User:Minglex/Galapagos
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The Galápagos tortoise (or Galápagos giant tortoise), is the largest living tortoise, endemic to nine islands of the Galápagos archepelago. Adults of large subspecies can weigh over 300 kg and measure 1.8 m long. Although the maximum life expectancy of a wild tortoise is unknown, the average life expectancy is estimated to be 150-200 years.
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| Geochelone elephantopus (Quoy & Gaimard, 1824) |
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[edit] Shells
The Galápagos tortoises have very large shells (carapace) made of bonewhich is an integral part of the skeleton. The bony plates of the shell are fused with the ribs and other bones to form a rigid protective structure. When a tortoise feels threatened it can withdraw its head, neck and forelimbs into its shell for protection, presenting a thick shield to a would-be predator. The legs have hard scales that provide an effective armour when withdrawn.
The scutes of the carapace are not coincident with the underlying bony plates and grow at their outer edges. Tortoises thus keep their characteristic scute pattern throughout life. These do have annual growth bands but are not useful for telling the age as the outer layers are rubbed off in the normal wear and tear of living.
The shape of the carapace and other physical features correspond to the habitat of each of the 13 subspecies. Larger, islands with more wet highlands such as Santa Cruz and Isabela (where the Alcedo Volcano is found) with lush vegetation near the ground have tortoises with 'dome-back' shells; these animals have restricted upward head movement due to shorter necks, and tend to have shorter limbs as well. These are the heaviest and largest of the subspecies.
Smaller, drier islands such as Española and Pinta are inhabited by tortoises with 'saddle-back' shells comprising a carapace elevated above the neck and flared or reverted above the hind feet, and longer, thinner limbs. This appears to allow them to browse taller vegetation. On the drier islands with tortoise populations, the Galápagos Opuntia cactus (a major source of their water) has evolved an more tree-like and taller form, giving evidence of an evolutionary arms race between progressively taller tortoises and correspondingly taller cacti. Saddleback tortoises tend to be smaller (females average 27 kg, males 54 kg) in size than their domeback counterparts.
In all subspecies, male has a concave undershell, which facilitates mating. The male is also always larger than the female. Shells are not either saddleback or domeback, they can also be of intermediate type with some characteristics of both the extreme types. The Sierra Negra volcano population that inhabits southern Isabela Island is notable for the flat, so-called "tabletop" shells, differing from both the domebacks and saddlebacks.
There is little variation in the dull-brown colour of the shell or scales between populations.
[edit] Behaviour
The totoises are herbivorous animals with a diet consisting of grasses, leaves, vines, and fruit. Fresh young grass in particular is the favourite food of the tortoises, and others are the poison apple (Hippomane mancinella), which is highly poisonous to humans, the endemic guava (Psidium galapageium), the water fern (Azolla microphylla), and the bromeliad (Tillandsia insularis). Tortoises studied in the Santa Cruz tortoise reserve ate well over fifty different plant species.(ref Linda Cayot (1981)) In the drier areas, fallen Opuntia cactus pads and fruits are an important element in the diet of tortoises. Galapagos tortoises eat a large quantity of food when it is available at the expense of incomplete digestion.
By acquiring most of their moisture from the dew and sap in vegetation (particularly the Opuntia cactus), they can go for long periods without actually drinking. They can also survive for long periods of time being forcefully deprived of all liquids, by breaking down their body fat to produce water.
The tortoises are slow-moving reptiles with an average long-distance walking speed of 0.3 km/h. However, although feeding giant tortoises move about slowly, browsing with no apparent direction, if they have a purpose, such as moving to water or nesting grounds, they can move with surprising speed and determination given their size. Marked individuals have been reported to have travelled 8 miles in 2 to 3 days.
On the wetter islands, the tortoises migrate down the gentle mountain slopes after the rainy season to feed on the grass-covered plains and they climb the back to feed on grasses of the mountain meadows in the dry season (the increased precipitation at that altitude keeps the grasses watered). On these islands, the tortoises appear to be gregarious, often found in large 'herds'.
Being cold-blooded, the tortoises bask for two hours after dawn, absorbing the energy through their shells, then becoming active for 8-9 hours a day. They may sleep for about sixteen hours, in a mud wallow or pool or a 'pallet' (a snug depressions in soft ground or dense brush) which probably help conserve heatthe, which may aid digestion. On Alcedo Volcano, where there is a large population, repeated use of the same sites has resulted in the formation of small sandy pits.
Although capable of withstanding drought, totoises seem to enjoy drinking and wallowing in water. When the tortoise arrives at a spring, seemingly ignoring any spectators, it puts his head in the water above his eyes, and swallows many mouthfuls, at the rate of about ten in a minute. On Alcedo Volcano in the wet season, large numbers of tortoises can be found partially submerged in rain-formed pools or even the dew ponds formed by garua-moisture dripping off trees. These pools tend to be churned up into mud baths. This may be both a thermoregulatory response and a protection from parasites such as mosquitoes and ticks.
Tortoises have a classic example of a mutualistic symbiotic relationship with some species of Galápagos finch. The finch hops in front of the tortoise to show that it is ready and the tortoise then raises itself up high on its legs and stretches out its neck so that the bird can reach ticks on its skin, thus freeing the tortoise from harmful parasites and providing the finch with an easy meal. Other birds, including Galápagos Hawk and flycatchers, often use tortoises as observation posts from which to sight their prey.
[edit] Reproduction and development
Mating occurs at any time of the year although it does have seasonal peaks, usually between January and August. When two mature males meet in the mating season, they will rise up on their legs and stretch up their necks to assess dominance. The shorter tortoise will back off leaving the taller, larger tortoise to mate with the female. In groups of tortoises from mixed island populations, saddleback males have an advantage over domebacks. Frustrated non-dominant males have been observed attempt to mate with other males and boulders.
The male tortoise bellows loudly and bobs his head to attract a female. The male then rams the female with the front of its shell and nips her exposed legs until she draws them in, immobilizing her. Mating may last for several hours and the males often makes hoarse roars. Males have a concave base to their shell and mount the females from behind. It brings its tail which houses the penis into female's cloaca.
After mating (between June and December), the females journey several kilometres to reach nesting areas of dry, sandy ground (often near the coast). Nest digging is an elaborate task and takes several hours sometimes spread out over several days. It is carried out blindly using only the hind legs to dig a 30 cm deep hole, in which it lays two to sixteen hard-shelled eggs the size of tennis balls (the number varies with population). The female makes a muddy plug for the nest hole out of soil mixed with urine and leaves the eggs to incubate.
The young emerge from the nest 120 to 140 days later (between December and April) and may weigh only 80 g and measure 6 cm (De Vries 1984). Temperature plays a role in the sex of the hatchling: if the nest temperature is low, more males will hatch; if it is high, more females will hatch. When the young tortoises emerge from their shells, they must dig their way to the surface, which can take up to one month. Hawks are probably the only native predator of the tortoise hatchlings.
Sex can be determined when the tortoise is 15 years old, and sexual maturity is reached at 20 to 25 years old. The tortoises grow slowly for about 40 years until they reach their full size.
"Some grow to an immense size ... several so large that it required six or eight men to lift them from the ground" (Darwin 1845)
Tortoises are much less abundant than they used to be, numbering only some 15,000 compared to an estimated 250,000 original population (MacFarland et al. 1974a,b), but they can still be seen by visitors in captivity and the wild. Several are kept at the Research Station in pens for captive-breeding purposes and for viewing and include representatives from many islands.
To see tortoises in the wild one must either hike into the tortoise reserve on Santa Cruz or make an expedition to the rim of Alcedo Volcano, where tortoises are still abundant.
Natural reproduction presently reduced (and in some populations prevented) by introduced mammal predators. Important captive breeding and rearing projects are being carried out at the Charles Darwin Research Station. Strictly protected in the Galapagos, which were declared a National Park in 1959.
[edit] The naming of the Galápagos
In February 1535, a Spanish ship sailed from Panama bound for Peru. During the voyage a great storm arose and for the next eight or nine days the ship was battered by rough seas. The crew survived, but the ship had been blown far off course. On March 10th an island was sighted which later proved to be just one of a group of thirteen major islands and many smaller islets, all of volcanic origin. The Spaniards were surprised to find many unknown species on the islands, including great numbers of giant tortoises. The sailors named the islands the 'Galápagos', deriving from the Spanish for 'saddle', referring to the distinctive shape of the saddleback subspecies. This tale may be entirely apocryphal.
[edit] Distribution
A current project to analyse their DNA should answer the question of how closely related the different races actually are. Ten races of giant tortoises still exist in the wild, on the islands of Santiago which has about 800 surviving tortoises, Pinzon (300 tortoises), Santa Cruz (3000), San Cristobal (700), Española (120) and on Isabela Island, which has a different race on each of its 5 volcanoes;- Cerro Azul with about 700 tortoises, Sierra Negra (500), Alcedo (5000), Darwin (1000) and lastly Wolf Volcano with 2000 tortoises.
[edit] Evolution
It is also thought that the saddle-backed type carapace evolved independently several times as a reaction to dry environments.
The Tortoise played an important role in the Theory of Evolution. When Charles Darwin visited the Galapagos Islands, the vice-governor of the Islands told him that he could identify what island the tortoise was from simply by looking at him.
The inhabitants...state that they can distinguish the tortoise from different islands; and that they differ not only in size, but in other characters. Captain Porter has described those from Charles and from the nearest island to it, namely Hood Island, as having their shells in front thick and turned up like a Spanish saddle, whilst the tortoises from James Island are rounder, blacker, and have a better taste when cooked.---Charles Darwin 1845
This is due to a phenomenon seen in many island ecosystems where gigantism evolves because there is no longer any need to hide from predators and because there are no other similar animals to compete with for food. Once the tortoises spread around the archipelago, they evolved on their isolated islands into the different races we see today, some with domed carapaces (shells), and others with saddleback carapaces. The unusual saddle shape is believed to have evolved several times on different islands, showing that it must be a very successful design for life in Galapagos.
It is likely that all the present races of giant tortoise evolved in Galapagos from a common ancestor that arrived from the mainland, floating on the ocean currents. Although this seems an incredible journey it is known that Galapagos tortoises can float easily in sea water. Only a single pregnant female or one male and one female needed to arrive in this way, and then survive, for Galapagos to be colonised. It is likely that the original colonist first washed up on the shores of San Cristobal Island and from there its descendants gradually dispersed around the archipelago, carried on the ocean currents. The closest living relative of the Galapagos giant tortoises is Geochelone chilensis, a small tortoise found in Chile.
The Galápagos tortoise is found on the Galápagos Islands west of Ecuador in South America. The shape of the carapace of some species of the tortoises reminded the Spanish explorers of a kind of saddle they called a "galápago," and for these saddle-shaped tortoises they named the archipelago. As many as 250,000 tortoises inhabited the islands when they were discovered. Today only about 18,000 are left, mainly due to harvest by whalers and pirates that killed them for food during the 18th and 19th centuries. Turned on their back where they could not move, the Galápagos tortoise could survive for months without food or water, making them a good source of fresh meat on a whaling ship (before refrigeration). Their diluted urine could also be used as drinking water. In addition, non-native species such as goats were introduced on some islands resulting in destruction of the vegetation that comprises the tortoises' diet; the resulting habitat loss further decimated their populations.
9,000 TO 10,000 TORTOISES SURVIVE ON THE Galapagos archipelago, 600 miles west of Ecuador. Ancestors of these reptiles may have floated there on clumps of vegetation disgorged from rivers of the continent. Another species of giant tortoise is found on the Indian Ocean island of Aldabra off East Africa.
. They have traditionally been treated as subspecies of Geochelone elephantophus but it has recently been proposed (1) that they might be more appropriately treated as full species of the genus Chelonoidis. Pending further discussion the more conservative arrangement is retained here. Population details for each subspecies are summarised below.
G. e. abingdoni
Formerly restricted to the southern slopes of Pinta (Abington Island) (3,10). Only one known individual is alive ("Lonesome George"), and is currently maintained at the Charles Darwin Research Station. This population was severely depleted by whalers and fishermen, and the introduction of goats in 1958 resulted in massive destruction of vegetation (12,14). Tortoise droppings, probably not more than a few years old, were found in the island in 1981, so there is a possibility that a second individual of this subspecies still exists (16). Further investigations are planned for 1982.
G. e. becki
Northern and western slopes of Volcano Wolf, Northern Isabela (Albermarle). Present population may be as many as 2,000. Reproduction appears to be successful despite the presence of black rats and feral cats, but the impact of these predators is not known (8,13).
G. e. chathamensis
Now confined to northeast San Cristobal (Chatham). Present population between 500 and 700. Heavily exploited and completely eliminated over much of its original range (3). Effective reproduction is now prevented by trampling of nests by feral donkeys, and the destruction of young by feral dogs (6,8,13). Eggs from wild nests have been removed for incubation and rearing to the Charles Darwin Research Station (5). In 1979 139 juveniles had been returned to the island and 13 were held at the station (13).
G. e. darwini
West-central San Salvador (James Island). Large numbers of tortoises were removed from the island in the early nineteenth century by whaling vessels, and introduced goats reduced the coastal lowlands to deserts, restricting the remaining tortoises to the interior (8). The sex ratio is strongly imbalanced in favour of the males (8) and most nests and young are destroyed be feral pigs (4,8). It is estimated that reproductive success diminished about 50 years ago and ceased altogether about 30 years ago (8). Some nests are now protected by lava corals and since 1970 eggs have been transported to the Charles Darwin Research Station for hatching and rearing. 115 individuals have been re-released on San Salvador (13).
G. e. elephantopus
Cerro Azul, Eastern Isabela (Albemarle). Range overlaps with G. e. guentheri and it may eventually be shown that these two taxa should be combined (6,8). This population was depleted by seamen in the last two centuries and by extensive slaughter in the late 1950's and 60's by employees of cattle companies based at Iguana Cove. Present population may number as many as 700 individuals. Although mating and nesting still occur naturally, very few young individuals are found, suggesting that predation by local feral dogs, cats and pigs is almost total (6,8). Eggs and hatchlings are removed to the Charles Darwin Research Station. Since 1971, 114 indiviuals have been returned to the island (13).
G. e. ephippium
Southwestern slopes of Pinzon (Duncan Island). Although relatively undisturbed by whalers, fairly large numbers of tortoises were removed by expeditions in the latter half of the nineteenth century and early this century (2,8). Present population is about 150 adults. Since the introduction of black rats some time before 1900, there has been no natural recruitment. Despite the age of the remaining population the females are still laying fertile eggs. Since 1965, eggs have been transported to the Charles Darwin Research Station for hatching and rearing. So far 182 young tortoises have been returned to the island (13).
G. e. galapagoensis
Floreana (Charles Island). Extinct. Formerly abundant but heavily exploited by visiting ships and a penal colony in the last century (8).
G. e. guentheri
Volcano Sierra Negra, Isabela (Albemarle). Severely depleted by settlement and exploitation for tortoise oil which continued until the 1950s. 300-500 individuals remain, divided into two groups by settlements. About 300 occur in the east and 200 over the western and southwestern slopes (4,13). Reproduction seems successful in the east but in the western-southwestern area pigs, dogs, rats and cats are present as predators (6).
G. e. hoodensis
Formerly Espanola (Hood). This population was very heavily exploited by whalers in the nineteenth century. The population appears to have collapsed around 1850 (8). 14 adults (2 males, 12 females) were found in the early 70's and are now held at the Charles Darwin Research Station as a breeding colony. Mating had not occurred naturally for some time because the individuals were so scattered that they did not meet. 129 young have now been produced. 79 have been returned to the island and 50 are held at the Station (13).
G. e. microphyes
Southern and western slopes of Volcano Darwin, Isabela (Albemarle). Present population between 500 and 1,000 individuals (8), heavily exploited in the nineteenth century by whaling vessels. Reproduction appears to be successful. The effect of populations of rats and cats needs to be investigated (13).
G. e. phantastica
Fernandina (Narborough Island). Only one specimen has ever been found, probably extinct (8).
G. e. porteri (Syn. G. e. nigrita).
The main population occurs in southwest Santa Cruz (Indefatigable Island) with a very small population in the northwest (8). Total population estimated at 2,000-3,000. Depleted by heavy exploitation for oil at least until the 1930s (3,8). Reproductive success has been severely hampered for many years by the presence of feral dogs and pigs (6,8,9,13). Approximately 15-20 hatchlings have been raised at the Charles Darwin Research station�annually.
G. e. vandenburghi
Caldera and southern slopes of Volcano Alcedo, Central Isabela (Albemarle). The largest population in the archipelago, possibly numbering as many as 5,000 individuals. Reproduction successful at present (6,8,13).
[edit] Threats and conservation
The inhabitants...state that they can distinguish the tortoise from different islands; and that they differ not only in size, but in other characters. Captain Porter has described those from Charles and from the nearest island to it, namely Hood Island, as having their shells in front thick and turned up like a Spanish saddle, whilst the tortoises from James Island are rounder, blacker, and have a better taste when cooked.---Charles Darwin 1845
As the hunters found it easier to collect the tortoises living round the coastal zones, the healthiest populations today tend to be those in the highlands. Persecution still continues on a much smaller scale; more than 120 tortoises have been killed by poachers since 1990.
All groups must have a guide and are asked to stay on the paths so the vegetation isn’t trampled on and the animals are not disturbed.
n the 1600s, buccaneers started to use Galapagos as a base, restocking on water and repairing their boats before setting off to attack the Spanish colonies on the South American mainland. But the main attraction of the islands were the giant tortoises which were collected and stored live on board ship where they survived for many months, providing invaluable fresh meat. In the 1800s, whaling ships and then fur-sealers collected tortoises for food and many more were killed for their fine 'turtle oil' from the late 1800s until early this century. Early settlers then hunted them for their meat and cleared large areas of their habitat for agriculture. The settlers also introduced domestic animals, many of which went wild and had a disastrous effect on the tortoises.
From the moment man discovered them, the future of the giant tortoises of the Galapagos was in question. First the Spanish sailors caught them and ate them. Then successive waves of pirates used them as a source of food. A prison colony was set up on the islands and further stocks of tortoises were taken. Sailors made a point of capturing a number of tortoises to use as fresh meat when their initial supplies went bad. The tortoises could live for a long time without water, so they were kept alive on the ships and given water only a short time before they were due to be eaten. Whalers were the next in line, and they too killed large numbers. The tortoises were killed and used a source of oil.
Feral goats threaten tortoise survival Populations, particularly on the more accessible islands, were severely depleted by passing ships (particularly whalers) taking tortoises on board for supplies. A total of over 15,000 tortoises is recorded in the logs of 105 whaling ships between 1811 and 1844 (12). Increased settlement in the 20th century encouraged commercial hunting of tortoises for oil and extensive collecting for museums (3). Introduced mammals now pose the greatest threat to the tortoises. Feral pigs, dogs, cats and black rats are extremely effective predators whilst feral goats, donkeys and cattle compete for grazing. Goats have had particularly drastic effects upon the natural vegetation (6).
In 1959, Ecuador declared all uninhabited areas in the Galapagos to be a National Park, and made it illegal to capture or remove many species from the islands, including tortoises or their eggs; in 1970, it became illegal to export any Galapagos tortoises from Ecuador, regardless of whether they had been reared in captivity or the wild, or whether from continental Ecuador or the islands; United States Public Law 91-135 (December 5 1969) automatically prohibits importation of Galapagos tortoises into the U.S.A. because their export from Ecuador has been declared illegal (4). A 1971 decree makes it illegal to damage, remove, alter or disturb any organism, rock or other natural object in the National Park (6). The Galapagos National Park Service systematically hunt feral predators and competitors where necessary. Some nests are protected by lava corrals and the eggs of many of the populations are taken from the wild and hatched and reared at the Charles Darwin Research Station. Juveniles that have reached a size that ensures a good chance of survival are returned to their original ranges (5,13).
Geochelone elephantopus is listed on Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Appendix I listing requires that trade in the taxon and its products is subject to strict regulation by ratifying states and international trade for primarily commercial purposes is prohibited.
At the same time, eradication campaigns aim to remove the introduced animals which threaten the tortoises in the wild. Tortoises could remain alive in a ship hold for up to a year at sea with little food or other necessities.
The Galapagos giant tortoise is now strictly protected. Young tortoises are being raised in a programme by the Charles Darwin Research Station in order to help keep the remaining races from becoming extinct. Eggs are collected from places on the islands where they are threatened and when the young tortoises hatch they are kept in captivity until they are large enough to fend for themselves.
This project, which began in the 1970's has been a success. Of the 11 species that were once endangered 10 species have been brought up to guarded levels. The most noted success story is that of the Española Tortoises. When the project began the Hood Tortoise population consisted of 2 males and 11 females. These tortoises were brought to the Darwin Station. Miraculously a third male was discovered at the San Diego Zoo and brought to the Darwin Station to join the others in a captive breeding program. These 13 tortoises are the parents of over 300 young tortoises now roam free on Española.
[edit] Species
Research has shown that there were probably thirteen species of Geochelone in the Galápagos Islands. Now only eleven species remain, five on Isabela island, and the other six on Santiago, Santa Cruz, San Cristóbal, Pinzón, Española and Pinta. The Pinta species is likely due to become extinct as only one single male, known as Lonesome George, is known to be alive (though the possibility of other individuals remaining cannot be completely discounted).
"George," after the U.S. actor George Goebel, who called himself "Lonesome George" in a television program.
the Pinta race through "Lonesome George" would pass along at least some of his genes into future generations. The Wolf race were the closest morphologically to the Pinta race. The aim was to maintain George's sexual activity for the possibility that a Pinta female was found, or at least back crossing to create as close an offspring as possible to the Pinta characteristics. Unfortunately, he has yet to succeed in breeding successfully with these females, and we do not yet fully understand the reasons. "Mounting" took place, but no eggs resulted. This could be because of the genetic distance between George and the tortoises of Northern Isabela.
Current data about "Lonesome George"
Age: estimated to be 70-80 years
Weight: 88kgs
Size: 102 cm length of shell
Food: George is fed 500 grams of papaya fruit 5 times per week.
Once a week 100 grams of a special balanced diet.
Three times a week 50 grams of grass.
Health: No indication of any illness or disease
Only one male, Lonesome George, of the four extinct races exists. Previously he lived on Pinta Island, but is presently kept at the Charles Darwin Research Station.The Park Service moved 'George' to the Darwin Station where they have made every effort to encourage him to breed with female tortoises from Wolf Volcano on Isabela (Wolf Tortoises were found to be the closest morphologically to the Pinta Tortoises). Yet over the past nearly 30 years of trying, no new tortoises have been born. Before Lonesome George was found, the last reported sighting of tortoises on Pinta was in 1906, when the island was visited by the Californian Academy of Sciences. They collected three males,
lone george found in n 1971
The oldest known living specimen is a giant Galápagos tortoise named Harriet in the Australia Zoo at Beerwah, Queensland, Australia. Its estimated date of birth is 1830, and it is believed to be the oldest living animal in the world after the death of Adwaitya . Galápagos tortoises may live to an age of 120-200 years or more.
This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.
[edit] See also
- Chambers, Paul. A Sheltered Life: The Unexpected History of the Giant Tortoise. John Murray (Publishers), London. 2004. ISBN 0719565286.
- Lonesome George
- List of extinct animals of South America
- Carrillo, E., S. Alda, M. Altamirano, F. Ayala, D. Cisneros, A. Endara, C. Márquez, M. Morales, F. Nogales, P. Salvador, M. de L. Torres, J. Valencia, F. Villamaría, M. Yánez, and P. Zárate. 2005. Lista Roja de los Reptiles del Ecuador. Fundación Novum Milenium, UICN-Sur, UICN-Comité Ecuatoriano, Ministerio de Educación y Cultura, Quito, Ecuador.
