ecosystems

• Ecosystem


  Includes all the organisms living in a particular area known as the community as well as all the non-living elements of that particular environment
• Distribution and abundance of organisms in a habitat


  • Controlled by both biotic (living) factors e.g. predators and pathogens and abiotic (non-living factors) such as light levels and temperature
  • Each species has a particular role in its habitat called its niche which consists of its biotic and abiotic interactions with the environment
• Succession


  1. Change of one community of organisms into the other

  2. Primary succession occurs when area previously devoid of life is colonised by communities of organisms

  3. Secondary succession occurs in a previously colonised area in which an existing community has been cleared
• Pioneer species

  Species adapted to survive in harsh conditions that first colonise an area
• As organisms die, they are decomposed by microorganisms thus adding humus, this in turn leads to formation of soil which makes the environment more suitable for more complex organisms
• Over time, the soil becomes richer in minerals thus enabling larger plants such as shrubs to survive
• Climax community

  The final seral stage of succession, a self-sustaining and stable community of organisms
• Biomass


  The mass of carbon or dry mass of tissue per given area per given time
• Net primary productivity (NPP)


  The rate at which energy is transferred into the organic molecules that make up new plant biomass, that is the chemical energy store in plant biomass after respiratory losses to the environment have been taken into account
• Gross primary productivity (GPP)


  The rate at which energy is incorporated into organic molecule in the plants in photosynthesis, that is the chemical energy store in plant biomass, in a given area or volume, in a given time
• NPP


  GPP - R
• The net primary production is available for plant growth and reproduction as well as to other trophic levels in the ecosystem such as decomposers and herbivores
• Net production of consumers (N)


  N= I - (F+R) where I represents the chemical energy store in ingested food, F represents the chemical energy lost to the environment in faeces and urine and R represents the respiratory losses to the environment
• Nitrogen cycle

  1. Nitrogen is first fixed by bacteria such as Rhizobium which live in the root nodules of leguminous plants

  2. Ammonium ions are subsequently released by bacteria in the putrefaction of proteins from dead organic matter

  3. Chemotrophic bacteria (Nitrosomonas) oxidise ammonium ions to nitrites

  4. Nitrobacter subsequently oxidise nitrites to nitrates in the presence of oxygen

  5. Plants absorb nitrates from soil for nucleotide synthesis

  6. In anaerobic conditions, denitrifying bacteria convert nitrates back to oxygen gas for respiration
• Carbon cycle


  Carbon is recycled through the environment by the processes of photosynthesis, feeding, respiration and decomposition
• Methods to measure abundance of organisms


  • Line transect
  • Quadrat
  • Belt transect
• Limiting factors determining carrying capacity


  • Food
  • Water
  • Light
  • Oxygen
  • Nesting sites
  • Shelter
  • Parasites
  • Predators
• Predator-prey relationships


  Give rise to a fluctuating population size of predators and prey
• Types of competition


  • Interspecific competition
  • Intraspecific competition
• Conservation


  Maintaining or increasing the biodiversity within a particular habitat by allowing a sustainable use of the resources
• Preservation


  Maintaining the biodiversity levels and the habitat intact by minimising the effects of human activities on the particular habitat
• Reasons for conservation


  • Economic
  • Social
  • Ethical
• Coppicing


  Cutting down of trees close to the ground to encourage new growth
• Selective felling

  Harvesting/removal of largest, mature trees, as well as diseased ones to enable other trees to grow, trees which are removed are replaced with seeds
• Pollarding


  Form of coppicing where the trees are cut higher up, to prevent deer from eating the new shoots
• Efficient production where most of the tree is used to minimise wastage
• Effects of human activities on ecosystems


  • Galapagos Islands - Increase in tourism, demand for resources, waste and pollution, introduction of non-native species, overfishing, depletion of giant tortoise population
• Ways to manage ecosystems


  • Controlling number of tourists/visitors
  • Involvement of local communities
  • Education of local communities
  • Active management of vegetation
  • Control of the introduction of species