M6:S7 Populations and sustainability

• Population size


  The total number of organisms of one species in a habitat
• Abiotic factors affecting population size

  • Amount of light
  • Amount of water
  • Amount of space
  • Temperature
  • Chemical composition of surroundings
• Ideal abiotic conditions


  Organisms can grow fast and reproduce successfully
• Population size


  The total number of organisms of one species in a habitat
• Abiotic factors


  • Non-living features of an ecosystem
  • Affect population size
• Ideal abiotic conditions


  Organisms can grow fast and reproduce successfully
• Non-ideal abiotic conditions


  Organisms can't grow as fast or reproduce as successfully
• Biotic factors


  Living features of an ecosystem
• Interspecific competition


  Competition between organisms of different species for the same resources
• Interspecific competition


  Reduces resources available to both populations, limiting their growth and reproduction
• Interspecific competition


  Can affect the distribution of species, with the less well-adapted species being out-competed
• Intraspecific competition


  Competition between organisms of the same species for the same resources
• Population growth and decline


  1. Population increases when resources are plentiful

  2. Population declines when resources become limiting

  3. Population starts to grow again as competition decreases
• Carrying capacity


  The maximum stable population size of a species that an ecosystem can support
• Predation


  An organism (the predator) kills and eats another organism (the prey)
• Predator-prey relationship


  1. Prey population increases, providing more food for predators

  2. Predator population grows, reducing prey population

  3. Prey population is restored, reducing food for predators, causing predator population to decrease
• Limiting factors


  Factors that stop the population size of a species increasing
• Limiting factors can be abiotic or biotic
• Carrying capacity


  Determined by limiting factors
• Conservation is the protection and management of ecosystems so that natural resources can be used without running out
• Conservation


  • Dynamic process, adapting to changes
  • Involves managing ecosystems and reclaiming damaged areas
• Reasons for conservation


  • Economic
  • Social
  • Ethical
• Preservation


  Protection of ecosystems so they are kept exactly as they are, with no removal of resources
• Sustainable resource use means meeting current needs without reducing the ability of future generations to meet their own needs
• Sustainable woodland management


  1. Trees cleared in strips or patches

  2. Cleared areas not too large or exposed

  3. Timber harvested by coppicing

  4. Native tree species planted

  5. Planted trees supported and protected

  6. Trees not planted too close together
• Sustainable fishing uses quotas to maintain fish stocks at a level where they can continue to breed
• Sustainable way


  Having enough food without using resources faster than they renew
• Fish stocks are declining because we're overfishing
• This means there's less fish for us to eat, the ocean's food chains are affected and some species of fish may disappear altogether in some areas
• To tackle this problem


  Maintain fish stocks at a level where the fish continue to breed
• Sustainable food production


  Having enough food without using resources faster than they renew
• Using Fishing Quotas


  1. Fishing quotas are limits to the amount of certain fish species that fishermen are allowed to catch

  2. Scientists study different species and decide how big their populations need to be for them to maintain their numbers. Then they decide how many it's safe for fishermen to take without reducing the population too much

  3. International agreements are made (e.g. the Common Fisheries Policy in the EU) that state the amount of fish each country can take, and where they're allowed to take them from

  4. Fishing quotas are supposed to help to conserve fish species by reducing the numbers that are caught and killed, so the populations aren't reduced too much and the species aren't at risk from becoming extinct

  5. There are problems with fishing quotas though-e.g. fish of the wrong species or size are still caught, but they end up being thrown back into the sea, often dead or dying, because the restrictions don't allow the fishermen to bring them ashore. However, new rules for the Common Fisheries Policy are banning the discarding of fish like this and the whole catch will have to be brought ashore to be counted against the quota
• Controlling Mesh Size of Nets


  1. There are different limits to the mesh size of the fish net, depending on what's being fished

  2. This is to reduce the number of 'unwanted' and discarded fish that are accidently caught, e.g. shrimp caught along with cod. Using a bigger mesh size will let the 'unwanted' species escape

  3. It also means that younger fish will slip through the net, allowing them to reach breeding age

  4. However, it can be difficult to determine exactly how big the mesh size should be in areas where several different fish species are fished for at the same time. And two nets, each of which meets regulations, could be used one inside the other-effectively reducing the reported mesh size
• The Terai Arc is an area of forest and grasslands on the border between Nepal and India. A variety of plants and animals are found there, including endangered species like the Bengal Tiger and Asian elephant.
• Nearly 7 million people also live in this area and many of them depend on the forest's resources to survive.
• Areas of the forest are also being destroyed to make way for more housing and other development this destruction of habitat brings humans and animals into closer contact and increases conflict between the two. For example, elephants can eat and trample crop fields and tigers can kill livestock. This increases the likelihood of these animals being shot and killed.
• Conservation charity the WWF has worked with local people to help balance their needs with conserving the forest and its wildlife.


  For example, the charity has provided people with things like solar cookers and biogas generators, so they don't need to use wood from the forest as fuel. Farmers are encouraged to plant mint hedges around their crops to keep animals (which don't like the taste of mint) away.
• The Maasai Mara is a national reserve in Kenya. It's a large area of grassland (savannah), which is home to huge populations of wildebeest and zebra, as well as lions and cheetahs. The Maasai Mara is named after the Maasai people who live in the area.
• The Maasai people traditionally earn a living by raising livestock, such as cattle. This can bring them into conflict with conservationists-e.g. overgrazing by livestock can destroy grassland for wildlife.
• Conservation trusts are working with the Maasai people to help them make money from their land through conservation and ecotourism projects rather than farming, and to farm in a sustainable way.


  So, the economic needs of the Maasai people are met, while still allowing the area to be conserved.