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Impoverishment in the Bird Community of a Finnish Archipelago: The Role of Island Size, Isolation and Vegetation Structure
Jean-Louis Martin and Jacques Lepart
Journal of Biogeography
Vol. 16, No. 2 (Mar., 1989), pp. 159-172
Published by: Wiley
Stable URL: http://www.jstor.org/stable/2845090
Page Count: 14
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The bird communities of forty-nine islands from the Sipoo archipelago are compared to the bird community of a nearby mainland forest. The islands were uniformly covered by forest habitat similar to the mainland forest. Thirteen island classes were defined in relation to island area and isolation. The bird communities were censused by 20 mn point-counts. Nine habitat variables were recorded for each point-count and between bird communities differences were analysed in relation to variations in island area, island isolation and vegetation structure. Variations in bird species distribution owing to habitat structure differences, or other factors independent of insularity, are overwhelmed by a general decrease in bird species observation frequencies with decreasing island area and increasing isolation. At the bird species level only some cases of frequency fluctuations are explained by differences in habitat structure. These differences explain mostly small fluctuations within a more general trend directly or indirectly linked with island area and/or isolation. The hypothesis of a random sampling of these insular bird communities out of the local (mainland) species pool does not seem to apply to the entire bird community. Effects of insularity at all levels of the living communities found on these islands may explain a good part of the observed pattern.
Journal of Biogeography © 1989 Wiley