Interpretation of Intraspecific Life History Patterns: Evidence from Columbian Ground Squirrels

1987 ◽  
Vol 129 (3) ◽  
pp. 382-397 ◽  
Author(s):  
F. Stephen Dobson ◽  
Jan O. Murie
1986 ◽  
Vol 67 (1) ◽  
pp. 154-158 ◽  
Author(s):  
F. S. Dobson ◽  
R. M. Zammuto ◽  
J. O. Murie

1985 ◽  
Vol 63 (9) ◽  
pp. 2105-2109 ◽  
Author(s):  
F. Stephen Dobson ◽  
Julia D. Kjelgaard

Life history characteristics were studied experimentally in Columbian ground squirrels (Spermophilus columbianus) at two elevations in the Rocky Mountains of southwestern Alberta, Canada, from 1981 to 1984. In two populations with supplemented food resources, survival of young increased, age at maturity of females decreased, litter size increased, and spring body weight increased in comparison with an initial unmanipulated period and with two populations monitored for reference. For individual ground squirrels, litter size and spring body weight increased under supplementation. Thus, life history characteristics exhibited phenotypically plastic responses to experimental manipulation of food resources. Life history patterns changed among natural ground squirrel populations at different elevations and these changes were likely due to changes in food resources. A general prediction of life history theory that reproductive effort should be highest in years favorable for juvenile survivorship was supported by the experimental results. The results did not support predictions from interspecific studies of changes in life history characteristics that scale to body weight.


1999 ◽  
Vol 68 (1) ◽  
pp. 73-86 ◽  
Author(s):  
F. Stephen Dobson ◽  
Thomas S. Risch ◽  
Jan O. Murie

2019 ◽  
Vol 222 (12) ◽  
pp. jeb203588
Author(s):  
Jeffrey D. Roth ◽  
F. Stephen Dobson ◽  
François Criscuolo ◽  
Pierre Uhlrich ◽  
Alexandre Zahariev ◽  
...  

1977 ◽  
Vol 55 (4) ◽  
pp. 693-703 ◽  
Author(s):  
Gail R. Michener

In 1975 and 1976 the times of spring emergence, breeding, and entry into hibernation were compared for Spermophilus richardsonii and S. columbianus in an area of sympatry in the foothills of the southern Alberta Rocky Mountains. Both species emerged earlier in 1976, which had a warmer than normal spring, than in 1975, which had a cooler than normal spring. In both years S. richardsonii emerged earlier than S. columbianus and remained active longer. Juvenile S. richardsonii entered hibernation when 17–20 weeks old whereas juvenile S. columbianus were 10–11 weeks old. Yearling S. richardsonii bred, whereas yearling S. columbianus did not. Breeding success affected the time of entry into hibernation but not the time of emergence from hibernation in the next spring. A possible relationship between the periodic arousals during hibernation and the emergence pattern of squirrels in spring is discussed. The significance of flexibility of spring emergence, length of the active season, and age at breeding to survival and species ecology is considered.


2005 ◽  
Vol 83 (4) ◽  
pp. 546-552 ◽  
Author(s):  
David R Broussard ◽  
F Stephen Dobson ◽  
J O Murie

To maximize fitness, organisms must optimally allocate resources to reproduction, daily metabolic maintenance, and survival. We examined multiple years of live-trapping and observational data from a known-aged population of female Columbian ground squirrels, Spermophilus columbianus (Ord, 1815), to determine the influences of stored resources and daily resource income on the reproductive investments of females. We predicted that because yearling females were not fully grown structurally while producing their first litter, they would rely exclusively on income for reproduction, while reproductive investment in older females (≥2 years of age) would be influenced by both stored resources (capital) and daily income. Results from path analysis indicated that both yearlings and older females were income breeders. However, initial capital indirectly influenced investment in reproduction of yearling and older females. Females with the greatest initial capital maintained high body masses while investing relatively more income in reproduction. By considering influences of both capital and income, important relationships can be revealed between these resources and their influence on life histories.


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