Are there many different routes to becoming a global biodiversity hotspot?

Abstract

A major question in evolution and ecology is why biodiversity is so unevenly distributed across the planet. The most obvious and salient diversity pattern is the order-of-magnitude greater species richness in the tropics compared with the temperate zones. Superimposed on this latitudinal diversity gradient is a much more complex and intricate pattern of regional and more local biodiversity hotspots (1, 2). These are places with unusually high concentrations of species and especially endemic species. Documenting these patterns is of great significance, most obviously for conservation, with ever more sophisticated and higher-resolution biodiversity hotspot maps becoming available as the world’s biota are mapped in greater detail (3). More fundamentally, we need to document hotspots to understand the underlying macroevolutionary and ecological processes shaping the distribution of diversity across the Earth. Most globally significant biodiversity hotspots lie firmly within the tropics or in the Mediterranean climate zones of the world, such as California and the Cape Floristic Region of South Africa. Several coincide with major mountain ranges, including most notably the tropical Andes and the temperate Hengduan Mountains, two of the world’s hottest hotspots (2, 4). It is this Hengduan Mountain hotspot that is the focus of Xing and Ree’s study in PNAS (5), which provides the first integrated analysis of the evolutionary origins and biotic assembly of Hengduan plant diversity. Although formal quantification of biodiversity hotspots really only started 30 y ago (1), the outstanding plant species richness of the Hengduan Mountains has been known for more than 150 y, having been first revealed by the intrepid 19th century plant collectors—Joseph Hooker, Ernest Wilson, George Forrest, Frank Kingdon-Ward, and others. These explorers penetrated into the deeply dissected and remote mountains and river gorges of Yunnan, Sichuan, Sikkim, and eastern Tibet in search of botanical novelties and especially garden plants, … [↵][1]1Email: colin.hughes{at}systbot.uzh.ch. [1]: #xref-corresp-1-1