Download ECOSYSTEM-structure and function

ECOSYSTEM-structure and function
Biotic and abiotic components.
Vertical distribution of different species occupying
different levels is called stratification.
The components of the ecosystem are seen to
function as a unit when we consider (1) productivity
(2) decomposition (3) energy flow (4) nutrient
cycling.
Productivity:- The rate of biomass production is
called productivity. It is expressed in terms of g yr .
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PRIMARY PRODUCTIVITY
• P P is defined as the amount of biomass or organic
matter produced per unit area over a time period
by plants during photosynthesis. It is measured in
terms of weight g-2 or energy kcal m-2.
• Productivity is divided into- Gross p p :- is the rate
of production of organic matter during
photosynthesis. Net p p:-GPP minus respiration
losses is the NPP. GPP-R=NPP.
• Secondary productivity:- The rate of formation of
new organic matter by consumers.
• Annual NPP of biosphere is 170 billion tons,
productivity of oceans is only 55 billion tons.
DECOMPOSITION
• The process of break down of complex organic
matter into inorganic substances like CO2 , H2O and
nutrients is called decomposition.
• Detritus:- dead plant remains such as leaves, bark,
flowers, dead remains of animals including fecal
matter. Various steps of decomposition are;
• Fragmentation: Process of break down of detritus
into smaller particles by detritivores (earthworm).
• Leaching: water soluble inorganic nutrients go
down into the soil horizon and get precipated as
unavailable salts.
Catabolism:
• Process of degradation of detritus into simpler
inorganic substances by bacterial and fungal
enzymes.
• Humification: leads to accumulation of a dark
coloured amorphous substance called humus.
• Humus is highly resistant to microbial action and
undergoes decomposition at an extremely slow
rate.
• Mineralisation: Humus is further degraded by some
microbes and release of inorganic nutrients occur.
Decomposition
• It is an oxygen requiring process. The rate of
decomposition is controlled by chemical
composition of detritus and climatic factors.
• Decomposition rate is slower if the detritus is rich
in lignin and chitin, and quicker if detritus is rich in
nitrogen and water-soluble substances like sugars.
• Temperature and moisture are the climatic factors
that regulate decomposition. Warm and moist
environment favour decomposition. Low
temperature and anaerobiosis inhibit
decomposition.
ENERGY FLOW
• Of the incident solar radiation less than 50 per
cent is photosynthetically active radiation (PAR).
Plants capture only 2-10 per cent of the PAR.
Energy flow is unidirectional from sun to
producers to consumers.
• Producers:
• Consumers: primary consumer or herbivores,
secondary consumer or primary carnivores,
tertiary consumer or secondary carnivore.
• Grazing food chain: Grass Goat Man.
Detritus food chain
• It begins with dead organic matter. It is made
up of decomposers mainly fungi and bacteria
(saprotrophs). Decomposers secrete digestive
enzymes that breakdown dead and waste
materials into simple inorganic materials
which are absorbed by them.
• In aquatic ecosystem GFC is the major conduit
of energy flow.
• In terrestrial ecosystem larger fraction of
energy flows through DFC than GFC.
• FOOD WEB:
Trophic level
• Specific place in the food chain. First , seond, third
trophic level. The amount of energy decreases at
each trophic level.
• Standing crop: each trophic level has a certain
mass of living material at a particular time. The
standing crop is measured as the mass of living
organisms (biomass), or the number in a unit
area.
• Transfer of energy follows 10 per cent law- only 10
per cent of the energy is transferred to each
trophic level from the lower trophic level.
Ecological pyramids
• Pyramid of number, biomass, energy.- always
upright.
• Inverted pyramid: small standing crop of
phytoplankton supports large standing crop of
zooplankton.(biomass)
• Limitations: it does not take into account the same
species belonging to two or more trophic levels. It
does not accommodate a food web . Saprophytes
are not given any place in ecological pyramids.
Ecological succession
• The gradual and fairly predictable change in the
species composition of a given area is E S.
• These changes lead finally to a community that is in
near equilibrium with the environment and is called
a climax community.
• The entire sequence of communities that
successively change in a given area are called sere.
• The individual transitional communities are termed
seral stages or seral communities.
• Primary succession: that starts where no living
organisms are there. Eg:- bare rock, newly cooled
lava, newly created pond or reservoir.
Secondary succession
• It begins in areas where natural biotic communities
have been destroyed such as in abandoned farm lands,
burned or cut forests, lands that have been flooded.
• Hydrarch succession takes place in wetter areas and the
successional series progress from hydric to the mesic
conditions.
• Xerarch succession takes place in dry areas and the
series progress from xeric to mesic conditions.
• The species that invade a bare area are called pioneer
species. In pri. Succ. On rocks- lichens bryophytes,
bigger plants, climax forest. In pri. Succ. In waterphytoplankton's, free floating angiosperms, rooted
hydrophytes, sedges, grasses, trees, climax forest.
Nutrient cycling
• The movement of nutrient elements through
various components of an ecosystem is called
nutrient cycling or biogeochemical cycle.
• The amount of nutrients such as nitrogen,
carbon, phosphorus, calcium, etc; present in
the soil at any given time is referred to as the
standing state.
• Two types- gaseous (nitrogen, carbon),
sedimentary (sulphur, phosphorus).
Ecosystem services
• The products of ecosystem processes are
named as ecosystem services. Eg:-healthy
forest ecosystem purify air and water, cycle
nutrients, generate fertile soil provide wildlife
habitat, pollinate crops, maintain biodiversity
provide aesthetic, cultural, spiritual values.
• Robert Constanza tried to put price tag on
nature’s life support services.