Demography of Belding's Ground Squirrels

Sherman, Paul W.; Morton, Martin L.

doi:10.2307/1939140

Cited by 216 publications

(115 citation statements)

References 55 publications

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“…The much higher male disappearance between emergence from their first and second hibernation is likely due to the male-biased dispersal found in Columbian ground squirrels (Boag and Murie 1981;Festa-Bianchet and King 1984;Wiggett and Boag 1993) rather than to mortality per se. A tendency for males to die younger than females has been shown in Richardson's and Belding's ground squirrels and black-tailed prairie dogs (Cynomys ludovicianus) (Sherman and Morton 1984;Michener and Locklear 1990;Hoogland 1995). In our study, however, male Columbian ground squirrels after the age of dispersal do not have higher mortality than females up to the age of 4 (Table 1).…”

Section: Discussionmentioning

confidence: 94%

Mortality in relation to season, age, sex, and reproduction in Columbian ground squirrels (Spermophilus columbianus)

Neuhaus¹,

Pelletier²

2001

Can. J. Zool.

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Abstract:We investigated the timing of and age at mortality in Columbian ground squirrels (Spermophilus columbianus) in relation to sex and reproductive status. Life-history data were collected from 1994 to 1999 in the foothills of the Rocky Mountains, Alberta, Canada. We predicted increased mortality for males during mating and for females during lactation. Further, we expected reproductively successful females to have higher mortality than females that did not reproduce successfully. Finally we assumed that at some age reproductive success of females would decrease and mortality increase because of old age. For both sexes, survival over winter was high (ca. 90%) for adults. While there was a significant increase in mortality of adult males during the mating season, females did not have higher mortality during lactation than during the rest of the active season. Reproductive status influenced mortality in females: non-reproducing females had a higher chance of surviving than reproducing females. Females that weaned young were more likely to die after the weaning period than females that lost their litter during lactation. There was a positive correlation between maternal survival and survival of offspring to yearling age. Our results showed evidence of trade-offs between reproduction and survival of male and female Columbian ground squirrels.Résumé : Nous avons étudié la phénologie de la mortalité et déterminé l'âge au décès chez le Spermophile du Columbia (Spermophilus columbianus) en fonction du sexe et du statut reproducteur à partir de données démograph-iques recueillies de 1994 à 1999 sur les contreforts des Rocheuses en Alberta, Canada. Nous avons posé en hypothèse que la mortalité augmenterait chez les mâles au cours de la période des accouplements et chez les femelles durant l'allaitement et que les femelles qui réussiraient leur reproduction auraient une mortalité plus forte que les femelles qui la rateraient. Enfin, nous nous attendions à un déclin de la reproduction chez les femelles à partir d'un certain âge et à une augmentation de la mortalité due à la vieillesse. Chez les adultes mâles et femelles, la survie en hiver est élevée (ca. 90 %). Il se produit une augmentation significative de la mortalité des mâles pendant la saison des accouplements, mais les femelles n'ont pas un taux de mortalité plus élevé durant l'allaitement que pendant le reste de la saison d'activité. Le statut reproducteur influence la mortalité chez les femelles : en effet, les femelles non reproductrices ont de meilleures chances de survie que les femelles reproductrices. La probabilité de mourir est plus forte chez les femelles qui gardent leurs petits jusqu'au sevrage que chez celles qui perdent leur portée pendant l'allaitement. Il y a une corrélation positive entre la survie des femelles et la survie des jeunes au cours de la première année. Nos résultats indiquent qu'il s'établit des compromis entre la reproduction et la survie chez les mâles et les femelles du Spermophile du Columbia.[Traduit par la Rédaction] 470Neuha...

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Section: Discussionmentioning

confidence: 94%

Mortality in relation to season, age, sex, and reproduction in Columbian ground squirrels (Spermophilus columbianus)

Neuhaus¹,

Pelletier²

2001

Can. J. Zool.

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“…About 1 month after natal emergence, juvenile females establish their own burrow system within 25 m of their natal burrow, whereas juvenile males begin to disperse permanently from their birthplace (Holekamp, 1984). Females live an average of 3.4 ±0.3 years (up to 12 years); males live 2.5±0.4 years (up to 9 years; Sherman and Morton, 1984; personal observation). The research reported here adheres to standards set forth by the NIH for animal research.…”

Section: Animals and Study Sitesmentioning

confidence: 99%

“…Anti-predator behaviors of juveniles born in captivity and released within a couple of months are qualitatively similar to those of field-reared juveniles (Mateo and Holmes, 1999b). In addition, the feeding regimen of captive animals results in higher body weights than those of same-aged, free-living animals, increasing the chances of released juveniles surviving their first hibernation (60% of field-born juveniles do not survive the winter, probably due to insufficient body-fat reserves; Sherman and Morton, 1984; personal observation).…”

Section: Captive Animalsmentioning

confidence: 99%

“…This rapid learning of appropriate responses is important because up to 30% of juveniles disappear during the first 2 weeks after emerging aboveground at about 1-month of age, presumably due to predation (Mateo, 1996). Predation can account for up to 60% of juvenile S. beldingi mortality (Sherman and Morton, 1984; personal observation) and overwinter survival in some ground squirrels depends on the accumulation of body fat prior to hibernation (Murie and Boag, 1984), thus creating a trade-off between foraging and vigilance (see also Bachman, 1993). In addition to threats from predators, newly emergent juveniles are vulnerable to infanticide by adults and are in the process of becoming nutritionally independent (Sherman, 1982;Mateo, 1996).…”

Section: Introductionmentioning

confidence: 99%

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Developmental and geographic variation in stress hormones in wild Belding's ground squirrels (Spermophilus beldingi)

Mateo

2006

Hormones and Behavior

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Extensive research has been conducted on the role of glucocorticoids in regulating growth, mobilizing energy, responding to stressors and modulating learning and memory. However, little is known about the production of corticoids during early development in free-living animals, particularly during sensitive periods of acquisition of important behaviors. In a four-year study of Belding's ground squirrels, Spermophilus beldingi, a non-invasive assay of glucocorticoids was used to quantify age and population differences among juveniles from three California locations. Fecal-cortisol metabolites are elevated during a short period when juveniles first emerge aboveground from their natal burrows at about 4 weeks of age. This period of cortisol elevation coincides with when young are learning survival behaviors such as anti-predator responses and foraging strategies. Population differences in juvenile cortisol levels, which may reflect local variation in habitat quality and predator environments, were not evident until 2 weeks after emergence. Elevated cortisol at the age of emergence was also observed in juveniles born and reared in captivity without exposure to typical stressors that occur around the age of emergence. These results indicate that corticoids are regulated during early development, and the possible functions of age-related corticoid levels are discussed, including mobilization of glucose for natal emergence and later facilitation of growth and energy storage during the short summer before hibernation. In some species, elevated corticoids can also facilitate learning and memory, and current work is exploring whether the higher cortisol observed in all three S. beldingi populations just after emergence function to promote rapid acquisition of survival behaviors.

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“…Michener and McLean (1996) found that in Richardson's ground squirrel (S. richardsonii), 55% of the breeding males disappeared immediately after the breeding season and were not seen again. Sherman and Morton (1984) concluded that in Belding's ground squirrel (S. beldingi), many, if not most, of the disappearances during and following the mating competition were due to death and not dispersal. From the work on the dasyurids in which the impact of male-male interactions has been decoupled from the impact of mating behavior, it is aggressive behavior that increases ACTH and cortisol levels, and ultimately causes death McDonald 1985, Scott 1987).…”

Section: Life History Consequencesmentioning

confidence: 99%

Reproduction at All Costs: The Adaptive Stress Response of Male Arctic Ground Squirrels

Boonstra

McColl

Karels

2001

Ecology

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Abstract. We tested the hypothesis that adult male arctic ground squirrels (Spermophilus parryii plesius) exhibit an adaptive stress response during the mating period that may compromise their survival, whereas males at other times (nonreproductive adult males and juvenile males) have a normal functional stress response. We assessed the physiological responsiveness of the stress axis, of energy mobilization, and of the immune response by subjecting adult breeding males, adult nonbreeding males, and juvenile males to a hormonal challenge and an immunocompetence challenge. At the onset of the breeding season in spring, only 25-30% of the population were males, and of those present during the mating period, half disappeared soon thereafter, and 82% were not replaced by immigrants. Adult breeding males had the highest levels of free cortisol, the lowest maximum corticosteroidbinding capacity, slight dexamethasone resistance, the lowest hematocrit, the lowest number of white blood cells, the highest number of eosinophils, and the poorest ability to respond to the foreign antigen challenge in comparison with the other two male classes. All of these characteristics were indicative of chronic stress in breeding males that may directly compromise their survival. Juvenile males in mid-August also showed many, but not all of these characteristics, indicative of a prolonged period of stress, presumably associated with the period of dispersal. Testosterone levels remained high irrespective of age or breeding condition, decreased when dexamethasone was injected, and increased when ACTH was injected. These latter results are unique in mammals. High testosterone levels and their augmentation with stressors may play a key role in maintenance of aggressive behavior. We conclude that breeding male arctic ground squirrels exhibit an adaptive stress response in which they trade off survival for reproduction. We hypothesize that similar stress responses may have evolved in other species with comparable life histories.

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Demography of Belding's Ground Squirrels

Cited by 216 publications

References 55 publications

Mortality in relation to season, age, sex, and reproduction in Columbian ground squirrels (Spermophilus columbianus)

Mortality in relation to season, age, sex, and reproduction in Columbian ground squirrels (Spermophilus columbianus)

Developmental and geographic variation in stress hormones in wild Belding's ground squirrels (Spermophilus beldingi)

Reproduction at All Costs: The Adaptive Stress Response of Male Arctic Ground Squirrels

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