Early Development and Population Fluctuations in Soay Sheep

Abstract

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Density–dependent selection on horn phenotype in Soay sheep

“…This was supported by evidence that horn type rarely had significant effects in models that included ewe weight as an independent variable. 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).…”

“…We also investigated whether it was possible that the relationship between horn type and weaning rate was a result of relationships between the mother's horn type and the birth date or birth weight of her offspring, both of which are known to affect juvenile survival in Soay sheep (Clutton-Brock et al 1992). There were no significant differences in lambing date between ewes belonging to different horn types (table 4a-d) or between ewes of different coat colour or ADA genotype (table 4e, h).…”

“…Here, we compare the fecundity and rearing success of scurred (SC) and non-scurred (NSC) females of different ages at varying levels of population size. Since fecundity and survival are known to be related to body weight (Clutton-Brock et al 1992, we also investigate whether the relationship between horn morphology and breeding success is generated by differences in body weight, offspring birth date or offspring birth weight between scurred and nonscurred animals.…”

The effect of initial weight of the ewe on later reproductive effort in domestic sheep (Ovis aries)

“…The lasting effect of initial weight of the ewe on the body weight of her lambs in all subsequent litters may affect subsequent offspring survival (Soay sheep: Clutton-Brock, Price et al, 1992; red deer: Guinness et al, 1978;Loison et al, 1999;fallow deer: Asher & Adam, 1985). For the lightest ewes, this may possibly lead to a reduced lifetime reproductive success, even after the effect of longevity is accounted for.…”

Roe deer face competing risks between predators along a gradient in abundance

“…These are mainly from islands or fenced areas where bottom-up effects dominate (e.g., red deer [Cervus elaphus] on the island of Rum, Coulson et al 1997, Soay sheep [Ovis aries] on St Kilda, Clutton-Brock et al 1992, Milner et al 1999 deer [Capreolus capreolus] in French reserves, Gaillard et al 1993Gaillard et al , 1997see Gaillard et al 1998a for a review). However, in most regions a range of predators (both human and non-human) usually occur, especially as large carnivore recovery is proceeding in many parts of Europe and North America.…”