• The term ‘ecosystem’ was coined by A.G. Tansley in 1935. An ecosystem is a functional unit of nature encompassing complex interaction between its biotic (living) and abiotic (non-living) components. For example- a pond is a good example of ecosystem.

Components of an Ecosystem

1. Abiotic components (Nonliving): The abiotic component can be grouped into following three categories:-

1. Physical factors: Sun light, temperature, rainfall, humidity and pressure. They sustain and limit the growth of organisms in an ecosystem.
2. Inorganic substances: Carbon dioxide, nitrogen, oxygen, phosphorus, sulphur, water, rock, soil and other minerals.
3. Organic compounds: Carbohydrates, proteins, lipids and humic substances. They are the building blocks of living systems and therefore, make a link between the biotic and abiotic components.

1. Biotic components (Living)

1.  Producers: The green plants manufacture food for the entire ecosystem through the process of photosynthesis. Green plants are called autotrophs, as they absorb water and nutrients from the soil, carbon dioxide from the air, and capture solar energy for this process.
2. Consumers: They are called heterotrophs and they consume food synthesized by the autotrophs. Based on food preferences they can be grouped into three broad categories:

• Herbivores (e.g. cow, deer and rabbit etc.) feed directly on plants,
• Carnivores are animals which eat other animals (eg. lion, cat, dog etc.) and
• Omnivores organisms feeding upon both plants and animals e.g. human, pigs and sparrow.

        3. Decomposers: Also called saprotrophs. These are mostly bacteria and fungi that feed on dead decomposed and the dead organic matter of plants and animals by secreting enzymes outside their body on the decaying matter. They play a very important role in recycling of nutrients. They are also called detrivores or detritus feeders.

Functions of Ecosystem

• Ecosystems are complex dynamic system. They perform certain functions. These are:-

1. Energy flow through food chain
2. Nutrient cycling (biogeochemical cycles)
3.  Ecological succession or ecosystem development
4.  Homeostasis (or cybernetic) or feedback control mechanisms

Classification of Ecosystems

Terrestrial Ecosystem

It is a land-based community of organisms and the interactions of biotic and abiotic components in a given area. Examples of terrestrial ecosystems include the tundra, taigas, temperate deciduous forests, tropical rainforests, grasslands, and deserts. The type of terrestrial ecosystem found in a particular place is dependent on the temperature range, the average amount of precipitation received, the soil type, and amount of light it receives.

Aquatic Ecosystem

The ecosystems found in bodies of water are called aquatic ecosystems. Two further categories, freshwater ecosystems and marine ecosystems, can be made from these. An aquatic ecosystem known as the freshwater ecosystem is made up of wetlands, lakes, ponds, rivers, and streams. These don’t contain any salt, in contrast to the marine ecosystem, which is made up of seas and oceans. Compared to the freshwater habitat, these have a higher salinity and more biodiversity.

Important Components of Sustainable Ecosystem

•  Population stabilisation
• Integrated land use planning
• Conservation of biodiversity
• Air and water pollution control
• Renewable energy resources
• Recycling of wastes and residues
• Environmental education and awareness at all levels.

Homeostasis

• Homeostasis is any self-regulating process by which an organism tends to maintain stability while adjusting to conditions that are best for its survival.The concept of homeostasis has also been used in studies of ecosystems. Canadian-born American ecologist Robert MacArthur first proposed in 1955 that homeostasis in ecosystemsresults frombiodiversity (the variety of life in a given place) and the ecological interactions (predation, competition, decomposition, etc.) that occur between the species living there. The term homeostasis has been used by many ecologists to describe the back-andforth interaction that occurs between the different parts of an ecosystem to maintain the status quo. It was thought that this kind of homeostasis could help to explain why forests, grasslands, or other ecosystems persist (that is, remain in the same location for long periods of time). Since 1955 the concept has changed to incorporate the ecosystem’s nonliving parts, such as rocks, soil, and water.

Ecotone

• An ecotone is a zone of junction or a transition area between two biomes [diverse ecosystems]. It is where two communities meet and integrate. For e.g. the mangrove forests represent an ecotone between marine and terrestrial ecosystem. Other examples are grassland (between forest and desert), estuary (between fresh water and salt water) and river bank or marsh land (between dry and wet).

Characteristics of Ecotone

• It may be narrow (between grassland and forest) or wide (between forest and desert).
• As it is a zone of transition, it has conditions intermediate to the adjacent ecosystems. Hence it is a zone of tension.
•  Usually, the number and the population density of the species of an outgoing community decrease as we move away from community or ecosystem.
• A well-developed ecotones contain some organisms which are entirely different from that of the adjoining communities.

Edge Effect – Edge Specie

• In ecology, edge effects refer to the changes in population or community structures that occur at the boundary of two habitats (ecotone).
  • Sometimes the number of species and the population density of some of the species in the ecotone is much greater than either community. This is called edge effect.
  • The organisms which occur primarily or most abundantly in this zone are known as edge species.
  • In the terrestrial ecosystems edge effect is especially applicable to birds. For example the density of birds is greater in the mixed habitat of the ecotone between the forest and the desert.

Ecological Nichse

• Niche refers to the unique functional role and position of a species in its habitat or ecosystem.
• In nature, many species occupy the same habitat but they perform different functions.
  • Habitat: It refers to place where the conditions for existence of organisms are favourable.
• The functional characteristics of a species in its habitat is referred to as “niche” in that common habitat.
•  Habitat of a species is like its ‘address’ (i.e. where it lives) whereas niche can be thought of as its “profession” (i.e. activities and responses specific to the species).
•  A niche is unique for a species while many species share the habitat. No two species in a habitat can have the same niche. This is because of the competition with one another until one is displaced.
  
  

Difference between Biome and Biosphere

Population Ecology

• Population Ecology is the branch of ecology that works to understand the patterns and processes of change  over time or space for populations of a single species. A species is typically defined as a group of organisms capable of interbreeding.
• Two types of population growth patterns may occur depending on specific environmental conditions:
  • An exponential growth pattern (J curve) occurs in an ideal, unlimited environment
  • A logistic growth pattern (S curve) occurs when environmental pressures slow the rate of growth

Exponential Growth

• Resource (food and space) availability is obviously essential for the unimpeded growth of a population. Ideally, when resources in the habitat are unlimited, each species has the ability to realise fully its innate potential to grow in number, as Darwin observed while developing his theory of natural selection. Then the population grows in an exponential or geometric fashion.
• Any species growing exponentially under unlimited resource conditions can reach enormous population densities in a short time. Darwin showed how even a slow growing animal like elephant could reach enormous numbers in the absence of checks.

Logistic Growth

• No population of any species in nature has at its disposal unlimited resources to permit exponential growth. This leads to competition between individuals for limited resources. Eventually, the ‘fittest’ individual will survive and reproduce. The governments of many countries have also realised this fact and introduced various restraints with a view to limit human population growth. In nature, a given habitat has enough resources to support a maximum possible number, beyond which no further growth is possible. Since resources for growth for most animal populations are finite and become limiting sooner or later, the logistic growth model is considered a more realistic one. 

Environmental Sanitation

• The literal meaning of sanitation is safeguarding health. Sanitation which can be referred as environmental sanitation was mainly concerned with safe disposal of human excreta and refuse. But by now according to WHO, it is defined as control of all those factors in man’s physical environment which may cause harmful effects on his living and health. It includes sanitation of housing, waste material, water, food, clothing etc.

Environmental Health

• The area of environmental sanitation is becoming very large and complex. It is being replaced by environmental health. It is defined as the “art and science of controlling all those factors in man’s physical, biological and psychosocial environment which have harmful effect on his life and health”

Environmental Calendar

• World Wetland Day February 2
• World Forest Day March 21
•  World Day for Water March 22
•  World Meteorological Day March 23
•  Earth Day April 22
•  International Biodiversity Day May 22
•  Anti-tobacco Day May 31
•  World Environment Day June 5
•  World Ocean Day June 8
•  World Population Day July 11
•  Ozone Week Sept. 16–23
•  World Car-free Day Sept. 22
•  Green Consumer Day Sept. 28
•  World farm Animal’s Day Oct. 2
•  World Habitat Day Oct. 3
•  World Animal Welfare Day Oct. 4
•  Wildlife Week Oct. 1–7
•  World Conservation Day Oct. 24
•  International Day for Natural Disaster Reduction Oct. 13
•  International Day for Biological Diversity Dec. 29