1. Manipulation of the food species• This is done to increase its saleability, yield and suitability for cultivation.eg by selective breeding, GM, use of hormones

2. Control of the environmentThis is done to maximise yield and marketability.eg control of water and nutrient supplies, temperature, light levels, pest populations

How do humans control agroecosystems?

Principles

Of the thousands of plant species we could eat, 80% of world grain production relies on just 8 species

Why?• They were easy to grow• High yields• Easy to cook• Nutritious

In terms of the animals we grow to kill, other factors include:

• Social: Europeans don’t eat dog meat, but people in N. Korea do• Religious: Cows are sacred species for Hindus• Ethical: Most of the world’s population don’t regard eating whale

meat as acceptable• Technological: We know how to culture fungi to produce single-

cell protein

Principles

Wild varieties of plants and animals have been manipulated to increase their yield, saleability and ease of cultivation

e.g. domestic pigs look and behave very differently from the wild boar from which they were developed

Wild boarDomestic pig

The environment in which plants and animals are grown is controlled to maximise productivity

Movement is very restricted so that they do not waste energy on muscle action, and so gain more biomass

Fed with optimum amounts of food to give maximum growth Animals are often injected with steroids and antibiotics to speed up

growth and reduce disease The temperature of their environment is strictly controlled so that the

animals do not use much energy in keeping warm and so gain more biomass

This is how chickens are kept in traditional farming

This is how chickens are kept in factory farming

Principles: Factory Farming

Manipulating Food Species

Title Page

1. Population ControlManipulating food species

Q: If you are a cattle rancher in Texas, is it possible to have too many cattle in any given area (or is more always better)

Q: If you are a cattle rancher in Texas, is it possible to have too many cattle in any given area (or is more always better)

A: Population densities> carrying capacity may result in:

• Overgrazing• Soil compaction & erosion• Disease

A: Population densities> carrying capacity may result in:

• Overgrazing• Soil compaction & erosion• Disease

• Increasing the population density of the food species can increase productivity but can increase competition and make the spread of disease easier.

• The optimum livestock stocking densities depends upon the agroecosystem involved. eg different stocking densities for lowland and upland sheep.

• Increasing the population density of the food species can increase productivity but can increase competition and make the spread of disease easier.

• The optimum livestock stocking densities depends upon the agroecosystem involved. eg different stocking densities for lowland and upland sheep.

Manipulating Food SpeciesWe also need to control the density at which we grow cropsThere is intraspecific and interspecific competition for:• Light• Water• Soil minerals• Rooting space• Carbon dioxide

e.g. The effect of stem density on potato yield

Q: Summarise the data

As stem density increases up to 15-20 stems/m2

total yield increases At higher densities, total yield stays about the same but the average tuber size decreases (relatively more small potatoes!)

As stem density increases up to 15-20 stems/m2

total yield increases At higher densities, total yield stays about the same but the average tuber size decreases (relatively more small potatoes!)

Manipulating Food Species

e.g Effect of tree density on cocoa yield in Sri lanka

Q: Summarise the data

Irrespectiveof density, optimum harvest time stays about the sameMaximum yield at 400 trees per acreIrrespectiveof density, optimum harvest time stays about the sameMaximum yield at 400 trees per acre

5 10 15 20 25

100

200

300

400

500

600

Yield of dry beans per acre (pounds wt)

Age of trees (Years)

400 trees per acre

300 trees per acre

200 trees per acre

100 trees per acre

Manipulating Food Speciese.g. Effects of frequency of weeding on the growth and yield of long-fruited jute in Nigeria

Technique Plant height (cm) Stem girth (cm) Edible yield g/m2

No weeding 39.50 7.53 17.33

Weeding once per week

77.02 6.63 126.93

Weeded once two weeks after sowing

67.97 4.93 109.60

Weeded once 4 weeks after sowing

52.10 4.86 60.80

Source: A.R. Adenawoola, R.D. Aladesanwa and T.D. Adenowuro (2005) Effects of frequency of weeding on the growth and yield of long-fruited jute (Corchorus olitorius) in a rainforest area of southwestern Nigeria Crop Protection, Volume 24, Issue 5, May 2005, Pages 407-411

Q: Summarise the data

Any weeding increases plant height, stem girth and edible yield of cropWeeding once per week gives best yieldEarly weeding better than later

Any weeding increases plant height, stem girth and edible yield of cropWeeding once per week gives best yieldEarly weeding better than later

Monocultures

Most habitats contain a variety of plant species, monocultures are relatively rare

However, in agriculture and forestry, we often plant monocultures

MonoculturesAdvantages

Can lead to pest epidemicsCan lead to pest epidemics

May look visually unattractive

May look visually unattractive

May lead to exhaustion of particular soil nutrients

May lead to exhaustion of particular soil nutrients

Mechanisation leads to job losses and is dependent upon fosiil fuels

Mechanisation leads to job losses and is dependent upon fosiil fuels

Easy planting, weeding,fertilising and harvesting

Easy planting, weeding,fertilising and harvesting

Favours mechanisation so low labour inputFavours mechanisation so low labour input

Offers economies of scale – cheaper to buy 10,000 tree seedlings of one species than 1000 of each of ten species

Offers economies of scale – cheaper to buy 10,000 tree seedlings of one species than 1000 of each of ten species

Disadvantages

PlenaryWrite down 4 key learning points from this lesson

• 1.

• 2.

• 3.

• 4.