The Pantepui "Lost World": Towards a Biogeographical, Ecological and Evolutionary Synthesis of a Pristine Neotropical Sky-Island Archipelago

Pantepui is an archipelago of sky islands formed by the flat summits of the Neotropical Guiana table mountains (tepuis) situated between the Orinoco and Amazon basins. Pantepui is a virtually pristine land and a natural laboratory to study the origin and evolution of Neotropical biodiversity. This review aims to synthesize the existing biological knowledge of Pantepui, with an emphasis on the latest developments in biogeographical, ecological and evolutionary studies. Biogeographically, Pantepui is a province of the Guiana region, within the Neotropical realm, but the precise definition of this province varies according to the taxonomic group studied. Here we adopt a definition based on elevation, with a diffuse lower boundary at 1200–1500 m and an upper boundary at the uppermost elevations of the Guiana Highlands (ca. 3000 m). The biodiversity and endemism patterns of Pantepui are outstanding. With almost 2600 known species (>5000 species/10,000 km2), plants are the most diverse organisms and situate Pantepui among the most diverse regions of the world. Endemism usually ranges from 30 to 40% but may reach 55% in amphibians. Ecology is poorly known. Autecological studies are lacking, and community studies are available only for vegetation and solely in descriptive terms. Paleoecological studies have shown that plant communities have changed through time under the action of Holocene climatic changes and fire. Glacial-interglacial alternation has deeply modified the Pantepui biota and this biogeographical unit has been recurrently disassembled during glaciations and reassembled during interglacials. The origin and evolution of the Pantepui biota has been explained by diverse evolutionary processes involving a variety of environmental drivers and diversification mechanisms. Most of these hypotheses emerged from the study of extant biogeographical patterns and geological-paleoecological reconstructions. The inception of molecular phylogenetics, albeit still incipient in Pantepui, has provided evidence useful for testing these proposals. Taken individually, none of the proposed hypotheses can explain the evolution of the whole Pantepui biota, whose proper understanding requires complex thinking and the consideration of multiple drivers and a diversity of ecological and evolutionary processes and mechanisms acting together across spatiotemporal scales. Pantepui pristinity could be threatened by direct human disturbance and global warming. Preliminary estimates suggest that, under the worst warming scenario, >80% (including >50% of endemics) of the unique vascular flora could lose their habitat by the end of this century. In situ conservation actions are difficult to implement, and ex situ strategies (germplasm banks, botanical gardens, managed relocation) should thus be considered. More systematic and target-focused, rather than exploratory, approaches are needed for future research on Pantepui. International cooperation and the improvement of bureaucratic facilities are required to preserve the still-pristine Pantepui biota and ecosystems