Overcompensation and population cycles in an ungulate

Grenfell, Bryan T.; Price, Owen; Albon, S. D.; Glutton-Brock, T. H.

doi:10.1038/355823a0

Cited by 144 publications

(124 citation statements)

References 15 publications

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“…Similarly, lambs born at relatively low birth weights were more likely to die before weaning than heavier ones (Clutton-Brock et al 1992), and the weaning rates of scurred females may have been higher because they tended to produce heavier lambs when population density was high (figure 5). Associations between horn type and weight may also have contributed to the differences in survival between scurred and non-scurred animals, for heavier adults, like heavier lambs, were more likely to survive the winter, especially when population density was high (Grenfell et al 1992;Marrow et al 1996;Clutton-Brock et al 1997).…”

Section: Discussionmentioning

confidence: 99%

Density–dependent selection on horn phenotype in Soay sheep

Clutton‐Brock

Wilson

Stevenson

1997

Phil. Trans. R. Soc. Lond. B

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In the naturally regulated population of Soay sheep Ovis aries L.) on Hirta (St Kilda), 12 % of males and 24% of females have scurred horns. This trait reduces the competitive ability of males in the mating season but is associated with higher overwinter survival rates in both sexes (Moorcroft et al . 1996). In this paper, we show that scurred females also show higher conception rates and weaning rates than non–scurred ones, and that these differences are associated with heavier maternal body weight as well as higher birth weights of offspring. Selection pressures favouring scurredness in females vary with population density and are generally more pronounced among younger animals than adults. We discuss these results with reference to recent suggestions that temporal fluctuation in selection pressures may help to maintain genetic diversity within populations. We suggest that selection against scurredness operating through male mating success is opposed by selection favouring this trait, operating through the breeding success of females and the survival of both sexes.

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Section: Discussionmentioning

confidence: 99%

Density–dependent selection on horn phenotype in Soay sheep

Clutton‐Brock

Wilson

Stevenson

1997

Phil. Trans. R. Soc. Lond. B

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“…Now we apply the measure of complexity K (Eq. (2)) to the model given by equation (19). It is straightforward to show that λ < 0.…”

Section: Sheep Population Modelmentioning

confidence: 99%

“…In Ref. [14] a nonlinear time-series model is constructed from sheep populations on two islands in the St. Kilda archipelago [18,19]. We investigate the complexity of this model using the new technique.…”

Section: Introductionmentioning

confidence: 99%

Intrinsic chaos and external noise in population dynamics

González

Trujillo

Escalante

2003

Physica A: Statistical Mechanics and its Applications

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We address the problem of the relative importance of the intrinsic chaos and the external noise in determining the complexity of population dynamics. We use a recently proposed method for studying the complexity of nonlinear random dynamical systems. The new measure of complexity is defined in terms of the average number of bits per time-unit necessary to specify the sequence generated by the system. This measure coincides with the rate of divergence of nearby trajectories under two different realizations of the noise. In particular, we show that the complexity of a nonlinear time-series model constructed from sheep populations comes completely from the environmental variations. However, in other situations, intrinsic chaos can be the crucial factor. This method can be applied to many other systems in biology and physics.

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“…In the summer of 1932, after evacuation of humans and all their domestic stock, 107 sheep were captured on Soay (20 rams, 44 ewes, 21 ewe lambs and 22 ram lambs (all of which were castrated)) and released onto the larger adjacent island of Hirta (637 ha) (Boyd, 1953). By 1952, the unmanaged Hirta population had reached an estimated size of 1114 sheep (Boyd, 1953) and since regular censusing began in 1955, has experienced frequent population crashes, sometimes occurring as often as one year in three, in which up to 70 per cent of the population dies Clutton-Brock et a!., 1991Grenfell et al, 1992). These population dynamics probably result from the fact that in a single breeding season the sheep population is able to increase far above the winter carrying capacity of the island (Grenfell et al, 1992);…”

Section: Study Populationmentioning

confidence: 99%

“…For a period in the 1970s and since 1985 (Clutton-Brock et al, 1991Grenfell et a!., 1992) the Soay sheep living in the Village Bay area of Hirta (a 170 ha bowl of land to the south-east of the island which holds around 30 per cent of the total population) have been intensively monitored. An interdisciplinary study aims to understand the population dynamics and identify the causes and consequences of variation in individual reproductive success.…”

Section: Study Populationmentioning

confidence: 99%

Extensive protein and microsatellite variability in an isolated, cyclic ungulate population

1995

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We investigated polymorphism at protein and microsatellite DNA loci in an isolated, umnanaged and cyclic population of Soay sheep on the island of Hirta, St. Kilda. Extensive molecular variation was revealed at both protein loci (mean heterozygosity 7.78 per cent) and microsatellite loci (mean heterozygosity 50.93 per cent). Typically, large mammals possess limited protein variation and we were surprised to observe such a level of protein heterozygosity, particularly considering the genetic history of the Hirta population. Indeed, compared to other mammals, Soay sheep lie within the top 17 per cent of the distribution of average protein heterozygosities. We discuss the level of protein heterozygosity in the context of other mammalian species, other breeds of sheep and the genetic history of Soay sheep. Possible explanations for a large average and interlocus variance in protein heterozygosity are proposed. Although little data are available from other studies to compare with microsatellite DNA variability in this population, we discuss the potential application of microsatellite markers to interpopulation and interspecific genetic studies.

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Overcompensation and population cycles in an ungulate

Cited by 144 publications

References 15 publications

Density–dependent selection on horn phenotype in Soay sheep

Density–dependent selection on horn phenotype in Soay sheep

Intrinsic chaos and external noise in population dynamics

Extensive protein and microsatellite variability in an isolated, cyclic ungulate population

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