O Level Geography: Food Chains and Food Webs
- In any ecosystem, organisms are interdependent on each other for survival.
- A food chain is a series of organisms where each one is eaten by the next organism in the chain.
- A food web, on the other hand, is a complex system of interrelated food chains in an ecosystem.
- A food chain is a linear sequence of organisms through which energy and nutrients pass as one organism eats another.
- The transfer of energy occurs from the sun to plants (producers), which are then eaten by herbivores (primary consumers), which are eaten by carnivores (secondary consumers), and so on.
- The arrows in a food chain represent the transfer of energy and nutrients from one organism to another.
- For example, in a grassland ecosystem, the food chain can be represented as follows: Grass → Grasshopper → Rat → Snake → Hawk
- A food chain shows how energy is transferred from one organism to another through their feeding relationships.
- In a food chain, producers (plants) are eaten by primary consumers (herbivores), which are then eaten by secondary consumers (carnivores), which may be eaten by tertiary consumers (top carnivores).
- Each level of the food chain is called a trophic level.
- At each trophic level, only about 10% of the energy is passed on to the next level.
- The rest of the energy is lost as heat or used by the organism for its own life processes.
- Decomposers (e.g. bacteria and fungi) break down dead organisms and waste material, returning nutrients to the soil or water for the producers to use again.
- A food web is a network of food chains that shows how energy and nutrients are passed from one organism to another in an ecosystem.
- In a food web, organisms are connected to multiple other organisms through different food chains, and they can be both predators and prey at different times.
- This complex network of interrelationships helps to maintain the balance of nature in the ecosystem.
- For example, in a pond ecosystem, the food web can be represented as follows: Algae → Daphnia → Small Fish → Large Fish → Heron ↘ Insects → Frog → Snake → Raccoon
- In the above example, the daphnia feeds on algae and is eaten by small fish, which are then eaten by larger fish.
- The heron feeds on the larger fish, while insects feed on the algae and are eaten by frogs, which are then eaten by snakes and raccoons.
- A food web shows the complex feeding relationships among different organisms in an ecosystem.
- It consists of many interconnected food chains, with some organisms feeding on multiple levels of the web.
- This makes food webs more realistic representations of ecosystems than simple food chains.
- Some organisms in a food web play important roles as keystone species, which have a disproportionate impact on the ecosystem relative to their abundance.
- Removing a keystone species from an ecosystem can cause significant changes to the food web and other aspects of the ecosystem.
- Food webs can be affected by changes in the environment, such as the introduction of a new species or the removal of a key predator.
- In a food chain or web, each organism occupies a specific trophic level.
- The trophic level of an organism refers to its position in the food chain, and it is determined by what it eats and what eats it.
- Producers occupy the first trophic level, herbivores the second, and carnivores the third and higher trophic levels.
Energy Transfer and Loss
- As energy is transferred from one organism to another in a food chain or web, some energy is lost as heat at each trophic level.
- This means that only a fraction of the energy available at each trophic level is transferred to the next level.
- As a result, there are fewer organisms at higher trophic levels compared to lower trophic levels.
Human Impact on Food Chains and Food Webs
- Human activities such as deforestation, overfishing, and pollution can disrupt food chains and webs, leading to imbalances in the ecosystem.
- For example, removing a keystone species (a species that has a disproportionate effect on the ecosystem) from a food web can cause the collapse of the entire ecosystem.
- It is therefore important to understand and protect the delicate balance of nature in food chains and webs.
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