Part 1 of this series is here.
|Image courtesy of http://masspictures.net/mount-roraima-venezuelabrazilguyana/|
South America has no shortage of wonders (see the Cano Cristales River in Colombia or the Salar de Uyuni in Bolivia) but for now lets look at its sprawling mesas. A sight to behold indeed. The image on the left is a helicopter photo of Mount Roraima, the highest tepui (isolated table mountain) in South America. Part of a chain of table mountains known as the Pakairama chain, which stretches across 3 nations: Brazil, Venezuela and Guyana.
The tepui are the remains of an ancient, Pre-Cambrian plateau, once part of the super-continent known as Gondwanaland, uplifted by tectonic activity and slowly eroded over untold eons, leaving these spectacular vistas of roiling clouds and waterfalls higher than anywhere else on Earth.
As you can see, the table mountains are isolated landforms, meaning of course, species that resemble no other can thrive in these geographically unique places. As my previous post pointed out, geographical isolation of small, isolated locales of a sample population leads to peripatric speciation. Lets take a closer look at Mount Roraima.
|Young Heliamphora nutans, red pitcher plants endemic |
to South American mesas
What does that mean? Well, because of the nutrient-poor ground, many of the plants have taken on carnivorous traits. Pitcher plants abound on top of this massive table mountain.
|Image courtesy of National Geographic video here|
Also pictured : the Roraima bush toad. I wont spoil too much, but just watch the linked video here to see how it escapes a hungry tarantula. Just a few of the unique species on Roraima.
In truth though, the plateau isnt as isolated as one would like to think: species from the plains below have occasionally been found on top. Even endemic species have been estimated to diverge from the ancestral population only a few million years ago, which is far younger than the age of the plateau itself.
Why would this be? My hypothesis is that birds may occasionally capture prey from the lowlands and bring them to nesting grounds on the cliff surface. The living species are escaped specimens. Perhaps, but there doesnt seem to be conclusive proof. Furthermore, there is actually a steep ramp to one side.
A caveat for aspiring visitors though: its not easy to get to the top, although thankfully, you dont need to scale the sheer cliff face with rope. There is a track on one side of the cliff face to the top.
See more info here.
Behold, the dragon's blood tree, its scientific name which is dracaena cinnabari, found nowhere else in the world but Socotra. So called because of the crimson sap harvested from their trunks, prized during the Middle ages, the unique, crown shape is a form of adaptation mechanism for survival in dry climate - the crown shape provides an "umbrella" to reduce water loss in the hot and dry climate.
What is unique about Socotra is that it is not a volcanic island. Located in the Indian Ocean, closest to Somalia, but under Yemeni jurisdiction, tectonic activity detached it from mainland Africa during the aforementioned Pliocene, from about 2.6 - 5 million years ago. What researchers believe is that this species went extinct on the mainland but the island's relative isolation prevented it from being out-competed or driven to extinction by fundamental shifts in climate. In fact, almost a third of all flora and fauna on Socotra Island is found nowhere else on Earth!
Another unique species found nowhere else on Earth is this cucumber tree, Dendrosicyos socotranus, related to the cucumbers we eat. (Note that another species of tree, the Averrhoa bilimbi is also known as cucumber tree but is in no way related to the agricultural ground cucumber.)
Just a few of the unique species here. As for endemic birds, I ll let pictures and attached links tell you all you need to know. Read this for starters.
As one can see, biogeography provides evidence for evolution via the process of natural selection. This post is a little sketchy on the details, nevertheless I will provide more info in the future.
|Socotra golden-winged grosbeak|