The tepuis from South America, also known as ‘islands in the sky’, are renowned for their unique flora and fauna. Recently a Belgian scientist, Dr. Kok, added two new species to their impressive species catalogue, with the discovery of two frogs of the genus Pristimantis on top of two Venezuelan tepuis. The tepuis are remnants of the sea floor of approximately two billion years ago, that lifted upwards and then around 300 million years ago started to erode. By around 70 million years ago these tepuis were above the surrounding landscape, creating sheer vertical cliffs of sometimes more than 1000 meters in altitude. I remember seeing a documentary, of which i can’t recall the name, in which explorers tried to climb these tepuis and had to sleep in a sleeping bag attached to their ropes, while staying suspended at a couple hundred of meters above the landscape. For a person with vertigo like me, a very frightening sight. It also shows how isolated these tepuis can be and how hard to reach.
Due to their peculiarity and the impressive sight they offer, tepuis have also earned their place in popular culture, starting with the release of the 1912-novel of Sir Arthur Conan Doyle named ‘The lost world’ that features these tepuis as havens for extinct creatures like dinosaurs. They were also an inspiration for the 2009 animation movie ‘Up’ and show a clear resemblance to the islands in the sky that featured in the movie Avatar.
Because of their vertical isolation these tepuis have hardly been explored, but expeditions that do have reached them, have shown that the flora and fauna on top of these table mountains is very different from the species seen in the surrounding lowlands. This can be explained by not only their geographical isolation, but also the very different climatic and ecological factors that are observed there.
Recently, two new species of the genus Pristimantis have been discovered on top of two of these tepuis in Venezuela. This was in the region known locally as Pantepui, in the northwestern part of the Guiana Shield. The Guiana Shield is one of the foremost centres of endemism in the Neotropics. The discovery did not come as a big surprise, as two researchers had collected on an earlier expedition in this region individuals of what they believed to be 15 new species of the genus. Now these two frogs found by Dr. Kok have been identified as indeed being new species. The Pristimantis genus was already the most specious genes among vertebrates with over 450 species known to science. In the light of these recent expeditions it seems very probable that even more species are awaiting discovery within this genus.
One of the two new discovered species is named after the movie director James Cameron, therefore dubbed Pristimantis jamescameroni. Dr. Kok wanted to honor him, because of his efforts for promoting environmental awareness in his movies, his natural exploration work and his support for the vegan diet. The vegan diet, that tries to limit animal suffering and environmental impact and therefore has a positive effect on the natural world. The species was found on the Aprada-tepui at an altitude of about 2560 meters. The tepui measures about 4,3 km2 and consists of open rock vegetation, tepui forest vegetation, small lakes and deep canyons. The P. jamescameroni was found living under rocks, and seems to have his habitat among them.
The second new species was named Pristimantis imthurni after the British explorer Sir Evrard am Thurn. He was to first to climb a major tepui, Mount Roraima, in 1884 and this inspired the novel ‘The lost world’. This species was found on another tepui, the Ptari-tepui, at an altitude of around 2470 meters. This tepui has a surface of about 1 km2 and is characterized by open rock surfaces and low tepui vegetation. The P. imthurni was found calling in small patches of vegetation.
These two species make a total of 11 species of this genus that have been found living exclusively on top of a tepui. The conservation status of both species is (critically) endangered, because of their restricted range and because these tepuis are known to be vulnerable to global warming. In a research it was predicted that up to 80% of the vascular flora in this habitat might go extinct due to global warming. Species on top of the tepuis are so vulnerable to climate change, because they have limited migration possibilities with a warming climate and might not be able to adapt quickly enough.
An interesting question surrounding the species on top of the tepuis deals with how they have reached these islands in the sky? And seeing how isolated the tepuis are, have they remained cut off from their sister species since about 70 million years, when these islands were created?
A lovely article by Zimmer discusses the results of a research that set out to answer this question. The starting point for the research was the ‘lost world hypothesis’ that proposes, just like in the novel, that the tepuis have provided a total isolation for these species from the surrouding landscapes. This would give rise to a very unique, mostly endemic flora and fauna, found nowhere else, that evolutionary speaking would considerably have diverged from the flora and fauna living below. They used tiny treefrogs as the ‘model species’ to find out whether their presumed isolation could be retrieved in their DNA. The treefrogs were chosen, because they use a small habitat and don’t disperse much during their lifetime, making it more plausible that they really stay isolated. The DNA however showed that differences between species above and below weren’t as great as to be expected with a 70 million year separation. They concluded that more likely about 5 million years ago most of the species had diverged, with some of them ‘only’ some 300.000 years apart. This means that indeed these treefrogs, tiny as they are, have managed to climb up and move down these tepuis several times in their history. The scientists do agree that for other species the results might be different: for example toads, really could have been isolated from each other for so long. Either way, they form a fascinating world of their own, these tepuis, with their own beautiful flora and fauna.