Soay Sheep: Dynamics and Selection in an Island Population by T. H. Clutton-Brock, J. M. Pemberton

By T. H. Clutton-Brock, J. M. Pemberton

Not like so much different huge mammals, the Soay sheep inhabitants of Hirta within the St. Kilda archipelago exhibit power oscillations, occasionally expanding or declining by means of greater than 60% in a 12 months. This learn explores the factors of those oscillations and their effects for choice on genetic and phenotypic version in the inhabitants, drawing on reviews over the last two decades of the life-histories and reproductive careers of many sheep. it is going to be crucial analyzing for vertebrate ecologists, demographers, evolutionary biologists and behavioral ecologists.

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While pregnancy has substantial costs to survival in years of high mortality, the number of offspring a female has raised in the previous year has no obvious effect on her weight in August, her probability of conception, her survival through the subsequent winter, or her chance of raising her subsequent offspring (Clutton-Brock et al. 1996). Differences in body weight in August among females that raise different numbers of offspring in the same year are relatively small and vary between age classes: among juvenile mothers, those that raise a lamb are slightly heavier in August than those that fail to do so; among yearlings, there are no significant differences in weight between those that breed successfully and those that fail to breed; Cambridge Books Online © Cambridge University Press, 2009 FIG.

As in wild sheep (Altmann 1970; Schaller 1977), development is rapid and Soay lambs will nibble grass by the time they are five days old. Weaning appears to be relatively early: the frequency and duration of sucking bouts starts to decline when lambs are two weeks old (Robertson et al. 1992) and, by mid June, sucking bouts are short and infrequent, though lambs suck occasionally throughout the rest of the summer. Though weaning is notoriously difficult to define, this suggests that it occurs substantially earlier than in bighorn sheep which, like red deer, continue to suckle their young until autumn or early winter (Geist 1971; Festa-Bianchet 1988a, 1998).

5), suggesting that the accuracy of counts over this period may have deteriorated. Over the whole period of this study, the sheep population of Hirta was entirely unmanaged. However, between 1978 and 1980 Jewell castrated seventy-two male lambs in the Village Bay area and these castrates were still in the population during the early years of the current study (see Chapter 9). 4 Physical characteristics of Soay sheep on St Kilda Soay sheep are small, relative both to wild sheep and to the earliest domestic sheep found in Mediterranean neolithic sites, which Cambridge Books Online © Cambridge University Press, 2009 25 26 t.

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