Abstract
The diversification dynamics of the Australian temperate flora remains poorly understood. Here, we investigate whether differences in plant richness in the southwest Australian (SWA) biodiversity hotspot and southeast Australian (SEA) regions of the Australian continent can be attributed to higher net diversification, more time for species accumulation, or both. We assembled dated molecular phylogenies for the 21 most species-rich flowering plant families found across mesic temperate Australia, encompassing both SWA and SEA regions, and applied a series of diversification models to investigate responses across different groups and timescales. We show that the high richness in SWA can be attributed to a higher net rate of lineage diversification and more time for species accumulation. Different pulses of diversification were retrieved in each region. A decrease in diversification rate across major flowering plant lineages at the Eocene-Oligocene boundary (ca 34 Ma) was witnessed in SEA but not in SWA. Our study demonstrates the importance of historical diversification pulses and differential responses to global events as drivers of present-day diversity. More broadly, we show that diversity within the SWA biodiversity hotspot is not only the result of recent radiations, but also reflects older events over the history of this planet.
Highlights
Biodiversity is unevenly distributed across the globe
Diversification dynamics across the two southern Australian mesic regions are primarily driven by different diversification pulses that correlate with major shifts in regional and global climate
Our meta-analysis indicated a net decrease in diversification rate for the southeastern Australia (SEA) flora compared with southwest Australian (SWA) at the E–O boundary
Summary
Biodiversity is unevenly distributed across the globe. In an analysis of both richness and threats, Myers et al [1] and Williams et al [2] identified 36 global biodiversity hotspots. High species richness in other hotspots, such as the mediterranean climate regions of South Africa and southwestern Australia, have been attributed to a combination of recent radiations [8,9], lower extinction rates [10,11,12] and sustained accumulation of lineages over time [13,14,15]. The southwest Australian (SWA) hotspot has the lowest average net diversification rate and a disproportionate number of old lineages compared with other regions of high plant diversity [3,13]. Most species-rich genera and families in SWA are widely distributed across temperate southern Australia, occurring in mesic southeastern Australia (SEA) (figure 1m). But different, pulses of diversification in the two regions, demonstrate the importance of these pulses and their effects on present-day diversity and provide insight into historical drivers of these pulses
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