Resource use, competition, and resource availability in Hawaiian honeycreepers.

Rosenzweig's models predict 3 occasions where resource scarcity will be accompanied by specialization: 1) In the shared-preference case, the dominant may be unable to exploit the poorer patch. If it can, it is likely to drive the subordinate to extinction, leaving a one species system. 2) The subordinate may specialize on clearly inferior resources because the dominant forces it from the better resources. 3) In the distinct-preference case, the scarcity of both resources leads to specialization of both species because interspecific competition (causing specialization) is greater than intraspecific competition (causing generalization). The 3 commonest endemic nectivores in and near the Hawaii Volcanoes National park fed principally on the flowers of Metrosideros collina and Sophora chrysophylla. During the study, Metrosideros went from few flowers per tree to peak bloom, and Sophora did the reverse. Both distinct- and shared-preference cases were noted. The former involved Himatione sanguinea on Metrosideros and Loxops virens on Sophora. The latter involved Vestiaria coccinea (the dominant) and subordinates Himatione and Loxops, with the preferred resources being trees with the highest numbers of flowers. Vestiaria only exploited trees with high numbers of flowers and may have had no alternative. Its competitors were forced onto poorer resources by its presence. These results support the theory's first 2 predictions. The data are also at least consistent with the 3rd prediction. -from Authors Hawaii Volcanoes National Park Metrosideros collina Sophora chrysophylla Himatione sanguinea Metrosideros Loxops virens Vestiaria coccineaDept. of Biological Sci., Texas Tech. Univ., Lubbock, Texas 79409, USA.

Duke Scholars

Author Stuart L. Pimm Environmental Sciences and Policy