BIOLOGY
Speciation Examples Practice
Name __________________
Hour _______ Date _______
Remember, there are 3 steps for speciation to occur:
1. Isolation of a Population: a population is split into two groups and cannot mate with each
other.
2. Adaptation/Evolution: each isolated group adapts differently to the environment
3. Reproductive Isolation: even when put together, the two groups can no longer breed
successfully (no fertile offspring; no grandchildren).
Read the stories and answer the questions that follow.
1. In the southwest part of the United States there are two kinds of similar ground
squirrels, the Albert and the Kaibab ground squirrel. They share many common
characteristics but do not interbreed in nature and are considered to be separate species.
Historically it is believed that at one time in the past they were both a part of the same
population and the same species. However, as time passed in their desert habitat the Colorado
River continued to erode deeper and deeper in the ground, eventually forming a big canyon.
This canyon was deep enough and without any kind of shelter or cover for the squirrels.
Rarely would any squirrels cross the canyon to get to the other side. In effect, the original
population was split in two parts. As time passed the habitat to the north of the canyon
became more shaded and the vegetation increased since it wasn't as hot. To the south of the
canyon, the area actually became warmer with less shade and only those squirrels with sparse
hair and good digging claws were able to reproduce well. Eventually each part of the
population adapted to their separate environments and habitats. Even mating behaviors of the
two populations are now no longer recognizable by the other population. They have evolved
(adapted) separately. Even if you bring the two populations together today, they will not
interbreed and are considered separate species.
a. Has speciation occurred? Yes or No? Mark the steps in the story above.
b. If speciation has occurred, how many times?
c. For each speciation occurrence, explain how the species became isolated and discuss
things that stopped interbreeding. If speciation has not occurred, explain what’s
missing.
2. There is a population of green tree frogs in a local forest. The owners of the forest sell their
land. The new developers split the land in half and put a gravel road through the middle of
the green tree frog’s habitat. The gravel road is not terribly busy. There are only two
families who drive down it.
a. Has speciation occurred? Yes or No? Mark the steps in the story above.
b. If speciation has occurred, how many times?
c. For each speciation occurrence, explain how the species became isolated and discuss
things that stopped interbreeding. If speciation has not occurred, explain what’s
missing.
3. A population of iguanas lives on a nice sandy beach. They like to eat many of the short
grasses living on the beach. One day, a storm hits their beach. Some iguanas end up floating
on driftwood in the ocean. They eventually land safely on a sparsely inhabited volcanic rock
island. The small island is able to support a few plant species. The iguanas especially like
the tasty cactus fruit. The iguana population continues to grow for many years taking up the
useable habitat on the island. Weaker iguanas that are unable to get cactus fruits and leaves
find seaweed in the water surrounding the island rather palatable. Over millions of years,
these iguanas develop adaptations to dive into the water for the seaweed. During this time,
the land iguanas and the marine iguanas drifted apart. The land iguanas stay by the plants in
the middle of the island whereas the marine iguanas stay near the water. The two groups
rarely interbreed, and there is no successful hybrid group.
a. Has speciation occurred? Yes or No? Mark the steps in the story above.
b. If speciation has occurred, how many times?
c. For each speciation occurrence, explain how the species became isolated and discuss
things that stopped interbreeding. If speciation has not occurred, explain what’s
missing.
4. A population of beetles lives in a tree. A new population of beetles from a nearby tree moves
in and interbreeds with the population. In a few years, you notice even more variation in the
beetles’ phenotypes yet they still mate and have fertile offspring.
a. Has speciation occurred? Yes or No? Mark the steps in the story above.
b. If speciation has occurred, how many times?
c. For each speciation occurrence, explain how the species became isolated and discuss
things that stopped interbreeding. If speciation has not occurred, explain what’s
missing.