1.4 Feeding People

1
1.4 Feeding People

• p. 25-34

2
Productivity

• The average amounts of new plant biomass produced
  each year per unit area.

3
Productivity of ecosystems

• Productivity is influenced by many factors

4

• Warm, wet areas have more productivity than cool,
  dry ones

5
Factors that influence productivity

• Sunlight
• Water
• Carbon dioxide
• Nitrogen
• Phosphorus
• Temperature

6
Changes in Productivity

• Add water and fertilizer to deserts
• Very expensive

7
Changing productivity

• Rain forests are productive, and they clearcut it
  to plant agricultural plants
• Not a good idea.
• Loss of diversity
• This can lead to disease, pests, weather
  fluctuations.
• Erosion!!

8
Food and Population Size

• Canadians consume more calories and more animal
  products per day than others in the world.
• 80 of the Earths population consumes grains as
  primary source of nutrition.

9
Monoculture

• A single crop (wheat, corn or rice) is often
  grown on huge areas of land.

10
Costs of monoculture pests
11
Poisons and food chains

• To keep pests from damaging crops, many farmers
  spray their fields with poisonous chemicals,
  called pesticides.
• The pesticides are designed to kill insects but
  not harm other animals, in small doses.
• Problems occurs when pesticides enter food chains
  and pass from one trophic level to another.

12
The DDT Story

• DDT used during WWII to kill lice, fleas and
  mosquitoes.
• Persistant pesticide that can remain in the
  ecosystem for large periods of time.

13
The DDT Story

• Used on crops to control damage caused by insect
  pests

14
The DDT Story

• In 1962 Rachel Carson published Silent Spring
• DDT restricted in Canada after 1969

15
The DDT Story

• DDT is a great example of biological
  magnification.
• The concentration of chemical increases as you
  move up each trophic level in a food chain.