The Galápagos Islands: Laboratory of Evolution
The Galápagos Islands
archipelago is home to a complex ecosystem with a fascinating geological
history, as well as unique examples of plant and animal life. The islands' flora
and fauna inspired renowned naturalist Charles Darwin to formulate his theory
of evolution, and thousands of tourists and scientists flock to the islands
every year to further study the wildlife.
Geography
Thirteen major islands,
seven smaller islands and about 125 islets and rocks make up the Galápagos
Islands, which lie about 600 miles (1,000 kilometers) off the coast of Ecuador
in the Pacific Ocean. Straddling the equator, the islands in the chain are
located in both the Northern and Southern hemispheres.
Isabela, the largest
island, covers 1,803 square miles (4,670 square km) and reaches an altitude of
5,600 feet (1,707 meters). The smallest of the main islands is South Plaza,
with an area of 0.05 square miles (0.13 square km), or about 20 city blocks.
Geology
The Galápagos Islands
are volcanic islands located on the Nazca Plate, which is moving to the
east-southeast, toward the South American Plate. The meeting of the two
tectonic plates has created a subduction zone as the Nazca Plate slides under
the South American Plate. The Andes Mountains were created as a result.
As the Nazca Plate
passed over the Galápagos hotspot — a point where magma pushes through the
crust — volcanoes erupted, and eventually, the Galápagos Islands were formed.
It is estimated that the hotspot has been active for at least 20 million years,
and that the islands as we see them today formed over the last three to four
million years. The movement over the hotspot is evident in the ages of the
islands, which increase in roughly the same direction. The oldest islands are
Isla Española and South Plaza, which are between 3 million and 4 million years
old, according to Volcanic Galapagos. The islands of Darwin, Fernandina,
Genovesa, Isabela, Marchena and Santiago are all approximately 700,000 years
old.
Many of the volcanoes
are still active. Isabela is made up of six distinct volcanoes, Loyc
Vanderkluysen, a geoscientist and volcanologist at Drexel University in
Philadelphia, told Live Science. Six volcanoes on three separate islands have
erupted in the Galápagos since 1990.
Climate
Although they lie
within the tropics, the Galápagos Islands don't have lush rainforests. The
islands sit in the path of three intersecting major ocean currents, according
to Cornell University: The Humboldt (or Peru) Current brings cold waters from
Antarctica; the Panama Current is warmer and comes from the north and the
Cromwell Current causes deep, cold water to rise to the surface (called
upwelling). The cooler waters keep the climate moderate and dry.
The islands experience
two seasons each year. The dry season is July through December, when average
temperatures are typically in the mid-70s degrees Fahrenheit (mid-20s degrees
Celsius) and rainfall averages less than half an inch (a little more than a
centimeter) per month. During the dry season, fog is typically found at higher
elevations, but there is little rain. The warm season is from January through
June, when average temperatures reach the low to mid-80s degrees F (upper 20s
to low 30s degrees C) and rainfall reaches a little over an inch (almost 3 cm)
per month. March and April are typically the wettest months (receiving 1.5 to 2
inches of rain), with much of the rain draining through the volcanic rock and
soil.
Every two to eight
years, El Niño brings warmer, less-nutrient-rich waters. Many species suffer
during this time as the food chain is disrupted, according to the World
Wildlife Fund. The El Niño events of 1982-1983 and 1997-1998 were especially
devastating; the marine iguana population declined by about 90 percent, and the
penguin population dropped by more than 75 percent. The total population of sea
lions declined by about 50 percent, but nearly all sea lions under age 3
perished.
With climate change
affecting the severity and frequency of El Niño events, the "new
normal" is forecast to be similar to El Niño periods year-round, with
warmer air and water and increased rainfalls, according to WWF. Climate change
may also cause sea levels to rise and levels of acidity to increase.
Plants
About 600 plants are
native to the Galápagos, and at least 30 percent of those are endemic, meaning
they're found nowhere else in the world, according to the Galapagos
Conservancy.
There are also an
estimated 800 introduced species, some of which are incredibly invasive,
meaning that they can quickly intrude into the environment and cause harm to
native plants and animals. These include quinine, guava and blackberry. A few
of the invasive species, such as tropical kudzu, have been successfully
eradicated, according to Plantwise.
There are three main
vegetation zones in the Galápagos: coastal, arid and humid highlands.
The coastal zone
follows the shorelines of the islands, and the mangrove trees that grow there
provide shelter and breeding grounds to many birds, iguanas, sea lions and sea
turtles. The roots of the trees provide a protected habitat for marine life
such as shrimp, crabs and small fish. Other plants that grow in this area
include saltbush and beach morning glory, according to The Galapagos Islands handbook.
The arid zone is the
largest in the islands and contains many plants typically found in deserts,
such as cacti, succulents and leafless shrubs, according to the handbook. This
zone extends from near the shoreline up to about 200 feet (60 m) in elevation.
A transitional zone
sits between the arid zone and humid highlands. It has characteristics of both
the arid and humid zones, with dense vegetation dominated by small trees and
shrubs with various types of ferns.
The humid highlands,
which start at about 1,000 feet (300 m), feature the scalesia tree and the
Miconia robinsoniana shrub, which is considered one of the most endangered
plant species on the islands, according to the handbook. These regions have
some of the most fertile soil on the islands, and vast portions of these zones
have been cleared for agriculture on the human-inhabited islands.
On the few islands that
are taller than about 2,000 feet (600 m), the Galápagos tree fern (Cyathea
weatherbyana) is the dominant plant.
Animals
The Galápagos are
famous for several unique animals, including giant tortoises, iguanas, Darwin's
finches and Galápagos penguins. According to the Galapagos Conservancy, about
80 percent of the islands' land birds, 97 percent of the reptiles and land
mammals, and at least 20 percent of the marine species are endemic to the
islands.
The tortoises in the
Galápagos are the largest in the world, with males reaching up to 6 feet (1.8
m) long and more than 550 lbs. (250 kilograms), according to the San Diego Zoo.
They live well over a century, with the oldest known tortoise living to
approximately 170 years old.
There are an estimated
20,000 to 25,000 giant tortoises in the wild, according to the Galapagos
Conservancy with the species as a whole ranked as vulnerable by the WWF. Four
species are extinct. Lonesome George, the last surviving member of Chelonoidis
abingdoni, the species native to Pinta Island, died in 2012. Threats to the
survival of the giant tortoises include invasive species and climate change.
The only marine iguanas
in the world — in addition to three land species — are endemic to the
Galápagos. Marine iguanas have been known to grow to be up to 4 feet (1.2 m)
long; land iguanas grow longer than 3 feet (1 m), according to the Galapagos
Conservancy. Marine iguanas live both on land and in the sea, primarily eating
in the water and resting and mating on land. They face relatively few predators
while in the sea, but on land, both marine and land iguanas may be hunted by
hawks, herons and introduced species, such as cats and dogs. Numbers in some
locations have dwindled significantly due to introduced species, although due
to conservation efforts, populations are considered to be healthy and
increasing.
Very few species of
mammals are native to the Galápagos Islands: Galápagos sea lions (Zalophus
wollebaeki), Galápagos fur seals (Arctocephalus galapagoensis), four species of
rice rats (Nesoryzomys narboroughii, Oryzomys bauri, Nesoryzomys swarthy, and
Nesoryzomys fernandinae) and two species of bats (Lasiurus cinereus and
Lasiurus brachyotis). Dolphins and whales also visit the islands, according to
the Galapagos Conservancy.
The Galápagos sea lion
is the islands' largest animal, with males weighing up to about 550 lbs. (250
kg). They are often found lounging on the docks and beaches. Sea lions tend to
gather in harems consisting of a dominant male and several females, or in
bachelor colonies, according to the Galapagos Conservancy.
Galápagos fur seals,
which are actually a type of sea lion, prefer the rockier, shadier beaches when
they aren't swimming. In the 1800s, the fur seals were hunted nearly to
extinction for their insulating coats. The population today has made a dramatic
comeback with numbers similar to those of the sea lions, according to the
Galapagos Conservancy
Twenty-nine species of
land birds live on the islands; 22 of them are endemic species, and four are
endemic subspecies. Thirteen of the endemic species are varieties of Darwin's
finches, and four are mockingbird species. Eight of the 22 endemic species are
considered vulnerable or higher. Two — the mangrove finch and the floreana
mockingbird — are critically endangered, according to the Galapagos
Conservancy.
Darwin's finches make
up the largest population group on the islands. Each of the individual species,
as noted by Darwin, has a distinctive beak shape and size depending on their
diet. Diets range from seeds, flowers and leaves to insects, including ticks
groomed from tortoises and iguanas, as well as the blood of seabirds. Darwin's
study of the differences among the finches helped him develop the theories of
natural selection and evolution.
There are six endemic
species of sea birds: the Galápagos penguin (Spheniscus mendiculus); the
flightless cormorant (Phalacrocorax harrisi); the waved albatross (Phoebastria
irrorata), the largest of the birds; the Galápagos petrel (Pterodroma
phaeopygia), the lava gull (Leucophaeus fuliginosus) and the swallow-tailed
gull (Creagrus furcatus), according to the Galapagos Conservancy. Additional
species that call the islands home include three species of boobies, great and
magnificent frigate birds, and red-billed tropicbirds.
The Galápagos penguin
is the only penguin that lives near the equator. The vast majority of the 2,000
penguins live on Fernandina and Isabela islands. The penguin is on the
International Union for Conservation of Nature's Red List of Threatened
Species, due to its small population size, which fluctuates with El Niño years.
According to a 2005 paper in the journal Biological Conservation, the numbers
may continue to drop because of increased El Niño events, which cause drastic
decreases in the food supply at the start of breeding season, when penguins
stock up on as much food as they can.
Among the large
populations of marine life living in the waters around the Galápagos,
approximately 20 percent of the species are endemic, according to the Galapagos
Conservancy. And 544 species of fish have been identified in the protected
waters around the islands as of 2016, according to the Darwin Foundation; at
least 79 species are endemic, and another 452 are indigenous (native to the
Galápagos but also found elsewhere). Of these species, nearly 30 are sharks,
including the whale shark (Rhincodon typus) — the largest fish in the world —
which reaches up to 40 feet long (12 m) and weighs up to 22 tons (20 metric
tons). There are also several types of rays (such as the 20-foot wide giant
manta ray) and many tropical fish species, according to Natural Habitat
Adventures.
History
Explorer Thor Heyerdahl
found pots and other artifacts on the Galápagos in the 1950s, suggesting that
South American people had visited the islands in the pre-Columbian era. The
first European to visit the Galápagos was Fray Tomás de Berlanga, the Spaniard
recently named the bishop of Panama. He accidentally reached the islands in
March 1535 after his ship was carried off course, according to Cornell
University. De Berlanga opined that there was little value to the islands due
to their difficulty in locating fresh water sources, and the limited plant and
animal life deemed valuable for humans.
The islands first
appeared on world maps by Gerardus Mercator and Abraham Ortelius around 1570,
with the name Insulae de los Galopegos (Island of the Tortoises), according to
Cornell University.
During the height of
the Spanish empire, pirates used the islands as a base for their raids on
Spanish ships heading back to Europe. Sir Francis Drake, an explorer
commissioned by England with tendencies towards piracy, was the first to use
the islands in this way in 1578, according to the Galapagos Conservancy.
By the end of the 18th
century, whalers began to replace the pirates. Besides whales, whalers also
hunted tortoises, birds and fur seals, leading some species into extinction or
close to it, according to Cornell. It is estimated that nearly 200,000
tortoises were hunted in the 19th century alone, and the fur seals were nearly
extinct by the end of the century.
During the War of 1812,
the USS Essex, commanded by Capt. David Porter, reached the islands and nearly
decimated the British whaling fleet. Porter also wrote detailed notes about the
islands, including descriptions of the eruption of Floreana in 1813 and some
differences in the types of giant tortoises, as well as carefully charted the
islands' coastlines, according to the Galapagos Conservancy.
The first European
resident of the Galápagos was Patrick Watkins, an Irishman, who arrived on the
island of Floreana in 1805, living in a drunken state for nearly his entire
stay, according to the Galapagos Conservation Trust. He escaped to Ecuador in
1809 after trapping a handful of men on the islands with him and stealing a
boat. Watkins, however, landed alone after most likely killing his crew on the
voyage. Although he had planned to return to the islands, it is unlikely that
he ever did, as it is rumored he was thrown in jail just before his boat
launched. "Moby Dick" author Herman Melville, who was a whaler for
several years, visited the islands in 1841 and used Watkins as his inspiration
for a part in his short story "Las Encantadas" (The Enchanted
Islands), which was published in 1854.
Colonization of the islands
began in the early 1830s, according to the Galapagos Conservancy. Ecuadoran
Gen. José María de Villamil brought over colonists, who were primarily
soldiers, to the island of Floreana. About 15 years later, the settlement was
deemed a failure. Two additional attempts to colonize Floreana occurred in 1858
and in 1893.
According to the
Galapagos Conservancy, in the 1920s, Norwegian settlers landed in Floreana, San
Cristóbal and Santa Cruz islands. Originally, they were looking to set up
whaling facilities but switched over to a fishing and cannery business. German
colonists began arriving in 1929 to work with the Norwegian farmers and
fishermen.
Penal colonies were set
up on Floreana and San Cristóbal in the mid-19th century and on Isabela in the
1940s, according to the Galapagos Conservancy. The penal colonies were closed
in 1959 after a rebellion in 1958 at the Isabela prison.
In 1959, the vast
majority of the land area — 97 percent — was designated a protected national
park, according to the United Nations Educational, Scientific and Cultural
Organization(UNESCO). Four of the islands — Floreana, Isabela, San Cristóbal
and Santa Cruz — have a total permanent population of about 25,000 people, who
are restricted to the remaining 3 percent of total land area across the
islands.
Darwin and evolution
Credited as the father
of evolution, Darwin was actually a trained geologist. Darwin had been
traveling around South America for about four years before landing in the
Galápagos in 1835, J. Bret Bennington, chair of the Department of Geology,
Environment, and Sustainability at Hofstra University, told Live Science.
During that time, Darwin became familiar with the plant and animal life that
lived in various climates around the mainland as well as with some of the
islands the ship visited in the Atlantic Ocean on its way to South America from
England, said Bennington, who also directs a study abroad program to the
Galápagos Islands.
Darwin was a
creationist when he began his journey on the HMS Beagle, but he slowly changed
his mind during the voyage, especially when he studied life on and around the
Galápagos. Darwin saw many islands of various sizes, close together and
geologically young inhabited by similar yet different species of plant and
animal life. Darwin concluded that life in the Galápagos didn't make sense with
the current views of creationism.
It took Darwin 23 years
after returning home from his voyage to put together the jigsaw puzzle that
fully supported evolution and natural selection, which is one of bases of
evolution that explains why certain traits get passed on to the following
generations, according to the University of California at Berkeley. Published
in 1859, Darwin's famous "On the Origin of Species" took the
foundations for the theories of evolution that had already been placed before
him and built upon them, providing the evidence that definitively supported
evolution. Within a decade of the theories' publication, according to Cornell,
scientists favored Darwin's theories of evolution and natural selection over
creationism, and these transformational ideas still hold today, about 160 years
later.
Environmental threats
and conservation efforts
According to UNESCO,
the primary threats to the Galápagos are invasive plant and animal species,
increased tourism, demographic growth, illegal fishing and governance issues.
Global warming is another threat that is beginning to affect the islands,
according to National Geographic.
According to the
Convention on Biological Diversity (CBD), there is an equilibrium in any
isolated habitat, such as an island, that affects species diversity, which is
maintained between the rates of increased species types and populations, and
extinction. Invasive plant and animal species can be introduced into the
environment by humans or via air or water; the invaders can upset the natural
equilibrium and thus greatly increase the extinction rate of native plants and
animals.
The spread of invasive
species is slowed through prevention measures, according to the CBD. Education
of the local population and any travelers to the islands is key to making
informed decisions on how to slow and eradicate species in order to help bring
the native ecosystem back to its natural equilibrium.
Illegal fishing is also
a major threat to the ecosystem. A 2014 article in the journal Aquatic
Conservation: Marine And Freshwater Ecosystems noted that fishing for sharks
simply for their fins, for example, creates an imbalance in the ecosystem: The
populations of other predatory species, such as sea lions, will increase,
leading to an increased consumption of fish, many of which are commercially
valuable. The imbalance eventually leads to an environment that is
unsustainable for both predator and prey. The researchers recommended that the
existing rules governing fishing around the islands be further enforced, and
that loopholes, such as the one allowing the fishing of sharks in certain
instances, be closed in order to maintain the islands' natural biodiversity and
health.
Dr. Jeffrey Roberg,
chair of political science at Carthage College in Wisconsin and who researches
environmental politics in South America, believes that tourists are the primary
invasive species disrupting the natural equilibrium of the islands. Even when
being as careful as possible, tourists can have negative effects on the
environment. This can be true even though paying tourists are a source of
funding for conservation efforts, Roberg said. Even with rules in place, more
tourists mean more opportunity for abusing those rules, he added.
According to the
Galápagos Conservatory, as of 2015, there were 291 authorized hotels and 74
cruise vessels with onboard accommodation housing the nearly 250,000 tourists
who visited the islands annually. There is currently no limit on the number of
tourists who can visit the islands. The number of tourists is forecast to rise
steadily over the next several years unless laws are put into place and
enforced.
Increased tourism
brings increased foot traffic and, therefore, increased potential for tourists
to go off the designated paths, which could disrupt local wildlife. More
tourists mean more supplies need to be brought in, such as potable water and
building materials for additional hotels, shops and residences. Also, the
potential increases for accidents that can affect the environment, such as a
large oil spill that occurred in 2001, according to Roberg. And there is also
the issue of what to do with the additional trash that would be produced with
growing numbers of tourists, as well as the treatment of additional liquid and
solid waste.
Even when tourists
primarily live and sleep on boats, Roberg said, the light from the boats
attract insects at night, and then these insects have been transported to other
islands, where they may not be indigenous. These species can in turn become an
invasive species wrecking havoc to other ecosystems, similarly to the behavior
of invasive species brought to the Galápagos Islands.
When visiting the
islands, Bennington told Live Science, respecting the rules keeps the islands
in their relatively pristine condition. A trip to the Galápagos is always an
adventure, he added. There is always something new and exciting, like
"bow-riding dolphins, a school of sharks, mating giant tortoises, flocks
of plunge-diving blue-footed boobies — you just can't anticipate what spectacle
nature will present," Bennington said
source:
https://www.livescience.com/62902-galapagos-islands.html
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