On the Nature of Gondwanan Species Flocks: Diversity of Proteaceae in Mediterranean South-western Australia and South Africa

Abstract

The Proteaceae, a Gondwanan family, are richly represented in South Africa’s Cape Floristic Region (CFR) (331 species, 14 genera) and Australia’s South West Botanical Province (SWBP) (682 species, 16 genera). Both of these regions have mediterranean-type climates, infertile soils, similar geomorphic and climatic histories, and show strong convergences in plant form and function. There are many similarities in the patterns and ecological correlates of diversity in the CFR and SWBP Proteaceae. First, both floras are overwhelmingly endemic, with many large genera and correspondingly high species to genus ratios, indicating massive in situ diversification (species flocks). Second, on both continents, high habitat (mainly edaphic) specialisation leads to similar levels of beta diversity. Third, most species are non-sprouters (i.e. killed by fire) and of intermediate size. There are, however, several divergences in these patterns and correlates. First, in the SWBP, Proteaceae invariably emerge as one of the largest families in florulas, whereas they occupy a much lower rank in the CFR. Second, species numbers in the SWBP peak in landscapes having intermediate levels of annual rainfall, whereas CFR Proteaceae diversity peaks in the wettest areas. Third, local diversity is higher in the SWBP where Proteaceae have exploited a wider array of temporal and spatial habitats than in the CFR. Fourth, despite lower environmental heterogeneity in the SWBP, gamma (geographical) diversity is higher there. Fifth, as a result of higher local and gamma diversity, regional richness in the SWBP is more than double that of the CFR. Finally, sprouting, serotiny, bird-pollination and tall stature are proportionally more important traits in the SWBP than the CFR where most species are low, non-sprouting, myrmecochorous, insect-pollinated shrubs. Subtle differences in the historical and contemporary climates of the two regions have resulted in different processes leading to the origin of these species flocks. In the CFR, milder conditions have favoured non-sprouters (short generation times): species have accumulated largely as a result of lineage turnover. Harsher conditions in the SWBP have favoured sprouters: here species have accumulated as a result of both persistence and turnover.