Ch 4

• • 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 have either an autotrophic or heterotrophic method of nutrition (a few species have both methods).
• • 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 formed by populations of different species living together and interacting with each other.
• • A community forms an ecosystem by 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
• • Skill: Classifying species as autotrophs, consumers, detritivores or saprotrophs from a knowledge of their mode of nutrition.
• • Skill: Setting up sealed mesocosms to try to establish sustainability.

  autotrophs for nutrient cycle, sun as a source of energy for photosynthesis
• • Skill: Testing for association between two species using the chi-squared test with data obtained by quadrat sampling.
• • Skill: Recognizing and interpreting statistical significance
• • Mesocosms can be set up in open tanks, but 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
• • Most ecosystems rely on a supply of energy from sunlight.
• • Light energy is converted to chemical energy in carbon compounds by photosynthesis.
• • 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 converted to heat.
• • Living organisms cannot convert heat to other forms of energy
• • Heat is lost from ecosystems.
• • Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels.
• Skill: Quantitative representations of 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 and so on.
• • The distinction between energy flow in ecosystems and cycling of inorganic nutrients should be stressed. Students should understand that there is a continuous but variable supply of energy in the form of sunlight but that the supply of nutrients in an ecosystem is finite and limited.
• • Autotrophs convert carbon dioxide into carbohydrates and other carbon compounds.
• • In aquatic ecosystems carbon is present as dissolved carbon dioxide and hydrogen carbonate ions.
• • Carbon dioxide diffuses from the atmosphere or water into autotrophs
• • Carbon dioxide is produced by respiration and diffuses out of organisms into water or the atmosphere.
• • Methane is produced from organic matter in anaerobic conditions by methanogenic archaeans and some diffuses into the atmosphere or accumulates in the ground.
• • Methane is oxidized to carbon dioxide and water in the atmosphere.
• • Peat forms when organic matter is not fully decomposed because of acidic and/or anaerobic conditions in waterlogged soils.
• • Partially decomposed organic matter from past geological eras was converted either into coal or into oil and gas that accumulate in porous rocks.
• • Carbon dioxide is produced by the combustion of biomass and fossilized organic matter.
• • Animals such as reef-building corals and mollusca have hard parts that are composed of calcium carbonate and can become fossilized in limestone.
• • Application: Estimation of carbon fluxes due to processes in the carbon cycle
• • Application: Analysis of data from air monitoring stations to explain annual fluctuations.
• • Skill: Construct a diagram of the carbon cycle.
• Carbon fluxes should be measured in gigatonnes