Fig. 1.

Hypothetical examples depicting the possible scenarios by which the ecological opportunity hypothesis, which focuses upon gradients in, for example, topographic diversity, seasonality, and water–energy, and/or the age and area hypothesis, here considered in terms of Late Pleistocene climate and biome stability, can explain plant diversity patterns in the CFR. Areas where both hypotheses would influence diversity achieve the highest values for all diversity metrics (A), except possibly for phylogenetic beta diversity (PBD), the value of which will vary depending on the proportion of range-restricted species and their distribution on the tree. In A, scenario 1 has a high proportion of range-restricted, recently diverged species and thus a low PBD, while in scenario 2 the range-restricted species are predominantly older, resulting in a higher PBD. The effect of the age and area hypothesis alone is shown in B, while the outcomes of the ecological opportunity hypothesis alone are depicted in C. In B and C, PBD will increase with higher proportions of range-restricted species but will be less affected by the distribution of these species (contrary to the situation in A); range-restricted taxa are expected to be more prevalent in C. An area that is ecologically homogeneous and with unstable biome and climate (D) has the lowest diversity metrics. Black dots and circles depict the distribution on the phylogenetic tree of the species present in each scenario.