Download File - Mrs. Campbell`s Science Class

Background Information: Darwin’s Finches
When Charles Darwin stepped ashore on the Galapagos Islands in September 1835, it was the start of
five weeks that would change the world of science, although he did not know it at the time. Among
other finds, he observed and collected the variety of small birds that inhabited the islands, but he did
not realize their significance, and failed to keep good records of his specimens and where they were
collected. It was not until he was back in London, puzzling over the birds, that the realization that
they were all different, but closely related, species of finch led him toward formulating the principle
of natural selection.
Vocabulary
Specimen – an
individual animal,
plant, piece of a
mineral, etc., used
as an example of
its species or type
for scientific study
or display.
Paucity – the
presence of
something only in
small quantities or
amounts; scarcity.
Archipelago –
chain of islands
Figure 1: Drawings of different heads and beaks of finches that Darwin found on the Galapagos Islands
In his memoir, The Voyage of the Beagle, Darwin noted, almost as if in awe, "One might really fancy
that, from an original paucity of birds in this archipelago, one species had been taken and modified
for different ends."
Indeed, the Galapagos have been called a living laboratory where speciation can be seen at work. A
few million years ago, one species of finch migrated to the rocky Galapagos from the mainland of
Central or South America. From this one migrant species would come many -- at least 13 species of
finch evolving from the single ancestor.
This process in which one species gives rise to multiple species that exploit different niches is called
adaptive radiation. The ecological niches exert the selection pressures that push the populations in
various directions. On various islands, finch species have become adapted for different diets: seeds,
insects, flowers, the blood of seabirds, and leaves.
The ancestral finch was a ground-dwelling, seed-eating finch. After the burst of speciation in the
Galapagos, a total of 14 species would exist: three species of ground-dwelling seed-eaters; three
others living on cactuses and eating seeds; one living in trees and eating seeds; and 7 species of treedwelling insect-eaters.
Scientists long after Darwin spent years trying to understand the process that had created so many
types of finches that differed mainly in the size and shape of their beaks.
Text from http://www.pbs.org/wgbh/evolution/library/01/6/l_016_02.html
Speciation –
changes in related
organisms to the
point where they
are different
enough to be
considered
separate species.
Niche – the
specific resources
a species
consumes and the
habitats it lives in.
Selection
pressures –
environmental
forces such as lack
of food or
extreme
temperatures that
result in the
survival of only
certain organisms
with traits that let
them survive.
Background Information: Bird Beaks
Did you ever wonder why there are so many types of bird beaks or bills? The most important function of a bird bill is
feeding, and it is shaped according to what a bird eats. The bill is one of the characteristics used to identify birds. You
can learn about bird behavior by looking at the bill and thinking about what it eats. Then you may think about where it
lives, and so on. Below are some common bill shapes and a description of the food they are especially adapted to eat.
A cone shaped bill is found in many birds such as finches and grosbeaks. It is a strong beak
used for cracking seeds.
Thin, slender, pointed beaks are found mainly in insect eaters. They are used to pick insects
off leaves, twigs, and bark. This warbler is a good example.
Woodpeckers have strong beaks which taper to the tip, forming a chisel for pecking holes in
trees for food or nests. Most feed on insects which live under the bark.
Hummingbirds have long, tubular bills that resemble straws, which they use to sip nectar
from flowers.
Mergansers, specialized for eating fish, have sharp tooth-like structures on the edge of the
bill to hold fish tightly.
Hawks, owls, and other birds of prey which catch and kill live prey have sharp, "hooked"
beaks. These are used to bite the skull or neck and also to tear the body into pieces small
enough to swallow.
The edges of a Mallard's bill are fringed to strain plants, seeds, and small animals from mud
and water.
Beaks which are flat and wide at the base are found in birds which catch insects in flight,
such as flycatchers. These birds also often have "whiskers," which are actually modified
feathers, at the corners of the mouth, which effectively widens the mouth opening,
allowing more effective capture of prey.
From: http://fsc.fernbank.edu/Birding/bird_beaks.htm
Name: __________________________________________________ Date: _________________ Period: _____
Clipbirds Lab: Background Information Questions
1. What did Darwin realize about the Galapagos Finches that led him to formulate the principle of Natural
Selection?
2. What did Darwin say about the Finches in his memoir, The Voyage of the Beagle? After writing down the
quote, put his statement in your own words.
3. What different diets are the Galapagos Finches adapted to eat?
4. Compare the beaks shown in Figure 1 of the article Background Information: Darwin’s Finches to the beaks
shown in the article Background Information: Bird Beaks to identify what kinds of food you think that the
four Finches shown the drawings of Darwin’s Finches eat:
5. What kind of variation do you think was in the original population of Finches that first migrated to the
Galapagos Islands from mainland South America? What evidence makes you think this?
6. ON THE BACK: Choose one Finch from the four in the drawing of Darwin’s Finches. Based on your
understanding of Natural Selection, draw a diagram and explain how that particular species of Finch might
have evolved from the original population of Finches that first migrated to the Galapagos Islands from
mainland South America:
(HINT: If you’re stuck, use the same format as your Natural Selection Explanation Cartoon homework)
Name: ___________________________________________ Date: ________________ Period: _____
Clipbirds
Evolution is the result of natural selection acting upon variation within a population. Organisms with adaptive
traits in an environment they are adapted to have an advantage over individuals with different traits.
However, it is important to remember that adaptations are only advantageous within the environment they
are adapted for, and may not help an organism survive in other environments. For example, a cat’s long tail
may help with balance on a tree branch, but be a problem in a house with frequently closing doors. The same
is true for specialized beaks on birds. The beak may be an adaptation in certain circumstances, but in others, it
may not help the bird survive.
Today, you will model a population of imaginary birds,
Clipbirds, that lives happily in a faraway fictional place
called Clipland. In this population of Clipbirds, there is
variation in the beak sizes. There are Clipbirds with big,
medium, and small beaks. One day, out of nowhere,
tectonic forces pushed a new mountain range into
existence. The population of Clipbirds became divided into
two smaller populations, east and west.
The birds of different beak sizes usually do just fine, but it
takes more food energy to maintain the larger beak size than the smaller sizes. There are multiple types of
food that Clipbirds eat, each having a different nutritional value.
Megacalories Needed for Clipbirds
Food Values in
Megacalories
Jewels
10
Lima Beans
Popcorn
To Survive
To Reproduce
Bigbeak
80
160
5
Mediumbeak
50
100
2
Smallbeak
25
50
You will model the Clipbirds over four seasons of changing environmental conditions. If you do not eat enough
food to survive, you must turn in your beak and sit down. If you manage to eat enough to survive, you will
continue on in the next season. If you manage to eat enough to survive and reproduce, you may choose
someone who is sitting out to represent your offspring (with a matching beak).
Over four seasons of changing environmental conditions, we will see if there is any natural selection
happening in Clipland, and if there will be any evolution in the two separate Clipbird populations.
HYPOTHESIS: Which birds do you think will be best adapted to the different food types? Why?
__________________________________________________________________________________________
__________________________________________________________________________________________
__________________________________________________________________________________________
HYPOTHESIS: If the food that is available in West Clipland becomes different from the food available in East
Clipland, do you think there will be any evolution in the two different Clipbird populations?
__________________________________________________________________________________________
INDIVIDUAL RESULTS:
Observations of Competition and Adaptations:
Your Beak Type: ____________________
Megacalories Needed for Survival: ___________
Megacalories Needed for Reproduction: __________
1st Season
Food Eaten
# Eaten
2nd Season
Megacalories
# Eaten
3rd Season
Megacalories
# Eaten
4th Season
Megacalories
# Eaten
Megacalories
Jewels
X 10 =
X 10 =
X 10 =
X 10 =
Lima Beans
X5=
X5=
X5=
X5=
Popcorn
X2=
X2=
X2=
X2=
Total =
Total =
Total =
Total =
CLASS RESULTS:
Clipbird Populations
West Clipland
1st
Season
2nd
Season
East Clipland
3rd
Season
4th
Season
1st
Season
Bigbeak
Bigbeak
Mediumbeak
Mediumbeak
Smallbeak
Smallbeak
2nd
Season
3rd
Season
4th
Season