Within the theory of evolution , the concept of adaptive radiation (evolutionary development of several species from a single parental stock) has had as its prime example, a group of birds known as Darwin's finches. Charles Darwin discovered and collected specimens of these birds from the Galápagos Islands in 1835 on his five-year voyage around the world aboard the HMS Beagle. His cumulative experiences, copious notes, and vast collections ultimately led to the publication of his monumental work, On the Origin of Species, in 1859. The Galápagos Islands and their unique assemblage of plants and animals were an instrumental part of the development of Darwin's evolutionary theory.
The Galápagos Islands are located at 90° W longitude and 0° latitude (the equator), about 600 mi (965 km) west Ecuador. These islands are volcanic in origin and are about 10 million years old. The original colonization of the Galápagos Islands occurred by chance transport over the ocean as indicated by the gaps in the flora and fauna of this archipelago compared to the mainland. Of the hundreds of species of birds along the northwestern South American coast, only seven species colonized the Galápagos Islands. These evolved into 57 resident species, 26 of which are endemic to the islands, through adaptive radiation. The only native land mammals are a rat and a bat. The land reptiles include iguanas, a single species each of snake, lizard, and gecko, and the Galápagos giant tortoise (Geochelone elephantopus ). No amphibians and few insects or mollusks are found in the Galápagos. The flora has large gaps as well—no conifers or palms have colonized these islands. Many of the open niches have been filled by the colonizing groups. The tortoises and iguanas are large and have filled niches normally occupied by mammalian herbivores. Several plants, such as the prickly pear cactus, have attained large size and occupy the ecological position of tall trees.
The most widely known and often used example of adaptive radiation is Darwin's finches, a group of 14 species of birds that arose from a single ancestor in the Galápagos Islands. These birds have specialized on different islands or into niches normally filled by other groups of birds. Some are strictly seed eaters, while others have evolved more warbler-like bills and eat insects, still others eat flowers, fruit, and/or nectar, and others find insects for their diet by digging under the bark of trees, having filled the niche of the woodpecker. Darwin's finches are named in honor of their discoverer, but they are not referred to as Galápagos finches because there is one of their numbers that has colonized Cocos Island, located 425 mi (684 km) north-northeast of the Galápagos.
Because of the Galápagos Islands' unique ecology , scenic beauty and tropical climate , they have become a mecca for tourists and some settlement. These human activities have introduced a host ofenvironmental problems, including introduced species of goats, pigs, rats, dogs, and cats, many of which become feral and damage or destroy nesting bird colonies by preying on the adults, young, or eggs. Several races of giant tortoise have been extirpated or are severely threatened with extinction , primarily due to exploitation for food by humans, destruction of their food resources by goats, or predation of their hatchlings by feral animals. Most of the 13 recognized races of tortoise have populations numbering only in the hundreds. Three races are tenuously maintaining populations in the thousands, one race has not been seen since 1906, but it is thought to have disappeared due to natural causes, another race has a population of about 25 individuals, and the Abingdon Island tortoise is represented today by only one individual, "Lone-some George," a captive male at the Charles Darwin Biological Station. For most of these tortoises to survive, an active capture or extermination program of the feral animals will have to continue. One other potential threat to the Galápagos Islands is tourism. Thousands of tourists visit these islands each year and their numbers can exceed the limit deemed sustainable by the Ecuadoran government. These tourists have had, and will continue to have, an impact on the fragile habitats of the Galápagos.
[Eugene C. Beckham ]
Harris, M. A Field Guide to the Birds of the Galápagos. London: Collins, 1982. Root, P., and M. McCormick. Galápagos Islands. New York: Macmillan, 1989.
Steadman, D. W., and S. Zousmer. Galápagos: Discovery on Darwin's Islands. Washington, DC: Smithsonian Institution Press, 1988.
Galápagos Islands, a group of nineteen volcanic islands and numerous islets in the eastern Pacific, lying astride the equator, 600 miles west of mainland Ecuador, of which the islands are a province. The island group, officially named the Archipiélago de Colón by Ecuador in 1892 to honor Christopher Columbus, encompasses a land area of 3,075 square miles and is spread out over 36,000 square miles of sea. The population of the Galapagos was listed as 9,785 in the 1990 census.
Each island was named by both Spanish and English explorers and renamed by Ecuador in 1892. The official Ecuadorian names are cited in this article; however, researchers will find the English names in most earlier descriptions of the islands. The largest island is Isabela, approximately 82 miles long, covering an area of 1,700 square miles, over half the land mass of the others combined. Isabela is typical of the islands in its lava composition; it also has the highest peak, Mount Azul, at 5,541 feet. The five other larger islands are Santa Cruz, Fernandina, San Cristóbal, San Salvador, and Santa María.
In 1535, Thomás de Berlanga, bishop of Panama, inadvertently discovered the Galápagos when his ship was blown off course en route to Peru. He named them Las Encantadas (The Enchanted) due to their mist-shrouded otherworldly appearance and the unusual wildlife typified by giant tortoises and iguanas. The islands were a haven for pirates in the seventeenth century and became a regular stop for whaling vessels in the eighteenth and nineteenth centuries. The islands were unclaimed until 1832, when Ecuador took official possession.
In 1835 the English naturalist Charles Darwin visited the islands and chronicled their flora and fauna. His experiences in the Galápagos contributed significantly to his ideas about evolution and natural selection and his account of the islands brought them international acclaim.
In the early twentieth century, Ecuador considered selling the islands to France, Chile, and the United States but decided to retain possession. In World War II, Ecuador permitted the United States to construct an air base on Baltra Island for the purpose of patrolling Pacific approaches to the Panama Canal. The base was turned over to Ecuador in 1946 and today serves as the principal airstrip.
The unique native animals and plants remain the main attraction of the islands. The archipelago's tortoise is thought to be the longest-lived animal on earth. While there are only nine mammals, two bats, and seven rodents, no amphibians, few reptiles, and approximately eighty species of birds indigenous to the islands, animal life is nevertheless of extreme scientific importance due to the islands' centuries of isolation from humans in an austere environment that has led to unique adaptive changes. Large parts of the islands are now preserved as national parks and wildlife refuges.
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William Beebe, Galápagos, World's End (1924).
Theodore Wolf, Geography and Geology of Ecuador (1933).
Herman Melville, The Encantadoas or Enchanted Islands, with an introduction, critical epilogue, and bibliographical notes by Victor Wolfgang von Hagen (1940).
Victor Wolfgang Von Hagen, Ecuador and the Galápagos Islands (1949).
Ian Thornton, Darwin's Islands: A Natural History of the Galápagos (1971).
John Hickham, The Enchanted Islands (1986).
De Roy, Tui. Galapagos, Islands Born of Fire. Toronto: Warwick Pub., 1998.
Luna Tobar, Alfredo. Historia política internacional de las islas Galápagos. Quito, Ecuador: Ediciones Abya-Yala, 1997.
Ospina Peralta, Pablo. Galápagos, naturaleza y sociedad: Actores sociales y conflictos ambientales en las islas Galápagos. Quito, Ecuador: Corporación Editora Nacional, 2006.
Palmerlee, Danny, Michael Grosberg, and Carolyn McCarthy. Ecuador and the Galápagos Islands. Footscray, Vic.: Lonely Planet, 2006.
Rachowiecki, Rob, and Teresa Bladé. Ecuador y las isles Galápagos. Barcelona: GeoPlanet, 2001.
Tagliaferro, Linda. Galápagos Islands: Nature's Delicate Balance at Risk. Minneapolis, MN: Lerner, 2001.
George M. Lauderbaugh
GALÁPAGOS ISLANDS. A strategically important archipelago (group of islands), the Galápagos lie some 600 miles off the coast of Ecuador. American interest in annexing the islands began in the mid-nineteenth century and peaked half a century later. In 1906 and 1911, negotiations to build a U.S. coal station failed, largely because of popular opposition in Ecuador. During World War II, the United States established weather and signal stations on the islands. In the 1960s and 1970s, Ecuador seized a number of U.S. fishing boats in the area. In retaliation, the United States temporarily suspended military aid to Ecuador.