Milk matters: offspring survival in Columbian ground squirrels is affected by nutrient composition of mother's milk

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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Benzodiazepine-like substances in mother's milk

The Lancet ◽

10.1016/0140-6736(90)90246-2 ◽

1990 ◽

Vol 335 (8686) ◽

pp. 413 ◽

Cited By ~ 9

Author(s):

SvenJ. Dencker ◽

Gunvor Johansson

Keyword(s):

Mother's Milk ◽

Mother’S Milk

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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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