The function of an ecosystem is a broad, vast and complete dynamic system. It can be studied under the following three heads.
- Energy flow
- Nutrient cycling (biogeochemical cycles)
- Ecological succession or ecosystem development
ENERGY FLOW
- Energy is the basic force responsible for all metabolic activities. The flow of energy from producer to top consumers is called energy flow which is unidirectional.
- The study of Trophic level interaction in an ecosystem gives an idea about the energy flow through the ecosystem.
Trophic level interaction
- Trophic level interaction deals with how the members of an ecosystem are connected based on nutritional needs.
- Energy flows through the trophic levels: from producers to subsequent trophic levels. This energy always flows from lower (producer) to higher (herbivore, carnivore etc.) trophic level. It never flows in the reverse direction that is from carnivores to herbivores to producers.
- There is a loss of some energy in the form of unusable heat at each trophic level so that energy level decreases from the first trophic level upwards.
- As a result there are usually four or five trophic levels and seldom more than six as beyond that very little energy is left to support any organism. Trophic levels are numbered according to the steps an organism is away from the source of food or energy, that is the producer.
The trophic level interaction involves three concepts namely:-
- Food Chain
- Food Web
- Ecological Pyramids
FOOD CHAIN
- Organisms in the ecosystem are related to each other through feeding mechanism or trophic levels, i.e. one organism becomes food for the other.
- A sequence of organisms that feed on one another, form a food chain. A food chain starts with producers and ends with top carnivores.
- The sequence of eaten and being eaten, produces transfer of food energy and it is known as food chain. The plant converts solar energy into chemical energy by photosynthesis.
- Small herbivores consume the plant matter and convert them into animal matter. These herbivores are eaten by large carnivores.
Types of Food Chains
In nature, two main types of food chains have been distinguished:
Grazing food chain
The consumers which start the food chain, utilising the plant or plant part as their food, constitute the grazing food chain. This food chain begins from green plants at the base and the primary consumer is herbivore.
For example:
In terrestrial ecosystem, grass is eaten up by caterpillar, which is eaten by lizard and lizard is eaten by snake.
In Aquatic ecosystem phytoplankton’s (primary producers) is eaten by zoo planktons which is eaten by fishes and fishes are eaten by pelicans.
Detritus food chain
It starts from dead organic matter of decaying animals and plant bodies consumed by the micro-organisms and then to detritus feeding organism called detrivores or decomposer and to other predators.
The distinction between these two food chains is the source of energy for the first level consumers. In the grazing food chain the primary source of energy is living plant biomass while in the detritus food chain the source of energy is dead organic matter or detritus. The two food chains are linked. The initial energy source for detritus food chain is the waste materials and dead organic matter from the grazing food chain.
FOOD WEB
- A food chain represents only one part of the food or energy flow through an ecosystem and implies a simple, isolated relationship, which seldom occurs in the ecosystems.
- An ecosystem may consist of several interrelated food chains. More typically, the same food resource is part of more than one chain, especially when that resource is at the lower trophic levels.
- “A food web illustrates, all possible transfers of energy and nutrients among the organisms in an ecosystem, whereas a food chain traces only one pathway of the food”.
- If any of the intermediate food chain is removed, the succeeding links of the chain will be affected largely. The food web provides more than one alternative for food to most of the organisms in an ecosystem and therefore increases their chance of survival.
- For example, grasses may serve food for rabbit or grasshopper or goat or cow. Similarly a herbivore may be food source for many carnivorous species.
- Also food availability and preferences of food of the organisms may shift seasonally e.g. we eat watermelon in summer and peaches in the winter. Thus there are interconnected networks of feeding relationships that take the form of food webs.
