Galápagos

[Galápagos Past & Present 1]

This is the Galápagos activity. For information on how to use this disc, select the Help menu. There are four sections and, if this is the first time you have studied this activity, you are advised to work through each section in sequence. When you're ready to start your voyage of discovery to Galápagos, select 'Galápagos past and present'.

[Galápagos Past & Present 2]

Welcome aboard. You're about to embark on a virtual voyage of discovery. The islands of the Galápagos archipelago are famous for their unusual assemblage of wildlife. They are one of the places that influenced Charles Darwin on the voyage of the Beagle, when he visited them in 1835. The islands are still quite close in appearance to what they were in Darwin's time. Human occupation has had an impact, with the inevitable introduced animals and plants. You are going on a virtual journey through the archipelago, sometimes following in Darwin's footsteps. As you go, bear in mind the unique - and highly fragile - nature of these islands and form your own views of the conservation issues that arise from our wish to keep the islands' wildlife intact.

[Galápagos Past & Present 3 ]

Touring round the islands, you'll see some of the ways in which plants and animals have become adapted to the conditions there. You'll get a glimpse of how changing conditions can lead to adaptation over only a short period - evolution in real time. And by tracing how the islands first became inhabited, you'll explore how such a unique variety of species exists there today. But first a little more about the islands and why they've been so important to biologists.

[Galápagos timeline]

(intro) There are 6 resources to look at, marking certain highlights in the history and scientific study of these islands.

(Islands formed) The islands are volcanic in origin. They're the tips of underwater volcanoes that have grown up from the ocean floor over 2,000 metres below the surface. The islands emerged between half a million and four million years ago.

(Islands colonised) When the first colonising species arrived at the islands they would have encountered the unique conditions of Galápagos, with few, if any, other species to compete with. They would also have benefited from the lack of predators. In adapting to the new conditions, the colonists evolved into new species found nowhere else in the world. Such species are said to be endemic to the Galápagos. Some are actually endemic to a single island.

(Islands discovered) The Galápagos archipelago is very isolated. It straddles the Equator some 600 miles off the west coast of Ecuador, in the Pacific Ocean. There are no other islands between Galápagos and the mainland. There are 13 large islands, 6 smaller ones and over 40 little islets, some of which are still unnamed.

(Darwin) Charles Darwin was one of the first biologists to visit the Galápagos. He travelled to the islands on board the Royal Navy Survey Ship HMS Beagle in 1835. He was the first to realise the significance of the unusual plants and animals living there.

(Grants) Of all the unusual species found on the islands, the ones that are perhaps most famous are surprisingly inconspicuous. Darwin found them flitting through the upland scrub, feeding on the flowers of the Opuntia cactus, on seeds and on insects. He saw them as very similar but at the same time as distinctly different. These birds continue to be the subject of extensive research today. Peter Grant is the world's expert on Darwin's finches and their behaviour.

Peter Grant: The advantage to an evolutionary biologist of going there is that almost all of the products of that evolution are still there in existence because the archipelago has hardly been spoilt by human activity.

(Present Day) The Galápagos continue to be a focus for scientific research. You'll be introduced to some of these studies. Professor Peter Grant is an evolutionary biologist at Princeton University. He and his wife, Dr Rosemary Grant, have conducted field work on the Galápagos finches for over twenty years. Dr David Snow reveals the challenge of these finches for taxonomy. Professor Mark Williamson discusses the significance of islands for ecology and evolution. Dr Martin Angel highlights the impact on wildlife of the unique climate of Galápagos.

[Galápagos Cabin]

(intro) The cabin is your base for the virtual field trip. There are a lot of resources here and you can return to the cabin at any time, to consult them. Move your cursor over an object to find out what information it contains. When you are ready to move on, select the guide to Adaptation, on the desk.

(videos on shelves)
(1) Islands come as nice discrete ecological packages, but it's their small size and isolation that really make islands important to a biologist. Isolation means you can't get genes flowing from the organisms on the island to the organisms on the mainland, and so evolution can proceed independently.You can get a bunch of islands; if you're lucky, evolution can proceed independently on 2 islands in an archipelago and you may get the occasional immigration from one island to another which will then have a very important evolutionary effect.

(2) The archipelago is unique because, although situated on the Equator, it's bathed for much of the year by the cool waters of the Humboldt and Cromwell currents. These cool currents result in water temperatures of around 22 degrees Celsius, which helps ensure an abundance of sea life. In the warm season, warmer waters from the Panama Basin flow through the islands and the average sea temperature may rise to 25 degrees. Warmer waters mean greater cloud formation, so the islands experience a more tropical climate with heavy rain showers.

(3) If we look beneath the ocean at the topography of the islands we can see mountains, ridges, plateaux and valleys that confirm the volcanic origins of the islands. Geologists have proposed a hotspot theory to explain the origin of the islands. In certain areas around the world, there are stationary areas of intense heat in the mantle that wax and wane in strength. When most active, these hotspots cause the crust to melt in certain places and give rise to volcanoes. The hotspot remains stationary but the sea-floor plate moves, so each time the hotspot erupts, it does so under a new piece of ocean floor. This results in a trail of volcanic peaks which become older and more eroded in the direction of the plate movement.

(4) The two main types of island, and they were defined by Darwin, are oceanic islands and continental islands. A continental island is a chunk of a continent, as Britain is a chunk of Europe, and you get the same types of rocks, same climate, rather little isolation. An oceanic island is one formed by a volcano coming up from the deeps of the ocean, isolated from the mainland by many hundreds of kilometres in most cases, formed of a restricted set of rocks from the volcano and with a restricted geological life, so they're short-lived compared with continental islands.

(5) Early sailors christened the islands 'The Encantadas' because of the strange currents which seemed to bewitch their ships and drag them off course. This was due to the very deep waters around the islands, arising from their volcanic origins.

(shelf 2)
(6) The Galápagos Islands are far from other land masses, so their climate is mainly influenced by the ocean currents bathing the archipelago. From June to December, cooler waters from the south-easterly Humboldt current predominate, giving sea temperatures of about 22 degrees Celsius. From January to May, warmer waters from the Panama Basin in the north-east predominate (the so-called El Niño current). The average sea temperature rises to about 25 degrees. In some years the flow of warm waters is much greater. Surface water temperature rises up to 30 degrees and rainfall increases. This results in a so-called El Niño year.

(7) It is very much easier to study the pattern of evolution on an archipelago of islands like the Galápagos or like the Hawaiian archipelago. These are absolutely ideal field laboratories for the study of evolution; they've been there long enough for evolution to happen. They're stable enough so that you can work out why it happened, and you have frequently both the ancestral species and the descendant species. You can see what the genetic changes have been during the course of evolution.

(8) In any species, more individuals are produced by reproduction than can survive. The essence of Darwin's theory is that evolution by natural selection can occur if three conditions are met. First, a struggle for existence between individuals who compete for resources such as food. Second, variation. No two individuals are exactly alike, and those with advantageous characters have a greater chance to survive and reproduce. Third, inheritance. If advantageous characters are inherited, they can be passed onto the next generation. To follow natural selection in the wild, we need to see whether these three sufficient and necessary elements are present in any population we're studying.

(9) I think the most important factors affecting evolution on the Galápagos has really been climate and I think one of the main messages are, that the climate is not stable. There are changes between seasons but superimposed on the annual seasonal changes are changes between years, and these can have dramatic effects.

(10) The Galápagos are remarkably seasonal for a group of islands that lie astride the Equator. From January through till about April or May rains come and as a result the plants respond by producing leaves and the world - the Galápagos world - looks very green. Then the vegetation at least at low elevation dries out, and for the rest of the year, from about May all the way through to December if there's rain at all it will be very light, and the islands look very dry.

(shelf 3)

(11) The archipelago is unique, because although situated on the Equator it's bathed for much of the year by the cool waters of the Humboldt and Cromwell currents. These cool currents result in water temperatures of around 22 degrees Celsius which helps ensure an abundance of sea life. In the warm season warmer waters from the Panama Basin flow through the islands and the average sea temperature may rise to 25 degrees. Warmer waters mean greater cloud formation, so the islands experience a more tropical climate with heavy rain showers.

(12) Many species around the world show geographical variation, that is a population in one area may be somewhat different from another population in another area. Although the differences are not great enough for the two variants to be classified as separate species, they're sometimes significant enough for biologists to want to recognise them. In this case the two variants are said to be different subspecies. Several species in the Galápagos are divided into a number of subspecies, each found only on a single island or small group of islands.

(13) In the Galápagos, because there's been sufficient isolation between populations on different islands, and that has enabled different populations to differentiate and to adapt to slightly different local conditions, it's been possible for them to differentiate into a number of different species. And this happens apparently when, if two populations are split and isolated on different islands and evolve differences, and then one re-invades the other's island, and if they become different enough they can then be maintained as two species. On a single island of course this can't happen. And this process is presumably what has been happening again and again in the Galápagos islands, which has allowed one founding species to evolve into thirteen distinct species.

(14) Probably the best example of how animals got to the islands by a combination of wind and sea are the tortoises because it looks as though they originated from the mainland, probably being transported on weed rafts and you see great rafts of weeds being washed down South American rivers even today. Now if the winds were stronger and the currents were a bit stronger then the tortoises would arrive on the islands, and we think that the first colonists were probably quite small, and when they got to the islands there were no predators and they were able to withstand the desert conditions. They flourished and in the absence of predators they found that they could grow bigger and bigger, and we think there was actually a selection for larger tortoises because the larger the tortoise, the better it could survive the drought conditions.

(15) They certainly came from one original coloniser, one colonising stock. The most likely one seems to have been a small finch-like bird called the sooty grassquit which has a sooty black male and a brown streaky female, and in structure and appearance and everything is extremely similar to Darwin's finches, but other species have been suggested and one simply doesn't know. It may be possible later perhaps by DNA studies to find the answer to that.

(16) The predominant weather systems around the Galápagos are determined by trade winds. These are winds that blow persistently at ten to twenty knots. For nine months of the year these trade winds tend to be south-easterly, that is they blow from the direction of South America, and at that time of the year the weather tends to be very cool and very misty around the islands. During the other three months of the year, trade winds are north-easterly blowing from the direction of Central America, and the weather tends to be very hot and very humid, and that's when most rain falls in the desert parts of the islands.

(Adaptation intro book in cabin)

On Galápagos there are plants and animals that occur nowhere else - they are endemic to the islands. And within the archipelago there are species that occur on one island only. There are a large number of endemic species of both plants and animals. Some, like the Galápagos hawk, are similar to hawk species elsewhere, but the endemic marine iguana is the only marine lizard. There are two endemic species. Each island that has populations of the famous giant tortoises has its own endemic form. It is the endemic species that contribute both to the uniqueness of the islands and their special scientific interest. Now go out, via the porthole, to explore two different habitats and search for the distinctive animal life in each.

(Evolution in real time intro book in cabin)
One myth about evolution is that it only occurs over millions of years. In this section you will look at the speed with which evolution can occur and how natural selection operates. This involves following organisms in their struggle to survive and reproduce. We'll see how changing environmental conditions and variation in natural populations can set the scene for intense selection pressures to occur.

(Species and speciation intro book in cabin)
The Galápagos has a large number of species endemic to the islands but with some similarities to species found on mainland South America. How did the Galápagos islands change from bare volcanic rock, newly emerged from the sea, to the thriving and unique ecosystems we see today? In this section we look at how the islands would have been colonised and how new species have since evolved.

[Adaptation - Coastal & Inland regions of the islands]

(start coastal panorama) This is Gardner Bay on Española. Use the four arrow keys to move around the scene, the shift key to zoom in and the Ctrl key to zoom out. Click on any animal that you find to get more information. When you have finished, move to the inshore habitat.

(start inland panorama) This lake on Santiago was visited by Charles Darwin. He wrote: The lake is quite circular, and is fringed with a border of bright green succulent plants; the almost precipitous walls of the crater are clothed with wood, so that the scene was altogether both picturesque and curious. A few years since, the sailors belonging to a sailing vessel murdered their captain in this quiet spot; and we saw his skull lying among the bushes. You won't see the skull, but look around for the animals, as you did at the coast.

(hotspots)
(marine iguana) The Galápagos marine iguana is the only marine lizard in the world. There are 7 endemic sub-species. This one on Española has distinctive red patches.

(Mocking bird) This species of mocking bird is endemic to Española. It's quite fearless and will investigate everything - even beach towels! Mocking birds are omnivorous, eating seeds, eggs, insects and this species has even been observed feeding on a sea lion placenta.

(Sally lightfoot crab) The Sally lightfoot crab is commonly found on rocks close to the shoreline. It is widely distributed and not endemic to the islands. The colours are quite variable.

(American oystercatcher) The American oystercatcher is a familiar sight on Galápagos beaches. The species is widely distributed in North and Central America.

(Turtle track) Green turtles lay their eggs on sandy beaches above the high water mark. They lay at night, and can be seen in the early morning returning to the sea. They leave characteristic tracks in the sand.

(Sea lion) The Galápagos sea lion is another endemic species, smaller than its close relative the Californian sea lion. The population was badly affected by the 1997 El Niño event and is now about a quarter of what it was in 1979.

(Frigate bird) There are two species of native frigate bird, neither endemic. The males have a patch of red at the throat, the gular sac, that can be inflated during a courtship display. The females have a white throat and breast.

(Galápagos hawk) Galápagos hawks are endemic. On some islands the birds form pairs, as here. On others there are polyandrous groups of one female and several males.

( Lava lizard) Lava lizards are found on most of the large islands and there are 7 endemic sub-species. The males are quite aggressive in protecting their harems.

(Dove) The Galápagos dove is an endemic species. It feeds mainly on seeds but also Opuntia flowers and caterpillars. The birds are very tame and as they forage on the ground are vulnerable to introduced predators such as feral cats.

(Land iguana) There are two endemic species of land iguana in Galápagos. When Darwin visited Santiago he saw huge numbers of land iguanas and found it hard to avoid their burrows. Today there are none, although their enemies - introduced goats, pigs and donkeys - have recently been eradicated. Some time in the future they may be re-introduced.

(Ground finch) Male medium ground finches are darker than the females. Distinguishing the different ground finches is difficult unless you are a real expert. All the finches are endemic to the islands.

(Tortoise) Darwin saw tortoises being salted for food down by the crater lake. Feral goats and pigs have reduced the population and they are now rare. During the heat of the day you are more likely to find them in the shade.

(Mocking bird) The Galápagos mocking bird is found on the majority of islands, except where there are other endemic species. They are at risk from introduced rats and cats, as well as an introduced bird, the smooth-billed ani.

(Hawk) The Galápagos hawk is endemic to Galápagos and recent studies have shown that the genetic difference between islands far exceeds the differences within islands. This may be a stage of divergence on the way to speciation.

(Flamingo) The Caribbean flamingo breeds on Galápagos, but is relatively rare, with less than 500 individuals in total. The birds are found mostly in the shallow lagoons bordered by mangroves.

[Adaptation - Topic 1 Introduction]

You've seen a number of the unusual animals that inhabit the Galápagos. Now for a chance to reflect on the link between the appearance of an organism and its lifestyle.

[Adaptation - Topic 1 Question 1 ]

(video 1) Iguanas have sharp claws with which to hold tightly to rocks. The force required to remove one can be measured using string and a spring balance.

(video 2) The iguana has been known to dive for food and can survive underwater for up to an hour.

(video 3) Small razor-like teeth and a blunted snout are essential for cropping short algae.

(feedback) In order to eat algae, iguanas need to graze close to the rocks and gather short strands of seaweed growing there. Sharp razor-like teeth and blunted snouts are very helpful. The iguanas also need sharp claws to grip the rocks and avoid being washed away by waves. Some iguanas dive deeper for their food and can survive underwater for long periods. However, the ability to breed in water would not help an iguana to feed on sea algae, and marine iguanas breed and lay eggs on land.

[Adaptation - Topic 1 Question 2]

(video 1) The main way that tortoises vary from island to island is in the shape of their shells. The larger, dome-shaped types are found on the higher, lusher islands where vegetation is dense and a protected front end is useful

(video 2) The smaller saddle-backed tortoises have the front of their shells turned up. They're found on the drier islands where vegetation is less dense and more difficult to reach.

(feedback) There's no obvious reason why a turned-up shell should help a tortoise cope with a dry climate. This type of shell is also more likely than a dome-shaped one to expose the tortoise's neck to damage when moving through dense vegetation. But a turned-up shell does allow the tortoise to stretch its neck up higher than a dome-shaped shell would, and so enables the animal to reach higher vegetation.

[Adaptation - Topic 1 Question 3]

(video 1) With its long legs and long flexible neck, the flamingo can wade into deeper water and reach down to the bottom.

(video 2) The bill acts as a specialised sieve, which separates the shrimps and water boatmen from the mangrove sediment.

(feedback) Flamingos wade through mangrove swamps with their long cane-like legs, whilst reaching the swamp floor with their long necks. Whilst all the listed features are important, it's the bill which enables them to sieve their food from the sediment.

[Adaptation - Topic 1 Exercise 1]

(entry) You will be shown a series of photographs of birds found on Galápagos. Click on 'Resources' for more details of the bird. Look closely at the bird's beak and decide whether it's likely to feed on fish in the coastal areas or seeds and insects inland. Predict the feeding environment of each bird by clicking on the relevant button.

(video 1) When swimming, the body of the flightless cormorant is submerged. Only the snake-like neck is visible above the surface.

(video 2) The Galápagos dove eats caterpillars and seeds, and flowers when they are in season.

(video 3) For finches, smaller bills mean smaller insect prey, as well as seeds and products of the Opuntia cactus.

(video 4) The frigate bird is a parasite on other seabirds.

(video 5) The masked booby feeds on fish and squid and can also fish at night.

(video 6) The Galápagos hawk is one of the few predatory species on the islands.

[Adaptation - Topic 2 Introduction]

Darwin's finches vary enormously in their habitat, feeding behaviour and their diet. What can we glean about the adaptive features of the birds simply by looking at their physical characteristics? How much can we infer from museum specimens, for instance? What extra information do field studies provide?

Rosemary Grant: One very important aspect of field studies is just finding out what these birds are feeding on. We can see from museum specimens that their beaks are very variable: some are small, needle-like, others are large crunching beaks and so now from live birds we can see exactly what they're feeding on, whether they're feeding on insects or seeds and if seeds, what size of seeds.

[Adaptation - Topic 2 Question 1]

(video 1) Look closely at how these 6 different finch species vary.

(video 2) They began to differentiate on different islands and form different species. But the islands are ecologically very simple, very simple vegetation, rather impoverished islands. And they didn't diverge very much, they basically evolved a certain number of different feeding mechanisms: bigger seeds or smaller seeds, or in one or two cases, soft fruits or insects. And so they evolved differences that mainly affected their beaks. They didn't evolve many differences of plumage or colour. The size differences were limited and so they have in fact produced a range of very, very similar species that differ mainly in their feeding adaptations.

(video 3) I think the first thing you'd start to do to narrow the field down a bit is to count the number of wing feathers, the primary feathers, the outer wing feathers. And the number would be either 9 or 10. And if you got the number 9, you'd immediately know that the bird belonged to a group of families of which Darwin's finches is one, and this would narrow down your search quite a lot. I don't think there's a single bird that can't be identified from its external characters: plumage, shape of beak, wing, head, shape of tail feathers etc. You can, that is sufficient. But there are some birds that are still very difficult and Darwin's finches from the Galápagos are among these, because the structural differences between these birds are very, very slight.

(feedback) There's considerable variation in size between species. But there's also considerable variation in size within a species: body size is very dependent on age for example. So it's not a good feature for distinguishing between species. Colour isn't useful because it varies only slightly: most finches are brown or black. Beak size and shape are the best features to use because they vary a great deal between species but are relatively consistent within a species.

[Adaptation - Topic 2 Question 2]

(video 1) Singing in birds doesn't depend on beak size and shape but on an organ called the syrinx at the bottom of the windpipe.

(video 2) Beak size and shape could also play a role in mate choice and in defence. In fact, females of the medium ground finch have been shown to prefer males with larger beaks.

(video 3) The most detailed field data available however, relate beak size and shape to the diet of the finches.

(feedback) Beak size and shape could influence to some extent the type of song the bird can sing, its fighting ability and its desirability as a mate but they will have an enormous effect on the type of food the bird can handle and therefore eat.

[Adaptation - Topic 2 Question 3]

(video 2) The beak of a finch can be compared to a tool in its mode of action. A probing beak is long and pointed, suitable for gaining access to flowers and foliage. A crushing beak is deep at the base but not as curved as in the tip-biting class, well equipped for crushing hard foods.

(video 3) A tip-biting beak is well adapted for feeding on fruits and leaves as well as arthropods in exposed areas on plants and on the ground.

(video 4) A probing beak is suitable for reaching into fruits and flowers, obtaining nectar and probing out insects hidden in crevices or in vegetation.

(feedback) A crushing beak is well equipped for feeding on a variety of seeds.

[Adaptation - Topic 2 Question 4]

(video 3) The beak of a finch can be compared to a tool in its mode of action. A probing beak is long and pointed, suitable for gaining access to flowers and foliage. A tip-biting beak is curved at the top and bottom and can apply force at the tip. A crushing beak is deep at the base but not as curved as in the tip-biting class, well equipped for crushing hard foods.

(feedback) The cactus finch displays both crushing and probing characteristics as shown by the way it forages for seeds on the ground and probes into this Opuntia cactus flower.

[Adaptation - Topic 2 Exercise 2]

(entry) Choose the beak type appropriate to each bird that you are shown and click the relevant button in the circle to place the bird in the correct sector.

The cactus ground finch has a pointed beak which is also deep at the base.

The beak of a finch can be compared to a tool in its mode of action. A probing beak is long and pointed, suitable for gaining access to flowers and foliage.

A tip-biting beak is curved at the top and bottom and can apply force at the tip.

A crushing beak is deep at the base but not as curved as in the tip-biting class, well equipped for crushing hard foods.

The cactus ground finch has a beak that's intermediate between crushing and probing.

The large tree finch has a more curved beak.

The beak of a finch can be compared to a tool in its mode of action. A probing beak is long and pointed, suitable for gaining access to flowers and foliage.

The tree finches have a tip-biting beak.

The small ground finch has a beak which is deep at the base.

The vegetarian finch has a curved beak which is also deep at the base.

The vegetarian finch has a beak that's intermediate between crushing and tip-biting.

The woodpecker finch has a pointed beak which is also curved.

The woodpecker finch has a beak that's intermediate between tip-biting and probing.

The medium ground finch has a beak which is deep at the base.

The ground finches have a crushing type of beak.

The warbler finch has a very narrow, pointed beak.

The warbler finch has a probing beak.

The small tree finch has a more curved beak.

The tree finches have a tip-biting beak.

The large ground finch has a beak which is deep at the base.

The ground finches have a crushing type of beak.

[Adaptation - Topic 3 Introduction ]

This is a representation of one of the highest islands in the Galápagos, Santa Cruz. On a visit to this island you will see various vegetation zones. These include the arid zone, the transitional zone, the Scalesia zone and the Miconia zone. The composition of the plant community which makes up these vegetation zones varies at different altitudes. The lowlands have cacti and bushes and the highland dense forest areas. This is due to differences in weather and temperature. For every 100 metres ascent there is a drop in temperature of 1 degree Celsius. There is also a marked difference in rainfall. The highlands receive much more rain and are much wetter. These differences in temperature and rainfall occur over very short gradients, which results in many different habitats especially for finches.

Try and answer the questions that follow. Click on the resource buttons for information that may help you to answer the questions.

For each question click on the box beside the answer that you think is most appropriate. Press Done when you've made your choice.

[Adaptation - Topic 3 Question 1]

(video 1) Plants provide both the materials for nest building and the foundations in which it can be built. All the finches build similar nests in similar trees and bushes.

(video 2) Plants such as the Opuntia cacti provide flowers with nectar and pollen in the dry season. In the wet season they produce fleshy fruits with large hard seeds. Their green pads also provide water. Many other plants provide berries and are a rich source of arthropods which live on them.

(feedback) Plants provide food, shelter and nesting material for finches and can also supply a certain amount of water, for example in the cactus pads eaten by cactus finches.

[Adaptation - Topic 3 Question 2]

(video 1) The Scalesia zone is rich in Scalesia pedunculata, an endemic plant species that represents one of the tallest members of the daisy and sunflower family. Caterpillars that feed on its flowers are eaten by finches. Many arthropods are hidden under the bark of these trees.

(feedback) The Scalesia forest provides a rich source of arthropods for woodpecker and warbler finches.

[Adaptation - Topic 3 Question 3 ]

(video 1) The Miconia zone contains introduced plants and ferns and is found at the top of Santa Cruz.

(video 2) The Scalesia zone is rich in Scalesia pedunculata, an endemic plant species that represents one of the tallest members of the daisy and sunflower family. Caterpillars that feed on its flowers are eaten by finches. Many arthropods are hidden under the bark of these trees.

(video 3) The arid zone is very dry for most of the year and is composed mostly of Opuntia cactus and small seed-yielding bushes.

(video 4) The transitional zone comes between the Scalesia zone and the arid zone. Cacti are present, but they are smothered by other plants during the wet season.

(feedback) The cactus finch is most likely to be found in the arid zone, where the Opuntia cactus is a rich source of fruit, flowers and seeds.

[Adaptation - Topic 3 Exercise 3]

(entry) For each food type that you are shown choose the most appropriate beak type for exploiting it. The 'Resources' give more information on each food item. Match the beak type to your chosen food type by pressing on the relevant button in the finch circle. There may be more than one food type for each beak type.

(video 1) Caterpillars are found in crevices in bark or under leaves and vegetation.

(video 1 answer) A probing beak is useful for reaching arthropods hidden in crevices or in vegetation.

(video 2) Large, hard seeds like Tribulus can only be cracked by the large and medium ground finches.

(video 2 answer) A crushing beak is well equipped for feeding on a variety of seeds.

(video 3) Spiders can be plucked from their webs or the surface of tree bark.

(video 3 answer) A tip-biting beak is useful for feeding on arthropods exposed on plants or on the ground.

(video 4) Pollen and nectar can be found towards the base of the Opuntia flower.

(video 4 answer) A probing beak is suitable for reaching into fruits and flowers.

(video 5) Berries can be pierced or plucked from the plant on which they grow.

(video 5 answer) A tip-biting beak is well adapted for feeding on fruits and leaves.

(video 6) Croton seeds are easy to crack, even by smaller beaked birds.

(video 6 answer) A crushing beak is well equipped for feeding on a variety of seeds.

(end) You've finished the final exercise for this section. Click on the ship's icon for a summary of this part of the tutorial.

[Adaptation - Summary]

(no audio)

[Evolution in Real Time - Climate changes on Galápagos]

(intro) Climate is a major factor affecting evolutionary change on Galápagos. Here's how the islands look in a normal wet season. By clicking on these arrows you'll be able to switch to the dry season. Click again to find out what happens during an El Niño year. For each screen, as you move the cursor, small icons will appear. Click on them to find out more information about the climatic conditions and their impact on certain species.

(icons)
(Marine iguana)
(Jan-May, hot and wet)
The breeding season for the marine iguana falls in this period. Adult males become more brightly coloured and defend their territory aggressively. They often do this at the expense of feeding. During mating, a male mounts the female, holds her by the neck and twists his tail around her, enabling him to penetrate. Egg laying takes place about 5 weeks later.

(Jun-Dec, cool and dry)
In the non-breeding season, marine iguanas show little aggressive behaviour. Much time is spent basking in the sun to maintain their body temperature, only diving for food in the middle of the day, when the sun is hottest.

(El Niño)
The warmer waters lead to a decrease in the normally rich nutrient levels of the oceans. The supply of algae declines and on some islands up to 90% of marine iguanas die.

(Penguins)
(Jan-May, hot and wet)
The penguin has different feeding strategies depending on the water temperature. If the water is warmer than 23 degrees Celsius, they feed singly or in small groups. Only when the waters are cooler and fish more abundant, do the penguins feed in large groups.

(Jun-Dec, cool and dry)
The breeding success of penguins and survival of their young are influenced by food supply. In a typical year, the cooler waters at this time result in a rich nutrient supply, so breeding failures due to food shortage are rare.

(El Niño)
With the rise in sea surface temperatures and the decrease in nutrient supply, penguins are no longer able to feed. In the 1983 El Niño, breeding ceased and up to three-quarters of the penguins on some islands died.

(Tortoises)
(Jan-May, hot and wet)
Giant tortoises usually mate during the warm wet season. The young from a previous season's egg-laying emerge between January and April. Survival of the hatchlings may be related to the humidity of conditions in their first year.

(Jun-Dec, cool and dry)
Most eggs of the giant tortoise are laid in the period between June and December. The young emerge about four months later.

(El Niño)
The breeding of giant tortoises may be affected when nests are flooded during El Niño. But lush vegetation allows the animals to build up their reserves of fat. These allow the tortoises to survive until conditions become more favourable for breeding.

(Finches)
(Jan-May, hot and wet)
The breeding of most finch species is strongly influenced by rainfall. Early in the wet season male finches begin to sing, build nests and display to females. Eggs are laid within a week of mating. Young birds fledge by the end of a month. If food conditions are good, further breeding attempts are made.

(Jun-Dec, cool and dry)
During the dry season, many finches move away from their breeding areas. Some tree finches move from the forests to coastal regions whilst ground finches move in the opposite direction. Food supply is scarce and many young birds die.

(El Niño)
Another feature of the Niño year that really took us by surprise, was the discovery that Darwin's finches are capable of breeding at an age much less than one year. We thought that birds were incapable of breeding in their year of birth, just simply for physiological reasons. El Niño of 1983 showed us that we were wrong in that respect, because birds that were hatched from eggs in December of '82 and January of 1983, were themselves breeding in April or May of 1983 at an age, minimum age, of ninety days, something under normal circumstances that would never happen because the conditions would never happen.

(Clouds)
(Jan-May, hot and wet)
January to May is the warm wet season. Maximum land temperatures may reach 30 degrees Celsius. Average sea temperatures are about 25 degrees Celsius. The average monthly rainfall is about 20 mm.

(Jun-Dec, cool and dry)
June to December is the cool dry season. Maximum land temperatures are about 25 degrees Celsius. Average sea temperatures are about 20 degrees Celsius. Average monthly rainfall is less than 10 mm.

(El Niño)
El Niño is an exaggerated form of wet season, caused by a combination of meteorological and oceanographic events. The immediate warning that an El Niño is upon us when we're on the Galápagos is a warming of the seas, the temperature rises, hot air rises, condenses and comes down as terrific rain storms, and those showers or storms can persist for a long period of time. They can be more intense than usually happens in a wet season.

(Cactus)
(Jan-May, hot and wet)
Most plant production occurs in the wet season. Leaves appear within a week of the first heavy rain. Seeds and fruits mature within a few months. The amount of rain and length of the wet season influence the number of seeds produced. There's also a rich supply of arthropods, especially caterpillars.

(Jun-Dec, cool and dry)
During the dry season, much of the green vegetation at low altitude dies. Birds like finches have to survive on the existing supply of fruits, seeds and arthropods. But towards the end of the dry season, a burst of flowering by the Opuntia cactus provides a source of nectar and pollen for finches.

(El Niño)
What happened in 1983 is that the cactus suffered very badly, vines grew up over the cactus, smothered the cactus. Very few of them could photosynthesise, and those that were not smothered by vines, often took up so much water that they were blown over in the storms that accompanies the heavy rains. And so there were very few cactus flowers and fruits produced.

[Evolution in Real Time - Topic 1 Introduction]

Now for a closer look at how the variable climate of the Galápagos poses a challenge to survival and leads to changes in the effects and intensity of natural selection.

[Evolution in Real Time - Topic 1 Question 1]

(video 1) The Galápagos Islands are far from other land masses so their climate is mainly influenced by the ocean currents bathing the archipelago. From June to December, cooler waters from the south-easterly Humboldt current predominate, giving sea temperatures of about 22 degrees Celsius. From January to May, warmer waters from the Panama Basin in the north-east predominate (the so-called El Niño current). The average sea temperature rises to about 25 degrees. In some years the flow of warm waters is much greater. Surface water temperature rises up to 30 degrees and rainfall increases. This results in a so-called El Niño year.

(video 2) January to May is the warm wet season, with maximum temperatures on land of up to 30 degrees Celsius. Average sea temperatures are about 25 degrees. July to December is the cool dry season with maximum land temperatures of about 25 degrees. Average sea temperatures are about 22.

(video 3) January to May is the wet season. The average amount of rain falling each month is over 20 mm. A variety of plants thrive during this period. The native Bursera, known as the incense tree or palo santo, flowers and produces fruits. In the dry season the trees lose their leaves, becoming grey white and appearing lifeless while they are dormant waiting for the return of the rains. The Croton is an endemic species with four varieties. There is also an introduced garden Croton that's quite different in appearance. There are two Lantanas on Galápagos. This one is endemic but there is another highly invasive one that has been introduced. The shrubs often form dense thickets on the lava. June to December is the dry season. Average monthly rainfall is less than 10 mm. Desert species such as Opuntia flower towards the end of this period.

(feedback) The Galápagos are remarkably seasonal, although they lie on the Equator and this effects the vegetation through the year. It's during the dry season, between June and December, that food supply on land may be scarce. We'll see later how this is a potential period when intense natural selection can occur.

[Evolution in Real Time - Topic 1 Question 2]

(video 1) The Galápagos Islands are far from other land masses so their climate is mainly influenced by the ocean currents bathing the archipelago. From June to December, cooler waters from the south-easterly Humboldt current predominate, giving sea temperatures of about 22 degrees Celsius. From January to May, warmer waters from the Panama Basin in the north-east predominate (the so-called El Niño current). The average sea temperature rises to about 25 degrees. In some years the flow of warm waters is much greater. Surface water temperature rises up to 30 degrees and rainfall increases. This results in a so-called El Niño year.

(video 2) El Niño is an exaggerated form of wet season caused by a combination of meteorological and oceanographic events. The immediate warning that an El Niño is upon us when we're on the Galápagos is the warming of the seas. The temperature rises, hot air rises, condenses and comes down as terrific rainstorms, and those showers or storms can persist for a long period of time. They can be more intense than usually happens in a wet season.

(feedback) Surface water temperatures during an El Niño may be up to 5 degrees higher than during a normal wet season. Warm water holds less oxygen, leading to less underwater plant and animal life. This in turn means less food for marine iguanas, sea-going mammals and birds.

[Evolution in Real Time - Topic 1 Question 3]

(video 1) Martin Angel: Well the effects of the El Niño on the animals and plants is basically divided into those who like El Niño and those who don't. Clearly the desert-type species, the cacti and so on, don't like the very humid conditions. Similarly, curiously enough a lot of marine species don't like El Niño. Because the water is warm, the productivity of the water falls right away so you get the sea lions, the fur seals and a lot of the seabirds all starving at this time when there's a persistent El Niño, but for a lot of the plants you get very rich growth of herbs and this results in a very heavy seed crop which benefits the finches so in the longer term the finches quite fancy El Niño.

(feedback) The warmer surface waters during an El Niño lead to a decreased nutrient supply in the oceans so marine life suffers. But apart from desert species such as the cactus, much of the vegetation on land thrives, favouring many land birds and mammals.

[Evolution in Real Time - Topic 1 Exercise 1]

(intro) For each species that you are shown, predict whether El Niño would cause the population size to decrease, increase or stay the same by clicking on the appropriate box. Click on Resources for more details of each animal.

(video 1) Giant tortoises feed on a variety of grasses and herbs as well as cactus pads and fruits. Mortality for young tortoises may be high during years when little rain falls in the wet season and food is scarce in the lowland nesting areas. Equally, in very wet years, animals may drown when nesting areas become flooded. But for adults, severe conditions appear to have a less dramatic effect on giant tortoises than other species because they're able to draw on fat reserves built up during favourable periods.

(answer 1) For giant tortoises, there should be little mortality due to food shortage during an El Niño, when land vegetation is lush. But an increase in population size is unlikely, with nesting affected by floods. So the population size of giant tortoises might be expected to stay the same.

(video 2) The Galápagos dove is found in the drier zones of most islands. It feeds on the seeds, pulp and flowers of the Opuntia cactus. It also eats seeds from the small flowering shrub Croton. On some islands the breeding of the dove coincides with the availability of these seeds.

During an El Niño, the Croton plant flourishes. It can set seed and produce new bushes that provide more seeds every month throughout this period.

(answer 2) Although the Opuntia cactus suffers during an El Niño, the increased seed supply from plants such as Croton will favour breeding in the dove. So population size will be expected to increase.

(video 3) Cold water species such as the penguin thrive when sea temperatures are between 18 and 22 degrees Celsius and nutrient levels in the oceans are high. In order to breed, these birds need a rich food supply within swimming distance of their nest. This occurs when there are upwellings of cooler water around the coast - a relatively irregular event. So the penguins don't necessarily breed every year.

(answer 3) Penguins will suffer a population drop during El Niño. Deaths due to food shortage are not replaced by young birds because breeding also fails.

(video 4) Flightless cormorants are found mainly on the coasts off the islands of Isabela and Fernandina, where the cool rich waters of the Cromwell current upwell. The birds feed within about a hundred metres of the coast on a diet of fish and octopus. Flightless cormorants breed throughout the year, though fewer clutches are laid in the period between November and March.

(answer 4) A decrease in population size amongst flightless cormorants might be expected due to lack of food.

(video 5) Marine iguanas spend much of their time basking in the sun. This raises their body temperature and speeds up their physiological processes. The iguanas feed mainly on algae in the intertidal zones or just below the sea surface. The food supply is plentiful when sea temperatures are below 25 degrees Celsius.

(answer 5) The population size of marine iguanas can drop dramatically during an El Niño year, when the warmer waters lead to a decrease in the nutrient levels of the oceans.

(video 6) During the dry season many finches move away from their breeding areas. Some tree finches move from the forests to coastal regions, whilst ground finches move in the opposite direction. Food supply is scarce and many young birds die.

The breeding of most finch species is strongly influenced by rainfall. Early in the wet season male finches begin to sing and build nests and display to females. Eggs are laid within a week of mating. Young birds fledge by the end of a month. If food conditions are good, further breeding attempts are made.

Another feature of the El Niño year that really took us by surprise, was the discovery that Darwin's finches are capable of breeding at an age much less than one year. We thought that birds were incapable of breeding in their year of birth, just simply for physiological reasons. El Niño of 1983 showed us that we were wrong in that respect, because birds that were hatched from eggs in December of '82, and January of 1983 were themselves breeding in April or May of 1983 at an age, minimum age, of ninety days, something under normal circumstances that would never happen because the conditions would never happen.

(answer 6) With the rapid growth of herbs and grasses plus a rich supply of arthropods during El Niño, finches may breed several times in a year. So the population size will increase.

[Evolution in Real Time - Topic 2 Introduction]

In this section we study the raw material on which natural selection operates - individual variations within a population. We focus on insights gained from field studies of Darwin's finches spanning over 20 years.

Peter Grant: We did not embark upon our studies with the idea of measuring and interpreting natural selection because we had no idea whether we would stand any chance of seeing natural selection occurring. But after the first field season, we realised that selection might be occurring, and if it did occur, in order to study it, we needed to measure a large number of individuals of birds and then follow their fates over a period of time.

[Evolution in Real Time - Topic 2 Question 1]

This sequence shows the mean beak depth for male birds of some finch species on the island of Santa Cruz. It highlights the range of variation between birds of different species.

(feedback) The large ground finch shows the greatest beak depth at 19.1 mm. The warbler finch shows the smallest beak depth, about 4 mm. The difference between these two measurements is 15.1 mm.

[Evolution in Real Time - Topic 2 Question 2]

There's also a great deal of variation in beak size within a species. Take the medium ground finch for instance. A population of such finches actually shows a range of beak sizes. These form a so-called normal distribution. Birds with the smallest and largest beaks lie at either end. Birds with the mean or average beak size are at the peak.

(feedback) The mean beak depth corresponds to the peak of the normal distribution curve. Medium ground finches from this population have a beak that's 12.8 mm deep on average.

[Evolution in Real Time - Topic 2 Question 3]

There's also a great deal of variation in beak size within a species. Take the medium ground finch for instance. A population of such finches actually shows a range of beak sizes. These form a so-called normal distribution. Birds with the smallest and largest beaks lie at either end. Birds with the mean or average beak size are at the peak.

(feedback) In this population, the largest beaks are 16.6 mm deep and the smallest, 10.7 mm. The difference between these is 5.9 mm. So the largest beaks can be as much as 50% bigger than the smallest beaks within a single population of medium ground finches.

[Evolution in Real Time - Topic 2 Question 4]

(video 1) The caltrop plant, known by its Latin name Tribulus, is an important source of food for large and medium ground finches. It produces green spiky balls of fruit, each about as long as the beak of a medium ground finch. When dry, these break into pieces called mericarps. Each piece holds up to 6 large seeds.

(video 2) Rosemary Grant: The medium ground finch eats seeds on the ground, but it is quite fascinating because it's an extremely variable finch in bill size. Individuals with the larger bills, are able to crack the Tribulus seeds, whereas individuals with smaller bills are unable to do this. They mainly eat small soft seeds, and we have found that they are more efficient at dealing with these seeds than larger billed members of the same population.

(feedback) Only medium ground finches with beaks larger than the average are equipped to deal with the large hard seeds of the Tribulus plant. Even these can't take a whole mericarp at once - they only peel off the lid of each section, and eat one or two seeds at a time.

[Evolution in Real Time - Topic 2 Question 5]

(video 1) Peter Grant: In a typical year not more than half the finches born or hatched from eggs that year will survive till the next year. It's a struggle for those young finches to find enough food, and beak size makes a difference in determining whether those finches will survive to their first year or not.

(video 2) January to May is the wet season. The average amount of rain falling each month is over 20 mm. A variety of plants thrive during this period. The native Bursera, known as the incense tree or palo santo, flowers and produces fruits. In the dry season the trees lose their leaves, becoming grey white and appearing lifeless while they are dormant waiting for the return of the rains. The Croton is an endemic species with four varieties. There is also an introduced garden Croton that's quite different in appearance. There are two Lantanas on Galápagos. This one is endemic but there is another highly invasive one that has been introduced. The shrubs often form dense thickets on the lava. June to December is the dry season. Average monthly rainfall is less than 10mm. Desert species such as Opuntia flower towards the end of this period.

(video 3) January to May, the warm, wet season, is the breeding period for finches. If food supply is good, several mating attempts are made. From June to December, the cool, dry season, finches move away from their breeding grounds. This is a period of potential food scarcity for finches. Mortality can be high, particularly for birds in their first year.

(feedback) From January to May, the rainy season, the supply of seeds, fruit and arthropods is high. During the dry season, from June to December, food supply gradually declines. Survival is at a premium: many birds, mostly young ones, die.

[Evolution in Real Time - Topic 2 Question 6]

(video 1) January to May is the wet season. The average amount of rain falling each month is over 20 mm. A variety of plants thrive during this period. The native Bursera, known as the incense tree or palo santo, flowers and produces fruits. In the dry season the trees lose their leaves, becoming grey white and appearing lifeless while they are dormant waiting for the return of the rains. The Croton is an endemic species with four varieties. There is also an introduced garden Croton that's quite different in appearance. There are two Lantanas on Galápagos. This one is endemic but there is another highly invasive one that has been introduced. The shrubs often form dense thickets on the lava. June to December is the dry season. Average monthly rainfall is less than 10mm. Desert species such as Opuntia flower towards the end of this period.

(video 2) The caltrop plant, known by its Latin name Tribulus, is an important source of food for large and medium ground finches. It produces green spiky balls of fruit, each about as long as the beak of a medium ground finch. When dry, these break into pieces called mericarps. Each piece holds up to 6 large seeds.

(feedback) During a prolonged drought, there will be little or no growth of new plants, so the standing crop of fruit and seeds gradually declines. There will also be fewer arthropods available. Medium ground finches would have to rely mainly on the existing seed supply. Small or soft seeds would probably be eaten first since they can be handled by most individuals in the population. As the smaller softer seeds disappear, larger harder seeds become the main food supply.

[Evolution in Real Time - Topic 2 Question 7]

(video 1) Here's the normal distribution curve for medium ground finch population. Section a represents birds with beaks smaller than the average. Section b represents birds with a beak size around the average. Section c represents birds with beaks larger than the average.

(feedback) Larger, harder seeds are the main food supply in a prolonged drought. So birds with a larger than average beak depth will be at an advantage because only they will be able to apply the cracking force needed to handle these seeds.

[Evolution in Real Time - Topic 2 Exercise 2]

(intro) Now explore the effect of different sets of conditions on a population of the medium ground finch. You will be given a scenario and asked to make predictions. Initially the finch population shows a normal distribution, as shown. For each scenario, predict the effect on the number of finches by clicking on the appropriate symbol. You can opt for an increase, a decrease or no change in finch numbers. Do the same for mean beak size, again predicting an increase, decrease or no change. Press 'Done' only when you've made your predictions for both finch numbers and beak size. There are resources that may help you make your predictions.

(video 1) The Opuntia cactus is a rich source of food for finches. In the dry season it produces flowers with nectar and pollen. The green pads of the cactus provide water. Rotting pads also harbour insect larvae. In the wet season, it produces fleshy fruits with large hard seeds.

Beak depth in the medium ground finch is normally distributed. At each point, the height of the curve represents the number of birds with a particular beak depth. The most common beak depth is the mean beak depth, while birds with very large or very small beaks are rare.

Factors that will tend to decrease the size of a population are death, emigration and failure to breed. Factors that will tend to increase the size of a population are birth, immigration and increased reproduction.

(feedback) In this scenario, the overall seed supply falls; some birds die from starvation and population size drops. But it's the larger seeds in particular that are in short supply. Birds with a beak depth smaller than average will be more likely to survive and reproduce because they can continue to feed on the smaller seeds. So mean beak size in the population will fall

No. You should have predicted that finch numbers drop and mean beak size decreases. Why does this happen?

(Scenario 2) How much of the ground finch diet is composed of seeds of different size. Each ground finch species eats a range of seed sizes. But the small ground finch eats mainly the smallest seeds, the medium ground finch larger seeds, and the large ground finch eats larger ones still. Some seed classes are eaten by more than one species. These are potential situations where competition can arise.

(feedback) Competition with the small ground finch means there's less food available for medium ground finches so some of them starve and the population size drops. But competition mostly affects the medium ground finches with smaller beaks, since both species want the smaller seeds. So medium ground finches with larger beaks are more likely to survive and reproduce. Mean beak size will increase.

[Evolution in Real Time - Topic 2 Exercise 3]

(intro) Now explore the effect of different sets of conditions on a population of the medium ground finch. You will be given a scenario and asked to make predictions. Initially the finch population shows a normal distribution, as shown. For each scenario, predict the effect on the number of finches by clicking on the appropriate symbol. You can opt for an increase, a decrease or no change in finch numbers. Do the same for mean beak size, again predicting an increase, decrease or no change. Press 'Done' only when you've made your predictions for both finch numbers and beak size. There are resources that may help you make your predictions.

(Resource1) The significance of variations in beak size becomes apparent when there's a change in the environment, particularly a change in the food supply. For example, in 1977 no rain fell on the little island of Daphne where we were studying. Most of the finches of the medium ground finch population that we were studying died, and at the end of 1977 we compared the beak measurements of the birds that died with those that survived, and we found that the survivors were bigger on average. The factor that was most obviously related to the mortality was the food supply.

(Resource2) In the dry season, in the first ten years of our study, the main food supply of the finches were cactus seeds and Tribulus seeds; there were very few small seeds and usually these small seeds were exhausted by about half way through the dry season.

(Resource3) The medium ground finch eats seeds on the ground, but it is quite fascinating because it's an extremely variable finch in bill size. Individuals with the larger bills are able to crack the Tribulus seeds, whereas individuals with smaller bills are unable to do this. They mainly eat small soft seeds, and we have found that they are more efficient at dealing with these seeds than larger billed members of the same population.

(feedback) During a prolonged drought, finch numbers are expected to decrease as the seed supply falls. Smaller, softer seeds tend to get eaten first so, as the drought proceeds, larger harder seeds become the main food source. So the mean beak size increases, because it's larger-beaked birds that are able to handle these seeds. In fact, the ground finch population fell to about 15% of its original size. The mean beak size shifted up by a half a millimetre. A subtle difference - but one that meant the difference between death and survival.

(Scenario 2)
(resource 1)There is a plant in the genus Croton, a small flowering tree that grows very rapidly when the conditions are right. A bush that we watched overall for eight months of the wet season of 1983 produced seeds that grew up to bushes, that produced seeds that grew up to bushes and so on, eight times on average, one generation per month for the whole of the eight month period.

(resource 2) What happened in 1983 is that the cactus suffered very badly. Vines grew up over the cactus, smothered the cactus, very few of them could photosynthesise, and those that were not smothered by vines often took up so much water that they were blown over in the storms that accompanied the heavy rains, and so there were very few cactus flowers and fruits produced.

(resource 3) The Tribulus, which is a plant that produces a very hard seed, grows very close to the ground, and that again was smothered by all the annuals, the grasses and plants that grew up. So the two plants producing large hard seeds suffered very much after 1983, but there was a terrific production of small soft seeds, and a large seed bank which lasted for more than ten years.

(resource 4) In 1984 and again in 1985, following an extraordinary El Niño event of 1983, there was very little rain in the archipelago, and there wasn't very much production of new seeds. What seeds were available had been produced by the plants growing in the El Niño of 1983 to a large extent, and those were predominantly those species that produced very small seeds. So the food supply available to the finches on the island we were studying in most detail was made up to a very large extent of small seeds only. Large-beaked members of the medium ground finch population suffered during the ensuing dry conditions because they couldn't get enough to eat. The smaller members of that population had the survival advantage.

(feedback) The overall seed supply drops so population size falls, but not as dramatically as in the previous drought since there's still a large seed bank available after El Niño. Plants bearing large hard seeds have been badly affected by El Niño, leaving small seeds as the main food source. So birds with smaller beaks are more likely to survive and reproduce. Mean beak size in the population decreases.

[Evolution in Real Time - Summary]

(no audio)

[Species & Speciation - Species origination]

(intro) All the species present on Galápagos today originate from the South American mainland. As you move your cursor over the two maps you will see icons of the species that live in both these areas today. Click on the icon to reveal information about each animal. As you do so their presence will be registered in the table. As you access each resource you will notice how some animals that came from the mainland have changed their appearance on Galápagos. More importantly you'll notice that some new species have evolved on Galápagos. These can be found nowhere else and are endemic to the islands.

(flamingo) Flamingos are very good long distance flyers. Those of Central America probably found their way to Galápagos.

(flightless cormorant) The Galápagos is home to the flightless cormorant, which has small stubby wings. This is the only species of cormorant to have lost the ability to fly.

(Mainland Cormorant) The mainland cormorant also dives for food but this species has large wings and is a strong flyer.

(Mainland Land Iguana) The Ecuadorian land iguana is smaller than that on the Galápagos and has a green colouration.

(Galápagos Land Iguana) Land iguanas can grow up to 1 metre in length and weigh as much as 6 kilos. Galápagos species have much yellow and brown colouration.

(Galápagos Marine Iguana) Marine iguanas are endemic to Galápagos and are found wherever there are suitable shores. These are the only sea-going lizards in the world.

(Galápagos Penguin) You don't expect to find penguins living on the Equator, but they are here on the Galápagos.

(Mainland Penguin) The Humboldt and Magellan penguins of southern South America are likely ancestors of the Galápagos penguin.

(Galápagos Tortoises) There are ten endemic subspecies of giant tortoise on Galápagos. Tortoises can live for a year without food or water.

(Mainland Tortoises) Tortoises on the mainland are smaller than those on the Galápagos, only measuring between 12 and 18 inches when fully grown.

(Galápagos Finches) There are 13 species of Darwin's finch, endemic to the Galápagos and one species endemic to the Cocos Islands. They are thought to have evolved from a common mainland ancestor.

(Mainland Sooty Grass Quit) There are no Darwin's finches on the mainland but one suggested ancestor is the sooty grass quit.

[Species & Speciation - Topic 1 Introduction]

Barren volcanic rock is still obvious on many islands of the Galápagos, even today. But even here plants such as cacti have begun to gain a foothold. The appearance of plants both on the land and in the sea off newly formed islands is the first step to colonisation. Once plants are growing, birds and other animals can survive by feeding on them. But predators can only colonise such islands later, after their plant-eating prey become established.

[Species & Speciation - Topic 1 Question 1]

(video 1) Seabirds may have come across the Galápagos many times before conditions were favourable for them to survive and colonise successfully.

(video 2) Newly formed islands are composed of volcanic rock on which nothing can grow.

(video 3) Seeds can be blown hundreds of miles by prevailing winds. Immediately upon landing, most seeds must find favourable conditions before they can implant and begin to grow. Others can lay dormant for long periods until such conditions exist.

(feedback) Some soil is needed for even the hardiest of plants to survive and weathering is the only process that will form it on an uninhabited island.

[Species & Speciation - Topic 1 Question 2]

(video 1) The hardier plants and cacti can survive with very little soil and nutrients. Cacti can be seen today growing in the most inhospitable of landscapes.

(video 2) Larger trees and bushes could not survive until a good soil base had been formed.

(video 3) Terrestrial birds depend on seeds or insects, which in turn depend on plants.

(feedback) Beach plants and cacti can exist with very little soil and do not depend on other species to survive.

[Species & Speciation - Topic 1 Question 3]

(video 1) The small land birds will happily survive as long as seeds and insects are available.

(video 2) Iguanas live off vegetation on land or in the sea and do not depend on other animals to survive.

(video 3) The Galápagos hawk is one of the few predatory species on the islands.

(feedback) As the major predator on Galápagos, the hawk depends on iguanas and small birds for food. Until these animals colonised Galápagos, predators like the hawk could not live there.

[Species & Speciation - Topic 1 Exercise 1]

You've seen that colonisation of newly formed islands occurs in a particular sequence. Now look at how some of the animals which live on Galápagos today actually made the journey from the South American mainland. For each animal, select its possible means of reaching the islands by clicking on the appropriate button. There are also resources that tell you about each animal.

(cormorants) (video 1) The mainland cormorants are strong flyers and could have flown to the islands; it was only after colonising Galápagos that they lost the power of flight.

(video 2) The predominant weather systems around the Galápagos are determined by trade winds. These are winds that blow persistently at ten to twenty knots. For nine months of the year these trade winds tend to be south easterly, that is they blow from the direction of South America, and at that time of the year the weather tends to be very cool and very misty around the islands. During the other three months of the year trade winds are north-easterly, blowing from the direction of Central America, and the weather tends to be very hot and very humid and that's when most rain falls in the desert parts of the islands.

(answer) The flightless cormorant probably flew to the islands, and only lost the power of flight after residing on Galápagos where it has no natural predators.

(Masked boobies)
(video 1) Masked boobies are strong flyers and can fish at night.

(answer) Masked boobies probably flew to the islands with help from the prevailing winds.

(tortoises) (video 1) Probably the best example of how animals got to the islands by combination of wind and sea are the tortoises, because it looks as though they originated from the mainland, probably being transported on weed rafts, and you see great rafts of weeds being washed down South American rivers even today. Now if the winds were stronger and the currents were a bit stronger then the tortoises would arrive on the islands, and we think that the first colonists were probably quite small, and when they got to the islands there were no predators and they were able to withstand the desert conditions, they flourished and in the absence of predators they found that they could grow bigger and bigger, and we think there was actually a selection for larger tortoises because the larger the tortoise the better it survived the drought conditions.

(video 2) The archipelago is unique because, although situated on the Equator, it's bathed for much of the year by the cool waters of the Humboldt and Cromwell currents. These cool currents result in water temperatures of around 22 degrees Celsius, which helps ensure an abundance of sea life. In the warm season, warmer waters from the Panama Basin flow through the islands and the average sea temperature may rise to 25 degrees Celsius. Warmer waters mean greater cloud formation, so the islands experience a more tropical climate with heavy rain showers.

(answer)The tortoises probably arrived on Galápagos by floating on rafts of vegetation from South America.

(seals)
(video 1) Sea lions are strong swimmers and can haul out to rest on floating debris.

(answer) Seals probably swam to the islands with help from the prevailing currents.

(penguins) (video 1) We know so little about freak events that it's very difficult to predict what might have happened, but there are longer scale cycles which we know occur and almost certainly had an impact on the way in which the colonists have arrived. The most important of these is probably the glacial cycle and during the glaciations it looks as though the wind speeds were much higher, and also the current velocities were much higher, and as a result what may have happened during these glacial periods is more cold water, flowed up the Humboldt current which flows up the coast of South America and with it may have come the penguins. Because the penguins in Galápagos are really very special, because that's the only place were you get penguins well to the north of the Southern Ocean.

(video 2) Penguins can easily become stranded on icebergs, which can then be carried for thousands of miles by strong currents.

(video 3) The archipelago is unique because, although situated on the Equator, it's bathed for much of the year by the cool waters of the Humboldt and Cromwell currents. These cool currents result in water temperatures of around 22 degrees Celsius, which helps ensure an abundance of sea life. In the warm season, warmer waters from the Panama Basin flow through the islands and the average sea temperature may rise to 25 degrees Celsius. Warmer waters mean greater cloud formation, so the islands experience a more tropical climate with heavy rain showers.

(answer) Penguins probably arrived on Galápagos by floating on icebergs pulled from the south by the Humboldt currents.

(finch)
(video 1) The Scilly islands, some 30 kilometres west of Land's End. Every spring, bird enthusiasts gather to look at song birds which have been blown thousands of kilometres from the North American and African continents. Even butterflies make the journey; the North American Monarch butterfly is a frequent spring visitor to the Scillies, blown off course in its migration from Mexico to New England.

(video 2) Finches are relatively poor flyers and can be seen flitting from tree to tree.

(video 3) The predominant weather systems around the Galápagos are determined by trade winds. These are winds that blow persistently at ten to twenty knots. For nine months of the year these trade winds tend to be south-easterly, that is they blow from the direction of South America, and at that time of the year the weather tends to be very cool and very misty around the islands. During the other three months of the year trade winds are north-easterly, blowing from the direction of Central America, and the weather tends to be very hot and very humid and that's when most rain falls in the desert parts of the islands.

(answer) Finches are poor flyers and would have been blown to the islands.

( Frigate birds)
(video1) Frigate birds can be seen gliding over the sea and are strong flyers.

(answer) Frigate birds probably flew to the islands with help from the prevailing winds.

[Species & Speciation - Topic 2 Introduction]

The finches of the Galápagos evolved from colonists blown over from the mainland. That single colonising species has subsequently diverged into at least 14 separate species. In this topic you'll look at the ways in which new species of finch might have formed.

[Species & Speciation - Topic 2 Question 1]

(video 1) The Galápagos islands vary both in size and altitude. The highest island, Isabela is 1700 metres and it is also the largest, stretching in a 130 km arc. The smallest of the thirteen major islands is Genovesa, covering about 14 square kilometres. It is also the lowest, peaking at 75 m.

(video 2) The higher islands have a greater number of vegetation zones and will receive much more rainfall at their peaks. Lower islands may only have one vegetation zone. This reduces the number of finch species which can be supported on that island.

(video 3) The islands are volcanic in origin. They're the tips of underwater volcanoes that have grown up from the ocean floor over 2000 metres below the surface. The islands emerged between half a million and four million years ago.

(feedback) All the islands are volcanic in origin, so the underlying rocks are similar throughout the Galápagos and the soil formed from those rocks will also be similar. Species present, climate, island size and the variety of habitats available are all likely to differ from island to island.

[Species & Speciation - Topic 2 Question 2]

(video 1) The founder effect is seen when a small number of individuals leave a population to colonise a new area. A few individuals cannot possibly carry copies of all the alleles found in the whole population, so the colonists will take with them only a subset of the total genetic variability of their species.

(feedback) A small group of colonists can take with it only a subset of the alleles carried by the much larger population it came from. Mutation rates should not be affected by moving to a different area, and although the colonists will affect the other species in the area they colonise, this is not called the founder effect.

[Species & Speciation - Topic 2 Question 3]

(video 1) Different islands have different habitats for finches. The higher islands have more habitats with a greater range of food sources. The range of finch adaptations has been greater on these islands.

(video 2) Genetic drift is the term used to describe changes that occur, simply by chance from one generation to the next, in the proportions of individuals in a population that carry a particular allele.

(feedback) If they are still members of the same species, the populations must be able to interbreed, so breeding behaviour cannot be so very different. Genetic changes due to mutation, genetic drift and adaptation to local conditions are all likely to differ to some extent.

[Species & Speciation - Topic 2 Question 4]

(video 1) Genetic drift is the term used to describe changes that occur, simply by chance from one generation to the next, in the proportions of individuals in a population that carry a particular allele.

(video 2) So many different mutations are possible that it is extremely unlikely that exactly the same mutation will occur in two different populations.

(video 3) As conditions on different islands vary a great deal, so also will the adaptations of the finches.

(feedback) Genetic drift is random, so is unlikely to happen in the same way in two separate populations. Local conditions will differ, so different adaptations will be selected in each. It's also unlikely that exactly the same mutations will occur in both populations.

[Species & Speciation - Topic 2 Exercise 2]

(intro) There are many factors which influence the formation of a species. You are going to explore the ways in which different species of finch might have evolved, using a number of imaginary scenarios in which a mainland bird is taken to some isolated islands. There are resources for each scenario. Predict how the finch beak will change in each scenario by clicking on the relevant button.

(Scenario 1)
(resource 1) A probing beak is suitable for reaching into fruits and flowers, obtaining nectar and probing out insects hidden in crevices or in vegetation.

(resource 2) A tip-biting beak is well adapted for feeding on fruits and leaves as well as arthropods in exposed areas on plants and on the ground.

(resource 3) The beak of a finch can be compared to a tool in its mode of action. A probing beak is long and pointed, suitable for gaining access to flowers and foliage. A tip-biting beak is curved at the top and bottom and can apply force at the tip. A crushing beak is deep at the base, but not as curved as in the tip-biting class, well equipped for crushing hard foods.

(answer) A crushing beak would be best suited to dealing with seeds as the main food source.

(Scenario 2)
(resource 1) If these larger beaked birds are left to develop with no other finches present there will be no selection pressure due to competition acting upon their beak size. But, as they survive through generations, a normal distribution of the beak sizes will be formed for this population. Some will have larger beaks and some smaller beaks but the mean beak size will still be that of the original colonisers of island B.

(answer) The mean beak size of the birds on island (B) will be larger than those on island (A).

(Scenario 3)
(resource 1) The significance of variations in beak size becomes apparent when there's a change in the environment, particularly a change in the food supply. For example, in 1977 no rain fell on the little island of Daphne where we were studying. Most of the finches of the medium ground finch population that we were studying died, and at the end of 1977 we compared the beak measurements of the birds who died with those who survived, and we found that the survivors were bigger on average. The factor that was most obviously related to the mortality was the food supply. The small-beaked finch has a narrow range of foods. The large-beaked finch has a broader range of food sizes, but also it is limited at the small end of that spectrum by the difficulties of getting the seed in its right position in order to apply the cracking force, quite apart from the fact that a very small seed is going to give a large bird hardly any energy, so it wouldn't be worth its while to even attempt to pick up an extremely small seed.

(resource 2) Larger seeds can only be cracked and physically manipulated by larger beaked birds. Smaller beaked birds cannot compete for these seeds and will eventually starve.

(answer) Mean beak size will be larger than before the shortage of small seeds began because the smaller beaked birds would starve and disappear from the population.

(Scenario 4)
(resource 1) The small-beaked finch has a narrow range of foods. The large-beaked finch has a broader range of food sizes, but also it is limited at the small end of that spectrum by the difficulties of getting the seed in its right position in order to apply the cracking force, quite apart from the fact that a very small seed is going to give a large bird hardly any energy, so it wouldn't be worth its while to even attempt to pick up an extremely small seed.

(resource 2) Competition between species for food will result in a species diverging, so they become more specialised in the food they eat. This reduces the level of competition between them.

(resource 3) Large-beaked birds are able to dip into the food supply of the small-beaked finches more easily than the small beaked finches can dip into the supply of the large-beaked finches. There's a greater variation in food sizes available to the large-beaked finches, in other words, than there is to the small-beaked finches.

(answer) The beak size of the original inhabitants will become smaller as they compete for food with the invading birds which have larger beaks.

[Species & Speciation - Topic 2 Exercise 3]

(intro) The more geographically isolated an island population is, the less likely it is to interbreed with a population from another island. In this exercise you will explore the link between the degree of isolation of an island and the percentage of endemic finch species it contains. If you prefer to do calculations on paper rather than on screen, there's another version of this exercise in book five. You will be shown a series of island groups. For each group, there are details of the number of finch species present and how many of these are endemic to those islands. There are also resources that provide you with more information. For each group of islands, calculate the percentage of finch species in the group that are endemic and type your result into the white box next to the percentage sign. When you're finished, press Done, check your answer and then move onto the next group of islands.

(video 2) Percentage endemicity can be calculated by dividing the total number of endemic species or subspecies by the total number of finch species present on the group of islands. Finally, multiplying the result by one hundred gives a percentage value.

(video 3) The finches themselves are endemic to the Galápagos, meaning that they are there and nowhere else. The species are found generally on more than one island, but what might be classified as sub-species, unusual forms of a species, can be recognised in many cases, and classified in this way. The species show the highest endemism in the remote, isolated, and generally small islands of the archipelago.

(video 4) If we can assume that all the species had the same amount of time to evolve, then the more distinctive the populations are on the isolated islands, the more likely it is that they are biologically isolated from their relatives on other islands. That sea distance separating these isolated islands from the central large islands is quite a barrier for individual finches to cross.

(Island grouping 1)
(video 1) There are ten different species of finch living on this group of islands, but they can also be found on other islands in the archipelago, so none is endemic to this group alone.

(correct) Correct.

(incorrect) No. Percentage endemicity can be calculated by dividing the total number of endemic species or subspecies by the total number of finch species present on the group of islands. Finally, multiplying the result by one hundred gives a percentage value.

(Island grouping 2)
(video 2) There are seven different species of finch on this island. One of these is a subspecies of the warbler finch and can only be found on this island.

(correct) Correct. This island is close to the central islands and has a low percentage endemicity.

(incorrect) No. This island is close to the central islands and has a low percentage endemicity.

(Island grouping 3)
(video 3) These islands are home to a total of ten finch species; two are endemic, one of which is a subspecies of the large tree finch.

(Island grouping 4)
(video 4) Of the nine species present on these islands, two are endemic subspecies, one of the warbler and one of the large tree finch.

(Island grouping 5)
(video 5) Eight finch species are present on this island; two are endemic - one a subspecies of the warbler finch, and the other a medium tree finch. Both can only be found on this island.

(Island grouping 6)
(video 6) Seven finch species live here, and three of them are endemic subspecies - a warbler, a woodpecker and a small tree finch.

(Island grouping 7)
(video 7) Of the four species present, two are endemic subspecies - one of the warbler, and one of the large cactus ground finch.

(correct) Correct. This island is further from the central islands and has a higher percentage endemicity.

(incorrect) No. This island is further from the central islands and has a higher percentage endemicity.

(Island grouping 8)
(video 8) There are only three finch species here, and two of these are endemic subspecies. One of the warbler and one of the large cactus ground finch.

(Island grouping 9)
(video 9) These islands are farthest away from the central islands, and have four species of finch living on them. Three of these finches are endemic subspecies, a sharp-beaked ground finch, a warbler finch and a large cactus ground finch.

(correct) Correct. These islands are the furthest from the central islands and have the highest percentage endemicity.

(incorrect) No. These islands are the furthest from the central islands and have the highest percentage endemicity.

 

[Species & Speciation - Recent research on finches]

(video 1) The fieldwork that Peter and Rosemary Grant have been carrying out has yielded a enormous amount of information about Darwin's finches. And they described some of their work in the interviews that we did almost 10 years ago now. They have shown very clearly that natural selection acts on the beak of the finch. So for example, large-beaked finches have an advantage when it comes to eating tough seeds. On the other hand, small-beaked finches have an advantage when there's lots of small seeds available in the seed bank. Well, recently they've extended their work into the field of molecular biology. And they're just beginning to show some of the genetic influences that underlie the beak of the finch.

(video 2) Chemical growth promoters are active in the developing beak in the embryo within the egg. And one of these is bone-promoting protein 4, or Bmp4 for short. Now in the large-beaked ground finch, this protein is active over a greater area of the developing beak and at a higher concentration than it would be in a short-beaked finch. So it looks as though beak size, in terms of depth and width, is directly related to the level of activity of Bmp4.

(video 3) The level of Bmp4 activity is under genetic control. You can carry out experiments with chick embryos to demonstrate this control. The structure of Bmp4 is coded in a particular gene and you can change the level of activity of that gene. If you increase it, you get chicks with larger beaks.

(video 4) Beak length is influenced by Calmodulin. Calmodulin has a complex role in the regulation of calcium. The production of Calmodulin is higher in cactus finches with their long pointed beaks than it is in ground finches with their shorter more robust beaks. So a bird like the cactus finch had, as an embryo, low production of Bmp4 but high production of Calmodulin and the long narrow beak is the result. Now the opposite would be true of the large ground finch with its short very deep beak - and of course as you know, beak shape and size correlate with food type. Now the suggestion is that the levels of activity of the genes that control Bmp4, Calmodulin and other promoters involved in beak development are the primary mechanisms on which natural selection acts.

[Species & Speciation - Summary]

(no audio)

 

(finished) You've finished the final exercise for this section. Click on the ship's icon for a summary of this part of the tutorial.

(end) You've now completed this exercise. Click on the ship's icon to return to the cabin.