Farming practices and production

• knowing about the efficiency of energy transfer in food chains can help farmers maximise the amount of energy in the food they produce
• food chains and food webs show how energy is transferred through an ecosystem:

  • food chains show simple lines of energy transfer - each of the stages in a food chain is a trophic level
  • food webs show lots of food chains in an ecosystem and how they overlap
• increasing efficiency:

  • most farming practices aim to increase the amount of energy that is available for human consumption
  • this means increasing the NPP of crops
  • and increasing the NP of livestock
  • two ways this can be done
• 1. energy lost to other organisms e.g. pests, can be reduced through the simplification of food webs
  2. the energy lost through respiration of livestock can be reduced
• simplifying food webs:

  • pests are organisms that reduce the amount of energy available for crop growth and therefore the NPP of crops
  • this ultimately reduced the amount of energy available for humans
  • by simplifying the food web, i.e. getting rid of food chains that don't involve humans, energy losses will be reduced and NPP of the crop will increase
• e.g. a simplified food web involving wheat - crop plant grown for human consumption

  • weeds, mice and aphids are pests
  • by eating the wheat or competing with it for energy the pests reduce the wheat's biomass and the energy it has for further growth
  • means whet's NPP and yield is smaller - less energy is transferred to humans
  • getting rid of food chains involving weeds, mice and aphids will mean less energy transferred to pests, increasing efficiency of transfer to humans
• to get rid of pests farmers need pest control - can reduce pest numbers using chemical pesticides:

  • insecticides kill insect pests that eat and damage crops - killing insect pests means less biomass is lost from crops - grow to be larger - NPP is greater
  • herbicides kill weeds - can remove direct competition with the crop for energy from the sun - also remove the preferred habitat or food source of the insect pests - further reduce their numbers and simplify the food web
• biological agents also reduce the numbers of pests, so crops lose less energy and biomass increasing the efficiency of energy transfer to humans:

  • parasites live in or lay their eggs on a pest insect - parasites either kill the insect or reduce its ability to function e.g. some wasp species lay their eggs inside caterpillars - the eggs hatch and kill the caterpillars
  • pathogenic - disease causing - bacteria and viruses are used to kill pests e.g. the bacterium Bacillus thuringienis produces a toxin that kills a wide range of caterpillars
• farmers can use integrated systems that combine both chemical and biological methods

  the combined effect of both can reduce pest numbers even more than either method alone meaning NPP is increased even more
• Reducing respiratory losses:

  • one way that farmers increase the net production of their livestock is by controlling the conditions they live in so that more of their energy is used for growth and less is lost through respiration and activities that increase the rate of respiration
  • e.g. movement increases the rate of respiration so animals may be kept in pens where their movement is restricted
  • the pens are often indoors and kept warm so less energy is wasted generating body heat
• • this means that more biomass is produced and more chemical energy can be stored, increasing the net production and the efficiency of energy transfer to humans
  • benefits are that more food can be produced in a shorter space of time, often at a lower cost
  • however enhancing NP by keeping animals in pens raises ethical issues
  • e.g. some people think that the conditions intensively reared animals are kept in cause the animal pain, distress or restricts their natural behaviour so shouldn't be done
• weeds compete with the crop for water, space and nutrients
• natural predators can be introduced to the ecosystem to eat the pest species e.g. ladybirds to eat aphids - useful but doesn't simplify the food web
• NPP is the energy in plant's that is available to the next trophic level in a food chain

  NP is the energy in consumers that is available to the next trophic level