Increasing returns in the life history of Columbian ground squirrels

Dobson, F. Stephen; Risch, Thomas S.; Murie, Jan O.

doi:10.1046/j.1365-2656.1999.00268.x

Cited by 99 publications

(122 citation statements)

References 88 publications

(120 reference statements)

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“…Litter birthdate (day of the year; 1 January = day 1) was used as a measure of reproductive timing. Maternal body condition at spring emergence was estimated by extracting the residuals from the regression of spring emergence body mass on zygomatic arch breadth (Dobson et al, 1999;Georges et al, 2001;Schulte-Hostedde et al, 2005;Skibiel et al, 2009). Measures of offspring performance included offspring body mass at weaning, growth rate during the lactation period and survival overwinter.…”

Section: Variablesmentioning

confidence: 99%

“…Indeed, previous studies of Columbian ground squirrels have shown that maternal body size and body condition, as well as reproductive timing, impact reproductive performance (King et al, 1991;Dobson et al, 1999;Skibiel et al, 2009). Larger mothers in better condition produce either more young or young that are heavier and grow faster during the lactation period (King et al, 1991;Dobson et al, 1999;Skibiel et al, 2009), and mothers that reproduce earlier have more of their young survive hibernation (Dobson et al, 1999). If these relationships are mediated through the nutritive properties of mother's milk, the levels of milk protein and fat and milk energy density should be particularly important for offspring growth and survival.…”

Section: Introductionmentioning

confidence: 99%

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

Skibiel

Hood

2015

Front. Ecol. Evol.

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Through maternal effects, information about environmental conditions experienced in the maternal generation can be transmitted to subsequent generations. Although maternal effects have been described and quantified in many mammalian species, the underlying causal links are often under-studied. The close association between mother and neonate during the extended period of lactation in mammals provides a unique opportunity for mothers to influence offspring phenotype through nutrient provisioning of milk. The purpose of this study was to examine sources of inter-individual variation in milk composition and impacts on offspring phenotype and survival. Variation in fat content, protein content, and energy density of mother's milk was associated with timing of reproduction. Mothers with intermediate birthdates produced milk that was higher in fat and energy density, but lower in protein than females with early or late birthdates. In turn, the pattern of change in milk composition affected juvenile overwinter survival. The protein content of Columbian ground squirrel milk typically increases to peak lactation and then declines before weaning. Pups consuming milk that was lower in protein in early lactation but then relatively high in protein at peak and late lactation had a higher probability of survival overwinter. Our results indicate that the interplay between the timing of reproduction and lactation performance has consequences for maternal and offspring fitness.

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Section: Variablesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Skibiel

Hood

2015

Front. Ecol. Evol.

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“…However, ␣ in some species inhabiting highly seasonal temperate and arctic environments shows little or no change even under experimental perturbations in the environment (e.g., Dobson 1988, Dobson and Michener 1995, Jouventin et al 1999. Conversely, survival and fertility rates may be extremely labile from habitat to habitat or year to year (e.g., Slade and Balph 1974, Dobson and Murie 1987, Dobson 1988. LTRE analysis combines sensitivity of to life history variables with observed demographic changes and thus quantifies the actual influence of demographic variables when population growth rate changes over time or space (Caswell 1989a, b, 2000, Levin et al 1996, Horvitz et al 1997, Ehrlèn and van Groenendael 1998.…”

Section: Introductionmentioning

confidence: 99%

“…Such experiments may involve manipulations that artificially cause changes in population growth rate, such as food supplementation (e.g., Cole and Batzli 1978, Jansson et al 1981, Dobson 1988, 1995, Guyer 1988, Boutin 1990), decrementing population size (e.g., Slade and Balph 1974, Arcese and Smith 1988), manipulation of predators (e.g., Marcströ m et al 1988, Krebs et al 1995, exposure to pollutants (e.g., Levin et al 1996), or a combination of several factors (e.g., Birch 1953, Taitt and Krebs 1983, Rao and Sharma 1986, Krebs et al 1995. The majority of such studies, particularly those of terrestrial vertebrates, have not applied LTRE analyses (but see Brault and Caswell 1993), although several have documented changes in demographic variables that could cause changes in population growth rate.…”

Section: Introductionmentioning

confidence: 99%

Effect of Density Reduction on Uinta Ground Squirrels: Analysis of Life Table Response Experiments

Oli¹,

Slade²,

Dobson³

2001

Ecology

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Abstract. The effects of natural or experimental environmental perturbations on populations can be diverse, simultaneously affecting several life history variables. Populationlevel responses to such influences frequently are measured as changes in projected population growth rate (). Sensitivity and elasticity analyses can be used to quantify the potential influence of small changes in different life history variables on . When a population is subjected to an experimental treatment, life table response experiment (LTRE) analysis allows decomposition of changes in into contributions due to observed changes in individual life history variables. We investigated the potential and actual influence of demographic characteristics (age at maturity, juvenile and adult survival, fertility, and age at last reproduction) on of Uinta ground squirrels (Spermophilus armatus) in the Wasatch Mountains of Utah, USA. Ground squirrels were studied in three different habitats, before and after an experimental reduction of population size. Survival and reproduction of squirrels increased in response to a reduction in population density. Consequently, increased by at least 21% in two of the three habitats. Population growth rate was potentially most sensitive to changes in age at maturity (␣) and fertility. LTRE analysis revealed that ␣ did not change and contributed nothing to changes in , but changes in fertility were large and contributed most to observed changes in . Age at last reproduction () increased after density reduction but contributed little to observed changes in because of low sensitivity of to changes in . Thus, there was little correspondence between potential influence and actual contributions to observed changes in . We concluded that some demographic variables, notably ␣, had little environmental or phylogenetic scope for reduction, whereas fertility and to some degree survival rates were considerably more plastic under the experimental treatment. Because LTRE analysis incorporates observed changes in life history variables and also sensitivity of to these changes, it worked well for quantifying the response of Uinta ground squirrel populations to density manipulation and holds promise for evaluating alternative management strategies in conservation biology.

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“…The reason for this might be that females in better condition not only survived better but also produced better offspring. Although "increasing returns" (Dobson et al 1999) could explain this result, it could also be interpreted by the timing of the active season: offspring of late-breeding females have a lower chance of survival to yearling age, and mothers have less time to prepare properly for hibernation (Neuhaus 2000b), leading to higher mortality and less reproductive success. This is likely caused by early-reproducing females being heavier than late-breeding females (Neuhaus 2000b life history of Columbian ground squirrels, affecting reproductive success and survival (Murie and Boag 1984;Dobson and Kjelgaard 1985).…”

Section: Discussionmentioning

confidence: 99%

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

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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Increasing returns in the life history of Columbian ground squirrels

Cited by 99 publications

References 88 publications

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

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

Effect of Density Reduction on Uinta Ground Squirrels: Analysis of Life Table Response Experiments

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

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