EcoSys Session 02

Modelling the internal dynamics of the ecosystem

Vocabulary: Ecosystem, Energy source, Heat Sink, Storage, Autotrophs/Producers, Heterotrophs/Consumers



Ref: Odum (1997) Chapter 3: The Ecosystem

Sir Arthur Tansley (1871-1955) was an english botantist, who in 1935, coined the term 'ecosystem' for the biotic and abiotic components that made a whole.

The key concept, in his own words, is “the idea of progress towards equilibrium, which is never, perhaps, completely attained, but to which approximation is made whenever the factors at work are constant and stable for long enough period of time”.

After his death this term came into general use, and now is part of everyday language, applied to many different contexts (technology, software)

Recent development of term … Ecosystem management: set up from trying to deal with the components seperately, to managing the system as a whole.
Energy is a necessary input. The sun is the ultimate energy source for the biosphere and directly supports most natural ecosystems.

Other energy sources may be important for many ecosystems, for example, wind, rain, water flow, fuel.

Energy also flows out of the system in the form of heat and in other transformed or processed forms such as organic matter (for example food and waste products) and pollutants.

Water, air, and nutrients necessary for life, along with all kinds of other materials, constantly enter and leave the ecosystem.

And organisms and their popagules (seeds and reproductive stages) enter (immigrate) and leave (emigrate) the ecosystem.


Ecosystems have 2 major biotic components.

Autotrophic: (self-norishing) component, able to fix light energy and manufacture food from simple inorganic substances (eg water, carbon-dioxide, nitrates) by the process of photosynthesis. Green plants on land, algae and water plants are these. “upper green belt”

These organisms may be thought of as producers.


Heterotrophic: (other-nourishing) component which utilises, rearranges, and decomposes the complex materials synthesised by the autotrophs. Fungi, non-photosynthetic bacteria, micro-organisms, animals , including humans, are these. “brown belt” of soil and sediment below the green canopy.

These organisms may be thought of as consumers, as they are unable to produce their own food and must be able to obtain it by consuming other organisms.


When Autotrophic and Heterotrophic organisms are linked together in a network of energy transfers, it is called a food web.

Herbivores (plant eaters), Carnevores (feed on other animals), Omnivores (feed on plants and animals) and Saprovores (feed on decaying organisms such as fungi and microrganisms)


Energy Language Symbols

“Energy language symbols” developed by H. T Odum (1971) represent renewable energy sources:

Circle: Energy source
downward arrow and earth: Heat sink: drains out degraded energy after its use in work
Rounded-rectangle: Producer: converts and concentrates solar energy; self-maintaining
Hexagon: Consumer: uses converted energy; self-maintaining)
Tri-circle: Storage
Chevron: Interaction: Two or more flows interact to produce a higher-quality energy



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Introducing Jane Jacob's 'The Nature of Economies'


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