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Food chains

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• Producers form the first trophic level in a food chain.
• Because producers in ecosystems make their own carbon compounds by photosynthesis, they are at the start of food chains. Consumers obtain carbon compounds from producers or other consumers, so form the subsequent trophic levels.
• Consumers gain chemical energy from carbon (organic) compounds obtained from other organisms. Consumers have diverse strategies for obtaining energy-containing carbon compounds.
• Carbon compounds and the energy they contain are passed from one organism to the next in a food chain. The stages in a food chain are called trophic levels. </aside>

Temperate Woodland Food Chains

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A food chain shows a single pathway of energy flow through an ecosystem, from producer to top consumer. In reality, most organisms feed on more than one food source and are prey to more than one predator. When multiple food chains interconnect, they form a food web, which better represents the complexity of feeding relationships in a community.

The following information describes the feeding relationships in a British temperate woodland ecosystem.

Producers (Autotrophs)

Primary Consumers

Herbivores: Organisms that obtain energy by consuming plant material

Detritivores: Organisms that obtain energy by consuming dead organic matter (detritus)

Secondary Consumers

Predators: Organisms that hunt, kill, and consume other living organisms

Parasites: Organisms that live on or in a host organism, obtaining nutrients at the host's expense

Scavengers: Organisms that feed on dead animals (carrion) that they did not kill

Tertiary Consumers (Top Predators)

Saprotrophs and Decomposers

Saprotrophs: Organisms that secrete enzymes onto dead organic matter and absorb the digested products

Note: Saprotrophs are the main decomposers. Detritivores (earthworms, woodlice) aid decomposition by fragmenting material, increasing surface area for saprotrophs.

Example Food Chains

Grazing food chain (4 trophic levels):

Oak leaves → Caterpillar → Blue tit → Sparrowhawk

Detritus food chain (4 trophic levels):

Leaf litter → Earthworm → Blackbird → Tawny owl

Detritivore food chain (3 trophic levels):

Leaf litter → Slug → Hedgehog

These individual food chains interconnect to form the woodland food web.

1. Identify three producers from the temperate woodland ecosystem.
2. Why are producers always placed at the start of a food chain?
3. Explain why oak trees are classified as producers while caterpillars are classified as consumers.
4. Using the example food chain below, identify the trophic level of each organism:
5. Using one of the example food chains, describe how carbon compounds made initially by a producer end up in a tertiary consumer.
6. One of you states, "Consumers make their own food just like producers do." Explain why this statement is incorrect.
7. The earthworm is referred to by its scientific name, Lumbricus terrestris, above.

Energy losses

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