioactive tags to locate carcasses. 219 out of the 454 individuals that disappeared were radioactively tagged during this three year study conducted in the University of British Columbia Research Forest near Haney, B.C. Most disappearance from increase and peak populations was due to dispersal. Two periods of declining numbers were observed; during one such period many individuals' remains were found on the study areas; but during the other period of declining numbers few remains were found. There was no increase in dispersal rate, as measured by the above techniques, during either decline period. It is concluded that during the first brief period of declining numbers individuals were dying in their nests from unknown causes, and during the second period of declining numbers individuals were moving long distances without going into traps. A computer simulation model of the trapping technique was constructed to test the reliability of the estimates of numbers. It was concluded that the index used (minimum number of animals known to be alive) was a very good representation of the actual population size.

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