The term environment means the surroundings of an organism. It includes both living and non-living components. Man and other living organisms are surrounded by non-living components such as land, air, atmosphere, water, and by living components like plants and animals, further, the environment includes the pollutants, and other factors that adversely affect our life. Environment, therefore, refers to the sum total of all the forces, materials and influences around us at a given point of time and place.
Environmental Science is the application of knowledge from many disciplines to the study and management of the environment. Ecology is a section of Environmental Science.
Ecology is the scientific study of plants and animals in relation to each other and to their environment. A German biologist, Hanns Reiter (1868), introduced the term 'ecology' (Oekologie) by combining two Greek words-Oikos (house) and logos (study of).
A year later, a German zoologist Ernst Haeckel (1869), defined ecology a s the investigation of the total relations of the animal to its inorganic and organic environment.
Ecology and environmental science
Ecology deals with the processes that limit life, interactions of living things and their use of resources. Environmental Science is the application of knowledge from many disciplines for the study and management of the environment. Ecology is one of the disciplines of environmental science.
The term ecosystem was coined by Sir Arthur Tansley in 1935. According to Fitzpatric, a group of organisms interacting among them and with environment is known as Ecosystem. Ecosystem is essentially a technical term for 'nature'. Ecosystem is a self-regulating and self-sustaining structural and functional unit of biosphere. This system depends upon the sun for its energy.
Ecosystems can be small or large and are placed in nature contiguously. There is an exchange of materials and energy within the ecosystem as well as between adjoining ecosystems. They are all interconnected and hence, interrelated. The vast network of all interconnected ecosystems constitutes the biosphere.
Organism: It refers to the organisms of the same species that are in proximity to one another, e.g., a group of rabbits.
Population: It refers to the organisms of the same species that are in proximity to one another, e.g., a group of rabbits.
Community: It includes all the populations occupying a given area. The size of a community depends on our scale of reference. We might use community to refer to all of the living things in a particular area like a pond or we might restrict our interest to the fish community or the plant community.
The community and the non-living environment together are referred to as an ecological system or ecosystem, e.g., a pond with fish and plants.
Biome: It refers to a large regional or sub continental ecosystem characterized by a major vegetation type or other identifying landscape aspects. For example, a grassland biome implies many ecosystems that are similar because grasses are their principal plants and grazers are their predominant animals.
The biosphere or ecosphere includes all the living organisms on the earth interacting with physical environment as a whole to maintain the system in a balanced state.
Components of an ecosystem
An ecosystem has two basic components:
These are the non-living components that affect the distribution, number, metabolism and behavior of organisms in an ecosystem. These include:
- Inorganic substances like carbon, nitrogen, oxygen and water.
- Dead organic matter containing proteins, carbohydrates, lipids, humid substances, etc.
- Climatic factors
- Atmospheric factors like temperature, moisture, sunlight.
- Edaphic factors such as soil texture and topography.
These include the living components of the ecosystem that interact with the non-living components. They are: producers and consumers.
Producers: They are autotrophic or self-nourishing. They are chlorophyll-bearing organisms, which produce their own food by fixing solar energy in the presence of Abiotic substances.
Consumers: They are heterotrophic or those feeding on other organisms. They derive their nutrition by feeding on other living organisms. A consumer which derives nutrition by eating plants is called primary consumer or herbivore (e.g., grazing cattle). The secondary consumer or carnivore is an animal that gets its nutrition by eating the flesh of herbivores or other animals. The organism which can feed on both plants and animals is called an omnivore (cockroaches, fox, human beings, etc).
Decomposers or saprotrophs: The word sapro means to decompose. These are other heterotrophic organisms, consisting mostly of bacteria and fungi which live on dead organic matter or detritus. In terrestrial ecosystem bacteria generally act on animal tissue; and fungi on plants. Decomposers do not ingest their food. Instead, they digest the dead tissue through enzyme secretion on it, thereby releasing basic elements of living organisms into the environment to be reused by reused by the producers. There is a constant interaction between Abiotic and biotic components of the ecosystem resulting in the transfer of food and energy, which makes it a dynamic but stable system.
Types of Ecosystem
Ecosystem is a self-regulating and self-sustaining structural and functional unit of biosphere. Living organisms cannot live in isolation from their non-living environment. This is because the non-living environment provides materials and energy for the survival of the living organisms. The community with all the plants and animals forms the living or biotic component. The organic and inorganic substances together with climatic factors constitute the non-living or abiotic component of the ecosystem. Therefore, an ecosystem is a natural functional unit comprising living organisms (biotic community0 and their non-living (Abiotic community) environment that interact with each other to form a stable self-supporting system. A pond, lake, desert, grassland, meadow, forests, etc. are common examples of ecosystems.
There are two types of ecosystems:
- Natural ecosystem: They are self-regulating systems without much direct human interferences and manipulations. For example, ecosystems existing in pond,lake,river,stream,spring,sea,ocean,forest,grassland,desert,etc.
Based upon the particular kind of habitat, the natural ecosystems are further categorized into terrestrial and aquatic. Terrestrial ecosystems include forests, grasslands and deserts. Aquatic ecosystems can be either freshwater (ponds, lakes, streams), or salt water (marine, estuaries) type.
- Artificial ecosystems: They are man-made. Human activities modify or convert natural ecosystems into man-made ecosystems. For example, natural forests are cut and the land is used for tree plantations or agricultural systems. Other examples of artificial ecosystems include gardens, parks and aquaria. In these ecosystems, man manipulates the physio-chemical environment for his own benefit.
Terrestrial or land-based ecosystems
Terrestrial ecosystems are governed by yearly differences of temperature, rainfall, soil condition, availability of nutrients and of sunlight and many other Abiotic as well as biotic factors of the environment.
The land-based ecosystems are of different types.
- Forest Ecosystem
- Grassland Ecosystem
- Desert Ecosystem.
A forest ecosystem is characterized by densely growing trees having closed canopy cover. These are usually found in regions where there is plenty of rainfall. Depending on the climate type, there are a wide variety of forest types like tropical rain forests, tropical deciduous forests and temperate evergreen forests.
Features of forest ecosystems:
- The forest ecosystem comprises complex collection of different kinds of biotic communities.
- Optimum conditions of temperature and ground moisture, responsible for the growth of trees, result in the establishment of forest communities.
- The nature of soil, wind and air currents determine distribution of forest vegetation.
- The Abiotic environment of forest ecosystem comprises nutrients present in the soil on forest floor. These nutrients are rich in dead and decaying organic matter. Producers are mainly big trees, some shrubs and ground vegetation.
- In tropical forests, only two seasons (rainy and dry) exist. The length of day light is 12 hours with little variation.
The Abiotic components include organic and inorganic compounds. These are water, nitrogen, oxygen, carbon dioxide, calcium, phosphorus, amino acids, humic acids, carbohydrates, proteins and fats. In addition, there is the organic matter which includes dead organic litter, which is an accumulation of dead plants, leaves, fruits, etc.
The forest ecosystem supports a vast diversity of biotic communities. High temperature, bright sunlight and thick soil moisture are responsible for the growth of many kinds of trees. Much of the nutrients in rain forests are stored in the tall vegetation, whereas the nutrient storage in soil is low as the soil is leached to a great extent. The deciduous forest soil has more nutrients due to lesser leaching.
Producers: Trees, shrubs, herbs and grasses are the main producers in the system. The forests are of different kinds depending on the climate.
The major forest systems in India are:
- Tropical Rain Forests: These are found along the Western Ghats and in the north-eastern Himalayas. These are areas with heavy rainfall. The canopy structure is 30-40 m tall. Most trees have swollen stem bases and have large leaves. Woody climbers and epiphytes grow profusely. The leaf-fall is all round the year.
- Tropical Deciduous Forests: These are found in the northern and southern parts of India in the plains and low hilly areas. Sal and teak are the dominant tree species in the system. Thendu, chiraunji, khairm, sandalwood, mango are other tree species which grow in the region. Herb vegetation includes orchids, ferns, etc.these forests are 10-20 m in height. During the rainy season, the forests have lush green foliage and a good herbaceous layer. The trees shed leaves before the advent of summer, turning the forests leafless.
- Temperate Broad Leaf Forests: these include oak forests that are between 1500 and 2400 m altitude in the western Himalayas. The other dominant trees are Acer, betula, thuja, etc. the forests are evergreen though the trees shed some leaves in summer.
- Temperate Coniferous Forests: These evergreen forests are located in the area Himalayas. The forests have economically valuable trees, like the pine, deodar, and cypress, spruce and silver fir. Coniferous forests grow to a height of 30 metres and form a canopy of long needle-like leaves.
Consumers: These are organisms that lack chlorophyll and are unable to make their own food. Therefore, they depend on the producers for their food. They are known as heterotrophs.
They include the following:
- Primary consumers: The animals mostly feed on leaves. Predominant among them are ants, flies, beetles, leafhoppers, spiders, etc. Bigger animals that live on shoots and fruits are elephants, monkeys, nilgai, deer, moles, squirrels, etc
- Secondary consumers: these include carnivorous animals feeding on the herbivores. They are snakes, birds, lizards, etc.
- Tertiary consumers: these are the top carnivores like lion, tiger, etc. they live on secondary consumers.
Decomposers: They breakdown the dead organic matter for their food and release to the environment simple organic and inorganic substances produced as by-products of their metabolism. The main decomposers are the fungi and bacteria. In the forest ecosystem, the dead biotic component is high because of the plentiful micro-decomposers. Rate of decomposition is more rapid in tropical and subtropical forests than that in temperate ones.
These terrestrial ecosystems occupy roughly 19 per cent of earth's surface. They are characterized by treeless herbaceous plant cove dominated by a wide variety of grass species.
Features of grassland ecosystem
- Land is dominated by grasses. Large shrubs or trees are absent.
- Grasslands have rich variety of animals.
- Grasslands have been the home for grazing animals for millions of years. Since the grass height is low and trees are few, animals found in their areas are exposed to the stress of sun and sweeping winds.
The main components are water, carbon dioxide, oxygen, calcium, nitrogen, phosphates, amino acids, humic acid, etc., present in the soil as well as in the atmosphere.
Temperature grasslands are found where rainfall varies from 25 to 75 cm per year and the temperature ranges from 5o to 25o. Such rainfall is insufficient to support a forest, but it is higher that the rainfall in deserts. These grasslands include the North American Prairies, the Argentine Pampas, the Tussock grasslands of New Zealand and the Russian Steppes.
Savannas are grasslands in tropical areas. They are characterized by a well-developed grass cover interspersed with scattered shrubs and small trees. Such grasslands are found in tropical areas with 100 to 150 cm rainfall and a very long dry season. Soil moisture may be modified by fire, soil nutrients and herbivores.
Low annual precipitation causes organic detritus to decompose slowly. Therefore, the soils are enriched by organic matter. The soils are not heavily leached and are rich in nutrients.
- Producers: The vegetation is dominated by grasses, which grow about two metres in the areas having moisture and less than 0.2 metres in dry regions.
Savannas have woody species with heights varying from 1-8 metres. Together with grasses legumes grow which enrich the soil with nitrogen.
The habitat dries up during late summer leading to the possibility of fire. Most grassland species, therefore, have fire-resistant underground stems, or rhizomes, from which shoots sprout again. Some grasses have fire-resistant seeds.
Tropical Savannas have grass species capable of growing even with low soil moisture. The root system of grasses is developed well in the upper 30cm soil. The woody species in the Savannas have deep roots. The type of grasses in Indian grasslands are: Dichanthium, Sehima, Phragmites, Saccharum, Cenchrus, Imperata, etc.
- Consumers: They include the following:
- Primary Consumers: The primary consumers are grazing animals. They include zebra, giraffe, bison, deer, antelopes, kangaroos, badger, coyote and rabbits. Besides, there are a number of burrowing animals like squirrels and a wide variety of insects and worms. Soil nematodes are the most important consumers are more than half of the plant tissues are consumed by them.
- Secondary Consumers: They prey upon herbivores and limit their population. These include cats (like lions, tigers and leopards). Hunting dogs, jackals, foxes, snakes, frogs, lizard and predatory birds. Dead animals provide food for scavengers such as vultures and hyenas.
- Decomposers: Decomposers bring the minerals back into the soil. Thus, the minerals become available to producers. Decomposers include fungi species (Aspergillus, mucur, Penicillium, Rhizophus, Fusarium, etc.), actinomycetes and other species of bacteria.
Deserts make up about 17 % of the surface of earth. The major deserts are the Sahara, the Arabian, Kalahari and Namib of Africa, the Atacama of South America, the Mojave, Sonoran and Chihuahuan of North America and the Australian deserts. Besides, there are the Thar Desert in western India and Pakistan and the Gobi Desert of Mongolia.
Features of Desert Ecosystem
- The soil in the desert is coarse
- In the deserts, days are very hot and nights are cold. So the plants and animals are exposed to both types of extremes.
- The predominant plants found in the deserts are succulent species with waxy surfaces, such as cacti, which can conserve water for longer periods of time, or deciduous shrubs, also with thick waxy leaves.
- The animal types in the deserts are few. These include burrowing and nocturnal rodents, reptiles, insects and arachnids (Scorpions, spiders etc.). These animals adapt themselves to the temperature extremes and desiccation of desert air by living beneath the surface during the day and moving out only at night. Most of them have remarkable water conservation adaptations.
- Most of the animals living in the deserts are nocturnal (active only at night). Common animals are camels, foxes, kangaroos, rats squirrels, etc.
- Many of the insects and arachnids have waxy coats and reduced water loss through the cuticles.
In desert regions the Abiotic components are different mineral salts, nitrogen, oxygen, carbon dioxide, soil, water, etc. The region has a very low rainfall, usually less than 25 cm and is not uniform over the year. The day temperature is very high and at night the temperature drops and it becomes cold.
The low rainfall makes the soils shallow, virtually devoid of organic matter, and neutral in pH.
- Producers: Desert plants are scattered over a large area. They are usually thorny bushes, water-storing succulents, cacti, etc. Perennial plants have a well developed root system and swollen stems. Subtropical deserts receive summer rainfall; soon herbaceous plants come up from dormant seeds, grow quickly, bloom and reproduce before the soils dry up. Wetter areas have succulent cacti, shrubs and small trees.
- Consumers: The most common animals that live in these regions are reptiles and insects, nocturnal rodents and birds. They have adapted themselves to the extreme climatic condition in the area. The 'ship of des