Sixth lecture

Trophic relationships

• Trophic level: how an organism gets its nutrition (energy).– All organisms at a particular trophic level are the

same number of transfer steps away from the energy input into the system

• Food Web: who eats whom in the ecosystem. Interconnected food chains

• Energy flows through ecosystems via trophic levels within the food web

Trophic Levels

• Primary producers: 1st trophic level-the autotrophs-capture sun energy (the initial energy source for almost all of earth’s ecosystems)

• Primary consumers: heterotrophs-herbivores (caterpillars, cows etc), feed on primary producers

• Secondary consumers: carnivores (birds, wolves etc), feed on primary consumers

• Tertiary consumers: carnivores that feed on other carnivores

Food chains

• A food chain represents the different links along which food is passed from one organism to another.

• AT each transfer a large proportion,80 to 90 %, of potential energy is lost as heat.

• Therefore, the number of steps “links” in a sequence is limited, usually to four or five.

Food chains

• Food chains are of two basic types:

1-The grazing food chain:

-It starts with green plants.

-The green plants serve as a source of food for herbivores,

-which in turn, are eaten by carnivores and for decomposers, which bring about decay in animals and plants.

Food chains

2-Detritus food chain,

- which goes from dead organic matter into

microorganisms.

-and then to detritus-feeding organisms (detritivores) and their predators

Aquatic food chain:

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Terrestrial food chain:

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Food Web

• Most organisms eat more the JUST one organism.

• When more organism are involved it is know as a food web.

• Food webs are more complex and involve lots of organisms.

Food webs

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