Ecosystem: Components, Functions, Biotic Interactions, Biogeochemical Cycles

Basic Definitions

• Environment: the natural landscape together with all of its non-human features, characteristics and processes
• Ecology: Subject which studies the interactions among organisms and between the organism and its physical (abiotic) environment.
• Biosphere: The biosphere is the biological component (supporting life) of earth which includes the lithosphere, hydrosphere and atmosphere.
• Habitat: A habitat is a place where an organism makes its home. A habitat meets all the environmental conditions an organism needs to survive. (All habitats are environments, but all environments are not habitats.)
• Ecosystem: Structural and functional unit of biosphere consisting of a community of living beings and the physical environment, both interacting and exchanging materials between them.
• Ecotone: An ”’ecotone”’ is a transition area between two biological communities, where two communities meet and integrate. E.g. Mangroves represent an ecosystem between marine and terrestrial ecosystems.
• Niche: Ecological niche is a term for the position of a species within an ecosystem, describing both the range of conditions necessary for persistence of the species, and its ecological role in the ecosystem. Ecological niche subsumes all of the interactions between a species and the biotic and abiotic environment, and thus represents a very basic and fundamental ecological concept.
• No two species have exactly the same niche. Different types of niches are – Habitat niche, Food niche, Reproductive niche, Physical and Chemical niche.
• Biomes: A biome is a community of plants and animals that have common characteristics for the environment they exist in. They can be found over a range of continents. Biomes are distinct biological communities that have formed in response to a shared physical climate. Biome is a broader term than habitat; any biome can comprise a variety of habitats.

Ecosystem: Major Abiotic Components #

An abiotic factor is a non-living part of an ecosystem that shapes its environment. In a terrestrial ecosystem, examples might include temperature, light, and water. In a marine ecosystem, abiotic factors would include salinity and ocean currents.

Ecosystem: Response To Abiotic Factors #

How do organisms living in extreme environment cope or manage with stressful conditions? 

Adaptations #

• Adaptation is any attribute of the organism (Morphological, Physiological, Behavioral) that enables an organism to survive and reproduce in its habitat. Adaptedness is the state of being adapted: the degree to which an organism is able to live and reproduce in a given set of habitats
• Example: Kangaroo rat in North American Deserts: in absence of water, has ability to meet its requirement through internal fat oxidation and has ability to concentrate its urine.

Ecosystem: Major Biotic Components  #

Components And Functions Of Ecosystem #

• Four basic components of the ecosystem– (i) Productivity; (ii) Decomposition; (iii) Energy flow; and (iv) Nutrient cycling.

(i) Productivity:

• The rate of biomass production is called productivity.
• Primary production is defined as the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis.
• Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis.
• A considerable amount of GPP is utilized by plants in
• Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP). GPP – R = NPP.
• Secondary productivity is defined as the rate of formation of new organic matter by consumers.

(ii) Decomposition:

• Decomposers break down complex organic matter into inorganic substances like carbon dioxide, water and nutrients and the process is called decomposition.
• The important steps in the process of decomposition are fragmentation, leaching, catabolism, humification and mineralization.
• Detritivores (e.g., earthworm) break down detritus into smaller particles. This process is called fragmentation
• By the process of leaching, water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.
• Bacterial and fungal enzymes degrade detritus into simpler inorganic substances. This process is called as
• All the above steps in decomposition operate simultaneously on the detritus
• Humification and mineralization occur during decomposition in the soil
• Humification is accumulation of a dark colored amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. Colloidal in nature it serves as a reservoir of nutrients.
• Humus is further degraded by some microbes and release of inorganic nutrients occur by the process known as mineralization

(iii) Energy Flow:

• There is unidirectional movement of energy towards the higher trophic levels and its dissipation and loss as heat to the environment.
• Of the incident solar radiation less than 50 per cent of it is photosynthetically active radiation (PAR)
• Plants capture only 2-10 percent of the PAR and this small amount of energy sustains the entire living world.
• The green plants in the ecosystem-terminology are called producers. e.g. phytoplankton, algae and higher plants.
• All animals depend on plants (directly or indirectly) for their food needs. They are hence called consumers and also heterotrophs.
• A trophic level is the representation of energy flow in an ecosystem.

Ecosystem: Food Chain And Food Web  #

Ecosystem: Ecological Pyramid #

• Steps of trophic levels expressed in a diagrammatic way are referred to as ecological pyramids.
• The base of each pyramid represents the producers or the first trophic level while the apex represents tertiary or top-level consumer.
• The three ecological pyramids that are usually studied are (a) pyramid of number; (b) pyramid of biomass and (c) pyramid of energy.

Pyramid of Numbers:

• Pyramid of numbers represents the total number of individuals of different species (population) at each trophic level, can be:
• Upright– number of individuals is decreased from lower level to higher trophic level, can be seen in the grassland ecosystem and pond ecosystem
• Inverted– number of individuals increased from lower to higher trophic level. e.g. Tree ecosystem.

Pyramid of Biomass:

• Pyramid of biomass is usually determined by collecting all organisms occupying each trophic level separately and measuring their dry weight. Each trophic level has a certain mass of living material at a particular time called the standing crop. Pyramid of Biomass can be:
• Upright: For most ecosystems on land, the pyramid of biomass has a large base of primary producers with a smaller trophic level on top.
• Inverted: Many aquatic ecosystems, the pyramid of biomass may assume an inverted form. (In contrast, a pyramid of numbers for the aquatic ecosystem is upright)

Pyramid of Energy:

Pyramid of energy is always upright, and can never be inverted, because when energy flows from a particular trophic level to the next trophic level, some energy is always lost as heat at each step. 

Ecosystem: Pollutants And Trophic Level #

Non degradable pollutants move from different trophic levels. Non-degradable (persistent) is which cannot be metabolized by living organisms. E.g. Chlorinated Hydrocarbons.

Biotic Interactions #

• Organisms are interlinked with each other. The interaction is fundamental for the survival of organisms and functioning of the ecosystem.
• Interspecific interactions arise from the interaction of populations of two different species.
• They could be beneficial, detrimental or neutral (neither harm nor benefit) to one of the species or both.

Biogeochemical Cycle #

The movement of nutrient elements through the various components of an ecosystem is called nutrient cycling. Another name of nutrient cycling is biogeochemical cycles (bio: living organism, geo: rocks, air, water). Nutrient cycles are of two types:

1. Gaseous – Reservoir for gaseous type of nutrient cycle (e.g. nitrogen, carbon cycle) exists in the atmosphere
2. Sedimentary– For the sedimentary cycle (e.g. Sulphur and phosphorus cycle), the reservoir is located in Earth’s crust.

Biogeochemical Cycle: Carbon Cycle

• 71 percent carbon is found dissolved in oceans. This oceanic reservoir regulates the amount of carbon dioxide in the atmosphere.
• Atmosphere only contains about 1 percent of total global carbon.
• Carbon cycling occurs through the atmosphere, ocean and through living and dead organisms.
• A considerable amount of carbon returns to the atmosphere as CO2 through respiratory activities of the producers and consumers.
• Decomposers also contribute substantially to CO2 pool by their processing of waste materials and dead organic matter of land or oceans.
• Human activities have significantly influenced the carbon cycle. Rapid deforestation and massive burning of fossil fuel for energy and transport have significantly increased the rate of release of carbon dioxide into the atmosphere.

Biogeochemical Cycle: Nitrogen Cycle

• Nitrogen is a constituent of amino acids, proteins, hormones, chlorophylls and many of the vitamins
• Plants compete with microbes for the limited nitrogen that is available in the soil. Thus, nitrogen is a limiting nutrient for both natural and agricultural ecosystems.
• Nitrogen exists as two nitrogen atoms (N2) joined by a very strong triple covalent bond (N ≡ N).
• In nature, lightning and ultraviolet radiation provide enough energy to convert nitrogen to nitrogen oxides (NO, NO2, N2O).
• Industrial combustions, forest fires, automobile exhausts and power-generating stations are also sources of atmospheric nitrogen oxides.

Step 1: N2 Fixing ➔ Nitrogen → Ammonia or Ammonium Ions

Step 2: Nitrification ➔ Ammonia or Ammonium Ions (bacteria: Nitrosomonas and/or Nitrococcus) → Nitrite (Nitrobacter)→ Nitrate

Step 3: Ammonification ➔ Dead Matter + Animal Waste (Urea, Uric Acid) → Ammonia or Ammonium Ions

Step 4: Denitrification ➔ Nitrate (bacteria: Pseudomonas and Thiobacillus) → Nitrogen

 Biogeochemical Cycle: Sulphur Cycle

• In the Sulfur cycle, there is a circulation of sulfur in various forms through nature. Sulfur occurs in all living matter as a component of certain amino acids.
• It is abundant in the soil in proteins and, through a series of microbial transformations, ends up as sulfates usable by plants.
• The Sulphur reservoir is in the soil and sediments where it is locked in organic (coal, oil and peat) and inorganic deposits (pyrite rock and Sulphur rock) in the form of sulfates, sulfides and organic Sulphur.
• It is released by weathering of rocks, erosional runoff and decomposition of organic matter and is carried to terrestrial and aquatic ecosystems in salt solution.
• The Sulphur cycle is mostly sedimentary except two of its compounds, hydrogen sulfide (H2S) and Sulphur dioxide (SO2), which add a gaseous component.
• Sulphur enters the atmosphere from several sources like volcanic eruptions, combustion of fossil fuels (coal, diesel etc.), from the surface of the ocean and gases released by decomposition.

Biogeochemical Cycle: Phosphorus Cycle

• Phosphorus is a major constituent of biological membranes, nucleic acids and cellular energy transfer systems.
• Many animals also need large quantities of this element to make shells, bones and teeth.
• The natural reservoir of phosphorus is rock, which contains phosphorus in the form of phosphates.
• When rocks are weathered, minute amounts of these phosphates dissolve in soil solution and are absorbed by the roots of the plants.
• Herbivores and other animals obtain this element from plants. The waste products and the dead organisms are decomposed by phosphate-solubilizing bacteria releasing phosphorus.
• Unlike the carbon cycle, there is no respiratory release of phosphorus into the atmosphere.

Ecological Succession #

• The gradual and fairly predictable change in the species composition of a given area is called ecological succession.
• The first plant to colonize an area is called the pioneer community.
• The final stage of succession is called the climax community.
• A climax community is the final stage of succession, remaining relatively unchanged until destroyed by an event such as fire or human interference. This is a community that is in near equilibrium with the environment.
• The entire sequence of communities that successively change in a given area are called

Succession In Plants #

• Succession of plants is called hydrarch or xerarch, respectively.
• Hydrarch succession takes place in wetter areas and the successional series progresses from hydric to the mesic conditions.
• As against this, xerarch succession takes place in dry areas and the series progresses from xeric to mesic conditions.
• Hence, both hydrarch and xerarch succession lead to medium water conditions (mesic) – neither too dry (xeric) nor too wet (hydric).