Introduction

When in its life should an individual first attempt to reproduce? How often should it breed thereafter? How much effort should it invest in each attempt? And does this vary between individuals in the same population? These questions are central to the many studies investigating adaptive life-history strategies, across the taxonomic spectrum, yet detailed answers are provided by few, particularly in large, free-ranging species. This is because comprehensive data on the costs and benefits of reproduction throughout life are essential for the task, but are difficult to collect in the wild, especially for males in polygynous species. With Soay sheep, however, we have the detailed information with which to investigate the reproductive benefits and costs for both sexes, and the way these vary with the environment and individual phenotype.

In Soays, the costs and benefits of reproduction take on even greater significance given the domestic roots of the population. A brief examination of the Soay life-history reveals unusual patterns that have led many to question whether these are simply the maladaptive legacy of past domestication. Soays certainly bear the hallmarks of artificial selection for high productivity (Chapter 1). Both sexes, but particularly males, mature early (Fig. 9.1) despite incurring high survival costs; and females continue to display fatally high fecundity at peak population densities (Chapter 2). These costs suggest that Soays are too fecund for their own good. Yet it remains possible that these are not the result of domestication, but are adaptive responses to their environment.