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1

Electronic Resource

The costs of reproduction in female columbian ground squirrels (1987)

Murie, J. O. ; Dobson, F. S.

Springer

Oecologia 73 (1987), S. 1-6

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ISSN: 1432-1939

Keywords: Spermophilus ; Cost of reproduction ; Survivorship ; Reproductive success ; Ground squirrel

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary The cost of reproduction for female Columbian ground squirrels was assessed using seven years of data from three populations in southwestern Alberta, Canada. Short-term costs, measured as reduced survival or lowered subsequent fecundity, were not directly associated with whether a female reproduced or not, nor with the females' litter size. In one of the populations, females that first reproduced as yearlings had slightly shorter lifespans, but almost 1.5 times the lifetime reproductive success, compared to those that first reproduced when older. Although short-term reproductive costs were not apparent from our data, we cannot conclude that reproduction was not costly. Such costs might exist but be masked by females' adjusting reproductive investment to their body condition. A weak association of spring (minimum) body weight of females and subsequent reproduction supported this possibility, as did correlated increases in body weight and litter size in a population given supplemental food.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00376969

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2

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Regulation of population size: evidence from Columbian ground squirrels (1995)

Dobson, F. Stephen

Springer

Oecologia 102 (1995), S. 44-51

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ISSN: 1432-1939

Keywords: Demography ; Density ; Food resources ; Population regulation ; Spermophilus

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The hypothesis that food resources regulate population size was tested in Columbian ground squirrels, Spermophilus columbianus, from 1981 to 1986 in southwestern Alberta, Canada. Two replicate populations received supplemental food resources from 1981 to 1983, and were subsequently monitored until 1986. Two reference (unmanipulated) populations were monitored throughout the 6 years. During the experiment, dramatic increases in population size of about 500% occurred. After supplementation, spring populations declined by about 20% per year, under conditions that produced stressful shortages of food (as evidenced by significant decreases in body mass of ground squirrels). The demographic process that contributed most to increasing and decreasing experimental populations was production of yearlings, through changes in reproductive success and survival of young. Changes in migration contributed secondarily to changes in population size, and changes in adult survival were least important. While similarities of demographic processes were evident between replicates during population increases, a dramatic decrease in survival of young contributed to population decline at one replicate, and “normal” levels of reproduction and survival were sufficient to produce a decline in the other replicate. Demographic mechanisms may vary, but population regulation of mammalian populations appears strongly dependent on food resources.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00333309

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3

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Environmental influences on the sexual dimorphism in body size of western bobcats (1996)

Dobson, F. Stephen ; Wigginton, John D.

Springer

Oecologia 108 (1996), S. 610-616

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ISSN: 1432-1939

Keywords: Body size ; Climate ; Geography ; Lynx ; Sexual dimorphism

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Sexual size dimorphism might be influenced by environmental constraints on sexual selection or by intraspecific competition between males and females. We studied bobcats (Lynx rufus) in collections of museum specimens from western North America to examine these hypotheses. Structural body size was estimated from several measurements of the skull, ln-transformed and indexed through principal components analysis. Sexual dimorphism in body size was estimated from the difference in size index of males and females, and compared to geographic and climatic variables associated with biotic provinces (ecoregions). Of several climatic variables that were associated with bobcat body size, only seasonality of climate was associated with sexual dimorphism. Sexual size dimorphism, longitude, elevation, and seasonality were intercorrelated. As longitude decreased (moving inland from west-coastal ecoregions), sexual dimorphism decreased with the increased elevation and seasonality of continental climates of the Rocky Mountains. We suggest that increased seasonality and the need for fasting endurance by females may place constraints on the degree of sexual dimorphism in bobcats. Sexual dimorphism of body size and sexual size dimorphism of trophic structures (teeth) exhibited a strong positive association over geography, thus indirectly supporting the hypothesis that intrasexual competition for prey could account for the geographic variation in sexual size dimorphism. Thus, both environmental constraints on sexual selection of body size and intersexual competition were supported as possible explanations of the degree of sexual size dimorphism that occurs in populations of bobcats.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00329033

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4

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Measures of gene flow in the Columbian ground squirrel (1994)

Dobson, F. Stephen

Springer

Oecologia 100 (1994), S. 190-195

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ISSN: 1432-1939

Keywords: Allozymes ; Dispersal ; F-statistics ; Immigration ; Spermophilus

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract From analyses of published data and a review of the literature, I studied indirect and direct measures of gene flow among populations of Columbian ground squirrels, Spermophilus columbianus. New analyses were used to examine an allozyme data set (seven polymorphic loci) that had been collected by Zammuto and Millar (1985a) from six populations of ground squirrels that were spread over 183 km. G-tests indicated significant variation in allele frequencies among populations, but F-statistics revealed relatively little population differentiation (average F ST=0.026). F ST values were used to estimate rates of gene flow indirectly and indicated fairly high rates of gene flow (average N e m=13.5). Recorded dispersal distances of individual ground squirrels were fairly short (most〈4 km, maximum recorded distance was 8.5 km), and the minimum distance between populations used to create the allozyme data set was about 25 km. Thus, direct dispersal among the populations in the allozyme data set was highly unlikely. Small genetically effective populations may have experienced high rates of migration over short distances (about 43% of adults in local populations were immigrants), however, resulting in homogeneous allele frequencies over the geographic range. This explanation provides an alternative to invoking gene flow in the recent past to explain discrepancies between dispersal distances in the field and homogenization of allele frequencies over large ranges, Mammalian species that have virtually complete dispersal of subadult males from the natal area might be expected to exhibit relatively high rates of gene flow, regardless of actual dispersal distances. Genetically effective populations may be much smaller than more extensive ecological populations and experience higher rates of gene flow.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00317146

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5

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The damping of a group of sea waves (1971)

Dobson, F. W.

Springer

Boundary layer meteorology 1 (1971), S. 399-410

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ISSN: 1573-1472

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract The signals from a wave probe, a buoy-mounted sensor at the water surface, and a three-component sonic anemometer were recorded during the passage of a discrete group of waves which were travelling against a light wind. Cross spectra between the wave signals and the pressure and sonic anemometer signals were obtained and are interpreted.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00184780

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