· The interaction between the living organism and the non-living environment is called ecosystem.
ECOSYSTEM – STUCTURE AND FUNCTION:
· Interaction of biotic and abiotic components results in a physical structure that is characteristic of each type of ecosystem.
· Identification and description of plant and animal species of an ecosystem gives its species composition.
· Vertical distribution of different species occupying different levels is called stratification.
· The components of the ecosystem are seen to function as a unit:
o Energy flow and
o Nutrient cycle.
· Description of pond as an ecosystem:
o The abiotic components include all dissolved inorganic and organic substances and the rich soil deposit at the bottom of the pond.
o The solar input, cycle of temperature, day length, regulates the rater of function of the entire pond.
o The producer (autotrophic) includes phytoplankton, some algae and the floating, submerged and marginal plants found in edge of pond.
o The consumers are represented by zooplankton, free swimming and bottom dwelling animals.
o The decomposers are the fungi, bacteria especially abundant at the bottom of the pond.
· Basic events (in terms of function) in an ecosystem:
o Conversion of inorganic into organic material (photosynthesis) by producers.
o Consumption of the autotrophs by heterotrophs.
o Decomposition and mineralization of the dead organic matter to release them back for reuse by the autotrophs.
o There is unidirectional flow of energy towards the higher trophic levels and its dissipation and loss as heat to the environment.
· Primary productivity:
o The amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis.
o It is expressed in terms of weight (g-2) or energy (kcal m-2)
o The rate of biomass production is called productivity.
· Gross primary productivity: (GPP) is the rate of production of organic matter during photosynthesis.
· Net primary productivity:
o A considerable amount of energy is utilized by plants in respiration.
o Gross primary productivity minus respiration losses (R) is the net primary productivity.
o GPP – R = NPP.
· Net primary productivity is the available biomass for the consumption to heterotrophs (herbivore and decomposers.
· Secondary productivity: is defined as the rate of formation of new organic matter by the consumer.
· Earthworm is said to be ‘friends’ of farmer:
o Breakdown the complex organic matter.
o Loosening of the soil helps in aeration and entry of root.
· The decomposers break down complex organic matter into inorganic substances like carbon dioxide, water and nutrients, called decomposition.
· Dead plant remains such as leaves, bark, flowers and dead remains of animals, including fecal matter, constitute the detritus.
· The process of decomposition completed in following steps:
o Fragmentation : Break down of detritus into smaller particles by detritivore (earthworm).
o Leaching: Water soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.
o Catabolism : Bacterial and fungal enzymes degrade detritus into simple inorganic substances.
o Humification: Accumulation of dark coloured amorphous substances called humus.
Importance of humus:
o Highly resistance to microbial action.
o Undergo decomposition at an extremely slow rate.
o Being colloidal in nature, it serves as reservoir for nutrients.
o Mineralization: The humus is further degraded by some microbes and release of inorganic nutrients occur.
Factor affects rate of decomposition:
· Decomposition is largely an oxygen-requiring process.
· Detritus rich in chitin and lignin has slow rate of decomposition.
· Detritus rich in nitrogen and water-soluble substance like sugar has faster decomposition.
· Temperature and soil moisture are most important climatic factor that regulate decomposition
· Warm and moist environment favor decomposition.
· Low temperature, dryness and anerobiosis inhibit decomposition.
Nutrient cycling means movement of nutrients through various component of ecosystem. This includes sedimentary and gaseous cycle where phosphorous is an element which is found on earth it flows in cyclic manner while carbon is found in gaseous state it cycles and return back to atmosphere.
Ecological succession is gradual and predictable change in species composition of given area.Succession in plants are of two types: xerarch and hydrarch succession.
Sun is the only source of energy on earth. Energy flow in the ecosystem is unidirectional. Food chain , food web and ecological pyramids are the ways of flow of energy from one trophic level to another trophic level.