A RESOURCE BROUGHT TO YOU BY THE GALAPAGOS
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A RESOURCE BROUGHT TO YOU BY THE GALAPAGOS CONSERVATION TRUST (REGISTERED CHARITY NO. 1043470) GALAPAGOSCONSERVATION.ORG.UK Simon Pierce Variation between species A little background The finches of the Galapagos Islands have been made
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01
A RESOURCE BROUGHT TO YOU BY THE GALAPAGOS CONSERVATION TRUST (REGISTERED CHARITY NO. 1043470)
GALAPAGOSCONSERVATION.ORG.UK © Simon Pierce Variation between species<br>
GALAPAGOSCONSERVATION.ORG.UK © Simon Pierce Variation between species<br>
02
A little background…
The finches of the Galapagos Islands have been made famous thanks to Charles Darwin.
Visiting the islands on board The Beagle in 1835 as the ship’s naturalist, he collected different animals and plants to take back to be studied and donated to museums and private collections. Although he collected some species of finch, he was unaware at the time of their importance. It was only when he returned home and began questioning why the finches appeared to be different on different islands, something he first noticed with the mockingbirds, that he set out to solve this tricky puzzle. By doing so, he developed a revolutionary theory – The Theory of Evolution through Natural Selection. He recognised that species adapt and change over time to suit their changing environment. The genes or characteristics that make them successful are passed onto the next generation. Individuals that are poorly adapted to their environment are less likely to survive and reproduce. Over time this can mean a new species evolves.<br>
The finches of the Galapagos Islands have been made famous thanks to Charles Darwin.
Visiting the islands on board The Beagle in 1835 as the ship’s naturalist, he collected different animals and plants to take back to be studied and donated to museums and private collections. Although he collected some species of finch, he was unaware at the time of their importance. It was only when he returned home and began questioning why the finches appeared to be different on different islands, something he first noticed with the mockingbirds, that he set out to solve this tricky puzzle. By doing so, he developed a revolutionary theory – The Theory of Evolution through Natural Selection. He recognised that species adapt and change over time to suit their changing environment. The genes or characteristics that make them successful are passed onto the next generation. Individuals that are poorly adapted to their environment are less likely to survive and reproduce. Over time this can mean a new species evolves.<br>
03
From the ancestor of the finches that colonised the islands about 3 million years ago, 13 species evolved, adapting to the different environments provided by the islands – for instance, by adapting to feed on the food sources available.
There are finches who not only feed on nectar in flowers but have learned to peck at the bodies of Booby birds to draw blood, which they drink. Cactus finches eat the seeds, pollen, flowers and nectar of the cactus, as well as nesting and sleeping there! Some finches have even evolved to use tools: they dig out tasty, fat grubs from inside dead branches using cactus spines or twigs that they sometimes shape using their beaks. Some even sit on the backs of the giant tortoises and eat their ticks and parasites; for which the tortoises are very grateful!
So although the shape and size of the finches vary, it is their beak that distinguishes one species from another. From top left anti-clockwise –
Vampire finch © Simon Pierce, Cactus finch © Johannes Kempf
Medium tree finch, Mangrove finch © Michael Dvorak<br>
There are finches who not only feed on nectar in flowers but have learned to peck at the bodies of Booby birds to draw blood, which they drink. Cactus finches eat the seeds, pollen, flowers and nectar of the cactus, as well as nesting and sleeping there! Some finches have even evolved to use tools: they dig out tasty, fat grubs from inside dead branches using cactus spines or twigs that they sometimes shape using their beaks. Some even sit on the backs of the giant tortoises and eat their ticks and parasites; for which the tortoises are very grateful!
So although the shape and size of the finches vary, it is their beak that distinguishes one species from another. From top left anti-clockwise –
Vampire finch © Simon Pierce, Cactus finch © Johannes Kempf
Medium tree finch, Mangrove finch © Michael Dvorak<br>
04
Enter the Grants… Over 100 years after Darwin’s initial visit, Rosemary and Peter Grant, British born scientists, came to Galapagos and the remote island of Daphne Major and decided to set up a research camp to investigate the finches of the island. They have returned every year for nearly 4 decades. Why did they choose a tiny, isolated island in the middle of the Pacific Ocean to study these little birds? What did they want to find out? Peter and Rosemary Grant © Peter and Rosemary Grant © Sarah Langford<br>
05
Peter and Rosemary Grant © Martin Wikelski Peter and Rosemary Grant To you this island may seem very unappealing! Sitting in the middle of the Pacific, made entirely of volcanic rock, there is no fresh water, little escape from the boiling hot equatorial sun, and absolutely no facilities for humans whatsoever. In fact, there have never been any human settlements or farming on the island. You even have to make a giant leap from your boat to land on a steep cliff on arrival. Discuss with a partner why this island would be perfect to study the finches. It is the isolation and size of the island that make it a biologist’s dream. Being small makes it more accessible and also means the populations of birds and plant species are small as well and so easier to study. There are no humans and agriculture or nasty invasive species to get in the way. It is also open to all sorts of weather. Perfect! Dreamy Daphne…<br>
06
The Grants wanted to study Natural Selection. They wanted to see it in the wild and maybe even happening in front of their eyes. Daphne Major offered them the perfect opportunity to do this.
Who got the role of the perfect study candidate? Why, the finch of course. To be exact, a little finch called the ‘medium ground finch,’ (Geospiza fortis) Medium Ground Finch Geospiza fortis © Peter and Rosemary Grant<br>
Who got the role of the perfect study candidate? Why, the finch of course. To be exact, a little finch called the ‘medium ground finch,’ (Geospiza fortis) Medium Ground Finch Geospiza fortis © Peter and Rosemary Grant<br>
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It’s all in the beak! After setting up their camp, the Grants began their study. What did they do? First they worked out the population of the medium ground finches. They used ‘mist nets’ to catch the birds. Early bird catches the worm – a 5.30 am job! They may not look very nice but the Grants handled the birds very carefully and put little numbered bands on their legs. (The bird in this image is not a ground finch) https://en.wikipedia.org/wiki/Mist_net Then they carefully took measurements for each bird, including – weight, length, leg and toe length and beak size (including the depth of the beak) A special tool called ‘calipers’ are used for measuring the beak.
Watch this biointeractive video from 6:00-6:58 to see this in action! © Peter and Rosemary Grant<br>
Watch this biointeractive video from 6:00-6:58 to see this in action! © Peter and Rosemary Grant<br>
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The Grants not only needed to study the birds but also the food they ate, as they wanted to study the relationship between beak size variability/difference and food source, or what the finches were eating. What did they do? Every day, they observed the birds feeding: breakfast, second breakfast, mid-morning snack, lunch….you get the picture!
They noted which kinds of seeds they chose and how long it took the birds to crack through and eat them.
From each plant on the island they measured the sizes of seeds and how hard they were.
They estimated how many seeds were available for the finches to feed on by digging up soil samples and counting seeds. A hot and dusty job….
At the end of the first year, they watched the finches eat over 4000 meals. I wonder how many seeds were eaten?
For 4 years after their initial study, they returned to the islands to continue their research and nothing seemed to change.<br>
They noted which kinds of seeds they chose and how long it took the birds to crack through and eat them.
From each plant on the island they measured the sizes of seeds and how hard they were.
They estimated how many seeds were available for the finches to feed on by digging up soil samples and counting seeds. A hot and dusty job….
At the end of the first year, they watched the finches eat over 4000 meals. I wonder how many seeds were eaten?
For 4 years after their initial study, they returned to the islands to continue their research and nothing seemed to change.<br>
09
This is what they had found out so far…
There were differences (variations) in the sizes of the medium ground finch beaks.
The medium ground finch and other finches that lived on the island fed on the same small seeds. This was a surprise to the Grants.
That beak size is a heritable characteristic. This means that birds with bigger beaks produced young with bigger beaks, and smaller beaked birds produced young with smaller beaks.
After the dry season when some seeds became less available, they found that the finches became specialist feeders. Those with bigger, deep beaks could feed on large, tough seeds, whilst those with smaller beaks could only feed on smaller seeds. There were even differences within the medium ground finch.<br>
There were differences (variations) in the sizes of the medium ground finch beaks.
The medium ground finch and other finches that lived on the island fed on the same small seeds. This was a surprise to the Grants.
That beak size is a heritable characteristic. This means that birds with bigger beaks produced young with bigger beaks, and smaller beaked birds produced young with smaller beaks.
After the dry season when some seeds became less available, they found that the finches became specialist feeders. Those with bigger, deep beaks could feed on large, tough seeds, whilst those with smaller beaks could only feed on smaller seeds. There were even differences within the medium ground finch.<br>
10
In 1977 a devastating drought hit the islands. There was no rain for 18 months. Many of the plants had withered and died with the lack of water, even the larger species. Only cactus and a few leafless trees were left. Drought disaster… What did this mean for the finches?
The medium ground finch had to compete for food. Competition between species is called inter-specific competition. After the favoured small seeds ran out, just the large ones were left. Only the birds with larger beaks could crack open the hard seeds and feed. It was a disaster for the smaller beaked birds, and over 80% of the medium ground finches died.
This must have been hard for the Grants to see as they knew many of the birds from their studies.<br>
The medium ground finch had to compete for food. Competition between species is called inter-specific competition. After the favoured small seeds ran out, just the large ones were left. Only the birds with larger beaks could crack open the hard seeds and feed. It was a disaster for the smaller beaked birds, and over 80% of the medium ground finches died.
This must have been hard for the Grants to see as they knew many of the birds from their studies.<br>
11
Disaster leads to revelation…
All was not lost! The population began to recover - they are hardy little birds, despite their size. But something had changed in the offspring of the finches of the 1978 generation - the size of their beak. The finches’ beak sizes were deeper than before. Why? They would have a better chance of surviving a drought. They passed on this characteristic to their young to improve their chance of survival. The story doesn’t end there... 5 years later the islands experienced 10 times more rain than normal and the plants and vines that produced small seeds flourished. Guess what happened to the beak size of the medium ground finch after a few generations? …..
Natural selection favoured the finches with smaller beaks as they could easily feed on the small seeds and so the depth of the beak decreased in size.
This was Natural Selection in action and had never been observed and documented like this before. Neither had the speed at which evolution could occur. Many scientists believed that evolution occurred over a very long time, but here is was happening in a much shorter time. The Grants had revolutionised the theory of Natural Selection by seeing and documenting it in action.
I wonder what the future holds for the finches of Daphne Major. Perhaps the Grants are there now, greeting their feathery friends! © Sarah Knutie © Robert Stebbings<br>
All was not lost! The population began to recover - they are hardy little birds, despite their size. But something had changed in the offspring of the finches of the 1978 generation - the size of their beak. The finches’ beak sizes were deeper than before. Why? They would have a better chance of surviving a drought. They passed on this characteristic to their young to improve their chance of survival. The story doesn’t end there... 5 years later the islands experienced 10 times more rain than normal and the plants and vines that produced small seeds flourished. Guess what happened to the beak size of the medium ground finch after a few generations? …..
Natural selection favoured the finches with smaller beaks as they could easily feed on the small seeds and so the depth of the beak decreased in size.
This was Natural Selection in action and had never been observed and documented like this before. Neither had the speed at which evolution could occur. Many scientists believed that evolution occurred over a very long time, but here is was happening in a much shorter time. The Grants had revolutionised the theory of Natural Selection by seeing and documenting it in action.
I wonder what the future holds for the finches of Daphne Major. Perhaps the Grants are there now, greeting their feathery friends! © Sarah Knutie © Robert Stebbings<br>
12
Challenge science! Questions
Write a scientific research question for the Grants study, imagining it was the title of their science paper.
Why was Daphne Major a good place to study natural selection in the wild?
Look back at the methodology (the things the Grants did in the study) and write a list of equipment they would need.
Describe in 2 sentences what happened to the finches after the drought of 1977.
Explain why 5 years later natural selection swung in favour of finches with smaller beaks.
If the weather phenomenon El Niño becomes more frequent and severe, what would you predict happening to the medium ground finch population on Daphne Major? (El Niño brings increased and prolonged rainfall to the islands – significantly more than in normal years)<br>
Write a scientific research question for the Grants study, imagining it was the title of their science paper.
Why was Daphne Major a good place to study natural selection in the wild?
Look back at the methodology (the things the Grants did in the study) and write a list of equipment they would need.
Describe in 2 sentences what happened to the finches after the drought of 1977.
Explain why 5 years later natural selection swung in favour of finches with smaller beaks.
If the weather phenomenon El Niño becomes more frequent and severe, what would you predict happening to the medium ground finch population on Daphne Major? (El Niño brings increased and prolonged rainfall to the islands – significantly more than in normal years)<br>