Sex-ratio variation in Soay sheep

Authored by T Coulson, J Lindstrom, L Kruuk, MC Forchhammer, DW Coltman, T Clutton-Brock

Date Published: 2002

DOI: 10.1007/s00265-002-0545-4

Sponsors: Scottish Natural Heritage National Trust for Scotland

Platforms: No platforms listed

Model Documentation: Other Narrative

Model Code URLs: Model code not found

Abstract

We studied the effects of ecological variables on the birth sex ratio of Soay sheep (Ovis aries) lambs on the island of Hirta, in the St Kilda archipelago, Scotland. Both individual- and population-level models were constructed. In the individual-based model, only population size was significantly associated with the sex of a lamb, with the probability of giving birth to a male lamb being positively associated with population size. However, this model explained a very small proportion of the variance in birth sex ratio. A multiple regression analysis of the annual population birth sex ratio also showed a slight increase in the proportion of males born in years following high autumn population density, but this result was not statistically significant. Population growth rate, Julian birthday, litter size, mother's age and weight, and the weather conditions during the gestation and neonatal period did not explain significant variation in the birth sex ratio.

Tags

selection mammals dominance investment Fluctuations Instability Population-density Red deer Ungulate Breeding success