Ecology
Food Chain
Linear energy transfer from producers through consumers — base of food webs
A food chain is a linear sequence of organisms through which nutrients and energy pass — each organism eats the one below and is eaten by the one above. Levels (trophic levels): (1) Producers (plants, algae) — convert sunlight to chemical energy. (2) Primary consumers (herbivores). (3) Secondary consumers (carnivores eating herbivores). (4) Tertiary consumers (top predators). Plus decomposers. Reality: food webs (interconnected chains). 10% rule: ~10% of energy passes between trophic levels. Top predators rare due to energy losses. Important for: ecosystem dynamics, biomagnification of toxins.
- DefinitionLinear energy/nutrient flow between organisms
- ProducersPlants, algae (photosynthesis)
- Primary consumersHerbivores
- Secondary consumersCarnivores eating herbivores
- 10% rule~10% of energy transfers between levels
- DecomposersBacteria, fungi (recycle nutrients)
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Why food chains matter
- Ecology. Foundation of ecosystem understanding.
- Conservation. Protecting key species.
- Pollution. Biomagnification.
- Agriculture. Pest control, IPM.
- Climate change. Disruption of trophic relationships.
- Fisheries. Sustainable harvesting.
- Education. Foundational ecology concept.
Common misconceptions
- Linear chains in nature. Webs are normal.
- Predators control prey. Often opposite (food limits predators).
- Energy increases up chain. Decreases (10% rule).
- All top predators apex. Multiple apex types per ecosystem.
- Decomposers separate from chain. Integral; recycle nutrients.
- Chains stable. Disruptions can cascade.
Frequently asked questions
What are trophic levels?
Position in food chain. (1) Producers (autotrophs) — plants, algae, photosynthetic bacteria. Convert solar energy. (2) Primary consumers (herbivores) — eat producers. (3) Secondary consumers (primary carnivores) — eat herbivores. (4) Tertiary consumers (apex predators) — eat carnivores. (5) Decomposers — break down dead organisms; not a separate level but recycle to producers. Most food chains: 4-5 levels.
What's the 10% rule?
Only ~10% of energy at one trophic level transfers to next. Other 90% lost as: heat (metabolism), waste, uneaten parts. Implication: each level supports much less biomass. 10,000 plants → 1000 herbivores → 100 carnivores → 10 top predators (rough). Why top predators rare; long food chains harder. Lindeman 1942 quantified.
What's a food web?
Interconnected food chains. More realistic than simple chain. Most consumers eat multiple species; multiple consumers eat same species. Example: fox eats rabbits AND mice; rabbits eaten by fox AND owl AND hawk. Webs are robust to changes (multiple paths); chains are vulnerable. Real ecosystems: complex webs, not simple chains.
What's biomagnification?
Concentration of pollutants up food chain. Each level eats many of previous; pollutant accumulates. Mercury in fish: small fish slightly contaminated; larger fish eat many small → more mercury; tuna eat many → very high. Top predators (humans) get high doses. Examples: DDT, PCBs, heavy metals. Drives many environmental concerns; banned chemicals due to biomagnification.
What about decomposers?
Bacteria and fungi that break down dead organisms. Return nutrients to soil/water; producers can use again. Critical for ecosystem function. Without decomposers: nutrients locked up in corpses; producers die from lack of nutrients. Detritivores (insects, worms): eat dead matter, produce simpler material that bacteria/fungi process.
Why don't food chains have more levels?
Energy losses (10% rule). Each level loses 90%; after 4-5 levels, very little remains. Top predator on level 5: 10⁻⁵ of original solar energy. Below sustenance threshold. Aquatic food chains can be longer than terrestrial (more efficient transfer in water). Anomalies: deep ocean (lower productivity, shorter chains).
How does climate affect food chains?
Many ways. (1) Disrupting timing: pollinators don't match flower timing → pollination fails. (2) Range shifts: species move to cooler areas; some can't keep up. (3) Trophic cascades: if predator disappears, herbivores explode, plants decline. (4) Bleaching of corals: loss of zooxanthellae symbionts. (5) Altered productivity: shifted growing seasons. Climate change disrupts food chains broadly.