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Mediterranean- and tropical-climate regions harbour the richest regional-scale floras globally. Until recently, however, comparisons of their diversities have been hindered by a lack of comprehensive inventories of tropical floras. Using taxonomically verified floras, we analyse area-adjusted plant diversities of five Mediterranean- and 35 tropical-climate regions to determine which are the most species-rich regions on Earth. On average, the Neotropics and tropical Southeast Asia support the most diverse floras globally. However, the area-adjusted diversities of the richest floras in these tropical regions are matched by those of two Mediterranean-climate floras, namely the Cape (second richest) and Mediterranean Basin (sixth richest). Except for Madagascar and Burundi, the Afrotropical regions were substantially less diverse than other tropical floras and half of the Afrotropical floras were poorer than the least diverse Mediterranean-climate region, namely Central Chile. We evaluate the likely ecological and evolutionary drivers of these plant diversity patterns in terms of three hypotheses that are apposite for global scale comparisons, namely water-energy dynamics, biome stability, and ecological heterogeneity. Water-energy dynamics appear to have little influence in explaining these diversity patterns: nodes of high global plant diversity are associated with climates that support year-round plant production (tropical climates) and those where the growing season is constrained by a winter rainfall regime (Mediterranean-type climates). Moreover, while the Afrotropics have higher primary production than the Neotropics and Southeast Asian tropics, they have markedly lower plant diversity. Instead, these patterns appear to be consistent with the hypothesis that the synergy of historical biome stability (reducing extinction rates) and high ecological heterogeneity (promoting speciation rates) better explain global patterns of regional-scale plant diversity.

Despite decades of broad interest in global patterns of biodiversity, little attention has been given to understanding the remarkable levels of plant diversity present in the world's five Mediterranean-type climate (MTC) regions, all of which are considered to be biodiversity hotspots. Comprising the Mediterranean Basin, California, central Chile, the Cape Region of South Africa, and southwestern Australia, these regions share the unusual climatic regime of mild wet winters and warm dry summers. Despite their small extent, covering only about 2.2% of world land area, these regions are home to approximately one-sixth of the world vascular plant flora. The onset of MTCs in the middle Miocene brought summer drought, a novel climatic condition, but also a regime of recurrent fire. Fire has been a significant agent of selection in assembling the modern floras of four of the five MTC regions, with central Chile an exception following the uplift of the Andes in the middle Miocene. Selection for persistence in a fire-prone environment as a key causal factor for species diversification in MTC regions has been under-appreciated or ignored. Mechanisms for fire-driven speciation are diverse and may include both directional (novel traits) and stabilizing selection (retained traits) for appropriate morphological and life-history traits. Both museum and nursery hypotheses have important relevance in explaining the extant species richness of the MTC floras, with fire as a strong stimulant for diversification in a manner distinct from other temperate floras. Spatial and temporal niche separation across topographic, climatic and edaphic gradients has occurred in all five regions. The Mediterranean Basin, California, and central Chile are seen as nurseries for strong but not spectacular rates of Neogene diversification, while the older landscapes of southwestern Australia and the Cape Region show significant components of both Paleogene and younger Neogene speciation in their diversity. Low rates of extinction suggesting a long association with fire more than high rates of speciation have been key to the extant levels of species richness.

Background and Aims The prevailing view from the areocladogenesis of molecular phylogenies is that the iconic South African Cape Proteaceae (subfamily Proteoideae) arrived from Australia across the Indian Ocean during the Late Cretaceous (100–65 million years ago, Ma). Since fossil pollen indicates that the family probably arose in North-West Africa during the Early Cretaceous, an alternative view is that it migrated to the Cape from North-West-Central Africa. The plan therefore was to collate fossil pollen records throughout Africa to determine if they are consistent with an African (para-autochthonous) origin for the Cape Proteaceae, and to seek further support from other palaeo-disciplines. Methods We used palynology (identity, date and location of records), molecular phylogeny and chronogram preparation, biogeography of plate tectonics, and palaeo-atmospheric and ocean circulation models. Key Results Our collation of the rich assemblage of Proteaceae palynomorphs stretching back to 107 Ma (Triorites africaensis) in North-West Africa showed its progressive overland migration to the Cape by 75–65 Ma. No key palynomorphs recorded in Australia–Antarctica have morphological affinities with African fossils but specific clade assignment of the pre-Miocene records is not currently possible. The Cape Proteaceae encompass three molecular-based clades (tribes) whose most recent apparent ancestors are sisters to those in Australia. However, our chronogram shows that the major Adenanthos / Leucadendron -related clade, originating 54–34 Ma, would have 'arrived' too late as species with Proteaceae affinities were already present ~20 million years earlier. The Franklandia / Protea -related clade arose 118–81 Ma so its distinctive pollen should have been the foundation for the scores of palynomorphs recorded at 100–80 Ma, but it was not. Also, the prevailing winds and ocean currents trended away from South Africa rather than towards, as the 'out-of-Australia' hypothesis requires. Based on the evidence assembled here, we list three points favouring an Australian origin and nine against; four points favouring an Antarctic origin and seven against; and nine points favouring a North-West-Central African origin and three against. Conclusions We conclude that a gradual migration of the Proteaceae from North-West-Central Africa southeast→south→southwest to the Cape and its surroundings occurred via adaptation and speciation during the period 95–70 Ma. We caution that incorrect conclusions may be drawn from literal interpretations of molecular phylogenies that neglect the fossil record and do not recognize the possible confounding effects of selection under matched environments leading to parallel evolution and extinction of bona fide sister clades. [ABSTRACT FROM AUTHOR]

Paleoanthropologists (scientists studying human origins) universally recognize the evolutionary significance of ancient climates and environments for understanding human origins. Even those scientists working in recent phases of human evolution, when modern humans evolved, agree that hunter-gatherer adaptations are tied to the way that climate and environment shape the food and technological resource base. The result is a long tradition of paleoanthropologists engaging with climate and environmental scientists in an effort to understand if and how hominin bio-behavioral evolution responded to climate and environmental change. Despite this unusual consonance, the anticipated rewards of this synergy are unrealized and, in our opinion, will not reach potential until there are some fundamental changes in the way the research model is constructed. Discovering the relation between climate and environmental change to human origins must be grounded in a theoretical framework and a causal understanding of the connection between climate, environment, resource patterning, behavior, and morphology, then move beyond the strict correlative research that continues to dominate the field.