Lecture 8

Question 1

Ecology of Ancient and Modern Food Production

Answer 1

• Quaternary period: last 2.68 MY, an ice age with alternating glacial and interglacial periods
• Humans emerged about 2 MYA
• Agriculture a post glacial phenomenon, about last 10,000 years = Holocene epoch, an interglacial period

Question 2

Early humans evolved and migrated as hunter/gatherers

Answer 2

• No agriculture until Homo sapiens
• Multiple branches, +/- independent
• Came late to americas

Question 3

Stable plant foods

Answer 3

• Primitive diet probably opportunistic and unreliable
• Humans not adapted for flavory, plant foods need to be higher quality/less defended: fruits, seeds, tubers
• What makes fruits good food? Selection for attractiveness -> dispersal
• What makes seeds and tubers good? Energy-storage organs

Question 4

Crops of antiquity: artificial selection on native plants

Answer 4

• Independent origins in different places
• Grasses
  
  • Wheat, rice, maize, barley
  • Key evolutionary innovations: non-shattering seed heads, amylase evolution
• Legumes
  - Beans, lentils, chick peas
• Fruits
  - Tomatoes, squash

Question 5

Ancient technical innovations

Answer 5

• Fishing by net
• Irrigation channels
• Domestication of cattle, sheep, poultry (and evolution of lactose tolerance)
• Plow replaced digging sticks
• Middle Ages: crop rotation, draft animals
• Human life transformed: nomadism replaced by stability, rise of cities

Question 6

Ecological and evolutionary limitations of primitive cropping systems

Answer 6

• Intrinsic growth performance of crops
  
  • Limited areas suitable for growth, plant ranges of tolerance typically limited by temperature, water, NPK
  • Edaphic factors: soil moisture and fertility
  • Soil exhaustion, buildup of insects, disease

Question 7

Issues in contemporary agriculture

Answer 7

• Return to 1950s and 1960s
  
  • Populations booming as never before
  • Famines occuring with much worse ones predicted

Question 8

Soil amendments

Answer 8

• Repeated crop harvests known to exhaust soils: crop yields decline over time (nutrients removed rather than recycled)
• Adding animal dung to soil known since antiquity
• Main chemical benefits are NPK which occur in higher concentrations in animals than in plant tissues
• But other benefits come from organic matter improving soil texture and water retaining capacity

Question 9

Transition from manure to industrial chemicals

Answer 9

• Lawes: Dramatic growth responses to chemical fertilizers, especially grasses to nitrates and ammonia
• Higher concentrations of compounds needed for optimal growth
• N fertilizer from high nitrate materials (saltpeter, KNO3 or NaNo3)
• Haber-Bosch process: natural gas + aerial nitrogen + catalyst + pressure = ammonia(fertilizer and explosive)

Question 10

Synthetic N and Human Society

Answer 10

• With synthetic N, world population increase and meat production increase

Question 11

Technology evading previous limitations

Answer 11

• Irrigation brings water to dry areas
• Fertilizer brings nutrients to poor soils
• Industrial chemistry makes fertilizer cheaper

Question 12

Green Revolution

Answer 12

• Use conventional plant breeding techniques (artificial selection and hybridization) to evolve high yielding dwarf crop varieties
• IR8 rice at least tripled seed yield/area
• Introduce high-intensity cultivation techniques

Question 13

Yuan Longping

Answer 13

• Father of hybrid rice
• Rice is self pollinating, male-sterile plants can be used as female plant in cross to make hybrid varieties
• Advocate of technology transfer, especially to other developing countries

Question 14

Plant allocations favored in nature

Answer 14

• Grow tall to compete for light and enhance pollination and seed dispersal
• Extensive roots to capture scarce water and nutrients
• Make physical and chemical defenses against herbivores and fungi

Question 15

Changes under modern agriculture

Answer 15

• Competition prevented by mechanized cultivation and herbicides; other selection reduced
• Supplied by irrigation and fertilizer. No need for root system
• Protection conferred by insecticides and fungicides

Question 16

Mixed bag of green revolution

Answer 16

• Yields went up. Famines averted (good)
• HYV are needy. Likely to interact with climate change (bad)
• HYV productivity likely saved other habitats from agricultural conversion (good). Without more efficient crops, need to use more land to get same yield
• HYV crops appear to be plateuing in yields (bad)

Question 17

Economic and Political Implications

Answer 17

• Cost of food tied to cost of petroleum and electricity
• China and India subsidize costs of N fertilizer to farmers
• With current technology, increasing food supply requires burning more fuel and clearing more land