Galapagos

Galápagos Islands

The Galápagos Islands are a chain of islands (also called "archipelago") in the Pacific Ocean best known for their impressive array of plant and animal species. Charles Darwin, during his voyages on HMS Beagle, landed on the Galápagos Islands. He observed the plants and animals there and collected samples from the islands. These studies contributed to the inception of Darwin's theory of evolution by means of natural selection. See the Science page, section 5, for a discussion of Charles Darwin and his theory.

The Galápagos archipelago belong to the Republic of Ecuador (South America) and lie about 966 kilometers (600 miles) off of the Ecuadorian coast. In Ecuador it is called "Archipiélago de Colón" in Provincia de Galápagos. The archipelago consists of 18 main islands, 3 smaller islands, and 107 rocks and islets. The largest of the islands is named Isabela. It is approximately 129 kilometers (80 miles) long. Isabela is on the equator. Some islands of the archipelago are south of the equator and others are on its north. Below are: (1) a map of the Galápagos Islands, and (2) a map of South America (showing Ecuador) and the Galápagos Islands.

The archipelago is located on the Nazca Plate (a tectonic plate), which is moving east/southeast, diving under the South American Plate at a rate of about 2.5 inches (6.4 cm) per year. It is also atop the Galápagos hotspot, a place where the Earth's crust is being melted from below by a mantle plume, creating volcanoes. As a result, the Galápagos Islands are an archipelago of volcanic islands. Volcanicity (the phenomenon of eruption of molten rock (magma) onto the surface of the earth) has been continuous on the Galápagos Islands for at least 20 million years, and perhaps even longer (possibly up to 90 million years). The mantle plume beneath the eastward moving Nazca Plate has given rise to a 3-kilometer-thick platform under the island chain and seamounts.

Numerous and repeated volcanic eruptions helped to form the rugged mountain landscape of the Galápagos Islands. In late June 2018, Sierra Negra, one of five volcanoes on Isabela and one of the most active in the Galápagos archipelago, began erupting for the first time since 2005. Lava flows made their way to the coastline, prompting the evacuation of about fifty nearby residents and restricting tourist access.

The first recorded visit to the islands happened by chance in 1535, when Fray Tomás de Berlanga, the Bishop of Panamá, was surprised to find this undiscovered land on a voyage to Peru. De Berlanga eventually returned to Spain. He wrote an account of his adventure (the first written record on the Galápagos) which he reported to King Charles V of Spain. Whilst it was largely unenthusiastic, it does at least contain some interesting and amusing facts about the animals he encountered. De Berlanga described the giant tortoises, marine iguanas and sea lions, among other species. He also commented on the “silliness” of the birds who “didn’t know how to flee” and were all too easily caught by hand. Subsequent Spanish explorers from the same era reinforced this original account, painting a picture of the islands as dry, inhospitable, lacking in water and food sources (aside from giant tortoises) and generally being very difficult places in which to live.

Owing in large part to early accounts of the Galápagos as inhospitable and barren, as well as to their relative isolation, the islands were rarely visited and largely ignored by colonial powers. Even so, the group of islands was shown and named "Ins: de los galopegos" (Islands of the tortoises) in Abraham Ortelius's map "America Sive Novi Orbis" published in 1570 (Abraham Ortelius (1527 – 1598) was a cartographer, geographer, and cosmographer, conventionally recognized as the creator of the first modern atlas, the Theatrum Orbis Terrarum (Theatre of the World)). In the three centuries after their discovery, they did however become a refuge for pirates (particularly the English pillaging Spanish galleons), as well as those looking to exploit the islands’ natural inhabitants. A number of wildlife species suffered as a direct result of human discovery. The Galápagos drew a large number of whalers and sealers in the nineteenth century. The discovery of huge groups of sperm whales encouraged an influx of whale ships to the islands from Europe, and fur seals were also highly prized for their luxurious fur and hunted to the brink of extinction.

Up until 1832, the Galápagos were owned by the Spanish Empire. After this point, they were claimed by the new Republic of Ecuador.

The Galápagos are best known for their diverse array of plant and animal species. Many species are endemic, which means they are not found anywhere else in the world. The archipelago and its immense marine reserve are known as the unique "living museum and showcase of evolution." The volcanic formation together with the extreme isolation of the islands led to the development of unusual plant and animal life – such as marine iguanas, flightless cormorants, giant tortoises, huge cacti, endemic trees and the many different subspecies of mockingbirds and finches. As another example, penguins live in Southern hemisphere, and especially Antarctica. The Galápagos penguin is endemic to Galápagos Islands and the only penguin species to live in the Northern hemisphere.

Scientists have studied this complex ecosystem for more than 180 years. British naturalist Charles Darwin may be the most influential scientist to have visited the Galápagos Islands. Darwin first came to the Galápagos in 1835, on a ship called the HMS Beagle. His observations of wildlife on the island inspired his theory of evolution by natural selection. Below are: (1) a drawing of HMS Beagle, and (2) an Admiralty chart of HMS Beagle published in 1841 CE showing the Galápagos Islands:

The following is description of some of the animals living on the Galápagos Islands.

(1) Marine iguana

Marine iguanas are the only lizards on earth that spend time in the ocean. They live only on the Galápagos Islands, and like many Galápagos species, they have adapted to an island lifestyle. Populations across the archipelago have been isolated from each other for so long that each island has its own iguana subspecies. Below is a picture of a marine iguana:

Regular iguanas climb in trees and eat leaves. Marine iguanas, however, have a totally different way of getting their food. When the tide is low, they’ll go out to sea and feast on algae and seaweed. It is interesting to study how they adopt to this new environment.

Marine iguanas are not a very agile species on land, but they are excellent swimmers – moving easily through the water as they feed on algae. Larger individuals go further out to sea and use their powerful claws to grip on to rocks in strong currents to feed, whilst the smaller ones stay inshore near rock pools, feeding on algae exposed at low tide. Marine iguanas can dive as deep as 30 m (98 ft), and can spend up to one hour underwater. Most dives are much shorter in duration and shallower than 5 m (16 ft). Marine iguanas have several adaptions that aid their survival. Their flattened tail is the primary means of propulsion in the water. Other adaptions in marine iguanas are blunt heads ("flat noses") and sharp teeth allowing them to easier graze algae off rocks.

This is a video of an iguana feeding on algae on a rock near the shore (note: the link at left links to an outside website). An image extracted from the video is shown below:

As an ectothermic animal (an organism in which there is little internal physiological sources of heat and mainly relies on environmental heat sources), the marine iguana can spend only a limited time in cold water diving for algae. Afterwards it needs to bask in the sun to warm up. Before warmed up, it is unable to move effectively, making it vulnerable to predation. However, this is counteracted by their highly aggressive nature consisting of biting and expansive bluffs when in this disadvantageous state. Their dark shade aids in heat absorption. In colder periods with cloudy weather and much wind, juveniles will stay in the lee of rocks, still gaining the heat from the sun. Adults may move inland to low-lying sites with less wind because of bushes and lava ridges but still exposed to direct sun. When in the water and their temperature is falling, their blood circulation is reduced to a low heart rate of about 30 beats per minute, allowing them to better conserve their warmth. When on land and heating up, the higher heart rate of about 100 beats per minute aids in spreading the heat throughout the body. To conserve heat during the night, they often sleep closely together in groups that may number up to 50 individuals, while others sleep alone below plants. Below is a picture of a group of marine iguanas basking in the sun:

Marine iguanas are also known for their very efficient salt glands, where they “sneeze” out salt. Because they feed underwater, they ingest a large amount of saltwater. In order to prevent dehydration, they must expel salt without expelling water, so they have specialized glands that remove salt from their blood.

They also have the incredible ability to shrink (in length and in overall size). In times of reduced food availability – particularly during El Niño climate events – they may shrink by as much as 20%. The now smaller individuals require less food. Once their preferred algae return to high levels, they quickly regain the lost size.

Not all iguanas in the Galapagos swim, some are vibrant and chunky lizards that prefer to stay on land.

(2) Darwin Finches (also known as the Galápagos finches)

These finches are famous for being the inspiration for Darwin’s theory of evolution. Darwin observed how the shape and function of these little bird’s beaks are so well adapted to their individual food sources. The largest of Darwin’s finches, the large ground finch, has a short and large beak that’s adapted for cracking nuts. Compare that to the small tree finch, who’s fast, sharp beak is well suited for snatching up small insects.

Below is excerpt from LibreTexts on the Darwin finches:

From 1831 to 1836, Darwin traveled around the world, observing animals on different continents and islands. On the Galapagos Islands, Darwin observed several species of finches with unique beak shapes. He observed these finches closely resembled another finch species on the mainland of South America and that the group of species in the Galápagos formed a graded series of beak sizes and shapes, with very small differences between the most similar. Darwin imagined that the island species might be all species modified from one original mainland species. In 1860, he wrote, “seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.”

Darwin observed that beak shape varies among finch species. He postulated that the beak of an ancestral species had adapted over time to equip the finches to acquire different food sources. This illustration shows the beak shapes for four species of ground finch: 1. Geospiza magnirostris (the large ground finch), 2. G. fortis (the medium ground finch), 3. G. parvula (the small tree finch), and 4. Certhidea olivacea (the green-warbler finch).

Darwin called this mechanism of change natural selection. Natural selection, Darwin argued, was an inevitable outcome of three principles that operated in nature. First, the characteristics of organisms are inherited, or passed from parent to offspring. Second, more offspring are produced than are able to survive; in other words, resources for survival and reproduction are limited. The capacity for reproduction in all organisms exceeds the availability of resources to support their numbers. Thus, there is a competition for those resources in each generation. Third, offspring vary among each other in regard to their characteristics and those variations are inherited. Out of these three principles, Darwin reasoned that offspring with inherited characteristics that allow them to best compete for limited resources will survive and have more offspring than those individuals with variations that are less able to compete. Because characteristics are inherited, these traits will be better represented in the next generation. This will lead to change in populations over generations in a process that Darwin called “descent with modification,” or evolution."

(3) Galápagos Tortoise

The Galápagos tortoise (or Galápagos giant tortoise) is one of the most famous animals only found on the Galápagos Islands. Actually, that’s how the Galápagos got its name. Spanish explorers, who explored the islands in the 16th century, named them after the Spanish word galápago, meaning "tortoise". These are without question the world’s largest tortoises, the biggest on record is over 5 feet long (1.5 m) and 920 pounds (420 kg). With lifespans in the wild of over 100 years, it is one of the longest-lived vertebrates. Captive Galápagos tortoises can live up to 177 years. For example, a captive individual, Harriet, lived for at least 175 years. Below is a picture of a Galápagos tortoise.

Below is a picture of Lionel Walter Rothschild (1868 – 1937), a British Zoologist, sitting on a Galápagos tortoise:

Galápagos tortoises are native to seven of the Galápagos Islands. Giant tortoises show large variation in size and shape between subspecies and populations, but all species can be classed into two main shell types: domed and saddle-backed. Dome-shelled tortoises lack an upward angle to the front of their carapace (shell), restricting the extent to which they can raise their heads. They tend to live on large, humid islands where there is lots of vegetation to eat. Saddle-backed tortoises have an upward curve to the front of their carapace, which allows them to stretch up to reach higher growing plants. They tend to live on arid islands in Galapagos, where food is less abundant.

The giant tortoise arrived in Galápagos from mainland South America 2-3 million years ago, where they underwent diversification into 14 species, differing in their morphology and distribution. All subspecies of Galápagos tortoises evolved from common ancestors that arrived from mainland South America by overwater dispersal. Genetic studies have shown that the Chaco tortoise of Argentina and Paraguay is their closest living relative. The minimal founding population was a pregnant female or a breeding pair. Survival on the 1000-km oceanic journey is accounted for because the tortoises are buoyant, can breathe by extending their necks above the water, and are able to survive months without food or fresh water. As they are poor swimmers, the journey was probably a passive one facilitated by the Humboldt Current, which diverts westwards towards the Galápagos Islands from the mainland.

All surviving subspecies of Galápagos tortoises are classified as "threatened" by the International Union for Conservation of Nature. Tortoise numbers declined from over 250,000 in the 16th century to a low of around 15,000 in the 1970s. This decline was caused by overexploitation of the subspecies for meat and oil, habitat clearance for agriculture, and introduction of non-native animals to the islands, such as rats, goats, and pigs. Tortoise populations on at least three islands have become extinct in historical times due to human activities. 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 subspecies is estimated to have exceeded 19,000 at the start of the 21st century.

The Galápagos giant tortoise spends an average of 16 hours per day resting. The rest of their time is spent eating grasses, fruits and cactus pads. They enjoy bathing in water, but can survive for up to a year without water or food. Small birds, such as Galápagos finches (also known as Darwin's finches), can often be seen sitting on the backs of giant tortoises. The birds and tortoises have formed a symbiotic relationship in which the birds peck the ticks out from the folds of the tortoises’ skin.

This is a video of a Galápagos tortoises walking slowly (note: the link at left links to an outside website). An image extracted from the video is shown below:

Breeding primarily occurs during the hot season (January to May), although mating may be seen at any time of year. Mating may last for several hours, with the male making loud roaring noises throughout. After mating, the female migrates to a nesting area, where she digs a hole with her back feet into which she lays 2 to 16 eggs, each the size of a tennis ball. The eggs are incubated by the sun, with the young tortoises hatching after around 130 days.

The most famous tortoise is Lonesome George, a giant tortoise from the island of Pinta in the northern regions of the Galápagos Archipelago. Below are: (1) a picture of Lonesome George, and (2) a map showing the location of Pinta Island:

He was considered one of the rarest creature in the world and was the last known survivor of the Pinta tortoise. Pinto Island used to have a population of tortoises. Similar to tortoises in other islands, Pinta tortoises were over-exploited by whalers, fur sealers, and others in the 1800s. The Pinta tortoise was thought to be extinct in the early part of the 20th century. Then in 1971, József Vágvölgyi, a Hungarian scientist studying snails on Pinta Island saw a tortoise on the island – Lonesome George. In the spring of 1972, Galápagos National Park rangers brought the tortoise to the Tortoise Center on Santa Cruz for its protection. The hope was that a female Pinta tortoise would eventually be found – in one of the zoos around the world or perhaps even on Pinta – and Lonesome George would have a breeding partner. Despite extensive searches and genetic analyses of any potential Pinta tortoise found in zoos, none has been located.

Lonesome George died on 24 June 2012.

(4) Scalesia (Darwin’s Finches of the Plant World)

Scalesia is endemic to the Galápagos Islands. They consist of 15 native shrubs and tree species with six subspecies. Scalesia have been referred to as the Darwin’s finches of the plant world due to their great ability of adaptive radiation. Each of the species has adapted to the different vegetation zones across the different islands. The dominant species is dependent on the island. (a) Scalesia pedunculata is dominant on Santa Cruz, San Cristobal, Floreana and Santiago, (b) Scalesia cordata is dominant on Isabela and (c) Scalesia microcephala on Fernandina.

Swathes of Scalesia sometimes grow in groups, all progressing at the same height and age, and often dying around the same time. They reach maturity after 15 years. There are very few young trees under the canopy and as such the whole population grows and collapses at the same time. El Niño events, droughts and floods can cause entire forests to collapse. The next generation of tree seedlings will then start to grow, so they are in a natural cycle of renewal, but if strong El Niño events are more frequent than the 15 year regrowth time there will be fewer mature trees able to reseed the forests.

The whole Scalesia Zone is most threatened by human settlement. The zone is some of the most fertile land area on the Islands and perfect for agriculture. This has led to much of the original Scalesia forest being chopped down and replaced. Livestock also proves a threat to remaining forests as goats, pigs and cows graze on young saplings and small individuals. The spread of introduced invasive species including vertebrates as well as plants can cause the Scalesia to be outcompeted. Fires and clear-cutting for wood reduces the habitat even further.

Below are picture of (1) Scalesia Pedunculata and (2) Scalesia Cordata

Below are picture of the flowers and leaves of (a) Scalesia Divisa, and (2) Scalesia Incisa

(5) Flightless Cormorant (also known as the Galápagos Cormorant)

Cormorants are fish-eating birds. The flightless cormorant is a cormorant endemic to the Galapagos Islands. It is unique in that it is the only known cormorant that has lost the ability to fly. Because they cannot fly away, they are therefore confined to the lava shoreline and beaches of Isabela and Fernandina. The adults are black on top and dark brown underneath with bright turquoise eyes. They have stunted wings that are one third the size of the wingspan they would require to fly. Although their wings are stunted, they are used for balance when the cormorant jumps from rock to rock along the coast. The keel on the breastbone, where birds attach the large muscles needed for flight, is also significantly reduced. Natural selection led to the species no longer having functional wings as they had very few land predators, while individuals that were better suited to swimming by reducing the wingspan were more successful in passing on their genes.

Below are pictures of: (1) a flightless cormorant showing its wingspan, and (2) a regular cormorant showing its wingspan:

The flightless cormorant is the largest extant member of its family, 89–100 cm (35–39.5 in) in length and weighing 2.5–5.0 kg (5.5–11.0 lb). The females tend to be smaller than the males.

Like all cormorants, it has webbed feet and sturdy legs that propel it through the water as it seeks its prey of fish, small octopuses, and other little marine creatures. The species feeds near the sea floor and no more than 200 meters offshore. Unlike penguins, they do not ‘fly’ underwater, but tuck in their wings and kick with their powerful hind legs, using their flexible necks to spear octopus and fish from inside small refuges in the reefs and rocks. On the surface they sit very low in the water, with only their necks visible from a distance. Like other cormorants, it's feathers are not waterproof, and they spend time after each dive drying their small wings in the sunlight.

This is a video of a flightless cormorant swimming underwater, presumably looking for food (note: the link at left links to an outside website). An image extracted from the video is shown below:

Currently there are around 1,000 breeding pairs of flightless cormorants on Isabela and Fernandina. Couples perform a strange and unique courtship dance that involves them intertwining their necks whilst twirling in a tight circle. The mated pair then makes a nest a few meters from the sea out of seaweed, flotsam and jetsam. Most eggs are laid between May and October, which are the coldest months, resulting in an abundance of marine food and less heat stress on the hatchlings. The eggs are incubated for 35 days until they hatch, after which the parents take turns to feed the chicks. Eventually the male is left to care for the chick and the female starts a new breeding cycle, which can happen up to three times in one season.

This is a video of two flightless cormorants performing courtship ritual while two others swimming around them (note: the link at left links to an outside website). An image extracted from the video is shown below:

Due to its small and concentrated population, this species is particularly vulnerable to any changes in environment such as El Niño. In 1983, half the population was lost during a severe El Niño event. Nest flooding and volcanic eruptions decrease the population. Oil spills could have a huge impact if the spill were to reach the seas around Isabela and Fernandina. They are also likely to be at threat from marine plastic pollution, both through ingesting it and through being entangled by it.

Below are publications related to Galápagos:

(1) Marine Iguana

Marine iguanas in Galapagos