ISLANDS AT THE CENTER OF THE WORLD.
My name is Bob Drewes; I am a research biologist, and I have worked in Africa’s wild places with considerable pleasure for over 35 years. I am Curator of Herpetology at the California Academy of Sciences, the western United States’ oldest academic research institution.
Very shortly, I will be leading the Academy’s third biodiversity expedition to the remote islands of São Tomé and Príncipe which lie off the west coast of Africa in the Gulf of Guinea,. These two mountainous islands together form the world’s second smallest republic (after the Seychelles Islands). São Tomé and Príncipe are biologically unique; they are the two middle members of a four-island chain (sometimes known as the Gulf of Guinea Islands) that is the only archipelago on earth comprised of both continental and oceanic islands. [island map]
Continental and Oceanic Islands
Unlike the northernmost island, Bioko (formerly Fernando Pó) which is a continental island separated from the Cameroon coast by only 20 miles of relatively shallow water, São Tomé and Príncipe arose some 2 to 4000m up from the ocean floor and thus have never been attached to mainland Africa; this means that the ancestors of all the plants and animals that are found on the islands today must have crossed hundreds of km of deep salt water to get there (dispersal) – this only occurs over time and is successful only by random chance. The colonizers that make it and survive are then separated from their mainland founder populations and over time begin to accumulate genetic changes, a process we all know as evolution.
Sao Tome Id at 1400m. GG II (D. Lin phot).
In the case of São Tomė and Príncipe, there’s been plenty of time for this to occur as São Tomé and Príncipe are very old islands. It is fact that the Hawaiian Islands and the Galapagos are only about 5 million years at the oldest; compared with the Gulf of Guinea islands, these two famous and well-studied archipelagos are relative infants! Solid geological evidence tells us that São Tomé is at least 15 million years old, and Principe is more than twice that, at over 30 million years. This is a very long time for successful dispersal, long-term isolation and evolution to take place, and it has — in spades! The evidence can be found in the high numbers of endemic plant and animal species that still inhabit the higher elevations on the two islands – species that are found nowhere else in the world.
Sao Tome endemic. Newton’s sunbird. GG II (J. Uyeda phot)
View Southeast from 1400 m, Sao Tome. GG I (RCD phot)
Fruit bat. Sao Tome. GG I (D. Lin phot)
Among the vertebrates, more than half of the 49 species and subspecies of land birds breeding on São Tomė and Príncipe are endemic, and they include the world’s largest sunbird, the world’s largest weaver and the world’s smallest ibis. Mammals make poor over-water dispersers (high metabolic rates) so as we would predict, endemic mammals are limited to a couple of bats and two shrews that have not been well studied. There are no endemic freshwater fish on the islands, but our first two expeditions yielded many more species in the rivers and streams than previously recorded. About half of the reptile species on the islands are unique to them; one of them is the largest lizard in its genus, Greef’s gecko (Hemidactylus greeffi). But most surprising of all is the presence of an amphibian fauna, especially because due to the nature of their permeable skin, amphibians almost never cross saltwater barriers; they are considered among the poorest dispersers, along with freshwater fish. Not only are six unique frog species present (we just described a new one), there is also a legless amphibian known as a caecilian that is found only on São Tomė; its nearest relative is found only in East Africa, thousands of miles away.
Sao Tome endemic caecilian, Schistometopum thomense GG I (D. Lin phot)
Principe endemic giant treefrog, Leptopelis palmatus GG I (D. Lin phot)
The invertebrate species and flora are also remarkable; so far as is known, about 14% of the flowering plants are endemic, including the world’s largest Begonia at 2 meters ! More than half of the ladybugs and spiders, 80% of the stag beetles and 2/3rds of the terrestrial snails are found nowhere else in the world; but these data are based on very limited sampling much of which was done in the late 19th Century, this is one of the reasons we are here. [Begonia ebaccata]. [bubba]
Sao Tome endemic, Begonia bacatta. world’s largest GG I (D. Lin Phot)
J. Ledford with Hysterocrates, Sao Tome endemic tarantula GG I (D. Lin phot)
We gratefully acknowledge the support of the Research Investment Fund of the California Academy of Sciences, the Société de Conservation et Développement (SCD) for logistics, ground transportation and lodging, STePUP of Sao Tome http://www.stepup.st/ and especially the generosity of three private individuals, George F. Breed, Gerry F. Ohrstrom and Timothy M. Muller, for making GG III possible.