Habitat Fragmentation and
Genetic Diversity
In this simulation, students learn how difficult it can be to maintain
a healthy gene pool in a fragmented habitat
by Gareth Thomson
Subject areas: science, social studies
Key concepts: genetic diversity, inbreeding depression,
dispersal, habitat fragmentation, umbrella species
Skills: pattern recognition, deductive reasoning, developing empathy, clarifying concepts, critical thinking
Location: outdoors or indoors in open space where
students can move about freely
Time: 30 minutes
Materials: several large pieces of fabric such as sheets;
several ropes or lengths of brightly colored twine; two 30
cm (12-in.) boards; class set of blue, green, red, and black
cards (or squares cut from poster paper)
The one process ongoing in the 1980s that will take
millions of years to correct is the loss of genetic and
species diversity by the destruction of natural
habitats. This is the folly our descendants are
least likely to forgive us.
— E.O Wilson, 19801
riting 150 years ago, naturalist John James
Audubon spoke of the sky darkening for days
as flocks of passenger pigeons numbering in
the billions passed overhead. We may feel a pang of bitterness toward those who hunted this marvel of nature
to extinction, but today the folly of over-hunting has
been replaced by a more insidious and far more devastating folly: the destruction of natural habitats. Scientist
E.O. Wilson estimates that loss of habitat is accelerating
normal rates of extinction by several thousand times, and
that we are, as a result, in the midst of an extinction
spasm unrivaled since the dinosaur age came to an end
65 million years ago.2
One means of preserving the Earth’s biodiversity has
always been through the establishment of protected areas
such as parks and wildlife refuges. Consequently, park
planners and managers have in recent decades been shaken to the core by studies showing that most protected
areas do not adequately protect many of the animals that
live there. For example, in a 1987 study of 14 national
parks in the western United States, conservation biologist William Newmark found that 13 of the parks had
lost some of the mammals that previously inhabited
those areas — simply because the parks are too small.
W
Canadian Parks and Wilderness Society
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Teaching Green: The Middle Years
Surrounded by developfind out how human activWe are in the midst of an extinction spasm
ities can get in the way of
ment, these protected areas
a bear’s plans for procreare, in effect, islands of
unrivalled since the dinosaur age came to
ation. The activity focuses
habitat. They cannot supan end 65 million years ago.
on the loss of genetic
port stable populations of
diversity that occurs when
animals, especially large
3
human
activities
make
it
impossible
for animals to travel
carnivores, whose natural behavior is to disperse over
freely within or beyond protected areas. It helps students
wide areas, traveling far from their birthplace to find
to understand that conservation of such animals as the
mates and new territories.
Consider the case of Pluie, a female wolf that was fit- wolf and grizzly bear will require unprecedented changes
in the way we design and manage our parks
ted with a satellite transceiver in northern Alberta. She
proceeded to astound researchers by traveling deep into
Bears of Banff simulation
the states of Montana and Idaho, a journey of more
than 1,000 kilometers (620 miles), crossing more than
Grizzly bears, the Great Bears revered in many aboriginal
30 jurisdictional boundaries and over an area ten times
cultures, are today symbolic of wilderness and considered
the size of Yellowstone Park. None of the parks in this
a valuable “umbrella” species, or indicator of ecosystem
region is large enough to protect such an animal; and
integrity. Grizzly bears were once found throughout the
current park designs, which include roads and town
Canadian prairies and all the way down to Mexico, but
sites, further fragment the habitats within parks. As a
in the last 150 years they have become extinct in more
result, populations of animals become isolated and, over
than half of their former range as their habitats have
time, begin to lose genetic diversity through inbreeding. been lost and their populations have become inbred.
This inbreeding depression, or loss of genetic fitness,
Scientists have noticed the first signs of inbreeding
often produces such harmful characteristics that animals
depression in the grizzly bear populations in Banff
can no longer reproduce and local populations go
National Park, even though the park is supposed to proextinct.
tect these animals.
There are two ways of solving the problem of local
extinctions within protected areas. The first is to dramat- Procedure:
ically increase the size of such protected areas, an option
1. Begin by inviting students into a large area that can
that in most cases is politically impossible because of the
comfortably hold the entire group. This could be
uses of the land surrounding protected areas. The secarranged simply by moving all desks to one end of the
ond is to connect protected areas by establishing wildlife
room, leaving half of the classroom for the activity.
corridors that allow animals to travel between refuges,
2. Inform the students that they are grizzly bears that
giving isolated populations access to other populations
have just entered a national park. Show them the
of the same species. An example is the proposed
boundaries of the park (this can be an imaginary line
Yellowstone to Yukon Conservation Initiative, a plan to
or some marker, which you identity to students). Tell
link protected areas along the spine of
them that the park borders
the continent from Yellowstone
are all impassable mounNational Park in western Wyoming
tains and that all activities
to the Yukon-Alaska border, a dismust occur within the
tance of nearly 3,200 kilomepark area you have
ters (2,000 miles). (See
defined.
page 59) Changes on
3. Ask the students
this scale will require a
to name four things
consciousness and
that every animal
desire for change
needs to survive (i.e.,
that permeates
food, water, space,
society, from
and shelter). Explain
decision makers
that, in this activity,
to the public
they do not need to
they represent.
worry about meeting
Bears of Banff is
these basic needs, but
an active simulation in
they will be tested on
which students assume the
their ability to mate and
role of grizzly bears in a
pass on healthy genes to
protected area. As they
try to survive and pass
new generations of grizzly
on their genes, they
bears.
Sustaining Ecosystems
61
diagnosed with incurable inbreeding depression;
they will be so harmed by generations of inbreeding
that they can no longer reproduce and will have to
leave the game.
4. Distribute four cards to each student: one each of
blue, green, red, and black. To save time, ask four
students to stand together, each holding all the cards
of one color. Have the rest of the students walk past,
taking one card from each.
5. Inform students that the long-term sustainability of
animal populations requires the mixing of genes to
keep the population healthy. Normally, individuals
ensure genetic mixing by dispersing, that is, traveling
long distances from their birthplace to mate with
individuals from other families. Explain that the colored cards students are holding represent their
genes. When you give the signal to disperse, their
task is to trade cards with other bears until they have
four cards of the same color.
6. Give the signal for dispersal. Students will likely need
only a minute to finish trading.
7. Ask students to raise their hands if they were able to
complete the task (usually, all or most will succeed).
Congratulate them on their ability to disperse and
their good genetic prospects.
8. Next, ask for a show of hands from students who
were not able to collect four identical cards. (If there
are none, postpone this explanation for the next
round, when inbreeding is represented by four samecolored cards.) Tell these unfortunate individuals
that they are the victims of inbreeding, or insufficient
gene mixing caused by mating between animals
that are closely related. Any bears that suffer from
inbreeding in three successive rounds will be
Note: If the students have studied genetics, explain
that inbreeding can reduce the fitness of offspring
because it increases the risk that harmful recessive
alleles will occur homozygously. Inbreeding depression is one of the reasons that most human societies
have taboos against incest.
9. For Round 2, place a piece of fabric in the center of
the space to represent a town (it should cover no
more than 20 percent of the total area of the park).
Place a rope across the center of the fabric and
extend it to the boundaries of the park to represent
a road that bisects the park.
10. Explain to students that humans have come to live in
the valley. They will be located in a modest town site
in the center of the park, represented by the fabric.
A simple road crossing through the park will supply
essential services to the town. Warn students that
towns and roads are dangerous for bears. Bears must
not go into the town (fabric); and if any bear is seen
in the town or stepping across the road, it will be
killed by you, playing the role of a truck.
11. Inform students that when you give the signal to
disperse this time, their task is to collect four cards
of different colors. Then give the dispersal signal.
12. Play six or seven more rounds, incorporating the
changes listed below and having students alternate
Canadian Parks and Wilderness Society
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Teaching Green: The Middle Years
between trading for identical cards and trading for
differently colored cards. At the end of trading for
each round, ask for a show of hands so that the
group can monitor the onset of deadly inbreeding
depression.
Make the following changes as the activity proceeds:
• Round 3, divide the park into quarters by adding a
railroad track, represented by a second length of
rope placed perpendicular to the road.
• Round 4, double the size of the town by adding
another piece of fabric to represent a commercial
shopping area built to give people “something to
do” when they come to the park.
• Round 5, build a large oil refinery by placing a
sheet of fabric just outside the park. Then pull
some of the fabric back over the boundary into the
park. Explain that the fabric represents the zone of
influence around a development that bears will not
enter.
• Round 6, build an affordable housing complex and
an airfield by placing pieces of fabric in two different places, each extending from the town site to the
boundary. This causes yet more habitat fragmentation. Bears going into these areas will be killed.
• Round 7, pause to inform the bears that an environmental group has proposed building a wildlife
overpass so that animals can cross the road. Place a
board over the highway to show them what it
would look like. Ask the bears if they are in favor of
this proposal. Then take the board away and tell
them that the government has turned down the
proposal without asking the bears for their opinion.
• Round 8, pause again and tell students that the
government has doubled the width of the road but
has built two wildlife overpasses over it. In addition, a new environmental study recommends closing the airfield. Ask the bears if they are in favor of
these changes. (Some dangerously inbred populations may be very happy about these changes.) Take
out the airfield and place two boards across the
rope on either side of the town site.
Wrap-up: The main intent of this simulation is to
demonstrate how incremental development in the park
makes genetic mixing more difficult. Ask students if they
think it would get easier or more difficult for the bears
Sustaining Ecosystems
in future rounds. Explain that things could go either
way, but one thing is certain: even in a national park,
humans often have a hard time saying “that’s enough.”
Extensions:
• Incremental development, in which human activities encroach on protected land in tiny increments
year after year, is a major threat to natural areas. To
reinforce this concept, place an empty box near the
edge of a desk and explain that the box represents
an intact ecosystem and your hand represents the
impact of humans on the ecosystem. Ask students
for examples of incremental impacts on ecosystems
(e.g., highway expansions). With each example,
push the container closer to the edge of the desk.
Continue until the box is partially overhanging the
desk edge. Point out that the box is still intact, but
that it is at risk. Ask students if the ecosystem will
survive unchanged if incremental development continues indefinitely. Discuss whether human activities
should have limits.
• Like many protected areas, Banff National Park is
the subject of debate between those who believe
that parks are for people and those who believe that
the first priority of a national park is to protect the
animals and plants that live in it. Ask your students
to discuss what they believe parks are for.
Gareth Thomson is Education Director of the Canadian
Parks and Wilderness Society, Calgary/Banff Chapter. He
lives in Canmore, Alberta.
The Bears of Banff activity is adapted with permission
from the activity guide Grizzly Bears Forever!, Canadian
Parks and Wilderness Society, Calgary/Banff Chapter,
2000. It and other activities can be downloaded free at
<www.cpawscalgary.org>.
Notes
1 Edward O. Wilson. “Resolutions for the 80s.” Harvard Magazine
January-February 1980, pp. 22-26. cited in Edward O. Wilson.
Naturalist. Warner Books, 1994, p. 335.
2 Edward O. Wilson. The Diversity of Life. WW Norton, 1992, pp. 280,
343, 346.
3 William D. Newmark. “A Land-bridge Island Perspective on
Mammalian Extinctions in Western North American Parks.” Nature.
vol. 325, no. 6103. January 29, 1987, pp. 430-32.
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