FOOD CHAIN AND FOOD WEB -DESCRIPTION OF THEIR ROLE AND IMPORTANCE FOR ECOSYSTEM

A food chain is a linear sequence that shows transfer of energy and nutrients from one organism to another. It depicts “who eats whom,” beginning with a producer, that can synthesize their own food and moves up to consumers.

However, there are difficulties if we try to describe the entire ecological feeding relationships using only food chain. Within an ecosystem, a consumer can eat more than one prey and be eaten by more than one consumer. Food chain alone cannot explain these interconnections. The interlinked network of feeding connections can be studied using food web.

A food web is a complex, interconnected network of multiple food chains that represents all the feeding relationships in an ecosystem. Food web provides a more realistic picture of the functioning feeding systems.

FOOD CHAIN

Food chain shows how energy is transferred in an ecosystem by consuming one another as an energy source in a linear fashion.

In a food chain, each organism occupies a specific position in the food chain which is known as trophic level.

The first trophic level at the base of food chain is occupied by producers. Producers are those organisms that are capable of synthesizing their own food. Most often these are organisms that perform photosynthesis like plants, algae or cyanobacteria.

The second trophic level belongs to primary consumers. Primary consumers feed on producers. For example, herbivores feeding on plants like goat, rabbit, cow.

Secondary consumers rank third in trophic level. Secondary consumers consume primary consumers. They are carnivores such as fish, hen.

At the fourth trophic level are tertiary consumers. They are carnivore eating carnivores. For example, lion, man, wolf, eagle.

The distinction between organisms of different trophic levels is not always clear cut. For instance, man can eat both plants and animals. So man can be primary, secondary or tertiary consumer depending on food habit.

Decomposers are organisms that consume dead and decaying matter. Examples include fungi, bacteria, earthworm, vulture. Decomposers break down complex organic matter into simpler inorganic substances by a process called decomposition. The level of decomposers runs parallel to various trophic levels. The nutrients released by decomposition can be used as raw material by primary producers. Thus decomposers play an important role in the energy recycling process.

Grazing food chain starts with living plants (producers). Whereas detritus food chain starts with dead organic matter like carcasses, animal waste and fallen leaves.

EXAMPLES OF FOOD CHAIN

• Wheat (producer) —– Rat (primary consumer) —– Crow (secondary consumer)
• Carrots (producer) —– Rabbit (primary consumer) —– Fox (secondary consumer) —– Lion (tertiary consumer)
• Algae (producer) —– Zooplankton (primary consumer) —– Fish (secondary consumer) —– Man (tertiary consumer)

FOOD WEB

Food web is the representation of all possible feeding interconnections between organisms in an ecosystem. It consists of overlapping food chains within an ecosystem.

It is a more realistic depiction of energy transfer in ecological system, since organisms do not necessarily occupy just a single trophic level. Same organism can act as primary or secondary or tertiary consumer depending on what they eat.

EXAMPLE OF FOOD WEB

ENERGY TRANSFER WITHIN AN ECOSYSTEM

• Energy gets transferred from one trophic level to next as one organism eats another.
• The transfer of energy across trophic levels follows the 10 percent law. Only 10 percent energy is passed on from previous to next trophic level. Rest 90 % is lost into the environment as heat and metabolic process and waste.
• This puts a restriction on the length of a grazing food chain.

ECOLOGICAL PYRAMID

An ecological pyramid is a diagram showing energy relationship between organisms at various trophic level. The relationship is expressed in terms of number, biomass or energy.

The base of pyramid represents producers or first trophic level. The apex represents top level consumer. Ecological pyramid is of three types: pyramid of number, pyramid of biomass and pyramid of energy.

PYRAMID OF NUMBERS

It displays the total number of individual organisms at each trophic level.

PYRAMID OF BIOMASS

Shows the total dry mass or living weight of organisms at each trophic level at any given time.

PYRAMID OF ENERGY

This model illustrates the total amount of energy present at each trophic level and and the rate at which it is transferred. Only 10 percent of energy is passed from one trophic level to next.

SIGNIFICANCE OF FOOD CHAIN AND FOOD WEB

• Food chains and food webs illustrate the manner in which nutrients and energy flow through an ecosystem.
• They depict the way nutrients are recycled back into the environment.
• Food chains and webs explain how natural balance is conserved in an ecosystem. They prevent any particular species from getting extinct or overly dominant. Predators eat herbivores so that overgrazing is kept in check and plants get protected.
• Food webs demonstrate interdependence and biodiversity. The complexity of a food web makes ecosystem resilient to environmental fluctuations, because organisms can feed on alternative food sources if population of one prey declines.