Trophic Levels & Food Chains (HL IB Environmental Systems & Societies (ESS))
Revision Note
Trophic Levels & Food Chains
What are trophic levels?
The trophic level is the position that an organism occupies in a food chain (or food web)
If multiple organisms occupy the same position in a food chain, they are in the same trophic level
Trophic Levels
Trophic Level | Name of Trophic Level | Description of Organisms in Trophic Level |
|---|---|---|
1 | Producers | Plants and algae—produce their own biomass using energy from sunlight |
2 | Primary consumers | Herbivores—feed on producers |
3 | Secondary consumers | Predators—feed on primary consumers |
4 | Tertiary consumers | Predators—feed on secondary consumers |
Producers are typically plants or algae and produce their own food using photosynthesis
They form the first trophic level in a food chain
The chemical energy stored in producers is then transferred to primary consumers as they consume (eat) producers
The chemical energy is then transferred from one consumer to the next as they eat one another
Consumers have diverse strategies for obtaining energy-containing carbon compounds
Consumer Strategies
Type of Consumer | Description | Examples |
|---|---|---|
Herbivores | Feed primarily on plants and plant-derived material | Deer: graze on grasses, leaves, and shrubs Rabbits: consume grasses, herbs, and vegetables |
Detritivores | Consume decomposing organic matter (detritus) and help break it down further | Earthworms: feed on decaying plant material and enhance soil structure Dung beetles: consume animal dung, aiding in nutrient recycling |
Predators | Hunt and consume other organisms (prey) for food | Lions: prey on various herbivores such as gazelles and zebras Wolves: hunt animals like deer and elk in packs |
Parasites | Depend on a host organism for survival, often harming but not immediately killing it | Tapeworms: live in the intestines of mammals, absorbing nutrients from the host's food Mosquitoes: feed on the blood of animals, including humans, for nourishment |
Saprotrophs and decomposers | Saprotrophs: decompose dead organic matter externally and absorb nutrients Decomposers: break down organic matter into simpler substances, playing a vital role in nutrient recycling | Fungi: break down dead plant material, such as fallen leaves and wood, into simpler compounds Bacteria: decompose organic matter, releasing nutrients for plant uptake |
Scavengers | Consume dead animal carcasses, helping to clean up ecosystems | Vultures: feed on the remains of dead animals, scavenging carrion Hyenas: opportunistic scavengers known to consume a wide range of animal remains |
Food chains
Feeding relationships in ecosystems can be modelled using food chains
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 are placed in the higher trophic levels
In a food chain, carbon compounds and the energy they contain are passed from primary producers to primary consumers to secondary consumers, and so on
Apex predators are at the very top of the food chain—they are carnivores or omnivores with no predators
The chemical energy stored within apex predators can be passed on to decomposers when apex predators die and are decomposed
Traditionally, decomposers are not included in food chains as they gain carbon compounds from a variety of trophic levels
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