Fig. 4. Changes in the niche centre, amount of food consumed and food properties between the short-term and long-term assays of food preferences. The plots show the estimates and standard error of the predicted responses of the model. The amount of total food, calories and nutrients consumed is in grams. Results for PCoA 2 are shown in Fig. S3.
Unlike niche centre, niche breadth only changed between the short and long-term assays in pigeons from MOIA (Fig. 5 ). In the short-term assays, their WIC was smaller than that of individuals from BCN and those raised in captivity. One year after, however, WIC had expanded to levels similar to those of the other two groups. Although individual niche expansion was also accompanied by an increase in population niche breadth (WIC), the ratio WIC/TNW increased around 48% from the short- to the long-term assays. This means that individuals used a larger fraction of the resources exploited by the entire population than they did one year before. While individuals from BCN and those raised in captivity did not show similar niche expansions, the ratio WIC/TNW also increased substantially as a result of a decrease in the population niche breadth. Thus, the degree of resource specialization within the population diminished over time.