Köchy, M., and H. Rydin (1997)
The increase of island species richness with area can be explained by an increase in habitat diversity or by an equilibrium of species immigration and extinction. We examined vascular plant species richness in 39 sites (24 habitat islands, 7 'habitat peninsulas' and 8 comparable 'mainland' sites). We sampled at three scales: whole sites, meadows within sites and quadrats (4 m x 4 m) within meadows. All sites (10 - 104 m2) contained natural vegetation within arable fields in east-central Sweden. There was a strong correlation between species richness and area for whole sites and for meadows. There was no correlation, however, between species richness in quadrats and site area. The difference between site and meadow results on one side and quadrat results on the other suggests that species richness increases with whole site area primarily because large sites are more diverse than smaller ones. Species-area relationships did not differ between islands, peninsula and mainland sites. Thus, patterns of species richness on our sites were more consistent with habitat diversity than an immigration-extinction equilibrium.