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

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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.

Afin de maximiser leur fitness, les organisme doivent répartir de façon optimale leurs ressources entre la reproduction, le maintien métabolique quotidien et la survie. Nous avons examiné des données de piégeage d'animaux vivants et des observations sur plusieurs années provenant d'une population de spermophiles du Columbia (Spermophilus columbianus (Ord, 1815)) femelles d'âge connu afin de déterminer l'influence des ressources emmagasinées et de l'apport quotidien de ressources sur les investissements reproductifs des femelles. Notre prédiction est que les femelles de 1 an, qui n'ont pas atteint leur maturité structurale au moment où elles produisent leur première portée, dépendent entièrement des apports quotidiens pour leur reproduction; en revanche, chez les femelles plus âgées (de ≥2 ans), l'investissement reproductif dépend à la fois des ressources emmagasinées (capital) et des apports quotidiens (revenu). Les résultats d'une analyse de sentier indiquent que les femelles tant de 1 an que plus âgées, se reproduisent à partir des apports quotidiens. Cependant le capital initial influence indirectement l'investissement reproductif des femelles de 1 an et des plus âgées. Les femelles possédant un capital initial plus important maintiennent une masse corporelle plus grande, tout en investissement relativement plus de leurs apports journaliers dans la reproduction. En tenant compte des influences à la fois du capital et des apports journaliers, on peut mettre à jour d'importantes relations entre ces ressources et leur influence sur les cycles biologiques.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: April 1, 2005

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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