Ecosystems

A community and its physical environment is called its Ecosystem. An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the non-living (abiotic), physical components of the environment with which the organisms interact, such as air, soil, water and sunlight.

What is an eco system?

Ecosystem is an open system with inputs, internal transfers and outputs of energy and nutrients. Sunlight is the initial energy source for nearly all ecosystems. 

Types of Ecosystem

The different types of ecosystems are

(i) Natural Ecosystem

(a) Terrestrial ecosystem

(b) Aquatic ecosystem

(c) Lentic (lake, pond or swamp)

(d) Lotic (river, stream or spring)

(ii) Artificial Ecosystems

ecological community

The species that live and interact in an area constitute an ecological community. Ecological communities are loose assemblages of organisms.

The organisms in a community can be divided into trophic levels (the position of an organism in food chain) based on the source of their energy.

Primary producers get their energy from sunlight. Herbivores that get their energy by eating primary producers are primary consumers; organisms that get their energy by eating herbivores are secondary consumers; and so on.

 A sequence of interactions in which a plant is eaten by a herbivore, which in turn eaten by a secondary consumer, and so on, is known as food chain. Food chains are usually interconnected to make a food web because most species  in a community eat and are eaten by more than one species. Most communities have three to five trophic levels. 

Energy and biomass decreases as it flows from lower to higher trophic levels and thus can be represented in the form of pyramid. Most of the energy ingested by organisms that is converted to biomass is eventually consumed by decomposers.

Ecological pyramids An important feature of energy flow is that most of the energy going from one trophic level to the next, in a food chain and food web, dissipates into the environment as a result of the second law of thermodynamics. Ecological pyramids often graphically represent the relative energy values of each trophic level. There are three main types of pyramids— a pyramid of numbers, a pyramid of biomass and a pyramid of energy.

Ecosystem productivity The gross primary productivity (GPP) of an ecosystem is the rate at which energy is captured during photosynthesis in a given period of time. In addition, a plant respires to provide energy for its own use; this acts as a drain on photosynthesis. Energy in plant tissues after cellular respiration has occurred is net primary productivity (NPP). 

Both GPP and NPP are expressed as energy per unit area per unit time. Humans consume (32%) far more of earth’s resources than any other of animal species. If we want our planet to operate sustainably, we must share terrestrial photosynthetic product with other organisms.

In environments that show variations in salinity, temperature and other environmental conditions, food webs tend to have short chains. In stable environments, such as parts of the deep ocean, food chains are longer. In addition to energy inputs, primary productivity and ecosystem structure require a cycling of nutrients. Water and minerals move slowly through the physical environment, rapidly through organisms, and back to the environment in biogeochemical cycles. 

Water moves through a hydrological cycle. In land ecosystems, plants stabilise soil and minimise nutrient loss during the cycle as runoff. In atmospheric cycles, a nutrient prevails mainly in gaseous form (such as carbon, in carbon dioxide). 

In the carbon cycle, carbon dioxide is the main gas in the atmosphere. The ocean is carbon’s main reservoir. Burning of fossil fuels, logging and conversion of natural ecosystems for farming disrupt the global carbon budget and may be responsible for global warming.

Nitrogen is a limiting factor in the total net productivity of ecosystem on land. Gaseous nitrogen is abundant in the atmosphere. Nitrogen–fixing bacteria convert N2 to ammonia and nitrates, which producers take up.

Mycorrhizae and root nodules, two symbiotic interactions, enhance the nitrogen uptake. Sedimentary cycles interact with the hydrological cycle to move mineral nutrients to and from ecosystems.

Certain human activities are depleting minerals from ecosystems, as when weathered soil of tropical forests is cleared for agriculture.

Some human activities are accelerating the process of eutrophication. They are adding nutrients such as nitrates and phosphates to aquatic ecosystems.

This promotes growth and decay of destructive algal blooms. The decomposition of these plants leads to the depletion of oxygen in the water, which threatens fish and other animal populations.