‘Along a gradient of ecosystems of increasing size, the numbers of species inhabiting those ecosystems increases; rapidly at first, but then more slowly for the larger ecosystems’ (Lomolino (2001) J. Biogeog. 27, 1). Losos and Schluter (2000) Nature 408 explain the relationship as the outcome of the effect of area on immigration and extinction rates. Báldi (2008) J. Biogeog. 35, 4 argues that habitat heterogeneity overrides the species–area relationship.