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.

1

st

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.

2

nd

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