Fitness Estimation for Ecological Studies: An Evaluation in Columbian Ground Squirrels

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.

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The effects of capital on an income breeder: evidence from female Columbian ground squirrels

Canadian Journal of Zoology ◽

10.1139/z05-044 ◽

2005 ◽

Vol 83 (4) ◽

pp. 546-552 ◽

Cited By ~ 25

Author(s):

David R Broussard ◽

F Stephen Dobson ◽

J O Murie

Keyword(s):

Path Analysis ◽

Observational Data ◽

Life Histories ◽

Reproductive Investment ◽

Ground Squirrels ◽

Initial Capital ◽

Spermophilus Columbianus ◽

Live Trapping ◽

Investment In Reproduction ◽

Columbian Ground Squirrels

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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TIMING OF HIBERNATION AND MOLT IN FEMALE COLUMBIAN GROUND SQUIRRELS

Journal of Mammalogy ◽

10.1644/1545-1542(2000)081<0571:tohami>2.0.co;2 ◽

2000 ◽

Vol 81 (2) ◽

pp. 571-577 ◽

Cited By ~ 12

Author(s):

Peter Neuhaus

Keyword(s):

Ground Squirrels ◽

Columbian Ground Squirrels

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Variation in reproductive success of male and female Columbian ground squirrels (Urocitellus columbianus)

Canadian Journal of Zoology ◽

10.1139/z2012-042 ◽

2012 ◽

Vol 90 (6) ◽

pp. 736-743 ◽

Cited By ~ 5

Author(s):

Philip H. Jones ◽

Jeffrey L. Van Zant ◽

F. Stephen Dobson

Keyword(s):

Reproductive Success ◽

Mating System ◽

Multiple Paternity ◽

Ground Squirrels ◽

Male Reproductive Success ◽

Offspring Production ◽

Bateman Gradient ◽

Coefficients Of Variation ◽

Males And Females ◽

Columbian Ground Squirrels

The imbalanced reproductive success of polygynous mammals results in sexual selection on male traits like body size. Males and females might have more balanced reproductive success under polygynandry, where both sexes mate multiply. Using 4 years of microsatellite DNA analyses of paternity and known maternity, we investigated variation in reproductive success of Columbian ground squirrels, Urocitellus columbianus (Ord, 1815); a species with multiple mating by both sexes and multiple paternity of litters. We asked whether male reproductive success was more variable than that of females under this mating system. The overall percentage of confirmed paternity was 61.4% of 339 offspring. The mean rate of multiple paternity in litters with known fathers was 72.4% (n = 29 litters). Estimated mean reproductive success of males (10.27 offspring) was about thrice that of females (3.11 offspring). Even after this difference was taken into account statistically, males were about three times as variable in reproductive success as females (coefficients of variation = 77.84% and 26.74%, respectively). The Bateman gradient (regression slope of offspring production on number of successful mates) was significantly greater for males (βM = 1.44) than females (βF = 0.28). Thus, under a polygynandrous mating system, males exhibited greater variation in reproductive success than females.

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Weight in relation to sex, age, and season in Columbian ground squirrels (Sciuridae: Rodentia)

Canadian Journal of Zoology ◽

10.1139/z81-139 ◽

1981 ◽

Vol 59 (6) ◽

pp. 999-1004 ◽

Cited By ~ 27

Author(s):

D. A. Boag ◽

J. O. Murie

Keyword(s):

Weight Gain ◽

Ground Squirrels ◽

Full Potential ◽

Age Classes ◽

Adult Weight ◽

Spermophilus Columbianus ◽

Large Colony ◽

Potential Weight ◽

Columbian Ground Squirrels

Annual weight gain in Columbian ground squirrels (Spermophilus columbianus) was studied over a period of 7 years in a large colony in southwestern Alberta. Juveniles approximately tripled their weight during the period from emergence to immergence, achieving about 60% of adult weight at onset of their first hibernation. Males were heavier than females and the weight gain in both sexes varied significantly among years. The weight characteristics of the age-classes up to 3 years were different from one another. Full potential weight was not achieved until squirrels were in their fourth summer. Males were always significantly heavier than females in nonjuvenile squirrels and the amount of weight gained by these classes varied significantly among years.

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