Biology 2 /SL Review Book Topic G.3 Human Impact on Ecosystems
Name _________________________
Review Book Topic G3: Human Impact on Ecosystems
Assessment Statements
G.3.1
G.3.2
G.3.3
G.3.4
G.3.5
G.3.6
G.3.7
G.3.8
G.3.9
G.3.10
G.3.11
Calculate the Simpson diversity index for two local communities.
Analyze the biodiversity of the two local communities using the Simpson index.
Discuss reasons for the conservation of biodiversity using rainforests as an example.
List three examples of the introduction of alien species that have had significant impacts on ecosystems.
Discuss the impacts of alien species on ecosystems.
Outline one example of biological control of invasive species.
Define biomagnification.
Explain the cause and consequences of biomagnification, using a named example.
Outline the effects of ultraviolet (UV) radiation on living tissues and biological productivity.
Outline the effect of chlorofluorocarbons (CFCs) on the ozone layer.
State that ozone in the stratosphere absorbs UV radiation.
Key facts
1. Biological diversity can be described by richness (number of different organisms in an area) and
evenness (how the quantity of each different organism compares with the other).
2. The Simpson Diversity Index takes into account both richness and evenness.
3. Reasons for conserving biodiversity include economic, ecological, ethical, and aesthetic. For
example, with rainforests:
a. Economic: agricultural productivity of rainforests cleared for farming has been poor
(nutrients held in rainforest plant tissue). Plant sources of medicines and chemicals are lost
if species are extinct. Ecotourism benefits the local economy.
b. Ecological: species are kinked together in ecosystems like puzzle pieces; if an organism is
lost, the ecosystem can suffer. Diversity protects an ecosystem from invaders (alien species).
Fewer plants in the biosphere means more carbon dioxide in the atmosphere. Disruption of
the ecosystem can lead to soil erosion and flooding.
c. Ethical: local populations are most affected by rainforest destruction; do we have the right
to destroy an ecosystem which might be enjoyed by future generations?
d. Aesthetic: Human well-being is linked to (and human artists and writers have been inspired
by) the ability to visit natural areas in our biosphere.
4. Arguments against conservation include slowing economic development, clearing rainforest
provides land for agriculture, and reducing some sources of pests and disease.
5. Introduction of an alien species into an ecosystem disrupts communities. They often out-compete
native species (one invader can run out many native species), which reduces biodiversity.
6. Alien species can be introduced deliberately (kudzu as a preventative to reduce soil erosion, but
rapid growth damages other plants by covering them or weighing them down) or accidental (zebra
mussels introduced to North America via cargo vessel, clogging water pipes, yet also clarifying the
water of some lakes, which may benefit the ecosystem) .
7. Prickly pear cactus introduced into Australia expanded incredibly rapidly but was brought under
control by introduction of a math that feeds on it.
8. Impacts of alien species on ecosystems includes interspecific competition, predation, and species
extinction.
a. Interspecific competition: Grey squirrels overtook red squirrels when introduced in the UK.
Biology 2 /SL Review Book Topic G.3 Human Impact on Ecosystems
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b. Predation: a species which invades an ecosystem can eat another species. Sea lampreys
from the ocean invaded the Great Lakes through the St. Lawrence Seaway, reducing the lake
trout and whitefish populations. Salmon introduced into the Great Lakes eliminated smaller
fish like alewives, which had also come from the ocean and spread out of control.
c. 200 of 400 species of cichlids in Lake Victoria have been driven to extinction by introducing
the Nile Perch to the lake.
Biological control is the idea of using a natural predator to control an unwanted or invasive species.
There is always risk involved in doing so. Purple loosestrife has invaded wetlands in the US and
Canada. Produces 2 million seeds a year. Beetles are being introduced to control these populations.
Phorid flies are being introduced to control red fire ant populations.
Biomagnification is a process by which chemical substances become more concentrated at each
trophic level. As consumer eat producers that have taken up chemicals, they become more
concentrated in the consumer because they are soluble in fat and get stored in fatty tissue.
DDT is an example of biomagnification. DDT in water  DDT in zooplankton  DDT in small fish 
DDT in large fish  DDT in fish-eating osprey (millions of time greater concentration). The first sign
of this problem was a reduction in predator bird populations (eggs of these birds were easily
cracked). DDT was banned in 1971.
Effects of ultraviolet (UV) radiation include non-lethal skin cancer, lethal skin cancer, mutation of
DNA, sunburn, cataracts, and reduced biological productivity.
Ozone is like a protective layer of sunscreen for the planet. Its presence in the stratosphere absorbs
UV radiation. The ozone layer is thinning. Chlorofluorocarbons (CFCs) used in refrigerator coolants,
propellants for aerosols, and for making packaging, were found to be the cause. This discovery led to
an international ban on CFCs.
CFCs break down to release chloride ions, which react with ozone molecules to produce ClO
(chlorine monoxide) and Oxygen. The ClO reacts with an oxygen atom to form more oxygen and
release a chloride ion. One CFC molecule can move up to the stratosphere in 15 years and remain
there destroying ozone molecules for a century.
Complete the following.
1. What do richness and evenness mean in terms of biological diversity?
2. Discuss the reasons for conservation of biodiversity.
3. What is an invasive species?
Biology 2 /SL Review Book Topic G.3 Human Impact on Ecosystems
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4. What is biological control?
5. Describe the biological control of red fire ants.
6. Outline the effects of UV rays on living tissue and biological production.
7. Describe the effect of CFCs on the ozone layer.