Population Fluctuations, Reproductive Costs and Life-History Tactics in Female Soay Sheep

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Animal Ecology. Summary 1. Though models of life-history decisions are traditionally based on age-related changes in the costs and benefits of reproduction, in nature both costs and benefits vary with individual differences in phenotype as well as with environmental changes. Using long-term records of individual reproduction and survival in the Soay sheep of St Kilda, we show that the costs and benefits of breeding to animals of different weight categories vary with population density.3. Subsequently, we use stochastic dynamic programming to predict the optimal fecundity of animals belonging to each category at high and low population density. Optimal strategies of fecundity vary with population density as well as between different weight categories of sheep. However, there is no evidence that the sheep track density-related changes in optimal fecundity. Instead, their behaviour approximates to an average, weight-related optimum that is well adapted to the range of conditions that they encounter.

Local effects of inbreeding on embryo number and consequences for genetic diversity in Kerguelen mouflon

“…Based on the number of definite incisors, all these females were age 2 and older, but we could not determine the age of females with precision. In other feral sheep, ewes between 2 and 6 years of age have identical fecundity (Clutton-Brock et al 1996). Given the short lifespan observed here (Kaeuffer et al 2007a), few ewes probably reached 6 years of age.…”

“…The genetics of litter size coupled with the cyclic dynamics could play a central role in promoting genetic variation (Hedrick 2007). Thus, homozygous twinning ewes may suffer higher costs of reproduction and increased mortality during population's crashes (Clutton-Brock et al 1996), which may increase average heterozygosity in the population over time. This cyclic selection, acting only on females, could contribute to the maintenance of genetic polymorphism in wild populations (Reinhold 2000;Hedrick 2007).…”

Male mate choice influences female promiscuity in Soay sheep

“…Body mass is known to be a key variable influencing female survival and their ability to raise offspring (Clutton Brock et al 1996). Such variation in female quality is also predicted to promote the evolution of male mate choice (Owens & Thompson 1994).…”

Characterizing demographic parameters across environmental gradients: a case study with Ontario moose (Alces alces)

“…However, few studies have actually compared variation in these demographic parameters across broad spatial gradients (but see Saether et al 2008). This is at least partly attributable to the relative difficulty of obtaining sufficient time series data on abundance across large areas, which limits most studies of demography to a single population or a small number of discrete subpopulations in a relatively small area (e.g., Clutton-Brock et al 1996, MacCracken et al 1997, Coulson et al 2001, Stephenson et al 2006. Those few studies with sufficient data have often focused on characterizing spatial variation in temporal population dynamics (i.e., cyclic vs. non-cyclic populations) rather than sources of spatial variation in key demographic parameters (e.g., Caughley et al 1984, Forchhammer et al 1998, Stenseth et al 2002, Lima et al 2003.…”