Figure 3.

The correlation between the Hairston et al. (2005) population-based method and Pelletier et al.'s (2007a) individual-based method was fairly strong: years when mean birth weight decreases the most are also years when the summed individual contributions to population growth are the largest in the Soay sheep population. The methods differ markedly, being linked by a chain of responses (see main text for details). The individual-based method is quantified as the summed contribution of juvenile mass to population growth; the Hairston et al. (2005) method is the absolute rate of change in mean juvenile mass.