Jan. 11, 2009 South America is the world’s most species-rich area. There have been many theories as to why, ranging from animals and plants accompanying the continent when it broke loose from Africa to variations in the extent of the rainforests over millions of years creating new species.
A thesis from Gothenburg University supports a different theory: that the formation of the Andes was a species pump which spread animals and plants across the continent.
South America’s unique richness of species has been explained by several hypotheses. One states that animals and plants “accompanied” the South American continent when it broke loose from Africa 100 million years ago. Another proposes that many species were formed when the rainforest shrank into smaller areas during the Ice Ages and then subsequently expanded.
Brazilian-born researcher Alexandre Antonelli, a doctoral student at Gothenburg University’s Department of Plant and Environmental Sciences has made several trips to South America and collected hundreds of species as research specimens. Using DNA technology, he has traced when and where some of South America’s plant and animal species developed by studying the relationships of different species, how long ago they separated out from a common ancestor and the geographical distribution of this ancestor when the species formed.
Plant and animal groups both too young and too old
The results indicate that most of South America’s plant and animal groups are far too young to have been alive when Africa and South America were a single continent. On the other hand, most animal and plant groups are too old for their origins to be connected to vegetation changes during the Ice Ages which was considered the primary reason for South America’s diversity.
There again, according to the thesis, there is a strong connection between the elevation of the northern Andes and a massive rise in species. This is the first time such a connection has been demonstrated.
“The spread southwards along the Andes was not possible until the northern part of the mountain range came into contact with its central tracts, an event which took place 10-12 million years ago. Prior to this, a long lowland corridor that was periodically submerged in seawater acted as an effective barrier to the spread. At the same time, the elevation of the Andes brought about the end of Lago Pebas, a gigantic sea covering the whole of western Amazonas. Thus, many species were able to spread from the northern Andes to areas such as Amazonas, Caribbean and Central America, where new species developed.
“In this way, the Andes became a “species pump” for the biodiversity of the entire American continent,” says Alexandre Antonelli.
The discovery that most of South America’s species are several million years old has given strong grounds for protecting their survival and Alexandre Antonelli’s thesis shows the important of long-term thinking when strategies for species preservation are being designed.
The thesis, Spatiotemporal Evolution of Neotropical Organisms: New Insights into an Old Riddle was defended by viva on 28 November. The supervisor was Dr Claes Persson.
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