Food Webs and Food Chains - Effects on Biodiversity

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How Does a Food Chain Work?

All plants and animals depend on another plant or animal to some degree for their survival as a species. Each food chain begins with some sort of plant and ends with an animal. Food webs and food chains are made up of producers, consumers, herbivores, carnivores, omnivores, and decomposers.

A food chain shows how energy and nutrients move through an ecosystem; in the process of eating or being eaten, energy flows from one level to another. Green plants use light energy from the sun to manufacture carbohydrates for food. What energy they don’t use is transferred to grazing herbivores. Carnivores prey on herbivores, who in turn are preyed upon by omnivores. At the final stage, whatever is left over is preyed up on by a decomposer. Usually there are only four or five levels in a food chain.

Food chains are a simple model and only show one pathway of energy and material transfer. Most animals need more then one source of food to survive.

Types of Food Chains & Food Webs

  • In one food chain, grass is a producer which is eaten by a grasshopper, considered a primary consumer. The grasshopper is eaten by a snake, considered a secondary consumer. The snake in turn is eaten by a hawk, a tertiary consumer. The hawks’ droppings are decomposed by fungi and converted back into energy which, when mixed with sunlight and water, can be used by grass and other microorganisms.

  • In a Marine food chain, Orcas – a species of whale eat seals, which eat squid. The squid eat fish, who in turn eat copepods or small crustaceans. Copepods feed on phytoplankton or algae which are the main producers in the food chain.

  • In African food chains, lions or other large predators eat zebra; who in turn eat grass and bushes. Lions or other cats also feed on giraffes who eat trees and leaves.

  • A food web takes the food chain idea from a single pathway to a complex network of interactions. In a food web animals usually have more than one food source. In a Marine food web, a polar bear might eat a seal or a whale might eat seals. Seals can eat artic cod, artic char or capelin but the same species of fish can also be eaten be artic birds or polar bears. Various species of zooplankton can eat phytoplankton which are eaten by fish species who are eaten by different seal species.

How is a Food Chain Affected by Biodiversity Loss?

All ecosystems depend upon a diverse group of species to survive. The greatest threat to biodiversity is the loss or fragmentation of natural habitat which accompanies overgrazing, deforestation, draining wetlands, and destroying coral reefs. Pollution also weakens habitat; oil spills, sewage, and pesticides effect oceans, air, soils, and freshwater ecosystems.

If an animal like the giant panda, oyster, cod, or elephant is overharvested or hunted to excess, it can become extinct or pushed to near extinction. The loss of an animal or plant from a food chain can effect the overall health of food chain and the balance of the ecosystem. In some cases it may push the ecosystem to diversify, but in most cases the loss of a plant or animal weakens an ecosystem.

Consumers play a vital role in controlling populations in a sustainable and balanced ecosystem, and their loss can skew entire populations one way or another. Likewise, depending on the selectiveness of the predators in a system, loss of producers can cripple an ecosystem, and being close to the base of the food chain or web tends to magnify the effects.