Does the species/area relationship account for the density/area relationship?

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Abstract
The best‐known macroecological generalisation is the species/area relationship: larger areas contain more species. It has also been observed that the estimated densities of individual species is lower when they are censused over a larger area. Let us call this the density/area relationship. Numerous explanations for the density/area relationship have been proposed – including the idea that the relationship is artefactual. One possible explanation is that it is a necessary consequence of the species/area relationship – after all, if a larger area is to contain more species then the average abundance of individual species must decline. We study a data set that allows us to study both relationships simultaneously. We conclude that the density/area relationship observed for the individual species in this study is consistent with the species/area relationship explanation: in other words, the densities of individual species decline, quantitatively, in the manner required to fit more species into communities with larger areas. We conclude that whatever explains the species/area relationship also explains the density/area relationship and discuss, in particular, the habitat heterogeneity hypothesis.