An Ecological Analysis of Chaparral and Pine Forest Bird Communities on Santa Cruz Island and Mainland California
1974
Yeaton, Richard Ivan
A comparative study of chaparral and pine forest bird communities on Santa Cruz Island and adjacent mainland areas was made during 1969—72. Five fewer species occurred in the island chaparral bird community and four fewer species in the island pine forest bird communities. Changes in bird species composition occurred most notably in the island pine forest, which is utilized by species commonly found in the chaparral. No significant changes in niche breadths were observed for the communities in general; however, a slight tendency for increased foraging height diversities on the island was observed. Average niche overlap values between species present on both the mainland and the island are greater on the island, mainly because of an increased vertical habitat overlap. By use of the observed mainland densities and competition coefficients composed of mainland overlap values, island densities were predicted for four bird species that show greater densities in the island chaparral community. Hence, competitive release occurs in the chaparral bird community. All communities studied are in a state of equilibrium, and the island communities are at least approaching a state of saturation equivalent to that of the mainland communities.
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