ECOSYSTEM

PRODUCTIVITY

• > In ecology, productivity refers to the rate of formation of biomass in ecosystem
• >Two types of productivity :
• PRIMARY PRODUCTIVITY. The amount of biomass or organic matter produced per unit area by plants for photosynthesis. Expressed in terms of weight or energy
• Primary productivity depends ono Topography- Altitude, latitude etc. o Environmental factors (temp., sunlight intensity, rainfall, wind, humidity, nature of soil etc.) o Availability of nutrients (water, minerals, O2 etc.) o Photosynthetic capacity of plants
• It can be divided into gross primary productivity and net primary productivity.
• (i) Gross Primary Productivity (GPP): It is the rate of total production of organic matter during photosynthesis.
• (ii) Net Primary Productivity (NPP): It is the balance biomass remaining after meeting the cost of respiration (R) of the producers. i.e., NPP = GPP – R
• >>it is the net energy stored in plants. This energy serves as food for the animals that feed on plants
• 2.SECONDARY PRODUCTIVITY: Rate of formation of new organic matter by consumers

DECOMPOSITION

• Decomposition: It is the breakdown of complex organic matter by decomposers into inorganic substances like CO2, water and nutrients
• Steps of decomposition
• (Step-1) Fragmentation: It is the breakdown of detritus (dead remnants of plants and animals) into smaller particles by detritivores (e.g. earthworm)
• . (Step-2) Leaching: Water soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.
• (Step-3) Catabolism: Degradation of detritus into simple inorganic substances by bacterial and fungal enzymes.
• (Step-4) Humification: Conversion of detritus to dark amorphous substance called humus
• Properties of Humus:-
• - It is resistant to microbial action and so decomposes slowly.
• - Being colloidal in nature it serves as a reservoir of nutrients.
• Mineralization: The degradation of humus to release inorganic substances by the action of some microbes.

Factors affecting rate of decomposition

• 1)Chemical composition:decomposition rate will be slow when detritus is rich in lignin and chitin.Rate of decomposition increases when detritus is rich in nitrogen and water soluble substances like sugars
• 2)Climatic conditions: warm and moist environment favour decomposition and low temperature and anaerobiosis inhibit decomposition

Energy flow

• > All living organisms are directly or indirectly dependent on producers, for their food.
• >There is a unidirectional flow of energy from the sun to producers and then to consumers
• > Photo synthetically active radiation(PAR) is responsible for the synthesis of food by plants
• >Animal obtain their food fro, plants so they are called consumers
• >Animals feed on green plants are called primary consumers or herbivorous
• >The animals eat herbivores are called secondary consumers or primary carnivores. Example,goat
• >The animals which feed on primary carnivores are called teritary consumers or secondary ucarnivores example- man

FOOD CHAIN & FOOD WEB

• Food chain: The transfer of food from the producers through a series of organisms with repeated eating and being eaten. 2 types of food chains can be recognised in an ecosystem
• I. Grazing Food Chain (GFC): It begins with a producer which is eaten by grazing herbivores which are then eaten by carnivores. Producers Herbivores Carnivores (e.g. Green plants) (e.g. Deer) (e.g. Tiger)
• II. Detritus food chain (DFC): It begins with detritus (dead organic matter) which is taken by decomposers (saprotrophs).
• Detritus ---------Decomposers
• (E.g. fungi, bacteria)
• DFC may be connected with the GFC at some levels: some of the organisms of DFC are prey to the GFC animals
• Food Web: Interconnections of food chains
• Food Web: Interconnections of food chains
• TROPHIC LEVEL
• Trophic level: The place of organisms in the food chain.
•  Standing crop: The total amount of living material present in different trophic at a particular time. - It is measured as the fresh or dry weight of living organisms (biomass) or the number in a unit area.
•  Law of 10%: It states that ‘Only 10% of the energy is transferred to each trophic level from the lower trophic level’. Proposed by Lindeman (1942)

ECOLOGICAL PYRAMIDS

• An ecological pyramid is a graphical represenation of the relatioonships of living organisms in different trophic level
• The base of pyramid represents the producers (first trophic level) while the apex represents top level consumer.
• The base of pyramid is broad and narrow along its apex
• Ecological pyramids are 3 types:
• (a) Pyramid of number
• (b) Pyramid of biomass
• (c) Pyramid of energy
• 

LIMITATIONS OF ECOLOGICAL PYRAMIDS

• It does not take into account the same species belonging to two or more trophic levels.
• It assumes a simple food chain that never exists in nature; it does not accommodate a food web.
• Saprophytes are not included in ecological pyramids.

NUTRIENT CYCLING

•  Nutrient cycling (biogeochemical cycles): The movement of nutrients through components of an ecosystem. \
•  The amount of nutrients present in the soil at a given time is referred to as the standing state. It varies with kinds of ecosystems and season.
• Nutrient cycles are 2 types:
• (i) Gaseous cycle: The reservoir exists in the atmosphere E.g. Nitrogen, carbon cycle etc.
• (ii)Sedimentary cycle: The reservoir is located in Earth’s crust. E.g. Sulphur and phosphorus cycle

NUTRIENT CYCLE

Phosphorus Cycle