Ecosystem Dynamics Chapter 8 page 189
Organisms and energy • All organisms are energy converters – they take in energy and use it to carry out body functions. This energy transfer is very inefficient with a lot of energy being lost as heat. • Autotrophs - convert light energy into chemical energy via photosynthesis (all plants can do this). • Heterotrophs – depend on energy from the food they consume.
Energy in Ecosystems • The majority of energy that sustains life on the planet comes directly from the sun. The total amount of energy ‘fixed’ on the planet sets the limit on the total amount of life possible at any one time.
Food Chains • The path that food takes from one organism to another is called a Food Chain – Producer (autotroph) then up through a range of consumers. • This chain includes three broad groups – producers, consumers and decomposers • Copy Fig 8 p 189 • Trophic - feeding
Producers • Producers convert simple inorganic chemicals such as carbon, oxygen, hydrogen and nitrogen (and many others) into complex organic (carbon based) molecules – food. Most use solar radiation to fuel this process, but some do use the chemical bonds in other inorganic molecules – eg chemotrophs on sub-marine volcanic vents. • Productivity is affected by the environment – temperature, sunlight, availability of chemicals all affect the photosynthetic efficiency of the producer. • The Gross primary production is the total amount of organic matter in an ecosystem whereas, • The amount of energy available for herbivores is term the Net primary productions
Consumers • Consumers use the food (energy) produced by the autotrophs to fuel their body functions. • First order consumers are herbivores – eat plant material. • Second order consumers are carnivores – eat herbivores • Third order consumers (and above) are carnivores – eat other carnivores – this may included predators, parasites or scavengers • Omnivores – occupy multiple layers simultaneously • Copy the Fig 8.2 p 190 – reached here
Decomposers • Decomposers are simple life forms – bacteria, fungi and some protozoans – they have external digestion and breakdown dead bodies into more simple chemicals that can be re-used.
Energy in Food Chains • There are rarely more than 6 links (levels) in any food chain. • Generally only 5-20% of energy is effectively transferred from one level to the next – we assume around 10% as the average. • Energy transfer efficiency Grass mouse snake kookaburra 100 10 1 0.1 All of the heat lost in each process radiates back to space and is permanently lost – energy is not re-cycled in an ecosystem.
Food webs • A food chain is a simplified view of the feeding relationships in an ecosystem • A food web represents the complex interactions of organisms in an ecosystem – a variety of plants (producers) will have a range of herbivores feeding on them, with a complex assortment of carnivores, predators, parasites and scavengers and many decomposers. • A food web is a more stable system then an simple food chain as there are usually alternative food sources available in all conditions.