Reproduction, Hibernation, and Population Regulation of Arctic Ground Squirrels (Spermophilus Parryii Plesius). PDF Download

Author: Timothy J. Karels
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Languages : en
Pages : 0

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Book Description
Populations of arctic ground squirrels in the boreal forest of the southwest Yukon were studied in order to answer the following questions: (1) What are the mechanisms of population regulation in arctic ground squirrel populations, (2) How does variation among individuals and their environment influence their reproduction and survival, and (3) How does variation in habitat influence hibernating strategies of arctic ground squirrels? In spring 1996, control densities of ground squirrels were 1.6 per ha, and four other populations ranged in density from 3.2 to 30.1 per ha as a result of a 10-year (1987-96) large scale manipulation of food and predators in the boreal forest of the Kluane Boreal Forest Ecosystem Project. When the Kluane project terminated in spring 1996, I measured population densities, reproduction, emigration, and survival in all populations using live-trapping and radio-telemetry techniques until spring 1998. Arctic ground squirrel populations were strongly regulated because all experimental populations declined to control densities within two years after the termination of the experimental manipulations. Two factors proved strongly density-dependent and hence were regulatory: (1) the proportion of females that weaned their litter and (2) overwinter survival. Simultaneous density-independent changes in weaning rate were also detected and were attributed to changes in the previous year's snow accumulation. Female ground squirrels exhibited positive associations of life history traits. Squirrels in better condition at spring emergence were more likely to give birth, wean their litter, survive to the next breeding season, and reproduce once again. Nearly all females who failed during lactation did not survive to the next breeding season. The overwinter survival rate of females that successfully weaned a litter declined at a greater rate with increasing population density than did squirrels that never gave birth, indicating a cost to reproduction. Ground squirrels hibernated distantly (24 m) from their summer burrows in relation to population density and in open or shrubby habitats that were likely to accumulate the most snow. Increased snow accumulation over hibernacula increased the minimum soil temperatures and decreased the rate of mass loss of hibernating squirrels suggesting a selective mechanism for the ability of ground squirrels to identify habitats that minimize their energy expenditure during hibernation.