The effect of island size and isolation on old growth forest habitat and bird diversity in Gwaii Haanas (Queen Charlotte Islands, Canada)

• Published in: Oikos 1995-02, Vol.72 (1), p.115-131
• Main Authors: Martin, J.-L, Gaston, A.J, Hitier, S
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; ANIMAL ECOLOGY; Animal, plant and microbial ecology; Aves; BIODIVERSIDAD; BIODIVERSITE; BIODIVERSITY; BIOLOGIA; Biological and medical sciences; BIOLOGIE; BIOLOGY; BIRDS; BOSQUES; CANADA; DISTRIBUCION NATURAL; DISTRIBUTION NATURELLE; ECOLOGIA ANIMAL; ECOLOGIE ANIMALE; ESPECE; ESPECIES; EVOLUCION DE LA POBLACION; EVOLUTION DE LA POPULATION; Extinct species; FAUNA; FAUNE; Forest canopy; Forest habitats; FORESTS; FORET; Fundamental and applied biological sciences. Psychology; HABITAT; Habitat conservation; HABITATS; ILE; Inlets; ISLANDS; ISLAS; LANDSCAPE; NATURAL DISTRIBUTION; OISEAU; PAISAJE; PAJAROS; PAYSAGE; POPULATION DYNAMICS; SPECIES; Synecology; Terrestrial ecosystems; Understory; VEGETACION; VEGETATION; Vegetation structure; Wildlife habitats
• ISSN: 0030-1299; 1600-0706
• DOI: 10.2307/3546045

We surveyed the vegetation and bird faunas of forests on 65 islands in the Gwaii Haanas archipelago of British Columbia, Canada, ranging in size from 1 to > 100 000 ha, using point counts at a uniform distance from the shore. Variation in habitat structure was correlated with variation in island area and isolation. Only among the smaller islands did the number of bird species recorded decrease with area. As some species became rarer with decreasing island size, others became more common. The distribution of bird species among the islands was correlated with the distribution of habitat features that were consistent with the biology and ecology of each species. In only a minority of species was their distribution related to area and isolation per se rather than to habitat features correlated with island size and isolation. Hence, we considered that variation in habitat structure mediated by area and isolation was the key factor involved in determining the local composition of the bird community. Only for a few species restricted to the largest islands, or missing from the very small islands, were high rates of extinction related to small population size the most parsimonious hypothesis explaining species distribution patterns. Our results emphasise how considering only the relationship between numbers of species and island area can mask all but the roughest species distribution patterns and prevent a deeper understanding of the biology of islands.