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• Biomass - the total amount of living tissue within a given trophic level• 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.

• Food Web - kiddy games but still very useful

Build your own ecosystem - this is complex and for advanced users

FOOD CHAIN• Food Chain - series of steps

in an ecosystem in which organisms transfer energy by eating and being eaten.

FOOD WEB

• Food Web - network of complex interactions formed by the feeding relationships among the various organisms in an ecosystem

FOOD PYRAMIDa diagram that depicts the energy flow in an ecosystem. Producers are on the bottom while consumers are on the higher levels of the pyramid - a model that shows the loss of energy from one trophic level to another.