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New progress in exploring the mechanisms underlying extraordinarily high biodiversity in global hotspots and their implications for conservation

Update time: 01/22/2022
 The extraordinarily high species richness makes global biodiversity hotspots the top priorities for conservation planning and management, and natural laboratories for biological studies. The term ‘biodiversity hotspot’ was proposed by Norman Myers, and the original 25 hotspots covered 2.1 million square kilometres, or 1.4% of the Earth's land surface (Myers, 1988; Myers et al., 2000). The updated range of global biodiversity hotspots included additional nine hotspots and increased the total range to 3.3 million square kilometres, 2.3% of the land surface (Mittermeier et al., 2004). These areas are characterized by a high level of species richness, endemism and anthropogenic pressures. In particular, they maintain 77% of all endemic plant species, 43% of vertebrates (including 60% of threatened mammals and birds), and 80% of all threatened amphibians. In addition to those terrestrial ecosystem's hotspot, Roberts et al. (2002) identified the 10 richest centers of endemism covering up to 15.8% of the world's coral reefs (0.012% of the oceans), but include between 44.8% and 54.2% of all restricted-range marine species. The natural resources of all hotspots are of great significance for developing agriculture, forestry, livestock and fisheries, as well as for scientific research and education. However, the earth is experiencing the sixth mass extinction, with current extinction rates are ~1000 times higher than natural background rates of extinction and future rates are likely to be 10,000 times higher (Ceballos et al., 2020; De Vos et al., 2015). Accelerated species loss under climate change and anthropogenic disturbance call for research on the mechanisms underlying the generation and maintenance of biodiversity in these hotspots, which can help support management and conservation decision-making (Margules & Pressey, 2000).

The extraordinary species diversity in biodiversity hotspots is often attributed to an accumulation of narrow-ranged/endemic species through elevated speciation rates, and/or preservation of species over a long time through low extinction rates. As such, biodiversity hotspots usually host ancient and young species and serve as “museums, where older lineages persist through evolutionary time, and “cradles”, where new species continue to be generated at the same time, as well as “accumulation centers”, which host a high proportion of species that migrate from nearby regions (Feijó, Ge, Wen, Cheng et al., 2022). Many of them are now relic taxa or living fossils that have historically flourished tremendously (Scheyer et al., 2013; Sun et al., 2020). Moreover, speciation rates are arguably higher in tropical regions (Brown, 2014; Schluter & Pennell, 2017). Given the current era of rapid biodiversity loss, there is an urgent need to understand the mechanisms driving the biodiversity dynamics in biodiversity hotspots because these results could guide make conservation actions to protect species under threat from rapid environmental changes and extensive human impacts.

To achieve this goal, we have organized this special issue in Diversity and Distributions that aims to explore patterns of community-level diversity in biodiversity hotspots, and identify key factors that determine phenotypic and genetic diversity. We also seek to better understand historical or contemporary processes that shape speciation and adaptation in different taxa, and illustrate the current diversity patterns of many taxa. Utilizing combined knowledge across different taxonomic groups, diverse geographical areas and research fields, we hope to not only provide novel insights into the mechanisms generating biodiversity, but to also identify conservation gaps that require future attention in conservation planning and management. This special issue includes 35 articles that, on the one hand, improve our knowledge of the mechanisms underlying the extraordinary diversity of hotspots, and, the other hand, propose new strategies to mitigate biodiversity losses (Table 1). These articles are broadly focused on the following four aspects: (1) Community composition and diversity patterns, (2) Ecological and genomic mechanisms underlying diversification and speciation, including phylogeographic pattern of representative taxa; (3) The current status of fauna and flora hotspots; (4) Conservation gaps and implications for future planning and management.