EVOLUTION on the
GALÁPAGOS ISLANDS
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TABLE of
CONTENTS
INTRODUCTION 6 - 23 LAND SPECIES 24 - 31 AIR SPECIES 32 - 37 MARINE LIFE 38 - 49 CONCLUSION 50 - 51 BIBLIOGRAPHY 53
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DESIGNERS DANTE CARLOS MIA J CHUANG HENRY DE LEON MELISSA MUELLER CRISTINA SCHUETT
ILLUSTRATOR SACHA-MIKHAIL ROBER TS
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Introduction
The Galápagos Islands are famous worldwide as a “natural laboratory of evolution,” home to several species of fascinating fauna and flora, many of which cannot be found anywhere else on earth. Nicknamed The Enchanted Isles by pirates who frequented their rocky shores in the 18th century, the thirteen islands are situated in the Pacific Ocean some 1,000 km from the South American continent. Ongoing seismic and volcanic activity reflects the process that formed the islands over four million years ago. It was this volcanic process, together with the extreme isolation of the islands, that led to the development of unusual animal life such as the land iguana, the giant tortoise, and the many types of finch, the same wildlife that inspired Darwin to write his influential On the Origin of Species when he visited in 1835.
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2000 km 1500 km
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Mantle plume breaks through the lithospherre and forms the first volcano.
1000 km
ARCHPELAGIO FORMATION
500 km 0 km
MANTLE PLUME
LITHOSPHERE
ASTHENOSPHERE
2000 km 1500 km
2
Horizontal movement of the lithosphere leads to the creation of a second volcano
1000 km
1
500 km 0 km
LITHOSPHERE
MANTLE PLUME ASTHENOSPHERE
2000 km 1500 km 1000 km
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As the first and second volcanos erode, a third one developes creating a series.
500 km 0 km
MANTLE PLUME ASTHENOSPHERE
Island Geology mantle plume columns of hot rock that rise from deep within the Earth lithosphere the rigid crust and uppermost mantle of the earth
Like many oceanic islands, such as Hawaii, the Azores, and Reunion, the Galåpagos are thought to be the product of a mantle plume and lithospheric plate movement. The lithosphere, the outermost layer of the earth’s crust, is broken up into about two dozen plates, which move with respect to one another. This plate motion, together with the flow of the underlying asthenosphere, the layer of hot rock below the lithosphere, is part of a system of convection that is the principal way in which the Earth looses heat.
As a lithospheric plate moves over a mantle plume, a chain of volcanoes is created. Mantle plumes are columns of hot rock, roughly 100 km in diameter, that rise from deep within the Earth. These plumes rise because they are hotter (by perhaps as much as 200 degrees centigrade) and therefore less dense, than the surrounding rock. The rate of ascent is about 10 cm/year.
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asthenosphere the layer of hot rock below the lithosphere
Overhead View
1 LITHOSPHERE
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1 LITHOSPHERE
3
1
2
LITHOSPHERE
2
1 LITHOSPHERE
As plumes near the surface, they begin to melt and force their way through the lithosphere producing a volcanic eruption. Successive eruptions over hundreds of thousands and years produce a volcano. The upward motion of the mantle plumes pushes the overlying lithosphere, the outermost part of the earth, upward. This, together with magmatic thickening of the crust, is responsible for the Galรกpagos Platform, an anomalously shallow region of the ocean upon which the Galรกpagos Islands sit.
Motion of the lithosphere eventually carries a volcano away from the plume and its magma source, so the volcano then becomes extinct. The volcano and the lithosphere beneath it then begin to cool. As it cools it contracts. As a result of this contraction, the volcano slowly sinks beneath the sea.
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AGE (Years)
400,000-1,500,000
1,500,000-2,400,000
DARWIN (Island) PINTA
WOLF (Island)
MARCHENA
ECUADOR
GENOVESA
WOLF (Isabela)
SANTIAGO DARWIN (Isabela)
ALCEDO FERNANDINA
SANTA CRUZ SANTA FÉ
SANTA CRUZ
NEGRA
AZUL
FLOREANA
=Volcano
ELEVATION (Meters) 2000 1500
WOLF (Isabela)
FERNANDINA AZUL
1000 500
DARWIN (Island)
NEGRA
SANTIAGO
SANTA CRUZ
ECUADOR WOLF (Island)
DARWIN (Isabela)
0
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ALCEDO
PINTA
MARCHENA
FLOREANA
SANTA FÉ
GENOVESA
The Galápagos Islands are located beneath the Nazca Plate, which is moving eastsoutheast; thus, the islands get older to the east-southeast. Española is the oldest Galápagos island. Similarily, the eastern islands tend to have a higher elevation because they have had less time to erode into the sea. The volcanos of highest elevation are all located on the main island, Isabela.
2,400,000 or greater
Most of the Galápagos volcanoes share the name of the islands themselves. Because Isabela, the largest of the islands, contains a series of volcanoes they have all been given unique names.
VOLCANOS: L O C A T I O N , A G E , E L E VA T I O N
SAN CRISTOBAL
ESPAÑOLA
SAN CRISTOBAL ESPAÑOLA
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Volcanic Survey Nazca Plate the lithospheric plate upon which the Galapagos Islands sit
ASON
DR
Y
SE
19-27 C clouds of moisture southeastern winds
cool waters
WEATHER PATTERNS
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The climate of the Galรกpagos Islands varies from season to season and year to year, and there is quite a difference in temperature between the coastal areas and higher elevations. It is generally mild and dry, with the temperature rarely rising above 27C.
RA
Climate
IN Y SEAS
During the dry season, when the winds blow in a southeasterly direction, the shores of the southern islands are bathed in cool waters, chilling the air and creating unusually cold conditions for equatorial islands. During this period, rain is scarce on the coastal regions. Higher up, however, clouds of moisture support the thick vegetation.
O
The rainy season is marked by decreased winds and warmer sea currents. The days are warm and the seas are calm during these months. Heavy rains in the upper elevations send streams of water down the slopes to even the lowest island points.
22-31 C heavy rains
warm waters
ACROSS SEASONS
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N
The plant life of the Galápagos Islands is just as extraordinary as its wildlife, although it has received less attention and publicity. There are many threats facing the vegetation, however, and world attention is currently focused on raising funds for botany campaigns to safeguard endangered species and control the many invasive plants introduced to the islands by humans.
Needle-leaf daisy, an endemic species
NATIVE FLORA There are about 560 native species of plants in the islands, in other words, plants which arrived in the islands by natural means. Of these, almost one third are endemic to the islands, meaning they are found nowhere else on earth. For example, Galápagos has its very own, endemic species of cotton, pepper, guava, passion flower and tomato. Not only that, but many species are so different from others elsewhere that they are grouped in their own endemic genera. These include Scalesia, the ‘daisy tree’, which has evolved into a whole host of different species in a direct botanical parallel to Darwin’s finches. Other endemic genera in the daisy family are Darwin’s aster Darwiniothamnus, the cut-leaf daisy Lecocarpus, and the needle-leaf daisy Macraea. There are also some endemic genera of cacti, Brachycereus, the lava cactus and Jasminocereus, the candelabra cactus.
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Flora Overview
native species plants or animals that arrived at the islands by natural means endemic plant or animal species found exclusively on the islands
pioneer species hardy plants which successfully cross oceans and manage to establish themselves in the often hostile environment of islands depauperate unusually low occurance of a given plant species compared to similar or related locations
INTRODUCED SPECIES On the whole, Galápagos plants tend to be pioneer species, hardy plants which successfully cross oceans and manage to establish themselves in the often hostile environment of islands. Because relatively few plants succeed in doing this, the flora is depauperate - there are far fewer species here than in similar environments on the South American mainland. Plants are also adapted to having very few insects or other animals to pollinate their flowers or disperse their fruits and seeds. This means there are few big, showy flowers to attract pollinators and few specialized fleshy fruits. But there are some fascinating relationships between plants and animals. The giant tortoises and land iguanas, for example, feed on Opuntia, the prickly pear cactus, and have influenced its growth form on different islands.
Tomato species endemic to the Galapagos
out this whole zone. The guava tree, being drought-resistant, can invade just about anywhere, replacing native trees and shading out all the smaller plants underneath. The endemic Scalesia tree dies out in huge numbers during severe El Niño events and there are fears that it will never recover from the 1997-98 event, as the introduced guava will prevent its natural regrowth. Other problem plants are passionflower, elephant grass, and kalanchoe, the ornamental mother-of-thousands.
One of the biggest problems in Galápagos comes from foreign plant species introduced to the islands by people, which then become pests and invade the native vegetation. Most of these species were brought on purpose either for agriculture or gardens, and the problem is therefore greatest on the inhabited islands. There were 475 known introduced species by early 1999 and the process is still continuing at the rate of about 10 new arrivals each year. At the current rate, it is estimated that introduced plant species will outnumber native species by the year 2007. About forty of these are already seriously invading the native vegetation and another sevety introduced plants are likely to cause problems in the future.
Introduced animals also have a detrimental effect on the native flora. Goats have decimated the vegetation on many islands and brought some plant species to the verge of extinction. Feral donkeys and cattle also graze on native plants or trample them. Insects and other invertebrates are also a major problem. For example, in 1982 a scale insect, the cottony cushion scale, was first reported in Galápagos and spread to another seven islands by 1997. It infests and often kills many kinds of native plants, and scientists looked at biological methods of control to safeguard the vegetation. In January 2002 the Australian ladybug, the natural enemy of the cottony cushion scale, was released following studies to ensure that the ladybug did not pose any threat to the Galápagos ecosystem.
Different introduced plants are problems on different islands around the archipelago. On Santa Cruz island, for example, the worst culprits are guava Psidium guayaba, the curse of India Lantana camara, a species of blackberry Rubus niveus, and quinine Cinchona pubesceris. Quinine trees have invaded a unique vegetation zone formed by the endemic plant Miconia robinsoniana, which is found on only two islands. Quinine shades out Miconia and eventually all the other plants around it, so if not controlled it could completely wipe
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Charles Darwin, aged approximately 23. Darwin joined the HMS Beagle in 1831 as a naturalist. During these notable voyages, he developed his theories of evolution, culminating in his book The Origin of Species.
Charles Darwin
to make a five-year voyage surveying the coast of South America. The consent of his father was obtained, and Charles sailed. He discovered modern geology in the first volume of Lyell’s Principles, and rediscovered it on the peaks of the Andes and the plains of Argentina. Evolution was then a discreditable heresy to which respectable scientists tried to close their minds. Charles tried conscientiously to close his mind, but certain facts about South American flora and fauna haunted him like ghosts. Secretly, guiltily while his Christian faith slowly evaporated away - he took up the problem of the origin of species.
Descended from a nationally famous grandfather and a locally famous father - both formidable in stature, voice, and authoritative fluency - Charles Darwin grew up as a rather unimpressive young man with a passion for beetle collecting and snipe shooting, and an apologetic sense that he ought to be doing something more important. He began to study for the family profession of medicine at the University of Edinburg, but finding himself too squeamish for the horrors of early nineteenth century surgery, turned once more to the pleasure of snipe shooting and an ample income. With thunders of despair, his father proposed he study for the ministry at Cambridge. Charles consulted a sensitive but docilely orthodox conscience and agreed.
Darwin returned to England; married his cousin Emma Wedgwood; published famous books on his travels, barnacles , and geology; collected more facts on evolution; perfected his theory of natural selection; wrote preliminary sketches - but put off publication year after year, unwilling to advocate a disreputable theory without at the same time being able to prove it. For though no man has affected them more profoundly, Charles Darwin was like many Englishmen always a little suspicious of ideas. Finally,
At Cambridge theology was so rational and secular that it was an excellent preparation for science. And even as he studied theology, beetle collecting led Charles, by a very devious and very English process of following his nose, into biology and geology. In 1831 his botany professor, J. S. Henslow, recommended him for the post of naturalist on the H.M.S. Beagle, a tin, 24-ton brig which was
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The HMS Beagle, birthed just outside Devenport, England.
Thomas Huxley in England, Asa Gray in the United States, and Ernst Haeckel in Germany, he found himself by 1870 the acknowledged pontiff of an ism and one of the most famous men in the world. Evolution was accepted as a fact and natural selection almost universally preferred as its explanation. Zoology, botany, and anthropology were revolutionized. Ethics, religion, philosophy, indeed, every field of thought were radically altered.
in 1858, he recieved from A. R. Wallace in Maylaya a scientific paper which exploded like a bombshell on his quiet world of anxious industry. Lying ill with malaria in a tropical jungle, Wallace had sketched out in a single week the theory which darwin had taken twenty years to elaborate. At the repeated urging of friends, Darwin finally wrote a brief paper similar to Wallace’s, and both papers were read before the Linnean Society. THey were received in grave and somewhat stunned silence. Darwin now wrote a further summary of his ideas, which as usual grew into a long book. The Origin of Species appeared in 1859.
Darwin’s second most important work was The Descent of Man, which appeared in 1871. Thereafter, he did what he wanted. That is he gave up all amusements and devoted himself to his favorite kinds of hard work. As much as possible, he abandoned his study and his desk for his garden and his hothouse, living more and more among facts and flowers and less and less among ideas and words, for writing caused him even more trouble and anxiety than thinking did. Having received many honors, including an L. L. D. degree from his own Cambridge University, he died of a heart attack in 1882 and was buried close by Sir Isaac Newton in Westminster Abbey.
So many facts, so ingeniously and cautiously explained could not possibly be received with calm, even by the calmest scientists. In fact, they produced over Europe and America intellectual hurricanes, earthquakes, avalanches, and deluges which lasted for more than a decade. Darwin was astonished. Still, he had planned a shrewd, far-sighted campaign for the acceptance of his book; and working as a charming and accomplished diplomatist behind the scenes, and enjoying before the world the aid of such men as
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The HMS Beagle Journey
jerkily as the result of a smaller number of major differences, which biliogists call saltations?
Darwin started his mometous voyage in HMS Beagle with biblical faith undimmed and no warning that his observations of nature would be the pebbles that loosed the avalance. Even during the second year of the voyage he couldl write to one of his sisters: “Although I like this knocking about, I find I steadly have a distant prospect of a very quiet Parsonage, and I can see it even through a grove of Palms.” It is by no means exactly clear when the significance of what he was noting first began to trouble him; exegesis voyage to his autobiography written forty-four years later, can be used to provide a distracting spread of dates. Their range is only partly the result of difficulty in deciding when vague suspicion hardens into tentative idea and when idea changes into credible theory. Yet as the Beagle chopped down the English Channel toward the open sea on December 27, 1831, Darwin would have known that over almost any investigation of nature there loomed on intractable problem: the riddle of species.
Darwin’s task, described in the first page of his Journal of Researches (1845) was “to complete the survey of Patagonia and Tierra del Fuego, commenced under captain King in 1826 to 1830: to survey the shores of Chile, Peru, and some island sin the Pacific - and to carry a chain of chronometical measurements round the World.” But FitzRoy was first to survey the coasts of Brazil and the Argentine. The Beagle would then round Cape Horn, survey the coasts of Chile, sail north to the Galapagos Islands, then westward across the Pacific. After Visiting Tahiti, and calling at New Zealand and Australia, she would make for home across the Indian Ocean, rounding the Cape of Good Hope, and after crossing the souther Atlantic for a last look at Brazil, would turn north for England. It was Sunday, October 2, 1836, before the ship docked at Falmouth, a flourishing port on England’s southwest coast.
By the time that Darwin began his voyage in the Beagle, there was thus already in existence a background of discussion not only about hte mutability of species but also about the question that was to divide evolutionists from the publication of The Origin of Species to the present day: did change take place by the slow accumulation of many minor differences or more quickly but more
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Captain Mess Hall Captain’s Store Room Gunroom Skylight Captain’s Cabin
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Gunroom Store Room Ship Room Midship Berth Spirit Room
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M. Ballast N. Sailroom O. Locker & Sickbay P. Coclhole
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Jolly Boat Poop Cabin Skylight Poop Deck Mizen Mast Azimuth Compass
F. G. H. I. J.
Cutter Second Boat Captain’s Skylight Captain’s Whale Boat Cannons Gunroom Skylight
K. Skids L. Main Bits M. Main Mast N. Main Hatch O. Booms, spare Spars
P. Q. R. S. T.
Cutter inside Yowl Fore Hatch Fore Mast Top Gallant Forecastle Cat Head
DIAGRAM OF THE HMS BEAGLE
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DAR WI N
PINTA
M A R C H E N A
G E N O V E S A
S A N T I A G O
F E R N A N D I N A
S TA .
C R U Z
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FLOREANA ESPANOL A
DARWIN’S JOURNEY THROUGH THE GALAPAGOS
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Darwin’s Tour of the Galapagos
He worked hard on the Galapagos. “Amongst other things, I collected every plant, which I could see in flower, & as it was the flowering season I hope my collection may be of some interest to you,” he wrote to Henslow, his aide back at Cambridge. “I shall be very curious to know whether the Flora belongs to America, or is peculiar. I paid also much attention to the Birds, which I suspect are very curious...”
Darwin started its momentous journey on December 27, 1831, as it chopped down the English Channel towards the open sea. The Beagle anchored off Chatham Island, the easternmost of the Galapagos group, on the morning of September 17, 1835. Including thirteen large and numerous smaller islands, 650 miles off the coast of Ecuador, which had acquired them from Spain in 1832, the group had first been visited by Fray Tomas de Berlanga, bishop of Panama, in 1535. “It looked,” he wrote, “as though God caused it to rain stones.” Woodes Rogers, a buccaneer who many years later landed there with Alexander Selkirk, the real Robinson Crusoe, gave no better account of the islands, describing them as “nothing but loos Rocks, like Cynders, very rotten and heavy and the Earth so parch’d, that it will not bear a Man, but breaks into Holes under his Feet, which makes me suppose there has been a Vulcano here; tho’ there is much shrubby Wood and some Greens on it, yet there’s not the least Sign of Water, nor is it possible, that any can be contain’d on such a Surface.”
They set out westward on October 20 and crossed the Pacific Ocean via Tahiti without incident. Darwin had mixed feelings. “I have always felt that I owe to the Voyage the first real training or education of my mind,” he was later to write. “I was led to attend closely to several branches of natural history, and thus my powers of observation were improved, though they were already fairly developed. The investigation of the geology of all the places visited was far more important, as reasoning here comes into play.” It was Sunday, October 2, 1836, before the ship docked at Falmouth, a flourishing port on England’s southwest coast.
Darwin gave no more enticing an account in 1835. “Nothing could be less inviting than the first appearance,” he wrote. “A broekn field of black basaltic lava is every where covered by a stunted brushwood, which shows little signs of life. The dry and parched surface, having been heated by the noonday sun, gave the air a close and sultry feeling, like that from a stove: we fancied even the bushes smelt unpleasantly.”
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Darwin’s Theories of Evolution
VARIATION UNDER DOMESTICATION
VARIATION UNDER NATURE
Conditions of life produce, directly or indirectly, changes which are either definite or indefinite. The conditions of life appear to act in two ways - directly on the organization or indirectly by affection the reproductive system. With respect to direct action, there are two factors: the nature of the organism and the nature of the condition. The reproductive system is extremely sensitive to surrounding conditions.
Natural selection creates incipient varieties from the raw material of individual differences; classifications merely denote accumulated degrees of difference. With respect to the more important and adaptive characters, the passage from one stage of difference to another, may be safely attributed to the cumulative action of natural selection, and to the effects of the increased use or disuse of parts.
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STRUGGLE FOR EXISTENCE
SURVIVAL OF THE FIT TEST
LAWS OF VARIATION
A struggle for existence inevitably results from the rapidity with which all things multiply. Owing to this struggle, variations, if they be in any degree profitable to individuals, will tend to the preservation of such individuals, and will generally be inherited by the offspring. THe offspring, also, will thus have a better chance of surviving, for, of the many individuals born, but a small number can survive.
Natural selection acts to preserve those organisms, which vary, however slightly to their own advantage. Variations neither useful nor injurious would not be affected by natural selection, and would ultimately become fixed. Natural selection leads to species diverging into genera, for by wide diversification a maximum of forms find places in the economy of nature.
Though the causes of variation are unknown, changes in conditions as well as use and disuse seem to stimulate variations. The fact of variations occurring much more frequently under domestication, and the greater variability of species having wide ranges, lead to the conclusion that variability is related to the conditions of life during several successive generations.
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Land Species
The Galรกpagos is home to many unique, endemic animals, most of which are fearless due to the lack of natural predators. One of the best known, the giant tortoise, has evolved into fourteen distinct forms on the different islands of the archipelago. Other reptiles include land iguanas, lava lizards, geckos and snakes. As the islands evolved, so did the animals that lived in them. The Land Iguana and the Great Tortoise have come a long way, but not without great challenge.
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Land Iguanas
The land iguanas are typically divided into
two species, Conolophus subcristatus and EARLY MAY
Conolophus pallidus, although there are some data to suggest that the later is merely a local variant, a subspecies, of the former.
Variant Something that differs in form only slightly from something else
These Adult two Female very different species of Land Iguana Iguana once covered the entirety of the GalรกMaleDue Iguana the Female pagos Adult Islands. to chosen naturalbyphenomenons and introduced predators, the numbers of Adult Male Iguanas not chosen by the Female land iguanas has been constantly rising and falling.Baby Female Iguanas Baby Male Iguanas
Condolophus Pallidus
Condophus Subcristatus
PAST LOCATIONS Only seen on Santa Fe. Possible locations elsewhere.
Widespread through Archipelago. Santiago was covered in burrows in 1835.
DESCRIPTION More uniform and paler in color. Pronounced ridge of spine.
1
Yellowish-orange belly, brownish- red above. Low facial angle.
PREDATORS The MalesMan gather the lower andonanimals Man and animals flanks, andintroduced stake out their territory. introduced by man by man such as dogs, cats, goats, and pigs.
such as dogs, cats, goats, and pigs.
TODAY Possibly still located on Santa Fe, however no one has seen them recently.
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Currently found on Santa Cruz, Isabela, Fernandina, Plaza and N Seymour.
VOLCANIC MATING RITUAL
LATE MAY
JUNE
MID JUNE
OCTOBER
EIGHT KILOMETERS
ONE KILOMETER
3
The females begin their epic migration to the volcano rim. This journey takes place over some of the toughest terrain on earth. 5
4 2
The females arrive and do their “rounds” to carefully select a mate.
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The eggs hatch 100 days after they were laid. The young iguanas are 8” long and extremely vulnerable. They climb out of the crater as best they can, and start their lives on the lower slopes of Fernandina.
The pregnant Iguanas reach the summit and go into the crater itself. When the eggs are laid and burrows are filled, the females 20 or so eggs, protecting them from latecomers.
Giant Tortoise
No animal is more synonymous with the Galápagos Islands than the giant tortoise. The saddle-back shape of the shell in many of the tortoise races reminded the early Spaniards of a type of riding saddle called “galápago,” and this term is in turn applied to the tortoises. Hence, by calling the islands the Galápagos, we are, in essence, calling “The Islands of the Giant Tortoises.”
great tortoises which were collected and stored live on board the ship where they survived for many months. These tortoises provided invaluable fresh meat.
On a Saddle-Backed Tortoise, pictured above-left, has a shell that is up higher on their necks so they have more room for motion to reach up for leaves overhead. This specific species of Tortoise frequents a dry climate.
Turtles are a vanishing species due to pollution, habitat destruction, and exploitation. Humans need to think twice before purchasing wild animals, littering, dumping chemicals, spraying pesticides, or destroying the habitats which turtles and tortoises have called home for millions of years.
In the 1800’s, whaling ships and then fursealers collected tortoises for food and many more were killed for their fine ‘turtle oil’ until early this century.
The Domed Tortoise’s shell, pictured above-right, is domed close to their bodies to protect them from predators. Because so little of their body is exposed, they have fewer weaknesses EXTINCTION OF A SPECIES In the 1600’s, buccaneers started to use the Galápagos Islands as a base, restocking on water and repairing their boats before setting off to attack the Spanish Colonies. But the main attraction of the islands were the
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Tortoise Evolution
The original ancestor of the tortoises was probably of normal size and evolved into the present day giants after its arrival in the Galรกpagos. 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 for food. Once the tortoises spread around the archipelago, they evolved on their isolated islands into the different species 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 the Galรกpagos.
Gigantism The quality or state of being gigantic; abnormally large size. Ecosystem An ecological community together with its environment, functioning as a unit Carapaces A hard bony outer covering, such as the fused dorsal plates of a turtle.
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BURYING THE EGGS
1 The Female Tortoise digs a hole in the ground and lays up to 20 leathery eggs each the size of a tennis ball.
2 She mixes soil, urine and leaves to make a muddy plug for the nest.
3 She then leaves the eggs to incubate in the heat from the sun.
Tortoise Mating Rituals
Giant tortoises probably only reach sexual maturity at the age of about 40. The breeding season is usually at the end of the hot season. Males have a concave base to their shell and mount the females from behind, bringing their tail, which houses the penis, into contact with the female’s genital region. Mating may last for several hours and the males often give hoarse roars.
The females then travel several miles to their nesting areas which must have dry sandy ground where they can dig their nests. They lay between up to 20 eggs, each the size of a tennis ball. The female makes a muddy plug for the nest hole out of soil mixed with urine and leaves the eggs to incubate in the heat from the sun. The young tortoises hatch after around 4 - 8 months.
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GROWTH PROCESS
NEWBORN
10 YEARS
20 YEARS
30 YEARS
4 The eggs take 4 - 8 months to hatch and the young tortoises have to fend for themselves.
5 At 10 years old, a giant tortoise gets to be around 160 pounds with a shell span of 20 inches.
Food and Water Intake
6 At 20 years old, a giant tortoise gets to be around 320 pounds with a shell span of 40 inches.
7 At 30 years old, a giant tortoise reaches it’s full maturity. They can weigh as much as 500 pounds with a shell span of 60 inches. A giant tortoise can live as long as 150 years.
Galápagos tortoises are herbivores. Their diet consists mostly of cactus, fruits, vines, grasses and other vegetation. Although most of the food Tortoises intake passes through their body without even being digested, they can go without eating and drinking for up to one year. They do this by breaking down their body fat to produce water. This quality is a vital part of the survival
the Galápagos Tortoise. For example when goats were introduced to the Galápagos Islands. The goats stripped away much of the vegetation, leaving the tortoises with inadequate supply of food. If the tortoise could not live for so long off of stored food and water, the survival of their species would have been affected greatly.
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Air Species
Evolution’s ornithological crown has fourteen jewels in it, and they reside on the Galápagos Islands. Known to science as the Geospizinae, these birds are much more widely recognized as Darwin’s finches. David Lack, in 1938-1939, was the first ornithologist to make a detailed study of Darwin’s finches in the field, and his work basically set much of the agenda for evolutionary biology and ecology for years afterward. After Lack’s synthesis, Darwin’s finches earned a place in virtually all introductory biology textbooks as the prime example of adaptive radiation. Although he was not the first to call these birds Darwin’s finches, it was Lack who promoted the use of Darwin’s finches as the popular name for the group.
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adaptive radiation The diversification of species from a single type.
The fourteen species of Geospinae, or Darwin’s Finches. From this point on the various genera are differenciated from each other by six different hues. See the legend on the top right corner of the figure.
Finch Species
The fourteen currently recognized species of Darwin’s finches are divided among five genera. As a curious point of history, John Gould also classified these birds into fourteen species, but not the same ones recognized Today. Two genera contain but a single, specialized species: the vegetarian finch (Platyspiza crassiostris) and the warbler finch (Certhidea olivacea). The Cactospiza genus contains the woodpecker finch (Cactospiza pallida) and mangrove finch (C. heliobates), each quite similar to the other. There are three species of tree finches, each in the genus Carmarhynchus, the large (C. psittacula ), the medium (C. pauper), and the small (C. parvulus). The largest genus is the ground and cactus finches, the genus Geospiza, of which there are six species. Four of the species are ground finches: the large (G. magnirostris), the medium (G. fortis), the small (G. fuliginosa), and the sharp-beaked (G. difficilis). Two are cactus finches, the common (G. scandens) and the large (G. conirostris). One last species, the Cocos Finch (Pinaroloxias inornata), resides on a distant Cocos Island away from the Galåpagos Archipelago.
Warbler Finch Certhidea olivacea
Woodpecker Finch Cactospiza pallida
Mangrove Finch Cactospiza heliobates
Vegetarian Finch Platyspiza crassiostris
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VA R I O U S S P E C I E S O F D A R W I N ’ S F I N C H E S
LEGENDS Certhidea
Geospiza
Platyspiza
Carmahynchus
Pinaroloxias
Cactospiza
Small Tree Finch Carmahunchus parvulus
Medium Tree Finch Carmahynchus pauper
Small Ground Finch Geospiza fuliginosa
Sharp-beaked Finch Geospiza difficilis
Large Tree Finch Carmahynchus psittacula
Medium Ground Finch Geospiza fortis
Common Cactus Finch Geospiza scandens
Cocos Finch Pinaroloxias inornata
Large Ground Finch Geospiza magnirostris
Large Cactus Finch Geospiza conirostris
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BODY LENGTH AND PLUMAGE VA R I A T I O N S O F D A R W I N ’ S F I N C H E S
GENERA SPECIES
LENGTH IN INCHES
PICTURES
Geospiza 1
Large Ground Finch
2
Medium Ground Finch
3
Small Ground Finch
Carmahynchus 4 5 6
Large Cactus Finch Common Cactus Finch Sharp-beaked Finch
1 2 3
Large Tree Finch Medium Tree Finch Small Tree Finch
1
7.00˝
4
6.78˝
1
6.23˝
2
5.91˝
5
6.13˝
2
5.47˝
3
4.81˝
6
5.25˝
3
4.59˝
3
3
6
2 5
1
DESCRIPTION OF PLUMAGE
Identification
2
1 4
Wholly black
Black heads
Streaky brown
Brownish green
Even a novice birder can appreciate the close genetic relationship among at least some of the finch species. It was reasonable for Charles Darwin to wonder if they were not mere varieties when he first encountered them. All of the ground and cactus finches have similar plumages. The three tree finch species all show identical patterns as well. On the other hand, The vegetarian finch look much like the ground finches. Woodpecker and mangrove finches are grayish-olive, with no plumage differences between the sexes. The warbler finch is also olive-gray regardless of sex. In the Cocos finch, the plumage for both sexes are similar to that of the Geospiza; but the regulating factors that distinguish them from the Geospiza is that the juvenile male acquires the black feathering irregularly all over , instead of first at the head and then posteriorly.
Any book dealing with Darwin’s finches, particularly bird guides, will compare them so that you may note the distinctions in body size and bill characteristics and thus go about identifying the birds in the field. But beware. Even experts are uncertain about the identities of some of the finches they encounter. For example, there is much variability in bill size among several of the species, particularly the medium ground finch. It gets worse. To make identifications just that much more tricky, hybrids occur between various species pairs that are placed in separate genera! For instance, medium ground finches are known to hybridize with small ground finches. The molecular data suggests frequent hybridization within Darwin’s finches. To some degree at least, many of Darwin’s finches still seem to be bathing
38
hybridization occurs when species not normally breeding breed and produce a new subspecies.
The fourteen species of Geospinae are all similar in basic form in terms of their plumage, which are slight variations from each other. This contributes to the argument that they may be descendents of the same ancestry.
Cactospiza 1 2
Platyspiza
Pinaroloxias
Certhidea
Woodpecker Finch Mangrove Finch
1
5.91˝
2
5.69˝
Vegetarian Finch
Cocos Finch
Warbler Finch
5.25˝
6.67˝
4.59˝
2
1
Grayish olive
Brown and partly black
Wholly black.
Olive gray
Grayish olive
Streaky brown
Somewhat darker than difficilis and more olive.
Olive gray
in the same gene pool. But from just where did this gene pool originate? Many other observers of birds have suggested the abundant blue-black grassquit as the ancestral Darwin’s finch, but there have been other candidates as well, such as the black-faced grassquit (Tiaris bicolor) from the West Indies and Central America. And there is a species that looks outwardly rather like a Darwin’s finch and whose DNA seems to make it a likely ancestor: the St. Lucia black finch (Melanospiza richardsoni). This species, confined to the small island of St. Lucia, was more likely candidate to colonizing the Galápagos than it now seems to be. Recent classifications of birds based on DNA similarity place the St. Lucia black finch as the likely sister species to the Geospizinae.
BLUE-BLACK GRASSQUIT
ST. LUCIA BLACK FINCH
BLACK-FACED GRASSQUIT
Possible ancestral species of Darwin’s Finches from the South America continent.
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DISTRIBUTION OF DARWIN’S FINCH SUB-SPECIES
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gene flow among those organisms. Unless gene flow is stopped, or at least dramatically reduced, they will not develop sufficient genetic distinctions to be reproductively isolated from one another and thus will not speciate. Lack’s work, on the other hand, helped define the “central dogma” of evolution, allopatric speciation. Once the finches re-encounter each other after they leave their endemic islands, when they again share the same ecosystem, they become “sympatric.” It is at this point that Darwin’s notion of competition driving further evolutionary divergence between the fledgling species takes effect. Several things are of real importance in understanding why Darwin’s finches evolved as they did. First, the founding species was a finch. As explained earlier, finches are seed-crunching herbivores, avian specialists to a strong degree. Bill characteristics had to evolve, if the ancestral species was to exploit the full range of resources available to it on the Galápagos Islands. Second, should a tramp species find itself in a habitat in which there are essentially no competitors or no predators, it can undergo what is termed ecological release. Does anyone seriously believe the Galápagos woodpecker finch would have evolved into a tool-using bark prober if the islands already held woodpeckers? Darwin’s finches are a wonderful example of ecological release, with regard not only to what they actually eat (grubs, blood, ticks, cactus pulp, nectar, leaves, buds, and seeds of all sorts) but also to the range of habitats they occupy. The finches came, and the finches conquered.
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Allopatric Speciation Populations that are geographically isolated from one another during a critical part of their evolutionary trajectories.
Endemism Native to or confined to a certain Island.
Divergence and Convergence
Ecological Release One ancestral speciees exploiting numerous kinds of resources that it would be prevented from using in a more species-rich community. This is the mechanism behind adaptive radiation.
GROUND FINCHES G. Magnirostris G. Fortis G. Fuliginosa G. Difficilis
Seeds and Nuts
Booby Blood Cactus Pulp
G. Scandens G. Conirostris
VEGETARIAN FINCHES P. Crassirostris
Nectar, Cactus Pulp, Grasses
DIET FOR EACH SPECIES
TREE, MANGROVE, AND WOODPECKER FINCHES C. Parvulus C. Pauper C. Psittacula C. Pallidus C. Heliobates
Insects
Insects, esp. From Wood
WARBLER FINCHES
COCOS FINCHES
C. Olivacea
P. Inornata
Nectar, Fruits and Insects
Nectar and Insects
Marine Life
Located at the confluence of five ocean currents, the climate in the Galapagos Islands is different than one might imagine from islands located on the equator. The climate is dominated by the prevailing current which creates strong, unpredictable tides between islands, cooler than normal temperatures, and ultimately results in the unique ecology of the islands. Life in the ocean is as varied and unique as that above it. The Galapagos is home to sharks, rays, Cetaceans. Green Turtles and Hawkbill Turtles can be seen in the waters. Almost 300 species of fish have been noted. This is the least studied portion of the Galapagos Wildlife. Over the past few years more attention was paid to the remarkable underwater world. These creatures consist of more than just the Fur Seals and Sea Lions that are ever present. It also includes 16 species of whales and 7 types of dolphin, 18 species of morays, 5 species of rays, 12 species of sharks as well as various other underwater creatures including from star fish to sea cucumbers. Created from a volcanic hot spot located on the ocean floor, the Galapagos are oceanic islands which have never been connected to a continent. All of the organisms found in the Galapagos arrived in the islands by swimming, flying or floating. The majority of organisms present in the Galapagos originated from North, South or Central America the Caribbean or the Antarctic. The unique location of the archipelago in relation to Southern Humboldt Cur-
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HUMBOLDT CURRENT
rent and Northern Panama Current has played a large role in the unique mix of plants that made their way to the islands. The currents and the trade winds have transported plants and animals to these remote islands that have a distinctly different biological make-up than those species found on the neighboring continent. California Sea Lions, Pink Flamingos, Finches, and Warblers made their way south from North America and the Caribbean while Fur Seals and Penguins made their way north from Antarctica.
Ocean Currents: Movements
Predominate in the third quarter of the year the Humboldt Current runs up the west coast of South America from Antarctica. As the Humboldt Current moves through the islands during the 3rd and 4th quarter from June to November, it cools temperatures. The winds come from the southeast and create an inversion over the area. Low straight formed clouds cover the islands much of the day. A drizzle known as ‘garúa’ occurs in the highlands. The “garúa” visibility is lower than the warmer months. Though there is more frequent precipitation this time of year the light rain made it difficult for settlers to collect water during this season. This time of year is referred to as the “dry season”. Water temperatures during the cooler months of August and September range from 60º to 65º F (16º to 19º C) in the western islands to around 78º F (25º C) near Darwin and Wolf at the far north of the archipelago. The average water temperature is 70º F (21º C). From October to December the water temperature drops to the between 60º to 70º F (16º - 21º C) range. These later months are a good time for Green Sea Turtle sightings (during their mating season) and shark sightings are still high, but rays are seen less frequently.
Species had 3 methods of arrival in the islands, marine life including whales, dolphins, fish, seals and penguins arrived by swimming along with the currents. Birds arrived by flying as did many seeds, mosses orchids and ferns, which arrived by air currents rather than actual flight. Other specieslike tortoises, iguanas, trees, insects, and some seeds arrived by floating either due to a builtin air chamber or by floating on trees and other plants. The main ocean currents effecting the Galapagos Islands are the cold Counter Equatorial (Cromwell) Current from the west, the cold Humboldt (Peruvian Oceanic and Peruvian Coastal) Current and the from the southeast, the South Equatorial Current from the east, and the warm North Equatorial (Panama) Counter Current from the northeast which brings with it the devastating and infrequent El Niño Current. The mix of these currents and the location of the island in relation to the mix cause a wide variation of water temperatures from month to month and island to island.
PANAMA CURRENT In November as the Humboldt Current leaves the Galapagos the warm waters from the Panama Current come to take their place. These warm waters dominate the climate in the islands from January to May. During these months the water temperatures rise to 70º to 80º F (21º-27º C). The air temperatures, which are no longer cooled create an inversion layer. The skies
44
Humboldt Current: This current is what brought Penguins and Fur Seals to the Galapagos).
Penguins
Galapagos Penguins (Spheniscus mendiculus) is the northernmost species of penguin found in nature.The Galapagos Penguins congregate along the rocky lava shores of Isabela, Fernandina, Santiago, and Bartolome, islands cooled off by both the Cromwell and Humboldt currents. The Humboldt Current is the one that brought them all the way up to these tropical latitudes. Want to analyze a movie that talks about this? Watch Walt Disney’s “The Three Caballeros�. Funny. Look carefully for crevices in the rocky lava shorelines for penguins nest inside them. Small lava tubes are favorite places too. Dare to see a torpedo in the water? Jump in with the penguins and watch these graceful, but rocket fast birds, fly through the water. This is the smallest of the warm weather penguins. Galapagos penguins live on the Galapagos Islands on the equator. These Galapagos Islands belong to the
country of Ecuador. The islands are located to the West of this country Northwest of South America in the Pacific Ocean. Penguins also inhabit in Isabela the biggest island on Galapagos. The breeding population is estimated to be as low as 800 pairs. Because of their restricted mobility compared with flying species and their natal site fidelity, penguins should show distinct spatial patterns of genetic variability that will be useful for population studies.The Galapagos Penguins are exclusive to the Galapagos Islands where 1,700 to 8,500 individuals breed on 6 main islands and several other small islands.Penguins have a narrow white band from the eye extending under the chin and a black band that runs in an inverted horseshoe shape around their fronts.
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genetic variability: The quality, state, or degree of being variable or changeble with in genes.
TWO SPECIES OF PENGUINS ON GALAPAGOS Pattern of banding on Galapagos penguin is similar to that on Magellanic Penguins, but the main black bank around the front is much narrower in the penguins of Galapago.s
MAGELLANIC PENGUIN
GALAPAGOS PENGUIN
Magellanic Penguins are considerably larger than Galapagos Penguins and also the main black band around the front is much narrower in the penguins of Galapagos.
Although the pattern of banding on Galapagos penguin is similar to that on Magellanic Penguins, they are easily distinguished. Magellanic Penguins are considerably larger than Galapagos Penguins and also the main black band around the front is much narrower in the penguins of Galapagos. Nests are rudimentary burrows. Two eggs are usually laid but only one chick reared. Incubation takes 38 to 40 days shared equally between both parents. Chicks are brooded and guarded for 30 days after hatching with feeding and guard duties shared between the parents. Chicks moult and go to sea when 60 to 65 days old. Penguins eat mostly fish such as mullet and sardine.
incubation: maintaining someting at the ost favorable temperature for its development.
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Marine Iguanas
Marine Iguana (Amblyrhynchus Cristatus), Growing to approximately 3 ft (1 m) in length these seagoing Iguanas exist only in the Galapagos Islands. Living on the black lava shore rocks they have developed into efficient swimmers feeding off shore mostly on marine algae and seaweed.
rocky shore. He picked one up and threw it into the ocean it instantly swam back to the shore. This was repeated several times and the Iguana continued to seek the safety of the shore when it could have easily swum off to escape Darwin. The black rocks under the equatorial sun provide needed warmth for the iguanas. On a warm day these rocks can heat up to deadly temperatures. Yet, territorial male Marine Iguanas, remain in the sun during the day. Cooled by a circulator y heat shunt carrying heat from the back to their bellies where the sea breezes coming off the cool ocean waters can cool them by convection. At night the iguanas pile by the hundred in order to provide heat for one another.
The cold waters of the Galapagos provide both the necessary food for the Marine Iguanas and its most deadly threats. The cold temperatures can immobilize an iguana if it remains in the water too long. Until the arrival of man, Marine Iguanas only threats were that of larger fish and sharks encountered while swimming. When Marine Iguanas are not feeding they seek safety and warmth of the land. In the 19th century when Charles Darwin visited the islands he found thousands of Marine Iguanas living along the
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circulator y heat: Heat given off by means of the the circulatory system in order to maintain body heat.
DAILY ACTIVITIES TO MAINTAIN BODY HEAT
I DD
NG
ER TH GE O T
STA YW AR M
BY
HU
DAY LIGHT HOURS
MID DAY
OR
FO
OD
EVENING
ST
AY
WA
FO RM
IN T
HE S
UN
DAY LIGHT HOURS
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G RA
E
F
Conclusion
From land to air to sea, the Galåpagos are home to hundreds of facinating species of fauna and flora, many of which cannot be found anywhere else on earth. Reading Darwin’s journal or studying finch genera gives us only a taste of the richness of life across the many islands. Today, along with a booming tourist industry, there are several non-profit organizations dedicated to continued research and conservation efforts in the Galåpagos. For more information on groups like these, visit The Charles Darwin Foundation, Inc. (www.galapagos.org), headquarters for an international membership of more than 10,000 individuals raising funds to support projects on the islands. The foundation conducts seminars, briefings, and other education and advocacy efforts to inform the general public about ecosystem protection issues and the scientific work being undertaken in the Galapagos by the Charles Darwin Research Station, Galapagos National Park Service, and similar organizations.
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BIBLIOGRAPHY Galapagos Ecuador. Nauti Diving. Galapaguide. 2000. 12 February 2004. http://www.galapaguide.com George, David. Iguanas Making a Comeback on Galapagos. 2000. CNN News. April 2, 2004. http://www.cnn.com/2000/NATURE/08/04/galapagos.iguana/ Grant, Peter. Ecology and Evolution of Darwin’s Finches. Princeton: Princeton University Press, 1986. Kricher, John. “One Small, Intimately Related Group of Birds.” Galapagos. Smithsonian Natural History Series. Ser. Washington, DC: Smithsonian Institution Press, 2002. 140-152. Lack, David. Darwin’s Finches. Cambridge Science Classics. Ser. Cambridge: Cambridge University Press, 1983. Leindecker, Nick. Out of Geological Time. 2003. March 13,2004. http://www.stanford.edu/class/anthisci10sc/WebPapers/Nick.htm Rothman, Robert. Land Iguana. March 13, 2004. http://www.rit.edu/~rhrsbi/GalapagosPages/LandIguana.html Woram, John. The Year of the Tortoise: Dating the Maps of the Galapagos Islands. 2000. April 2, 2004. http://www.galapagos.to/TEXTS/TORTOISE.HTM United States. Department of Geological Sciences at Cornell University. Galapagos Geology on the Web. 2001. 30 January, 2004. http://www.geo.cornell.edu/geology/Galapagos.html United States. Galapagos Conservation Trust. Galapagos Conservation Trust. 1998. 30 January 2004. http://www.gct.org/about.html United States. Charles Darwin Foundation. Charles Darwin Foundation. 1999. 12 February 2004. http://www.darwinfoundation.org/ Unknown. Galapagos Land Iguanas and Their Protection. 2001. The Charles Darwin Foundation for the Galapagos Islands. April 2, 2004. http://www.darwinfoundation.org/terrest/iguana.html Unknown. The Dragons of Galapagos. 1999. Australian Broadcasting Corporation. April 7, 2004. http://www.abc.net.au/nature/dragons/liguana.htm
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