Despotic Distribution, Unequal Reproductive Success, and Population Regulation in the Jay Garrulus Glandarius L.

Abstract

A population of European Jays (Garrulus glandarius L.) in south—central Sweden occupied territories in most forest habitats. However, there was a strong preference for dense forest, characterized by trees older than 10 yr and a composition of >30% Norway spruce (Picea abies Karst.). Individuals having territories in this preferred habitat exhibited the highest breeding success. This supports the Fretwell—Lucas model of ideal—despotic distribution. Differences in nest predation, and perhaps also in food abundance and adult predation, caused higher breeding success in forest dominated by Norway spruce than in other forests. Despots were not distinguished by size, but age might be more important in long—lived species like the Jay. Territoriality means that certain individuals monopolize some resources at the expense of other individuals, which results in unequal resource partitioning. Following current ideas of population regulation due to unequal resource partitioning in a heterogeneous environment, I discuss the effect of having the preferred habitat unequally divided among individuals, which will result in a density—dependent breeding output, and also suggests a possible system of population regulation.