Components of Niche Width in a Territorial Bird Species: Habitat Utilization in Males and Females of the Chaffinch (Fringilla coelebs) on Islands and Mainland

Publisher Website
Google Scholar
Abstract
The effect of interspecific competition on intrapopulation variation in traits (morphological and/or behavioral) involved in resource utilization was discussed. Decreased intensity of interspecific competition will lead to an increase in variation within a population. This increase in variation may be continuous or discontinuous (e.g., sexual dimorphism). For a territorial species within a given macrohabitat the increased variation is expected to take the form of sexual dimorphism. This prediction was tested by a comparison of the habitat utilization of the chaffinch, a territorial species, on small islands in a lake and the surrounding mainland. Both the number of potentially competing species and food (arthropod) abundance decreased from mainland to islands; there was a greater decrease in competitors than in food abundance. Components of niche width did show different patterns on the islands and the mainland; on the islands, but not on the mainland, there were significant differences between males and females in habitat utilization. Thus, on the islands, as compared to the mainland, the between-sex component of the population niche width was relatively large and the within-sex component relatively small. Sexual dimorphism entails an adaptive increase in variation within the population in that it reduces intrapair competition.