Resource Availability Controls Bird-Assemblage Composition Through Interspecific Aggression

High-value resources are often defended aggressively by consumers, which can alter assemblage structure and dynamics. Here, we describe a system of nectarivorous bird assemblages exploiting pockets of eucalypt woodlands that differ dramatically in flowering and provision of nectar. The behavioral dominant, the Red Wattlebird (Anthochaera curunculata), aggressively reduces the occurrence and activities of other honeyeaters of the genera Lichenostomus and Melithreptus on sites of intense flowering. The latter genera predominate in moderately flowering areas, but few honeyeaters occupy poorly flowering sites. To understand such systems, in which temporal variation in habitat quality can be great, one needs to consider not only the disparity in habitat quality among locations but also the spatial extent of habitats of different quality. Isoleg analysis is a theoretical tool developed to understand how dominant and subordinate species partition habitats as a function of their respective densities. Our results suggest that isoleg analysis needs to be developed with spatial explicitness to capture variation in extent of habitats of different qualities and consequent effects on the usefulness of aggression for domination of resources. La Disponibilidad de Recursos Controla la Composición de los Ensambles de Aves a través de las Agresiones Interespecíficas