Topic 4: Ecology
This is an introduction to the ecology topic. It lists understandings and skills expected for Topic 4 including terminology like species, communities, ecosystems, the nature of energy flow and carbon cycling including carbon reservoirs, carbon flux and climate change. Helpful for revision.
Detailed revision notes, activities and questions can be found on each of the sub-topic pages:
- 4.1 Species, communities and ecosystems
- 4.2 Energy flow
- 4.3 Carbon cycling
- 4.4 Climate change
4.1 Species and communities
- Species are "groups of organisms that can potentially interbreed to produce fertile offspring".
- Members of a species may be reproductively isolated in separate populations.
- Species can be autotrophic or heterotrophic in nutrition (a few species are both).
- Consumers are heterotrophs that feed on living organisms by ingestion.
- Detritivores are heterotrophs that obtain organic nutrients from detritus by internal digestion.
- Saprotrophs are heterotrophs that obtain organic nutrients from dead organisms by external digestion.
- A community is "populations of different species living together and interacting with each other."
- An ecosystem is "a community and its interactions with the abiotic environment."
- Autotrophs obtain inorganic nutrients from the abiotic environment.
- The supply of inorganic nutrients is maintained by nutrient cycling.
- Ecosystems have the potential to be sustainable over long periods of time
Skills (can you ....)
- Classify species as autotrophs, consumers, detritivores or saprotrophs from a knowledge of their mode of nutrition.
- Set up sealed mesocosms to try to establish sustainability. (Practical 5)
Mesocosms in sealed glass vessels are preferable because entry and exit of matter can be prevented but light can enter and heat can leave. Aquatic systems are likely to be more successful than terrestrial ones.
- Test for association between two species using the chi-squared test with data obtained by quadrat sampling.
For example An ecosystem chosen where varying factors affect the distribution of the chosen species. Random quadrat sampling should be used to measure the presence or absence of the chosen species.
4.2 Energy flow
- Ecosystems get a continuous supply of energy from sunlight.
- Photosynthesis converts light energy to chemical energy in carbon compounds, eg glucose.
- Chemical energy in carbon compounds flows through food chains by means of feeding.
- Energy released from carbon compounds by respiration is used in living organisms and is eventually converted to heat which is lost from ecosystems.
- Living organisms cannot convert heat to other forms of energy.
- The length of food chains is restricted by energy losses as is the biomass of higher trophic levels.
- Biomass in terrestrial ecosystems diminishes with energy along food chains due to loss of carbon dioxide, water and other waste products, such as urea.
- Inorganic nutrients are cycled within ecosystems - and their supply is finite - this is in contrast to energy.
Skills (can you ....)
- Show energy flow using pyramids of energy. Pyramids of energy should be drawn to scale and should be stepped, not triangular. The terms producer, first consumer and second consumer and so on should be used, rather than first trophic level, second trophic level.
4.3 Carbon Cycle
- Carbon dioxide is converted (by photosynthesis) into carbohydrates and other carbon compounds in autotrophs.
- Carbon is present as dissolved carbon dioxide and hydrogen carbonate ions (HCO3-) in aquatic ecosystems.
- Carbon dioxide moves from the atmosphere or water into autotrophs by diffusion.
- Carbon dioxide is produced by respiration and diffuses out of organisms into water or the atmosphere.
- Methane (CH4) is produced from decaying organic matter in anaerobic conditions by bacteria
- Methane is oxidized to carbon dioxide and water in the atmosphere.
- Peat forms when organic matter is not fully decomposed in waterlogged soils.Organic matter was converted into coal, oil and gas that accumulate in porous rocks.
- Carbon dioxide is produced by the combustion of biomass and fossil fuels.
- Animals such as reef-building corals and mollusca have hard parts that are composed of calcium carbonate (CaCO3)and can become fossilized in limestone
- Students need an awareness that carbon fluxes are estimates
Skills (can you ....)
- Analyze data from air monitoring stations.
- Draw a diagram of the carbon cycle.
4.4 Climate change
- Details of the carbon cycle are assumed (from 4.3)
- In aquatic ecosystems carbon is present as dissolved carbon dioxide and hydrogen carbonate ions.
- Details of the Greenhouse effect are assumed.
- Carbon dioxide and water vapour are the most significant greenhouse gases.
- Other gases including methane and nitrogen oxides have less impact.
- The impact of a gas depends on its ability to absorb long wave radiation and its concentration in the atmosphere.
- Global temperatures and climate patterns are influenced by concentrations of greenhouse gases.
- There is a correlation between rising atmospheric concentrations of carbon dioxide since the start of the industrial revolution 200 years ago and average global temperatures.
- Recent increases in atmospheric carbon dioxide are largely due to increases in the combustion of fossilized organic matter.
Skills (can you ....)
- Apply understanding to the threat to coral reefs from increasing concentrations of dissolved carbon dioxide.
- Use correlations from data to justify your arguments.
- Evaluate claims that human activities are not causing climate change.
Carbon Cycle 4.3
The processes of the carbon cycle include photosynthesis and respiration. This topic gets tricky in other connected aspects of the global carbon cycle. These include storage of carbon containing molecules in peat, fossil fuels, coral, and the oceans.
Climate change 4.4
Greenhouse gases in the atmosphere, including water vapour, carbon dioxide, methane, and nitrogen oxide, absorb heat energy, keeping the Earth’s lower atmosphere warm. Through increased burning of fossil fuels humans are increasing climate change.
Energy flow 4.2
The transfer of energy within food webs. This topic is all about the way that energy from sunlight is trapped by photosynthesis and then passed from organism to organism in a food web.
Species and communities 4.1
Ecology is the study of the interconnections between living organisms and their environment. There is such a complex network of links in any location that ecologists have to break down and classify these relationships. That's the essence of this topic.