Habitat destruction
According to many scientists, the destruction of habitat is the leading cause for the
loss of biodiversity. Wherever humans settled, the surrounding ecosystems were
dramatically changed. Human activities that can lead to habitat destruction are
agriculture, oil and gas exploration or commercial development. Due to such
activities, the landscape today is much more homogenous than it used to be. This of
course leads to the extinction of species: the less diverse habitats we have, the less
room we have for biodiversity. There are three different dimensions of habitat
destruction:
1. Habitat loss
2. Habitat degradation
3. Habitat fragmentation
Habitat loss occurs when a habitat completely vanishes. A typical example for
habitat loss is a bulldozer pushes down trees in order to build new houses or roads.
Whenever a wetland is drained, a field is mowed or trees are cut down, habitat is
lost. When a certain ecosystem or biotope changes in one way or the other, we
speak of habitat degradation. When forests, meadows and prairies are converted to
farmland, habitat degradation occurs: Although we will still find some wildlife, most of
the original animals and plants inhabiting the former meadow or forest will have
disappeared. Pollution is another example for habitat degradation. Today, nearly
60% of the Earth’s ecosystems are degraded.
Habitat fragmentation
While it is becoming increasingly easy for us
humans to move around freely all over earth,
most of our animals are losing more and more of
their freedom of movement. Habitat fragmentation
happens when a habitat is cut up into fragments,
like when roads are built through a certain habitat,
or some parts of a forest are cut down. Whereas
most of Germany’s surface used to consist of
continuous forests, today only about 30% of our
country is forested. Fig. 1 shows an example for a
forest that has been fragmented by the
construction of roads and deforestation.
Fig. 1: a fragmented forest habitat in Germany
Words you might not know:
freedom of movement: Bewegungsfreiheit
habitat fragmentation: Landschaftszerschneidung
vulnerable:
weak, delicate
http://biologiebilingual.jimdo.com/teaching-material/biodiversity/threats-to-biodiversity/
Habitat fragmentation is dangerous for several reasons. First of all, smaller habitats
can only hold less species: often the new fragments are too small to support species
that need a large territory to find food or mates. This is the reason why large
mammals such as tigers or gorillas are so threatened by the destruction of
rainforests. Secondly, habitat fragments are comparable to islands: animal
populations separated by fragmentation are just as isolated as island populations.
This means that no more genetic exchange is possible, which leads to a smaller
genetic diversity and makes a population more vulnerable to diseases or natural
disasters. Also, it can lead to the danger of inbreeding. Another reason why smaller
habitats are a threat to biodiversity are so-called edge effects, which make a habitat
less attractive to species. Imagine a piece of forest and compare its edge to its
center: along the clear-cut edge, lighting and wind conditions are different and
animals and plants are a lot more exposed than they are in the center. Because of
this, the smaller the edge of a habitat, the more attractive it is to a species.
Wildlife Corridors
Because so many habitats are
fragmented, conservationists use
wildlife corridors to connect the
fragments. For example, in southern
California,
corridors
underneath
freeways help mountain lions to
cross the road without the danger of
being hit by a car. In Germany, there
are many bridges across freeways
for game. By connecting habitats with Fig. 2: wildlife corridor across a freeway in Birkenau, Germany
each other, populations also have a larger area to live in, and are less likely to go
extinct. The BUND, a environmental organization in Germany has started a project
which aims at connecting German and European forests by creating a 20,000 km
long “green belt”, to ensure more habitat for our wildlife.
Words you might not know:
Task:
wildlife corridor:
game:
edge effects:
Wildtierkorridor
das Wild
Randeffekte
http://biologiebilingual.jimdo.com/teaching-material/biodiversity/threats-to-biodiversity/
The job of many conservation biologists is to preserve and establish wildlife reserves.
Which of the following four examples would you pick as the most ideal reserve for an
endangered deer population? Explain your decision.
hint:
area of a circle:
circumference:
π x r²
2xπxr
Answer:
The students will hopefully pick different kinds of solutions, which highlights that there
isn’t ONE correct answer. Students will have to either pick the reserve with the
largest surface or area or the smallest edge, or pick something in between. It will be
up to them to argue WHY the reserve they picked is the best by applying what they
have learned in the text.
A)
B)
C)
D)
A = 2200, U = 220
A ~ 2872, U ~ 188,5
A = 2025, U = 180
A ~ 2482, U ~ 188,5
http://biologiebilingual.jimdo.com/teaching-material/biodiversity/threats-to-biodiversity/