The Geography of Phytochemical Races

Chapter 6
Oceanic Islands
Over the past decade or so, the topic of origin and evolution of oceanic island biota
has almost become a growth industry. So much information is now available on
island geology, continental origins of island endemic taxa, and, in the case of multiisland
archipelagos, relationships of closely related taxa between and among individual
islands. Thus, introductory information for the following island groups will
be kept to a minimum.
6.1 The Galapagos Islands
From an evolutionary perspective, the Galapágos Islands are likely the most historically
famous archipelago on the face of the Earth. As every student of biology
knows, it was on the Galapagos that Darwin is thought to have perceived the full
force of evolution at work. Some think that this may be an oversimplifi cation of the
history of the subject, as has been masterfully discussed by Quammen (1996) in his
The Song of the Dodo. Nonetheless, examples of divergence on these islands have
continued to fascinate and attract biologists over the years, the results of which can
be found in several comprehensive volumes: Darwin’s Island. A Natural History
of the Galapágos (Thornton, 1971); The Galapágos: Proceedings of the Symposia
of the Galapágos International Scientifi c Project (Bowman, 1966); and Patterns of
Evolution in Galapagos Organisms (Bowman et al., 1983).
The Galapagos Islands (renamed the Archipiélago de Colón in 1892 by the
Republic of Ecuador) lie at approximately 90°W longitude and are centered on
the Equator with Hood (Española) lying at 1° 20′S, and Darwin at 1° 40′N. The
shortest distance from the South American coast is about 935 km. Thornton (1971)
describes the archipelago as consisting of four fairly large islands, 11 smaller ones,
and numerous smaller islets and rocks. The largest island, Albermarle (Isabela), is
approximately 75 miles long with an area that exceeds the sum of areas of all the
rest (Fig. 6.1).
The Galapagos archipelago consists of a series of volcanoes rising above the
Galapagos platform, which lies on the Nazca Plate, which is moving eastward such
that the entire assemblage will eventually disappear into the Chile-Peru Trench
B.A. Bohm, The Geography of Phytochemical Races,
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