Download Rat Islands: An Exploration in Speciation

Rat Islands: An Exploration in Speciation
Background: After many years of studying nature and observing animals and their traits, Charles
Darwin came up with his theory of evolution. In 1838, the idea came to him that organisms with
favorable variations would be better able to survive and to reproduce than organisms with
unfavorable variations. He called this process Natural Selection, because nature "selects" the
survivors. The results of natural selection would be evolution.
Darwin published a book in 1859, On the Origin of Species by Means of Natural Selection. Darwin's
book was supported by many examples. The six main points of his theory are as follows:
1. Overproduction – Most species produce too many offspring than needed to maintain a
population but only a small fraction of those offspring live.
2. Competition – Offspring must compete against one another for food and shelter, only a
small fraction will survive long enough to reproduce.
3. Variation – Some characteristics of species are different (variation). These characteristics
are vital in the survival of the individual. Some may affect the ability to get food, run faster,
escape enemies or find a mate.
4. Adaptations – Because of variations, some individuals may be better adapted to reproduce
and survive than others. An adaptation is an inherited trait that improves the organism's
chances of survival and reproduction.
5. Natural Selection – The environment selects plants and animals to be the parents of the
upcoming generations. They must have desirable traits in order to survive. Those offspring
better adapted to survive in their environment will pass those traits on to their offspring.
6. Speciation – Over many generations, favorable traits accumulate in species and form new
species. The formation of a new species is called speciation.
Introduction:
A ship, infested with black rats (Ratus rattus) as many ships are, has hit a submerged rock and is
starting to sink. While the people have lifeboats to escape onto, and will be rescued by the Coast
Guard, the rats aboard are not so lucky, they have to swim to shore to survive.
There are 4 nearby tropical islands which the rats can reach before they drown or get eaten by
hungry predators, but these rats are not well adapted to survive on these islands. They do,
however, have good senses of hearing, sight, and smell, and can eat a wide variety of food; not to
mention that rats are highly intelligent. Random mutation and natural selection will allow the rats
to evolve into a new species that is adapted to survival on the island.
Assignment:
Knowing what you do now about evolution and Darwin's theory of natural selection, your job is to
design a rat which has adapted to the conditions of the island you were assigned. Adaptations can
be structural (to the body itself), physiological (to the body processes or proteins and enzymes
the body produces), or behavioral. Think about the build and anatomy of a normal rat then give
your rat the necessary variations and adaptions to survive the environment of this new island.
Be ready to share your rat and its environment to the class; your presentation should include the
following:
1. Following the engineering design process, develop your new species of rat
2. Draw your island, and your rat with its adaptations
3. Complete the table that lists your rat’s adaptations, their origins (what structures they
arose from) and explain how each adaption allows the rat to survive
4. Calculate the proportion in size between your new rat and a common rat
5. Present your rat to the class
ISLAND A:
The island is fairly flat, with an
occasional hill. The ground consists
of soft dirt. Several species of
shrubs grow toward the center of
the island. There is no animal life
on land, but the water is full of
friendly fish that swim around the
island. The island is also
surrounded by a coral reef which
keeps predators out. The shore is
sandy with no algal growth. Fresh
water is available.
ISLAND B:
The island has a rocky shoreline.
Numerous tide pools dot the island
along the shore where the wave
action is somewhat sheltered by
rock outcrops. The tide pools host
barnacles, chitons, abalone, sea
urchins and crabs. Algae grow all
around the island; however it is
quite sparse in the tide pools
where the various animals feed.
The current is quite strong along
the rocky outcrops where the
algae grow best. Freshwater is
available.
ISLAND C:
The island is somewhat barren. A
few species of cactus thrive on
the bare rocks. A large cactuseating tortoise inhabits the island.
A species of very large bird nests
on the island annually. They build
their nests in the rocks, and
protect their eggs from the sun by
standing over the nests with
outspread wings. The nests are
always found on the windy side of
the island which is somewhat
cooled by offshore breezes.
ISLAND D:
The island is an inactive volcano.
Vegetation in the island changes
with the altitude moving up the
volcano. Grasses grow at the base.
Further up the slope the grasses
give way to low shrubs. Half way
up, the island becomes quite lush;
tropical plants and trees dominate
the landscape. At this altitude,
the island experiences frequent
rain showers. There are two
species of birds that inhabit the
island. One raptor and the other is
a small finch. The raptor enjoys
eating small rats.
Table 1: Rat Adaptations and their Benefits
Adaptations for Island ____
Adaptation
Derived From
Type: S, P, or B
Survival Benefit