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 environment This 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 boar Domestic 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 Control Manipulating 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) 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 Species We also need to control the density at which we grow crops There 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 stems/m 2 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 stems/m 2 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 same Maximum yield at 400 trees per acre Irrespectiveof density, optimum harvest time stays about the same Maximum yield at 400 trees per acre 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 Species e.g. Effects of frequency of weeding on the growth and yield of long-fruited jute in Nigeria TechniquePlant height (cm)Stem girth (cm)Edible yield g/m 2 No weeding Weeding once per week Weeded once two weeks after sowing Weeded once 4 weeks after sowing 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 Q: Summarise the data Any weeding increases plant height, stem girth and edible yield of crop Weeding once per week gives best yield Early weeding better than later Any weeding increases plant height, stem girth and edible yield of crop Weeding once per week gives best yield Early 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

Monocultures Advantages Can lead to pest epidemics May look visually unattractive May lead to exhaustion of particular soil nutrients Mechanisation leads to job losses and is dependent upon fosiil fuels Easy planting, weeding,fertilising and harvesting Favours 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 Disadvantages

Plenary Write down 4 key learning points from this lesson