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Ch. 2: Change and Stability in
Ecosystems pg. 48
Change and recovery in Great Lakes
2.1: Cycling of Matter in Ecosystems pg. 50.
Organic Substances
- always contain atoms of carbon ( C) and
hydrogen (H) and usually oxygen(O) and nitrogen
(N)
- atoms are present on Earth in “fixed amounts”
- include: carbohydrates, fats, proteins and nucleic
acids that make up all living cells (food)
- are the building blocks of living organisms and
must be recycled since there is a limit to the
number of atoms and molecules on Earth
Organic Compounds
Living Cells
Cycling of Organic Matter
• All organic compounds are recycled into
new life forms.
• Involves:1 digestion of food to break down
complex organic compounds into simplier
molecules ( sugar, amino acids, fatty acids
+ glycerol) to be used by cells to build
complex molecules for cell structure
• 2. decay of dead organisms to make the
materials available to other living organisms
which is carried out by DECOMPOSERS.
Decomposers
• Bacteria, fungi and mould break down
break down dead organic matter and return
nutrients into ecosystem.
2.2: Pesticides pg. 52
• Pests are organisms that people consider
harmful or inconvenient
• Ex. Weeds, insects, fungi, rodents
• Pesticides are chemicals designed to kill
pests: insecticides, herbicides, fungicides,
herbicides, bactericides (see table 1 pg. 53)
Questions
a. Which organisms in figure 1 could be
considered a pest?
b. What would happen if one pest were
removed from the food chain?
c. List 3 possible short term benefits of using
pesticides.
st
1
Generation Pesticides pg. 53
• Sulfur, lead, arsenic and mercury were
applied to crops to kill insects (500 BC)
• 1800’s chemicals were abstracted from
plants to kill aphids since plants had
developed chemical defences against
animals.
2nd Generation Pesticides
• Chemicals made in laboratories ( >500 used
in Canada)
• Since 1939 DDT has been used an an
insecticide but was banned in 1971
• Ex. Aldrin, endrin, deldrin
• Cause “bioamplification” in food chain
• Toxic, organism specific, persistant, fat
soluble, short lived
Bioamplification pg. 55
• Process that results in increasing
concentrations of a toxin in the bodies of
consumers at each succeeding trophic level
• Occurs in pesticides that are soluble in fat
but not in water so they cannot be released
in sweat or urine so they accumulate in fatty
tissues of animals
• Consumers at each level get more toxin
because each predator eats many prey.
Questions…
d. Why might chemicals taken from plants
create a much lower risk for humans and
ecosystems?
e. How would a chart showing the
concentration of toxins differ from a
biological pyramid of biomass for the same
food chain?
f. Vultures and some species of beetles feed
on the dead bodies of animals from several
trophic levels. Predict how these animals
might be affected by bioamplification.
Effects on Humans/Animals
- Bioamplification of DDT detected in the
1950’s
- DDT banned in Canada in 1971
- Migratory birds and fish still perpetuate the
problem ex. Canada Goose, Peregrin
Falcon, Whales, Dolphins
- Causes thinning of egg shells
- Impairs nervous system, liver, kidney,
immune system
Questions…
g. Why is the fact that other countries have
not banned DDT of concern to Canadians?
h. Breast milk contains fat. Speculate about
how breast feeding might affect the
concentration of DDT in a mother and her
baby.
Modern Chemical Pesticides
• Act like “nerve gas” and either kill the pest
or make it vulnerable to predators
• Are soluble in water and cannot be stored in
body tissues
• Chemicals are broken down by the liver and
are removed during excretion.
• Are broken down quickly in the soil
Problems
1. Must be applied more often because they
break down quickly
2. Are capable of killing many other animals
(unintentionally)
3. Bioamplification still occurs in the food
chain
4. Continued application leads to gradual
“resistance to pesticide” by the pest
5. Some are carcinogens
6. Contaminate ground water
7. Residue in food
8. Sprays and vapors
Questions…
i.
Why are the new pesticides less harmful
to ecosystems than DDT?
j. Speculate about how less competition for
food helps increase the reproductive
success of the remaining insects after a
pesticide is applied.
k. According to Fig. 6 in which decade was
there the greatest number of species that
became resistant to pesticides? Explain.
Atlantic Canada and Spruce Bud Worm
• Adult moths lay eggs which hatch into
larva, larva move into interior of tree to
hibernate.
• Larva feed on balsam fir, and spruce trees
(needles, buds, male flowers, new shoots)
• Pesticides; malathion, dimethoate, acephate
• Biological control: bacteria and growth
regulator hormones
• Cape Breton allowed the infestation to run
its course but lost 50% of its forest
Questions…
l. Speculate about why the spruce budworm
hasen’t been eliminated after 40 years of
spraying.
m. Why wouldn’t biologists just use
extremely high concentrations of
insecticides to kill all the spruce budworms.
n. Identify groups who have benefitted from
the New Brunswich spraying program.
o. Identify groups of people in Cape Breton
who might have suffered as a result of the
decision now to spray.
p. What are the benefits of not spraying?
Pesticides and the Great Lakes
• Spring runoff of melted snow and ice into
aquatic ecosystems have increased
concentrations of pesticide which enter the
food chain:
• aquatic insects small fish, amphibians 
larger fish small mammals birds
eagles
• Bald eagles can live for 25 years and
accumulate high amounts of fat soluble
toxins which are released through the laying
of eggs
Questions…
q. Explain why insecticides such as DDT
would pose a greater threat to freshwater
ecosystems than newer water-soluble
pesticides.
r. Why would female eagles have slighty
lower levels of toxins than male eagles?
Compare egg laying in eagles with breat
feeding in humans.
s. Draw a food web, showing the movement
of pesticides in a lake from aquatic insects
to the bald eagle
Alternatives
1. Organic Farming – uses natural oils and
soaps that come from plants to control
pests
2. Biological Control – uses predators,
parasites and pathogens to control pests
ex. Lady bugs eat aphids, aphids eat plants
3. Crop rotation to interrupt pest reproductive
cycles
4. Use plant species resistant to disease
5. Use GPS to apply minimal amount of
pesticide