Fluctuating trade-offs favour precocial maturity in male Soay sheep.

Although trade-offs between reproductive effort and survival are commonly proposed, empirical studies that quantify the true costs and benefits of breeding activity are rare. This information is crucial, however, for examining the adaptive value of important life history traits such as age at maturity. Here we estimate both the survival cost, and genetic benefits, of precocial male maturity in a highly polygynous naturally limited population of Soay sheep. While we demonstrate that early reproduction does indeed carry a survival cost, we find that young males also achieve unexpectedly high reproductive success and that precocial mating is favoured due to the fluctuating demographic structure of the population.