Do plant communities exist? Evidence from scaling-up local species-area relations to the regional level

One long tradition in ecology is that discrete communities exist, at least in the sense that there are areas of relatively uniform vegetation, with more rapid change in species composition between them. The alternative extreme view is the Self-similarity concept - that similar community variation occurs at all spatial scales. We test between these two by calculating species-area curves within areas of vegetation that are as uniform as can be found, and then extrapolating the within-community variation to much larger areas, that will contain many 'communities'. Using the Arrhenius species-area model, the extrapolations are remarkably close to the observed number of species at the regional/country level. We conclude that the type of heterogeneity that occurs within 'homogeneous' communities is sufficient to explain species richness at much larger scales. Therefore, whilst we can speak of 'communities' for convenience, the variation that certainly exists at the 'community' level can be seen as only a larger-scale manifestation of micro-habitat variation.