Download Darwin`s Finches

Geology 105 - History of Earth
Name
____________________________________
Darwin’s Finches: Adaptations and Natural Selection
The objectives of this lab are to:
o Understand individual variations within a population, and how natural selection acts upon these variations
o Explore how changes to the environment affect food resources and the differential reproductive success of
individuals
o Explain how natural selection can lead to the evolution of new species
o Interpret the role of random change (mutations) and non-random change (natural selection) in evolution
Materials:
o Printed copy of lab exercise
o Pencil
o Island (astroturf), food resources (rubber bands, beans, seeds, rice, playdoh), beaks (needle nose pliers,
blunt pliers, tongs, tweezers, staple pickers), dice, dishes/food trays
Instructions:
Get into groups of 4 or 5 students.
Read over the introductory information, and begin answering the questions. Once all the groups have
finished with the first exercise of this lab, the instructor will begin preparing you for the second exercise.
INTRODUCTION:
In this lab, your group will be recreating the conditions of an experiment played by nature approximately 3
million years ago, when a group of South American birds was blown by a storm or a tsunami 600 miles
offshore to the brand new volcanic islands of the Galapagos, trapping them there. What happened next?
We are looking particularly at the
island of Daphne Major as a model for
your island home: a small cinder cone
with no trees and very little fresh
water. Here’s some background on
your new home: despite being on the
Equator, cold water brought north
from Antarctica by the Humboldt
Current keeps this island from getting
too hot. But it is very dry, with not
enough water to support trees.
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A rainy season occurs from January to May, when warm wet water from the north brings moisture. No rain
falls for the rest of the year, from June to December. The climate here is also greatly affected by a cycle in
ocean temperature every 7-10 years known as El Niño (sea surface temperatures heat up, resulting in
heavy rainfall/floods) and La Niña (sea surface temperatures cool down, resulting in droughts). We’ll
discuss plate tectonics, climate, and currents in a later lab, but for now, that’s all you need to know!
SO. Your group of finches lands here. Your food options are limited, and only those individuals who are able
to get enough food to live will survive to reproduce.
Exercise 1: Exploring Variation Within A Species
A. List at least three physical features that you and your teammates have in common as a species (members of
Homo sapiens).
Ex: all 5 have eyelashes, all 5 have fingers
B. Describe how those three physical features VARY among your classmates. You can use rulers (quantitative
measurements) or general descriptions (qualitative observations).
Ex: members 2&3 have longer eyelashes; members 1,4&5 have shorter
C. These variations between individuals is a result of RANDOM MUTATION during sexual reproduction – we
won’t go into the mechanics of mutation here (take a genetics course for the nitty gritty on this!), but you
should be aware that mutation is introduced to a population through sexual reproduction and slight mistakes
can occur when male and female DNA combine. Also be aware that these variations are HERITABLE and can
be passed on to offspring.
For the purposes of this lab, you are all now members of the same species of
South American bird, the blueblack grassquit. You have many traits in
common and are able to interbreed and produce fertile offspring, but there
are some slight variations, just like the ones you listed on for humans – for
example, in the slight color differences of the feathers, or in the shape and
size of your beaks.
NOW. With all that in mind, pick a beak from the stack of tools at the table
and describe it here. NOTE: IF YOU ARE IN A GROUP OF 4, do NOT choose the
tweezers – leave them out.
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Give a brief description of each beak below, and circle your own chosen beak.
Tweezers: _______________________________________________________________________
Staple-picker: ____________________________________________________________________
Tongs: __________________________________________________________________________
Blunt pliers: _____________________________________________________________________
Needle-nosed pliers: _______________________________________________________________
The food resources on the island are as follows. Since we can’t provide the actual grubs and insects and spiky caltrops
seeds found on the islands and eaten by the finches, we’ve provided the closest possible analogue for you guys to
“eat.”





water plants (rubber bands, which can be eaten more than one
at a time)
insects (rice grains, must be picked up one at a time)
spurge seeds (small seeds, must be picked up one at a time)
caltrops seeds (white beans, - no spikes as we see in the wild,
but the hard seed case must still be crushed in order for the
nutritious inner seed to be eaten; think a nastier smaller version
of a walnut!)
cactus grubs (playdoh in cups – you can pick up the cup in your
hand, but must use a toothpick placed in your beak to pierce the
grubs through a hole in the side)
D. Based on your beak’s size and shape, make a prediction which foods you will be the best at eating, and which
you will be the worst at.
_________________________________________________________________________________________
_________________________________________________________________________________________
E. But not all food is created equal – some resources are more nutritious than others. Let’s say your bird needs
300 calories minimum to survive a year (since we don’t have a year, we’re using 30 seconds to model your
survival). If:
1 water plant (rubber band) = 10 calories
1 spurge seed (small seed) = 30 calories
1 insect (rice) = 50 calories
1 cactus grub (playdoh in cup) = 60 calories
1 caltrops seeds (beans) = 40 calories
How many do you need to survive? ______
How many do you need to survive? ______
How many do you need to survive? ______
How many do you need to survive? ______
How many do you need to survive? _____
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Exercise 2: Practice with Your Beaks and Food Resources
Before we begin, we’re giving you a chance to get used to handling your beaks/the food resources. We’ll have five 30
second practice rounds.
HOW TO CREATE YOUR PRACTICE ROUND ISLANDS:
When you’ve finished setting up/cleaning up between rounds, please raise your hands so the professor knows when
all the groups are ready to get started. The professor will give a 3 second countdown, and then you have 30 seconds
to obtain as much food as possible. Remember the rules for how to eat each food! Caltrops seeds have to be cracked,
insects can only be eaten one at a time, etc.





30 seconds of just Water plants – scatter 1 food dish full of rubber bands for this practice round.
When done, return rubber bands to bag.
30 seconds of just Insects – scatter a palmful of rice grains, shake out back onto table when done
30 seconds of just Spurge seeds – scatter a palmful of small seeds onto island, return to bag at end.
30 seconds of just Cactus grubs – set out 5 cups, with 5 grubs per cup
30 seconds of just Caltrops seeds – set out 25 white beeds, and be sure to discard the cracked seeds
when done in trash can
DON’T CALCULATE THE CALORIES FOR THE PRACTICE ROUND, just make general observations. Assuming food
resources are limited, which 3 foods do you predict each bird should focus on eating to get the minimum 300 calories
needed to survive?
Tweezers: _______________________________________________________________________
Staple-picker: ____________________________________________________________________
Tongs: __________________________________________________________________________
Blunt pliers: _____________________________________________________________________
Needle-nosed pliers: _______________________________________________________________
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Exercise 3: LIFE AND DEATH, or SURVIVAL AND REPRODUCTION
OKAY, PRACTICE ROUNDS: OVER.
Remember, your finches have landed on a hypothetical island – please come up with a name for this island with your
group. However, assume it looks basically identical to Daphne Major and is located in the same general
area/circumstances.
YOUR ISLAND NAME: ____________________________
Now that the practice is over, on to the life and death competition. You have 30 seconds to get enough food to
survive and more importantly, to reproduce. The bird with the LEAST amount of food at the end of the round dies
and doesn’t pass on its genes. The bird with the MOST calories has lots of babies and will pass on the most genes
to the next generation. This is a competition! NOT EVERYONE CAN SURVIVE. Will it be you or your friend who dies?
Don’t forget to eat strategically – you can eat more than one
type of food! Think of it as a more complex version of Hungry
Hungry Hippos: food is limited on this island, and you only have
so much time to get enough calories. Some foods are richer than
others, and some are easier to obtain than others.
At the end of the 30 seconds, count up the food items you
consumed and calculate the total # of calories for each member
of your group. Be sure to record everyone’s numbers!
Practice for the real world
Hunger Games
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YEAR 1: THE FIRST GENERATION
HOW TO CREATE YOUR YEAR 1 ISLAND:
Mix and scatter the following amounts of foods on your “island” square of astroturf. When finished, please raise your
hands so the professor knows when all the groups are ready to get started.
 Water plants – scatter ½ a food dish full of rubber bands
 Spurge seeds – scatter a quarter-sized amount of rice grains
 Insects – scatter 30 small seeds onto island
 Cactus grubs – set out 4 cups, with 2 grubs per cup
 Caltrops seeds – set out 20 white beans
You now have 30 seconds to obtain enough food to survive. Record your group’s numbers below.
YOUR GROUP’S #s
Tweezers
Tongs
Staple-picker
Needle-nose
Blunt pliers
Water plants/rubber bands
(10 cal)
Insects/rice grains
(50 cal)
Spurge seeds/small seeds
(30 cal)
Caltrops seeds/white beans
(60 cal)
Cactus grubs/playdoh in cup
(40 cal)
Total # calories consumed:
Which beak/tool-type got the most calories for this round (aka was fat and happy and had lots of babies)?
____________________
Which beak/tool-type got the least calories for this round (aka died and had no babies)?
____________________
If your beak-type died, you do not get to contribute offspring to the next generation! Instead pick up a new
beak, aka the tool which had the highest average calorie intake.
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YEAR 2: THE SECOND GENERATION
How has the population of finches changed from the previous generation? List the # of beaks you have of each type.
Tweezers:
____
Staple-picker:
____
Tongs:
____
Blunt pliers:
____
Needle-nosed pliers: ____
Unfortunately, this is a La Niña year (unusually cool sea surface conditions in equatorial waters, resulting in a much
drier climate in this part of the world), and as a result for 365 days no rain has fallen. This changes the amount of
food resources available.
HOW TO CREATE YOUR YEAR 2 ISLAND:
Mix and scatter the following amounts of foods on your “island” square of astroturf. When finished, please raise your
hands so the professor knows when all the groups are ready to get started.
 Water plants – 15 rubber bands scattered
 Spurge seeds – scatter 20 small seeds
 Insects – scatter a nickel-sized amount of rice grains
 Cactus grubs – set out 2 cups, with 2 grubs per cup
 Caltrops seeds – set out 30 white beans – turns out the drought has increased their numbers!
HOWEVER, A MUTATION HAS OCCURRED IN THE STAPLE-PICKER BIRDS! The vampire mutation – see video
(https://www.youtube.com/watch?v=d39oZ_TYImY), which your professor should play on the SMART Board. These
birds now are able to gain an extra +50 calories by strategically drinking the blood of their fellow birds during times of
food scarcity. (Please, however, do not actually stab your fellow birds)
You now have 30 seconds to obtain enough food to survive. Record your group’s numbers below.
YOUR GROUP’S #s
Water plants/rubber bands
(10 cal)
Insects/rice grains
(50 cal)
Spurge seeds/small seeds
(30 cal)
Caltrops seeds/white beans
(60 cal)
Cactus grubs/playdoh in cup
(40 cal)
Total # calories consumed:
Which beak/tool-type got the most calories for this round (aka was fat and happy and had lots of babies)?
____________________
Which beak/tool-type got the least calories for this round (aka died and had no babies)?
____________________
If your beak-type died, you do not get to contribute offspring to the next generation! Instead pick up a new
beak, aka the tool which had the highest average calorie intake.
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YEAR 3: THE THIRD GENERATION
How has the population of finches changed from the previous generation? List the # of beaks you have of each type.
Tweezers:
____
Staple-picker:
____
Tongs:
____
Blunt pliers:
____
Needle-nosed pliers: ____
Unfortunately, La Niña continues, and now for over 500 days no rain has fallen. This drastically changes the amount
of food resources available. Also, remember the vampire mutation? Those who with the vampire mutation who
survived have passed the mutation on to their offspring, so the blood-drinking continues!
HOW TO CREATE YOUR YEAR 3 ISLAND:
Mix and scatter the following amounts of foods on your “island” square of astroturf. When finished, please raise your
hands so the professor knows when all the groups are ready to get started.
 Water plants – 5 rubber bands scattered
 Spurge seeds – scatter 15 small seeds
 Insects – scatter a dime-sized amount of rice grains
 Cactus grubs – set out 2 cups, with 2 grubs per cup
 Caltrops seeds – set out 35 white beans
You now have 30 seconds to obtain enough food to survive. Record your group’s numbers below.
YOUR GROUP’S #s
Water plants/rubber bands
(10 cal)
Insects/rice grains
(50 cal)
Spurge seeds/small seeds
(30 cal)
Caltrops seeds/white beans
(60 cal)
Cactus grubs/playdoh in cup
(40 cal)
Total # calories consumed:
Which beak/tool-type got the most calories for this round (aka was fat and happy and had lots of babies)?
____________________
Which beak/tool-type got the least calories for this round (aka died and had no babies)?
____________________
If your beak-type died, you do not get to contribute offspring to the next generation! Instead pick up a new
beak, aka the tool which had the highest average calorie intake.
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YEAR 4: THE FOURTH GENERATION
How has the population of finches changed from the previous generation? List the # of beaks you have of each type.
Tweezers:
____
Staple-picker:
____
Tongs:
____
Blunt pliers:
____
Needle-nosed pliers: ____
Things have drastically changed on Daphne Major! This is an El Niño year – warm humid waters have been moving
south down from the Equator). As a result, there’s been torrents of rain, and the spurge plants and water plants have
taken over the island, choking out the caltrops plants that formerly dominated.
ALSO, recessive genes and inbreeding among limited population numbers has resulted in a beak type reappearing.
Everyone should take turns rolling the dice – if you get a 5 or a 6, take up THE TONGS as your new beak.
HOW TO CREATE YOUR YEAR 4 ISLAND:
Mix and scatter the following amounts of foods on your “island” square of astroturf. When finished, please raise your
hands so the professor knows when all the groups are ready to get started.
 Water plants – 50 rubber bands scattered (don’t forget, you can grab more than one of these
at a time!)
 Spurge seeds – scatter 40 small seeds
 Insects – scatter a quarter-sized amount of rice grains
 Cactus grubs – set out 4 cups, with 2 grubs per cup
 Caltrops seeds – set out 10 white beans
You now have 30 seconds to obtain enough food to survive. Record your group’s numbers below.
YOUR GROUP’S #s
Water plants/rubber bands
(10 cal)
Insects/rice grains
(50 cal)
Spurge seeds/small seeds
(30 cal)
Caltrops seeds/white beans
(60 cal)
Cactus grubs/playdoh in cup
(40 cal)
Total # calories consumed:
Which beak/tool-type got the most calories for this round (aka was fat and happy and had lots of babies)?
____________________
Which beak/tool-type got the least calories for this round (aka died and had no babies)?
____________________
If your beak-type died, you do not get to contribute offspring to the next generation! Instead pick up a new
beak, aka the tool which had the highest average calorie intake.
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YEAR 5: THE FIFTH GENERATION
How has your population of finches changed from the previous generation? List the # of beaks you have of each type.
Tweezers:
____
Staple-picker:
____
Tongs:
____
Blunt pliers:
____
Needle-nosed pliers: ____
Go to the board, and list your Island name, and the above numbers. Copy the numbers from the other islands
around the room.
Island ______________
Tweezers:
Staple-picker:
Tongs:
Blunt pliers:
Needle-nosed pliers:
Island ______________
Tweezers:
Staple-picker:
Tongs:
Blunt pliers:
Needle-nosed pliers:
Island ______________
Tweezers:
Staple-picker:
Tongs:
Blunt pliers:
Needle-nosed pliers:
Island ______________
Tweezers:
Staple-picker:
Tongs:
Blunt pliers:
Needle-nosed pliers:
Island ______________
Tweezers:
Staple-picker:
Tongs:
Blunt pliers:
Needle-nosed pliers:
____
____
____
____
____
____
____
____
____
____
____
____
____
____
____
____
____
____
____
____
____
____
____
____
____
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1. How do your group’s numbers compare to the rest of the classes numbers? Do you have any identical islands,
or are some different?
_________________________________________________________________________________________
_________________________________________________________________________________________
_________________________________________________________________________________________
2. Discuss this with your group and explain what could have caused the differences.
_________________________________________________________________________________________
_________________________________________________________________________________________
_________________________________________________________________________________________
3. You should see a GENERAL trend in evolution of the finch population of the islands. If we had more groups
the statistical average would be more obvious, but alas, we only have 5-6 experimental islands to work with.
Given what we have, though, what is the most common beak type? ___________________________
4. Why do you think that beak was better at surviving/reproducing than the others?
_________________________________________________________________________________________
_________________________________________________________________________________________
DARWIN’S CONCEPT OF EVOLUTION THROUGH NATURAL SELECTION is based on some of the concepts you’ve just
observed through our classroom experiment.
1.
2.
3.
4.
More organisms are born than can survive given the resources of the environment.
Those organisms are not all exactly the same – random variation exists within a population.
Some of those variations will be better at obtaining food/mates than others.
Those variations will have DIFFERENTIAL REPRODUCTIVE SUCCESS – aka, be more likely to survive
and reproduce, passing on their genes to the next generation.
5. This causes the population to EVOLVE, or change over time.
6. Over enough time, new species can emerge from an ancestral group.
Looking at your population of finches, what do you predict will happen to the average beak type if the El
Niño conditions continue for another three years? Explain your reasoning.
_________________________________________________________________________________________
_________________________________________________________________________________________
_________________________________________________________________________________________
_________________________________________________________________________________________
_________________________________________________________________________________________
_________________________________________________________________________________________
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Exercise 4: Findings and Analysis
Fast-forward 2-3 million years, assuming the process of natural selection is still occurring. There are now 14-15
species of finch living on the different Galapagos Islands. Darwin encountered these different finch species when he
visited in 1835 and eventually observed they were all closely related to each other, and that they bore a resemblance
to the current blueblack grassquit living in South America. Keep in mind that not all the Galapagos islands have the
same conditions – for example, some have higher elevation and thus more rainfall as a whole, because higher
elevation = cooler temperature = moist air condenses as precipitation = more rain.
1. Which finch would you match to which tool type from our experiment, and why? Be sure to justify/explain your
answers in the space below the pictures.
2. What do you predict would be the most common food resource on this bird’s island, and why?
The sharp-beaked ground finch aka the
vampire finch (Geospiza difficilis):
Tool type: ____________
Why?
Food type: ____________
Why?
The large ground finch
(Geospiza magnirostrus):
Tool type: ____________
Why?
Food type: ___________
Why?
The small ground finch
(Geospiza fulignosa):
The woodpecker finch
(Camarhynchus pallidus):
Tool type:___________
Why?
Food type: __________
Why?
Tool type: ____________
Why?
Food type: ____________
Why?
The vegetarian finch
(Platyspiza crassirostris):
Tool type: ______________
Why?
Food type: _____________
Why?
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3. Based on your data/observations, explain how a single population (i.e. finches with one type of beak) could
diversify and populate different areas of different islands in the region. How does natural selection contribute to
adaptation(s)? Use the specific examples of birds and their beak-types to explain your answer.
_________________________________________________________________________________________
_________________________________________________________________________________________
_________________________________________________________________________________________
4. Read the excerpt from Darwin’s journal below. This is one of Darwin’s earliest interpretations of adaptations in
finches on the Galapagos Islands. What does he mean by the statement, “Seeing this gradation and diversity of
structure in one small, intimately related group of birds, one might really fancy that from an original paucity* of
birds in this archipelago, one species had been taken and modified for different ends”?
(*definition of PAUCITY: a scarcity, or a small number)
_________________________________________________________________________________________
_________________________________________________________________________________________
_________________________________________________________________________________________
Darwin’s notes, made during his voyage on the HMS Beagle, after arriving in the Galapagos Islands in 1835:
“…The remaining land-birds form a most singular group of finches, related to each other in the structure of their
beaks, short tails, form of body, and plumage: there are thirteen species, which….may be divided into four subgroups. All these species are peculiar to this archipelago; and so is the whole group, with the exception of one
species of the sub-group Cactornis, lately brought from Bow Island, in the Low Archipelago. Of Cactornis, the two
species may be often seen climbing about the flowers of the great cactus-trees; but all the other species of this group
of finches, mingled together in flocks, feed on the dry and sterile ground of the lower districts. The males of all, or
certainly of the greater number, are jet black; and the females (with perhaps one or two exceptions) are brown. The
most curious fact is the perfect gradation in the size of the beaks in the different species of Geospiza, from one as
large as that of a hawfinch to that of a chaffinch, and … even to that of a warbler. The largest beak in the genus
Geospiza is shown in Fig. 1, and the smallest in Fig. 3; but instead of their being only one intermediate species, with a
beak of the size shown in Fig. 2, there are no less than six species with insensibly graduated beaks. The beak of the
sub-group Certhidea is shown in Fig. 4. The beak of Cactornis is somewhat like that of a starling; and that of the
fourth sub-group, Camarhynchus, is slightly parrot-shaped. Seeing this gradation and diversity of structure in one
small, intimately related group of birds, one might really fancy that from an original paucity of birds in this
archipelago, one species had been taken and modified for
different ends. In a like manner it might be fancied that a bird
originally a buzzard had been induced here to undertake the
office of the carrion-feeding Polybori of the American continent.”
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5. Here are two individuals of
Geospiza fortis, the medium
groundfinch. Are they
identical? Which tool-type
would you compare to the
finch on the left? The finch on
the right? Which do you
predict would be more likely
to survive a La Niña drought
year? What about an El Niño
year?
____________________________________________________________________________________________
____________________________________________________________________________________________
___________________________________________________________________________________
6. Evolution is defined as descent with modification from a common ancestor by means of natural selection – ie,
individuals with traits that better help them survive in their environment will pass on their genes to the next
generation, changing it from its ancestral condition. Based on this and what you observed in class, does evolution
produce “perfect” species? Why or why not?
____________________________________________________________________________________________
____________________________________________________________________________________________
___________________________________________________________________________________
7. This is a quote from the famous evolutionary biologist J. B. S. Haldane: "No scientific theory is worth anything
unless it enables us to predict something which is actually going on. Until that is done, theories are a mere game
of words, and not such a good game as poetry." Does this hold true in the short term for evolution, based on
what you’ve learned today?
____________________________________________________________________________________________
____________________________________________________________________________________________
___________________________________________________________________________________
8. However, do you think you’ll be able to make accurate predictions in the long-term? (AKA over thousands of
years?) Why or why not?
____________________________________________________________________________________________
____________________________________________________________________________________________
9. Which of these three units can actually evolve over time? Explain:
 An individual
__________________________________________________________________________________
 A population (a specific geographic group of interbreeding individuals)
__________________________________________________________________________________
 A species (all populations capable of interbreeding)
_________________________________________________________________
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