Topic 9

• Levels of organisation in an ecosystem

  • Individual
  • Population
  • Community
  • Ecosystem
• Population


  All organisms of the same species living with one another in a habitat
• Community


  All of the populations of different species living together in a habitat
• Ecosystem


  The community of organisms and non-living components of an area and their interactions
• Interdependence


  Organisms are dependent upon each other, a change in the population of one species can affect other populations within a community
• Examples of interdependence


  • Plants depend on pollinators e.g. bees
  • Herbivores are dependent on plants
  • Animals are dependent on mates
• Mutualism


  The interaction between two organisms where both benefit as a result of their relationship
• Parasitism


  The interaction between two organisms where only one organism, the parasite, benefits whilst the host does not
• Abiotic factors


  The non-living aspects of an ecosystem e.g. temperature, water availability, light intensity, pollutants
• How communities are affected by environmental conditions

  1. Environmental conditions (e.g. temperature, light intensity, water availability) affect the abundance and distribution of organisms within communities

  2. e.g light intensity affects the rate of photosynthesis in producers which serve as a source of food and shelter for other organisms
• How communities are affected by pollutants

  1. Toxic chemicals (e.g. pesticides) bioaccumulate in food chains to deadly concentrations at higher trophic levels, killing tertiary and quaternary consumers

  2. Fertilisers that contaminate water sources can cause eutrophication, killing multiple populations within a community

  3. Air pollution can affect the ability of some plant species to survive
• Biotic factors


  The living components of an ecosystem e.g. competition, predation
• How competition affects communities

  1. The presence of competitors affects population distribution and size

  2. If one species is better adapted to survive in a certain environment, it will outcompete other species, causing their populations to decline
• How predation affects communities

  1. Predation affects prey populations within a community

  2. e.g. if the number of predators decreases, the number of prey will increase as fewer are killed

  3. Populations of all other organisms within the food chain will also be affected
• Quadrat


  Piece of apparatus used to measure the abundance and distribution of organisms in an area
• Belt transect


  Piece of apparatus used to study the distribution of organisms across a gradient
• Food chain


  It describes the feeding relationships between organisms and the resultant stages of biomass transfer
• Biomass


  The total mass of living material
• Trophic levels


  The stages in a food chain
• Arrows in a food chain

  The direction of biomass transfer
• Simple food chain


  • producer → primary consumer → secondary consumer → tertiary consumer
• Producers are the first trophic level because they provide all biomass for the food chain (via photosynthesis) and the rest of the food chain involves the transfer of this biomass
• Pyramid of biomass


  It represents the dry mass of living material at each trophic level of a food chain
• A pyramid of biomass is almost always pyramid-shaped because producers (at the bottom of the pyramid) have the greatest biomass so have the longest bar, and as you move along the food chain (and up the pyramid) biomass is lost so the bars decrease in length
• Biomass is lost between each trophic level in a food chain because glucose is immediately used for respiration in plants, respiration to generate heat energy and energy for movement, some parts of organisms are indigestible, and egestion and excretion
• There are rarely more than four or five trophic levels in a food chain because above this, there is insufficient energy to support another breeding population
• The equation for calculating the efficiency of biomass transfer between trophic levels is: Efficiency = (Biomass of next trophic level / Biomass of previous trophic level) x 100
• Biodiversity


  The variety of living organisms in an ecosystem
• Fish farming


  • Food used to feed the fish and waste can leak into water sources, causing eutrophication
  • Parasites from fish farms may spread and contaminate surrounding ecosystems
  • Other organisms may become tangled in netting
• Use of fertilisers


  • Excess fertiliser can wash into water sources causing eutrophication and death of many species. This reduces biodiversity.
• Eutrophication caused by fertilisers

  1. Fertiliser run-off into rivers and lakes

  2. Nutrients build-up in water

  3. Algal bloom blocks sunlight

  4. Aquatic plants cannot photosynthesise ∴ less oxygen produced

  5. They die and decompose

  6. Decomposers further deplete oxygen levels

  7. Animals can no longer respire aerobically so die
• Introduction of non-indigenous species

  • They may out-compete native species, causing a reduction in population numbers
  • Native species may become the prey of non-indigenous species
  • They may bring new diseases which could kill large numbers of native species, reducing biodiversity
• Reforestation


  Replanting forests to help restore biodiversity
• Conservation schemes


  They prevent species from becoming extinct and increase population numbers, maintaining biodiversity
• Benefits of maintaining biodiversity

  • Ensures future food requirements can be met, reduces damage to food chains
  • Increases the likelihood of species adapting to future environmental change
  • Many plant species are yet to be discovered and may contain chemicals that could be used in future medicines
  • Safeguarding valuable future resources e.g. fuels, paper
  • Aesthetics - culture, ecotourism etc.
  • Jobs provided by ecotourism, reforestation and conservation schemes
• Food security


  Ensuring that populations have access to adequate amounts of safe and nutritious foods
• Biological factors affecting food security

  • Rising human population
  • Changing diets
  • New pests and pathogens
  • Environmental change
  • Sustainability
• Rising human population


  As human population increases, global food production must also increase in order to meet the growing demand for food
• Changing diets


  • Greater consumption of meat and fish in wealthier populations
  • Less energy and biomass available from livestock than crops
  • Livestock use land for grazing and are fed crops that could otherwise be used for human consumption
  • Less food is available for humans ∴ reduction in food security
• New pests and pathogens

  Pests and pathogens can reduce or destroy crop yields, negatively impacting food security