Unravelling the plant biodiversity hotspots of Mediterranean-type ecosystems

What evolutionary mechanisms lie behind the unusually high plant diversity in Mediterranean-climate biodiversity hotspots?

GBIF-mediated data resources used : 9,762 species occurrences
Pincushion hakea (Hakea laurina)
Pincushion hakea (Hakea laurina) by linger via iNaturalist. Photo licensed under CC BY-NC 4.0.

Although much lower in productivity than tropical regions, some ecosystems with Mediterranean-like climates (MTE) are biological hotspots with species diversity comparable to that of the tropics. The evolutionary and ecological mechanisms behind this phenomenon are poorly understood.

In this study, researchers test the hypothesis that processes similar to those driving diversity in the tropics (known as the Tropical Niche Conservatism Hypothesis) could explain the MTE hotspots. Focusing on four large plant genera with most of their species found in two MTE hotspots - the floristic regions of 1) the Greater Cape in South Africa and 2) Southwest Australia - the researchers estimated the environmental niches of 136 species using occurrence data from GBIF combined with climate and soil data.

Using biogeographic modeling to infer ancestral areas, they designated species as being either hotspot or nonhotspot in origin, and compared the tempo and modes of niche evolution between the groups. Their results suggest that niche conservatism, too, is the underlying process in which plant diversity in MTEs results from longer time for speciation.

Skeels A and Cardillo M (2017) Environmental niche conservatism explains the accumulation of species richness in Mediterranean-hotspot plant genera. Evolution. Wiley-Blackwell 71(3): 582–594. Available at: https://doi.org/10.1111/evo.13179.