ECOSYSTEM – Structure and Functions.
Definition: Ecosystem is the total interaction between living (biotic) and non-living (abiotic) components capable of independent existence.
Stratification: vertical distribution of different species occupying different levels in an ecosystem (each layer has plants and animals).
Functions of an Ecosystem:
1. Productivity
2. Decomposition
3. Energy flow
4. Nutrient cycling
PRODUCTIVITY:
The rate at which radiant energy is fixed in the form of organic food due to the photosynthetic and chemosynthetic activity of producers is called productivity.
· Primary productivity –Biomass produced by plants in an ecosystem through the process of photosynthesis. Measured in terms of Kcal/.
a. Gross primary productivity (GPP) - it is the total rate of photosynthesis during the measurement period.
b. Net primary productivity (NPP) - available biomass for the consumption of consumers/heterotrophs.
NPP=GPP-R
· Secondary productivity – Rate of formation of new organic matter by consumers/heterotrophs.
DECOMPOSITION:
Breakdown of complex organic matter into simple inorganic substances like CO2, water and nutrients. Dead plant and animal remains, including faecal matter, constitute detritus.
The main steps in the process of decomposition are:
i. Fragmentation – breakdown of detritus by detritivores (ex. Earthworms, maggots) into smaller particles.
ii. Leaching – it is the process whereby water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.
iii. Catabolism – it is the process whereby detritus is degraded into simpler inorganic substances by bacterial and fungal enzymes.
iv. Humification – it is the process of formation of an amorphous substance called humus.
Characterization:
-they are highly resistant to decomposition
-have high water-retaining capacity.
v. Mineralization – the humus is further degraded by some microbes and the release of inorganic nutrients occurs by the process known as mineralization.
Factors that affect decomposition:
- Chemical composition of detritus
- Temperature
- Humidity
ENERGY FLOW:
Energy flow is a non-cyclic process. The radiant energy of the sun enters into the ecosystem through the photosynthetic activity of plants; travels via consumers and decomposers, and ultimately disappears in space in the form of heat energy, which never returns to the source. This phenomenon is called the flow of energy.
Plants use 2-3 % of PAR.
FOOD CHAIN:
The sequence of living organisms in an ecosystem in which one organism consumes another organism to transfer food energy is called a food chain.
Types:
a. Grazing food chain – it starts from living green plants, goes to herbivores, and then to carnivores. In an aquatic ecosystem, GFC is the major conduit for energy flow as the rate of decomposition is slow in saltwater.
b. Detritus food chain – it starts from dead organic matter of decaying animals and plant bodies to micro-organisms and then to organisms feeding on detritus.
FOOD WEB:
The interconnected food chains operating in an ecosystem that establish a network of relationships between various species is called a food web.
Credits: Leo Karen Jerusha
