Galapagos Giant Tortoise
by Venetia Featherstone-Witty
Title
Galapagos Giant Tortoise
Artist
Venetia Featherstone-Witty
Medium
Photograph - Photographs
Description
The Galápagos tortoise complex or Galápagos giant tortoise complex (Chelonoidis nigra) are the largest living species of tortoise. Modern Galápagos tortoises can weigh up to 417 kg (919 lb). Today, giant tortoises exist only on two remote archipelagos: the Galápagos Islands 1000 km due west of mainland Ecuador, and Aldabra in the Indian Ocean, 700 km east of Tanzania.
The Galápagos tortoises are native to seven of the Galápagos Islands, a volcanic archipelago about 1,000 km (620 mi) west of the Ecuadorian mainland. With lifespans in the wild of over 100 years, it is one of the longest-lived vertebrates. A captive individual lived at least 170 years. Spanish explorers, who discovered the islands in the 16th century, named them after the Spanish galápago, meaning "tortoise".
Shell size and shape vary between populations. On islands with humid highlands, the tortoises are larger, with domed shells and short necks; on islands with dry lowlands, the tortoises are smaller, with "saddleback" shells and long necks. Charles Darwin's observations of these differences on the second voyage of the Beagle in 1835, contributed to the development of his theory of evolution.
Tortoise numbers declined from over 250,000 in the 16th century to a low of around 3,000 in the 1970s. This decline was caused by overexploitation of the species for meat and oil, habitat clearance for agriculture, and introduction of non-native animals to the islands, such as rats, goats, and pigs. The extinction of most giant tortoise lineages is thought to have also been caused by predation by humans or human ancestors, as the tortoises themselves have no natural predators. Tortoise populations on at least three islands have become extinct in historical time due to human activities. Specimens of these extinct taxa exist in several museums and also are being subjected to DNA analysis. Ten species of the original 15 survive in the wild; an 11th species (Chelonoidis abingdonii) had only a single known living individual, kept in captivity and nicknamed Lonesome George until his death in June 2012. Conservation efforts, beginning in the 20th century, have resulted in thousands of captive-bred juveniles being released onto their ancestral home islands, and the total number of the species is estimated to have exceeded 19,000 at the start of the 21st century. Despite this rebound, the species as a whole is classified as "vulnerable" by the International Union for Conservation of Nature.
The tortoises are herbivores that consume a diet of cacti, grasses, leaves, lichens, berries, melons, oranges, and milkweed. They have been documented feeding on Hippomane mancinella ('poison apple'), the endemic guava Psidium galapageium, the water fern Azolla microphylla, and the bromeliad Tillandsia insularis. Juvenile tortoises eat an average of 16.7% of their own body weight in dry matter per day, with a digestive efficiency roughly equal to that of hindgut-fermenting herbivorous mammals such as horses and rhinos
FEATURED 11/28/17 in "Images That Excite You"
FEATURED 11/28/17 in "Kingdom Animalia"
FEATURED 11/30/17 in "Wildlife One A Day"
FEATURED 11/30/17 in "Our 4-legged Friends"
FEATURED 12/0/17 in "Animal Photographs"
Uploaded
November 27th, 2017
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