Energy transfers within ecosystem

A food chain shows how energy is transferred from one living organism to another, through trophic levels

Producer ---> Primary Consumer ---> Secondary Consumer ---> Tertiary Consumer

Within an ecosystem, living organisms are usually members of more than one food chain and often at different trophic levels in different chains. Therefore, food webs are used to illustrate the complexities to help us understand just excatly how energy flows through the whole ecosystem.

Energy transfers can be calculated by measuring the energy content of samples of organisms from each trophic level. Each sample is dried to constant mass in an oven and then burned in oxygen in a bomb calorimeter. The heat energy produced by the oxidation passes to a known mass of water, and the temperature rise of the water is measured. Given that 4.14J of heat energy rises 1g of water 1C, the energy content of each sample can be calculated.

At each trophic level, some energy is lost from a food chain, and is therefore unavailable to the organism at the next trophic level. Energy is lost because organisms:
- never eat all the availabel food
- cannot digest all the food they eat
-use energy in respiration and other metabolic reactions
- lose heat energy to their surroundings
- lose energy in urine and faeces (although this energy often passes on to decomposers)

Because of this, there is less energy available to sustain living tissue at higher levels of the food chain, and so less living tissue can be kept alive. When the organisms in a food chain are about the same size, this means there will be fewer consumers at the higher levels. Pyramids of numbers represent this idea.....

Human activities in farming, forestry and fishing manipulate the flow of energy through an ecosystem by altering the productivity of one or more trophic levels.....
- replacing natural vegetation and fauna with crops and livestock
- deflecting natural succession to maintain grassland
- increasing productivity of producers through soil improvements, irrigation, fertilisers and removal of competing weeds and damaging pathogens and pests
- increasing productivity of producers and consumers through selective breeding and genetic engineering
- sheltering organisms from damaging environmental factors

How can we improve secondary productivity?
- harvest animals before adulthood
- treat with steriods (illegal in the UK)
- selective breeding to increase growth rate
- treat with antibiotics to avoid loss of energy to pathogens
- stop animals moving about