Life on the earth is found almost everywhere. Living organisms are found
from the poles to the equator, from the bottom of the sea to several km in the
air, from freezing waters to dry valleys, from under the sea to underground water
lying below the earth’s surface. The biosphere and its components are very
significant elements of the environment. These elements interact with other components of the natural landscape such as land, water, and soil. They are also influenced by atmospheric elements such as temperature, rainfall, moisture, and sunlight. The
interactions of the biosphere with land, air, and water are important to the growth, development and evolution of the organism.
The term ecology is derived from the Greek word ‘oikos’ meaning ‘house’, combined with the word ‘logy’ meaning the ‘science of’ or ‘the study of ’. Literally, ecology is the study of the earth as a ‘household’, of plants, human beings, animals, and micro-organisms. They all live together as interdependent components. A German zoologist Ernst Haeckel, who used the term ‘oekologie’ in 1869, became the first person to use the term ‘ecology’. The study of interactions between life forms (biotic) and the physical environment (abiotic) is the science of ecology. Hence, ecology can be defined as a scientific study of the interactions of organisms with their physical environment and with each other.
Types of Ecosystems
Ecosystems are of two major types: terrestrial and aquatic. The terrestrial ecosystems can be further be classified into ‘biomes’. A biome is a plant and animal community that covers a large geographical area. The boundaries of different biomes on land are determined mainly by climate. Therefore, a biome can be defined as the total assemblage of plant and animal species. interacting within specific conditions. These include rainfall, temperature, humidity, and soil conditions. Some of the major biomes of the world are forest, grassland, desert, and tundra biomes. Aquatic ecosystems can be classed as marine and freshwater ecosystems. The marine ecosystem includes the oceans, estuaries, and coral reefs. The freshwater ecosystem includes lakes, ponds, streams, marshes, and bogs.
Structure and Functions of Ecosystems
The structure of an ecosystem involves a description of the available plant and animal species. From a structural point of view, all ecosystems consist of abiotic and biotic factors. Abiotic factors include rainfall, temperature, sunlight, atmospheric humidity, soil conditions,
inorganic substances (carbon dioxide, water, nitrogen, calcium, phosphorus, potassium, etc.). Biotic factors include the producers, the consumers (primary, secondary, tertiary), and the decomposers. The producers include all the green plants, which manufacture their own food through photosynthesis. The primary consumers include herbivorous animals like deer, goats, mice, and all plant-eating animals. The carnivores include all the flesh-eating animals like snakes, tigers and lions. Certain carnivores that feed also on carnivores are known as top carnivores like hawks and mongooses. Decomposers are those that feed on dead organisms (for example, scavengers like vultures and crows), and further breaking down of the dead matter by other decomposing agents like bacteria and various microorganisms.
The producers are consumed by the primary consumers whereas the primary consumers are, in turn, being eaten by the secondary consumers. Further, the secondary consumers are consumed by the tertiary consumers. The decomposers feed on the dead at each and every level. They change them into various substances such as nutrients, organic and inorganic salts essential for soil fertility. Organisms of an ecosystem are linked together through a food chain. For example, a plant-eating beetle feeding on a paddy stalk is eaten by a frog, which is, in turn, eaten by a snake, which is then consumed by a hawk. This sequence of eating and being eaten and the resultant transfer of energy from one level to another is known as the food-chain.
The Nitrogen Cycle
Nitrogen is a major constituent of the atmosphere comprising about seventy-eight percent of the atmospheric gases. It is also an essential constituent of different organic compounds such as amino acids, nucleic acids, proteins, vitamins, and pigments. Only a few types of organisms like certain species of soil bacteria and blue-green algae are capable of utilizing it directly in its gaseous form. atmosphere through transpiration and respiration processes of plants. Nitrogen is a major constituent of the atmosphere comprising about seventy-eight percent of the atmospheric gases. It is also an essential constituent of different organic compounds such as amino acids, nucleic acids, proteins, vitamins, and pigments. Only a few types of organisms like certain species of soil bacteria and blue-green algae are capable of utilizing it directly in its gaseous form. Generally, nitrogen is usable only after it is fixed. Ninety percent of fixed nitrogen is biological. The principal source of free nitrogen is the action of soil micro-organisms and associated plant roots on atmospheric nitrogen found in pore spaces of the soil. Nitrogen can also be fixed in the atmosphere by lightning and cosmic radiation. In the oceans, some marine animals can fix it. After atmospheric nitrogen has been fixed into an available form, green plants can assimilate it. Herbivorous animals feeding on plants, in turn, consume some of it. Dead plants and animals, excretion of nitrogenous wastes are converted into nitrites by the action of bacteria present in the soil.
Other Mineral Cycles
Other than carbon, oxygen, nitrogen, and hydrogen being the principal geochemical components of the biosphere, many other minerals also occur as critical nutrients for plant and animal life. These mineral elements required by living organisms are obtained initially from inorganic sources such as phosphorus, sulfur, calcium, and potassium. They usually occur as salts dissolved in soil water or lakes, streams, and seas. Mineral salts come directly from the earth’s crust by weathering where the soluble salts enter the water cycle, eventually reaching the sea. Other salts are returned to the earth’s surface through sedimentation, and after weathering, they again enter the cycle. All living organisms fulfill their mineral requirements from mineral solutions in their environments. Other animals receive their mineral needs from the plants and animals they consume. After the death of living organisms, the minerals are returned to the soil and water through decomposition and flow. change in the species distribution. This change is due to competition where the secondary forest species such as grasses, bamboos or pines overtakes the native species changing the original fo