Concept of an Ecosystem
Living organisms cannot live isolated from their non-living environment because the latter provides materials and energy for the survival of the former i.e. there is an interaction between a biotic community and its environment to produce a stable system; a natural self-sufficient unit which is known as an ecosystem.
An ecosystem, therefore includes all of the living things (plants, animals and organisms) in a given area, interacting with each other, and also with their non-living environments (weather, earth, sun, soil, climate, atmosphere). A pond, lake, desert, grassland, meadow, forest etc. are common examples of ecosystems. Ecosystems are the foundations of the Biosphere and they determine the health of the entire earth system.
This very complex, but wonderful interaction of living things and their environment, has been the foundations of energy flow and recycling of carbon and nitrogen
Anytime a ‘stranger’ (living thing(s) or an external factor such as rise in temperature) is introduced to an ecosystem, it can be disastrous to that ecosystem. This is because the new organism (or factor) can distort the natural balance of the interaction and potentially harm or destroy the ecosystem.
Usually, biotic members of an ecosystem, together with their abiotic factors depend on each other. This means the absence of one member or one abiotic factor can affect all parties of the ecosystem.
Structure and Function of an Ecosystem
Each ecosystem has two main components:
(1) Abiotic Components:
The abiotic components of an ecosystem are all of the nonliving elements. They include the water, the air, the temperature and the rocks and minerals that make up the soil. Abiotic components of an ecosystem might include how much rain falls on it, whether it is fresh water or salt water, how much sun it gets or how often it freezes and thaws.
Abiotic components are mainly of two types:
(a) Climatic Factors:
Which include rain, temperature, light, wind, humidity etc.
(b) Edaphic Factors:
Which include soil, pH, topography minerals etc.?
The functions of important factors in abiotic components are given below:
Soils are much more complex than simple sediments. They contain a mixture of weathered rock fragments, highly altered soil mineral particles, organic matter, and living organisms. Soils provide nutrients, water, a home, and a structural growing medium for organisms. The vegetation found growing on top of a soil is closely linked to this component of an ecosystem through nutrient cycling.
The atmosphere provides organisms found within ecosystems with carbon dioxide for photosynthesis and oxygen for respiration. The processes of evaporation, transpiration and precipitation cycle water between the atmosphere and the Earth’s surface.
Solar radiation is used in ecosystems to heat the atmosphere and to evaporate and transpire water into the atmosphere. Sunlight is also necessary for photosynthesis. Photosynthesis provides the energy for plant growth and metabolism and the organic food for other forms of life.
Most living tissue is composed of a very high percentage of water, up to and even exceeding 90%. The protoplasm of a very few cells can survive if their water content drops below 10%, and most are killed if it is less than 30-50%.
Water is the medium by which mineral nutrients enter and are trans-located in plants. It is also necessary for the maintenance of leaf turgidity and is required for photosynthetic chemical reactions. Plants and animals receive their water from the Earth’s surface and soil. The original source of this water is precipitation from the atmosphere.
(2) Biotic Components:
The living organisms including plants, animals and micro-organisms (Bacteria and Fungi) that are present in an ecosystem form the biotic components. The biotic components of the ecosystem both live on and interact with the abiotic components.
On the basis of their role in the ecosystem the biotic components can be classified into three main groups:
(C) Decomposers or Reducers.
- Producers are the living organisms in the ecosystem that take in energy from sunlight and use it to transform carbon dioxide and oxygen into sugars.
- Plants, algae and photosynthetic bacteria are all examples of producers. As the green plants manufacture their own food they are known as Autotrophs (i.e. auto = self, trophos = feeder). Producers form the base of the food web and are generally the largest group in the ecosystem by weight, or biomass.
- They also act as an interface with the abiotic components of the ecosystem during nutrient cycles as they incorporate inorganic carbon and nitrogen from the atmosphere.
- The chemical energy stored by the producers is utilized partly by the producers for their own growth and survival and the remaining is stored in the plant parts for their future use.
- Consumers are living organisms in the ecosystem that get their energy from consuming other organisms. Conceptually, consumers are further subdivided by what they eat.
- Herbivores eat producers, carnivores eat other animals and omnivores eat both. Along with producers and decomposers, consumers are part of what is known as food chains and webs, where energy and nutrient transfer can be mapped out.
- Consumers can only harvest about 10 percent of the energy contained in what they eat, so there tends to be less biomass at each stage as you move up the food chain.
The consumers are of four types, namely:
(a) Primary Consumers or First-Order Consumers or Herbivores:
These are the animals which feed on plants or the producers. They are called herbivores. Examples are rabbit, deer, goat, cattle etc.
(b) Secondary Consumers or Second Order Consumers or Primary Carnivores:
The animals which feed on the herbivores are called the primary carnivores. Examples are cats, foxes, snakes etc.
(c) Tertiary Consumers or Third Order Consumers:
These are the large carnivores which feed on the secondary consumers. Example are Wolves.
(d) Quaternary Consumers or Fourth Order Consumers or Omnivores:
These are the largest carnivores which feed on the tertiary consumers and are not eaten up by any other animal. Examples are lions and tigers.
(C) Decomposers or Reducers:
- Decomposers are the living component of the ecosystem that breaks down waste material and dead organisms. Examples of decomposers include earthworms, dung beetles and many species of fungi and bacteria.
- The decomposers are known as Saprotrophs (i.e., sapros = rotten, trophos = feeder).
- They perform a vital recycling function, returning nutrients incorporated into dead organisms to the soil where plants can take them up again.
- In this process, they also harvest the last of the sunlight energy initially absorbed by producers. Decomposers represent the final step in many of the cyclical ecosystem processes.