1. Food supply as a limiting factor Chapter 37

2. Today’s lesson  Understand the concept of natural succession, land overuse, & deforestation  Discuss the use of chemicals to increase food production  Discuss how selective plant breeding & DNA technology has potential benefits for food production  Discuss the effects of food shortages on the world’s population

3. Natural Succession  Bare rock colonised by a pioneer community  - e.g lichen  Other species would follow  - e.g moss, soil, plants, grasses  Eventually a climax community would form  - e.g. deciduous trees  Human land use ensures that vast natural forests are cleared for agriculture etc.  Natural succession very rare these days

4. Developing countries  Population increase leads to land overuse (soil fertility drops)  Demand for fertile land rises dramatically  Forests cleared – prevents natural succession  Causes deforestation – often irreversible  Often cleared land used for cash crops, not food (v risky)  Often wood is needed for fuel  Use of marginal land can accelerate deforestation

5. Use of chemicals to increase food production  Monoculture – vast cultivation of one identical type of crop  E.g. wheat, maize, rice, potatoes  Fertilisers raise nutrient supply to soil  Eliminate need for natural cycling of chemical nutrients  - by decay & nitrification  Supports continuous use of land for growth of a crop  Disadvantages  - Doesn’t substitute humus – poorer soil aeration  - Nitrates can get washed into water supplies  - Eutrophication – makes a waterway over-rich (algal blooms)

6. Herbicides/Pesticides  Herbicides eliminate weeds which may compete with crops for nutrients etc.  Can be selective or non-selective  In a monoculture, pests & parasites have unlimited food  Insecticides wipe out invertebrate pests  - e.g. nematode worms, slugs, insects  Without their use 25-45% of cereal crops could be lost  Fungicides kill fungi (e.g. mildew)  Sprayed onto crop plants or grains covered in spores  - require repeated applications  All pesticides must be specific, short- lived & safe  Genetically engineered pesticides now widely developed

7. Selective plant breeding  To produce food plants with desirable characteristics  E.g. higher yields, disease resistance, faster growth etc  Plants can be inbred (self-pollination)  Maintains uniformity in future generations  Can lead to inbreeding depression  Plants also can be outbred (cross- pollination)  Benefit – hybrid viguour  Disadvantage – new strains not guaranteed to have desirable characteristics  These have led to a Green Revolution  Risks  – if all plants are identical, could all suffer from one disease strain  - require vast amounts of fertiliser (V. costly)

8. Genetic manipulation  Recombinant DNA technology allows DNA from one species to be transferred to another  E.g lectin transferred from pea to potato plants  Somatic fusion allows non-sex cells from different species to be fused together  Can form a hybrid protoplast  This has a mixture of parental plant traits  E.g. potato leaf roll disease control

9. Effects of food shortage  Famine – spell of food shortage  Balanced diet – supply of proteins, fats & carbs  - min. of 9500kJ/day  STARVATION:  1. Undernutrition  – failure to receive enough food  - tissue death, emaciation, death  2. Malnutrition  – lack of a balanced diet  Leads to a deficiency disease e.g. kwashiorkor (lack of protein)  World food distribution very uneven (40 million die every year)  Food production exceeds population growth  Excess food often stored, rather than be shared to the needy  Overeating & irregular food chains prevalent in developed countries