It is often claimed that we do not understand the forces driving the global diversity gradient.
However, an extensive literature suggests that contemporary climate constrains terrestrial
taxonomic richness over broad geographic extents. Here, we review the empirical literature
to examine the nature and form of the relationship between climate and richness. Our goals
were to document the support for the climatically based energy hypothesis, and within the
constraints imposed by correlative analyses, to evaluate two versions of the hypothesis: the …