CH15 Ecology

• Organisms in an ecosystem are dependent on one another for survival
• Photosynthesis


  1. Green plants absorb light energy from the sun

  2. Convert light energy into chemical potential energy stored in organic nutrients
• Chemical potential energy in organic nutrients


  Can be transferred to consumers through feeding relationships
• Our actions as a human population have deep implications on the health of the ecosystem
• The need to feed the rapidly increasing human population is placing great strains on earth's natural resources
• Deforestation and the increased use of fossil fuels have caused an increase in atmospheric carbon dioxide concentration and is leading to global warming which affects the survival and health of all living organisms
• The excessive and unsustainable use of plastic has also led to harmful effects on wildlife
• Human ingenuity with a responsible mind-set can rise to this challenge through the sustainable use of natural resources that will contribute to a balanced ecosystem and potentially mitigate the effects of climate change, including global warming
• Population


  A group of organisms of the same species living in a particular habitat
• Habitat


  A location in which an organism lives and reproduces
• Community (biotic environment)


  Refers to all the populations of organisms living and interacting with one another within a particular habitat
• Abiotic environment


  The physical conditions that affect the habitat and its community
• Ecosystem


  Refers to all populations, of a community, interacting with one another and with the abiotic environment of the habitat
• Energy flow in an ecosystem

  1. Sun radiates light energy

  2. Producers like plants absorb light energy to carry out photosynthesis to produce glucose hence convert light energy into chemical potential energy stored in glucose

  3. Energy from producers are passed from one trophic level to the next via feeding

  4. At every trophic level, energy is lost to the environment as heat, which cannot be used to do work

  5. The flow of energy through an ecosystem is non-cyclical or linear
• Roles of producers, consumers and decomposers


  • Producer: Autotrophic organisms which absorb energy from the environment and use that energy to synthesise organic nutrients from inorganic raw materials
  • Consumer: Heterotrophic organism which obtains organic nutrients, hence energy, from feeding on other organisms
  • Decomposer: Heterotrophic organism which obtains organic nutrients, hence energy, from feeding on or metabolising dead organisms or faecal matter
• Food chain


  A linear sequence illustrating the feeding relationship, hence the flow of materials and energy, from one trophic level to another
• Trophic level


  The position a population of organisms occupies in a food chain
• Food web


  A food web is made up of two or more food chains that are interlinked. It represents the relationship between food chains
• Only approximately 10% of the energy is passed from one trophic level to the next
• Approximately 90% of the energy in a trophic level is lost in the form of heat energy released during respiration, trapped in uneaten or undigested material, metabolic waste products, and kinetic energy for locomotion or to do work
• Food chains are usually short (no more than 4 links) as there will not be enough energy to sustain the higher trophic levels in longer chains
• Pyramids of numbers


  • Upright pyramid

  Shrub (100) -> deer (10) -> wolf (1)

  Inverted pyramid

  Tree (1) -> aphid (100) -> beetle (10)

  Inverted pyramid (parasitism)

  Cabbage (100) -> rabbit (10) -> fox (1) -> ticks (50)
• Pyramids of biomass


  • Upright pyramid

  Shrub (1000 kg) -> deer (100 kg) -> wolf (10 kg)

  Dumbbell shaped pyramid

  Tree (20 kg) -> aphid (1 kg) -> beetle (2 kg)

  Upright pyramid

  Cabbage (100 kg) -> rabbit (10 kg) -> fox (1 kg) -> ticks (0.1 kg)
• Pyramid of energy is ALWAYS upright. 90% of energy is approximately lost at every trophic level
• Carbon cycling in an ecosystem

  Forests as carbon sinks: Trees absorb CO2 for photosynthesis, store carbon in biomass, animals feed on plants and incorporate carbon into their biomass, dead organisms fossilise to form fossil fuels

  Oceans as carbon sinks: Phytoplankton and algae absorb CO2 for photosynthesis, store carbon in biomass, larger marine animals feed on them and incorporate carbon into their biomass, dead organisms fossilise to form fossil fuels, corals and shellfish incorporate carbonate ions
• Carbon source


  A geographical area that produces more carbon dioxide than it absorbs, e.g. deforestation, leading to a net increase in atmospheric CO2 concentration
• Effects of untreated sewage and fertilisers on water bodies

  Untreated sewage/fertilisers -> ↑ nitrates and phosphates -> eutrophication -> ↑ algae -> ↓ light intensity -> ↓ photosynthesis -> ↓ plants -> ↑ bacteria -> ↑ aerobic respiration -> ↓ oxygen -> ↓ other aquatic organisms -> ↓ biodiversity
• Untreated sewage and fertilisers contain high levels of nitrates and phosphates which are washed into water bodies and stimulate rapid algal growth, leading to eutrophication
• Algal bloom covers the surface of the water body and reduces light intensity, preventing submerged plants from photosynthesising and causing their death
• Bacteria decompose dead plant matter and use up dissolved oxygen in the water for aerobic respiration, leading to lack of oxygen and death of aquatic organisms, reducing biodiversity
• Plastic wastes are non-biodegradable and their burning produces greenhouse gases and toxic gases, leading to global warming and other environmental issues
• Plastic waste buried in landfills may leach harmful chemicals into the groundwater, and plastic waste washed into the sea may be mistaken for food and choke marine animals
• Plastic wastes break up into microplastics and can be ingested by marine organisms leading to bioaccumulation and biomagnification along the food chain
• Inorganic wastes like mercury and pesticides are non-biodegradable, hence remain in the water for a very long period of time and undergo bioaccumulation and biomagnification up the food chain, impacting top carnivores
• Conservation and sustainable use of natural resources contribute to the maintenance of biodiversity and a balanced ecosystem
• Conservation


  Protection and preservation of natural resources in the environment
• Biodiversity


  The measure of species richness (number of species) and species abundance (number of individuals in each species) in a specific area
• Reasons for conservation


  • Maintain natural scenery and wildlife for recreational and aesthetic appreciation

  Maintain biodiversity and prevent extinction of species which are a source of food, raw materials, have scientific value, and maintain a large gene pool

  Mangrove forests protect coastal regions from destructive winds and waves
• Conservation and restoration of forests


  Limit logging to specified areas and rotate, prohibit logging in protected areas, reforestation and rehabilitation, forest fire prevention and control, education programmes
• Conservation and restoration of coral reefs and marine biodiversity


  Avoid use of harmful sunscreen, prohibit harvesting of corals, remove trash from coastline, implement fishing quotas and bans, fish ranching, regulate mesh sizes of nets, ban harvesting of endangered species