The Reptiles of Galapagos.
Due to the isolation, only 28 species of reptiles are found on the islands, and eighteen of these are endemic. There are members of five groups; Tortoises, iguanas, lizards, geckos and snakes. The surrounding sea hosts a few more species; both turtles and a snake. My photos of Galapagos' reptilians can be seen here.
The Giant Tortoises of the Galapagos islands have named the islands. Their shell reminded the bishop of
Panama (who made the first recorded
of the islands) of a type of saddles: Spanish; "galápago".
Somehow, their ancestors have made the more than 1000
kilometres journey cross the sea. Most belong to one
species which use to have fourteen subspecies on the
islands. The closest living relative of these Galapagos giant
Geochelone chilensis, a small tortoise found in
Argentina. The split between Geochelone chilensis and
the Galápagos lineage probably occurred 6-12 million years
ago based on mitochondrial DNA analysis.
There was once more than 250.000 of these giants on the islands. Now, only 15.000 is found. The adults have been eaten by sailors, the eggs by introduced rats, dogs and pigs. The Darwin Research Station have a breeding program, and they are re-introduced along with the clearing of invasive species on the islands.
The Galapagos tortoise is an herbivore that eats cactus, grasses, leaves, vines, and fruit. Fresh young grass is a favourite food of the tortoises, and others are the Manzanillo; Hippomane mancinella, the endemic Galapagos guava; Psidium galapageium , the floating water fern; Azolla microphylla, and the bromeliad; Tillandsia insularis. They have tremendous water storage capacities, enabling them to survive the long arid season in the cold period.
The social structure of the Galapagos tortoise is a dominance hierarchy based on the height to which the tortoise can stretch its head. They matures at 20-25 years of age and can live to they reach 200 years, reaching a weight up to 300 kilos. Compared to most tortoises, the birth rate of Galapagos tortoises is extremely low, a result of the lack of predators. Where many other tortoises can lay up to hundreds of eggs at a time, the Galapagos tortoise only lays between 2 and 16 eggs.
The mating occurs at any time of the year, although it does have seasonal peaks between January and August. After mating, in June-December, the females journey up to several kilometres to reach nesting areas of dry, sandy ground, often near the coast. These eggs are laid in a 30 centimetre deep hole. The female makes a muddy plug for the nest hole out of soil mixed with urine and leaves the eggs to incubate, which takes between 120-140 days. Then it can take them up to a month to dig them selves free. These small, only six centimetre large replicas weight only 80 grams.
The tortoises can vocalise in aggressive encounters, whilst righting themselves if turned upside down and, in males, during mating. The latter is described as "rhythmic groans", and can be heard for a hundred meters around. They 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 pick off ticks that are hidden in the folds of the skin (especially on the rear legs, cloacal opening, neck, and skin between plastron and carapace), thus freeing the tortoise from harmful parasites and providing the finch with an easy meal.
(Synonym: Geochelone nigra, Quoy & Gaimard 1824
and Chelonoidis) have evolved into different subspecies on each island and
habitats on the single island. That way, they have been able
to survive in these sometimes
habitats. These differences were noted by Captain Porter,
even before Charles Darwin. Larger islands with more wet
highlands such as Santa Cruz and the Alcedo Volcano on
Isabela have lush vegetation near the ground. Tortoises here
tend to have 'dome-back' shells. These animals have
restricted upward head movement due to shorter necks, and
also have shorter limbs. These are the heaviest and largest
of the subspecies.
The subspecies of Geochelone elephantopus:
The snakes on the island include some species of the Alsphis family; Banded Galapagos Snake; Antillophis slevini, found on Isabela, Fernandina and Pinzon. The Galapagos Racer; Alsophis biseralis, the Hood Racer; Philodryas hoodensis which is only found on Espanola and the Striped Galapagos Snake; Antillophis steindachneri which is found on Seymour, Baltra, Rapida Santiago and northern Santa Cruz.
Synonym for Alsophis is Philodryas and Dromiscus.
The snakes, which all
are small; 60-90 centimetres, are only found on the
southern islands. They feeding on insects,
Lava Lizards, grasshoppers,
geckos, finch nestlings and from young
Marine Iguanas. They are
quite similar looking, about two to three feet long, brown
with yellowish longitudinal stripes.
The Iguanas are represented by three species, all endemic. The Marine Iguana; Amblyrhynchus cristatus is unique in that it is the only seagoing lizard in the world. The Land Iguana; Conolophus subcristatus, and the Santa Fe Land Iguana; Conolophus pallidus.
The Marine Iguana; Amblyrhynchus cristatus are found on most or even all the islands of the Archipelago. Even though they may vary in size and colours from island to island but they are all considered to be a single species. The most colourful are found at Española, the biggest ones are located at Fernandina and Isabela and the smallest one can be seen at Genovesa. The feed on algae, found in the sea. They have to heat up for hours to do a 20 minutes dive. Older and larger animals swim further out to sea. They can grow to 80 or even 90 centimetres.
The Land Iguana on Galapagos are divided into two species, Conolophus subcristatus and Conolophus pallidus, which are only found on Santa Fe. This particular species is paler in colour and has more prominent spines, moor drooping crest and redder eyes. Conolophus subcristatus are found on North Seymour, South Plaza, Baltra, Santa Cruz, Isabela and Fernandina. They feed on grass, centipedes, plants and especially Opuntia fruits and their yellow flowers. Land Iguanas are different from Marine Iguanas in that they do not have a square nose; they have pointed noses. They get to be around 90 centimetres long.
Lava Lizards; Tropidurus sp. are the most
abundant Galapagos reptiles. All species of lizards found in
Galapagos are differences in colour and shape, from 12,5-25
centimetres, which show the incredible way they have adapted
to the environment of the Islands. They feed on insects,
flowers and fruits.
The Galapagos Geckos or Galapagos Leaf-toed Gecko: Phyllodactylus galapagoensis. are represented by six subspecies that all are endemic to the Islands. They are found on Santa Cruz, San Cristobal, Baltra, Isabela, and Floreana. They are all greyish. The subspecies are: Phyllodactylus galapagensis daphnensis, Phyllodactylus galapagensis galapagensis, Phyllodactylus galapagensis maresi and Phyllodactylus galapagensis olschkii.
Phyllodactylus barringtonensis is found on Santa Fe, Phyllodactylus bauri is both on Floreana and Pinta, while Phyllodactylus gilberti is only found on Wolf. San Cristobal Leaf-Toed Gecko; Phyllodactylus leei is another San Cristobal species.
Some species that have
been introduced to the islands: Gonatodes caudiscutatus
on San Cristobal along with Lepidodactylus lugubris
Phyllodactylus tuberculosus while Phyllodactylus
reissi have been brought in on Santa Cruz.
Several other sea turtles can be seen: Hawksbill Turtle; Eretmochelys imbricata. The huge Leatherback Turtle; Dermochelys coriacea and Olive Ridley; Lepidochelys olivacea.
Yellow-bellied Sea Snake; Pelamis platurus. The tail section has spots, and the body is yellow and black, this snake gets to be up to 85 centimeters long. The venom is dangerous, even more poisonous than the venom of the cobra snake. Fortunately, the Yellow-bellied Sea Snake is pretty rare, except for during the El Nino times, when waters get warmer because of the Nino current.
Amphibians was not found on the islands, but roomers have it, that two species have been realised recently. Only the goods and the insane know why!