Food Chain and Food Web: Difference, Types

Key Concepts

• Food Chain
• Food Web
• Producers
• Consumers – types
• Decomposers

Introduction: 

An ecosystem is a community of living organisms in a particular geographic area. It is composed of biotic (living) and abiotic components (non-living).  All living organisms in an ecosystem are dependent on each other either directly or indirectly.   

Abiotic components: 

Abiotic components of an ecosystem refers to the non-living components of an ecosystem. It includes chemical and physical components such as water, air, solar energy, minerals and nutrients of soil and various organic compounds present in the environment. These abiotic components have a direct impact on the living organisms of the ecosystem.  

Biotic components: 

Biotic components of an ecosystem refers to all living organisms present in that ecosystem. It includes plants, animals, and micro organisms such as bacteria and fungi. Biotic components of an ecosystem can be classified into different types. 

Biotic Components of Ecosystem: 

Producers: 

Solar energy is a major source of energy in an ecosystem. Plants are the producers of an ecosystem. Green plants make use of the chlorophyll pigment to trap the solar energy and undergo the process of photosynthesis. With the use of solar energy and inorganic compounds, plants manufacture their own food. Hence, plants are known as autotrophs (auto – self ; trophos- feeder). 

Consumers:  

Animals do not have the ability to synthesize their own food. Therefore they depend on the producers for their food. They are known as heterotrophs (heteros – other; trophos- feeder). Consumers are of five types which are as follows:  

1. Primary Consumers 

Primary consumers are animals that feed on plants or producers. They are also known as herbivores or first order consumers.  

Example: Rabbit, deer, goat, cattle etc. 

2. Secondary Consumers 

Secondary consumers are animals that feed on herbivores. They are also known as primary carnivores or second order consumers.  

Example: Cats, foxes, snakes etc. 

3. Tertiary Consumers 

Tertiary carnivores are animals that feed on secondary consumers. They are also known as secondary consumers or third order consumers. 

Example: Wolves 

4. Quaternary Consumers 

Quarternary consumers are the largest consumers that feed on tertiary consumers. They are also known as fourth order consumers or apex predators. These animals are the top predators and they do not have any predators in the ecosystem. 

Example: Lion, tiger 

5. Omnivores 

Omnivores are animals that feed on both plants and animals. As these animals consume a wide variety of food sources, they are also known as ‘all-eaters’. 

Example: Pigs, dogs, chimpanzees 

Decomposers:  

Decomposers are also known as saprotrophs (sapros – rotten; trophos- feeder). Bacteria and fungi belong to this category. They feed on dead organic materials of producers and consumers. As a result of metabolism they release simple organic and inorganic substances into the environment. These substances are reused by the producers thereby resulting in a cyclic exchange of materials between the biotic and abiotic components of the ecosystem. 

Food Chain: 

In an ecosystem, flow of energy is unidirectional whereas nutrient movement is cyclic. Food chain refers to the order of eating or energy transfer in an ecosystem. Food chain is the arrangement of different biotic groups in a sequence of energy transfer. In other words, food chain refers to the sequence of living organisms in a community in which one organism consumes another organism to transfer food energy. 

Trophic Levels of Food Chain: 

Trophic levels of food chains refer to various steps in the food chain at which transfer of food or energy takes place. In other words, trophic level refers to the position of organisms along a food chain. In a food chain each organism obtains energy from one level below it.

A food chain consists of four or five trophic levels.  The first trophic level is composed of plants, the producers. The herbivores or primary consumers form the second trophic level. Carnivores or secondary consumers constitute the third trophic level.  Large carnivores or the tertiary consumers which feed upon the small carnivores constitute the fourth trophic level.  

Types of Food Chain: 

Grazing Food Chains: 

Grazing food chain is the most common type of food chain which begins from green plants. Sun is the primary source of energy in this food chain. Plants make use of solar energy and prepare their own food by photosynthesis. Herbivores are the primary consumers of this food chain. Grazing food chain could be classified into two types,  

1. Predatory Food Chain:  

In this type of food chain one animal consumes another animal. In simple terms, a plant eating animal is eaten by a flesh-eating animal. The animal that is being eaten is known as prey. A predator is the animal that hunts and feeds on its prey. All carnivores are predators. Herbivores, some omnivores, or other carnivores are their prey.  

Example: Snake is a predator to mouse but a prey to hawk. 

2. Parasitic Food Chain:  

This type of food chain starts from herbivores and the energy is transferred from large organisms to smaller organisms. Here, parasites infect plants and animals.  

Example: Herbivores consume producers. Parasites infect herbivores. Hyperparasites consume parasites. 

Detritus Food Chains:  

The food chain that starts from dead organic matter is termed as detritus food chain. Decomposers / detrivores are at the first trophic level. These food chains are less dependent on direct solar energy. Energy for the food chain comes from organic wastes or dead matter which are termed as detritus. A large amount of energy flows through the detritus food chain as compared to grazing food chain. Inorganic nutrients bound to organic matter are released through this food chain. Detritus food chains ensure maximum utilization and minimum wastage of the available material. Organisms of detritus food chain includes bacteria, fungi, algae, protozoa, insects, nematodes etc. 

Food Web: 

Food web is defined as the network of food chains which are interconnected at various trophic levels. These interconnected food chains form a number of feeding connections among different organisms of a biotic community. Food web are also known as consumer – resource system. Food webs represent the feeding relationships between species in a community. Food webs serve as important tools to analyze energy flow in an ecosystem. They also help to understand the predator- prey relationship.  

Complexity of Food Webs: 

The diversity of organisms in an ecosystem determines the complexity of food webs. Two important factors determine the complexity of food webs. 

1. Length of food chain 

2. Alternatives at different trophic levels 

Length of food chain: Diversity of organisms and their food habits in an ecosystem determine the length of food chain. More diverse organisms and their food habits make the food chain to be longer. 

Alternatives at different trophic levels: More number of alternatives at different trophic levels of a food chain increases the complexity of food webs. Increase in the number of alternatives also increases the interlocking pattern of the food web. For example, the presence of a wide variety of organisms in deep sea and oceans make these aquatic food webs more complex.  

Types of food web: 

Food web shows the relationship between species in an ecosystem. These interrelationships vary based on energy flow and dynamics of species populations. Food webs are classified into different types namely,  

1. Connectedness food webs 

2. Energy flow food webs 

3. Functional / interaction food webs 

Connectedness Food Webs: 

These food webs are also known as topological food webs. They indicate a feeding relationship. These food webs indicate only the presence or absence of a trophic interaction. They do not show the strength of the interaction or changes taking place in the trophic relationships. Hence, these food webs are also known as static food webs. 

Energy Flow Food Webs: 

These food webs indicate information about the strength of feeding interactions. They indicate the quantity of energy flow from one species to another. The strength of relationship between species is indicated by the thickness of arrow.   

Functional or Interaction food webs: 

These food webs show the influence of one group of species over the other. They represent the significance of each species in maintaining communal integrity. 

Significance of food chains and food webs: 

• Food chain and food web help to understand the feeding relationship between organisms in an ecosystem. 

• Food chains and food web provide a clear understanding about nutrient cycling and energy flow in an ecosystem. 
• Food chains help to check the population size of different organisms in an ecosystem.  
• Example: In a grassland ecosystem, if there is an increase in the deer population, food availability will be more for the carnivores which feed on them. Similarly, if there is a reduction in the deer population, some carnivores would starve and die. As a consequence, deer population would increase. 
• Food webs help to understand the natural stability of an ecosystem. If one species gets affected, it provides an impact on the subsequent trophic levels. 
• Food chains and food webs help to understand the natural balance about the population of each species in an ecosystem. 

Summary

• An ecosystem is composed of biotic (living) and abiotic components (non-living)
• Biotic components of an ecosystem refers to all living organisms present in that ecosystem including plants, animals, and micro organisms such as bacteria and fungt
• Blotic components of an ecosystem can be classified into different types – producers, consumers, and decomposers.
• Plants are the producers of an ecosystem. They make use of solar energy to produce
• food.
• Animals that do not have the ability to synthesize their food are known as consumers. Consumers are classified into five different types – primary, secondary, tertiary and quarternary consumers, omnivores.
• Decomposers feed on dead organic materials of producers and consumers. As a result of metabolism they release simple organic and inorganic substances into the environment.
• Food chain refers to the sequence of living organisms in a community in which one
• organism consumes another organism to transfer food energy.
• A food chain consists of four or five trophic levels.
• Food chains are classified into different types – grazing food chains, predatory food chains, parasitic food chain and detritus food chains.
• Food web is defined as the network of food chains that are interconnected at various trophic levels.
• Food webs are classified into different types namely, connectedness food webs, energy flow food webs, functional/interaction food webs.
• Food chain and food web help to understand the feeding relationship between
• organisms in an ecosystem. Food chains and food web provide a clear understanding about nutrient cycling and energy flow in an ecosystem.
• Food chains and food webs help to understand the natural stability and balance in the population of each species in an ecosystem.