ECOSYSTEM – Biology CBSE :-
British ecologist Arthur Tansley first defined the term Ecosystem.ECOSYSTEM :- the functional unit of nature, where living organisms interact among themselves and with the surrounding physical environment.
Types of Ecosystems:
· Pinocchio: long nosed frog found in Indonesia
· Bald headed parrot in Amazon
· Yeti Crab (Kiwa hirsuta) near Easter islands.Structure of Ecosystems
An Ecosystem has two components:
· Biotic components and
· Abiotic components
Stratification:
This is the Vertical Distribution of Different Species occupying Different Levels.
The levels are called STRATA.
Aspects Affecting the Functioning of an Ecosystem are:
1. PRODUCTIVITY
The rate of synthesis of organic matter (biomass) during a given period of time. It is measured as weight (g-2) or as energy (kcal m-2). It is used to compare productivity of different ecosystems.
- Primary productivity:
It is the amount of biomass produced per unit area in a given time period by Plants during Photosynthesis.
GPP – R = NPP
*GPP-Gross Primary Productivity *NPP-Net Primary Productivity
- Secondary productivity
It is the amount of biomass produced at any of the Consumer levels in a given period of time.
2. DECOMPOSITION
It is the process of breaking down of dead organic matter into smaller organic molecules and inorganic molecules by Decomposers (bacteria, fungi)
DETRITUS: Dead remains of plants and animals is called detritus.
DETRITIVORES: Animals that feed on decaying organic matter (detritus).
Examples: earthworms, termites, snails etc
Mechanism of Decomposition:
- Fragmentation of Detritus: Detritivores feed on detritus —breakdown — increases the surface area of detritus particles for microbial action.
- Leaching: Soluble inorganic nutrients dissolve in water -– percolate through the soil —removed due to leaching action.
- Catabolism: Decomposers (bacteria, fungi) release enzymes — decompose detritus — simpler inorganic compounds.
- Humification: Simplified detritus— converted to HUMUS
– Humus is a Dark, Amorphous substance.
– Highly resistant to Microbial Action
– Undergoes Decomposition very Slowly.
– Reservoir of nutrients (due to colloidal nature)
5. Mineralisation: Humus is degraded – releases inorganic substances
( CO2, H2O etc) and nutrients (Ca2+, Mg2+,K+ etc)
Factors affecting rate of Decomposition:
-
- Chemical composition – decomposition rate will be slow when detritus is rich in lignin and chitin and rate increases when detritus is rich in nitrogen and water soluble substances like sugsrs.
- Climatic conditions – warm and moist environment favour decomposition and low temperature and anaerobiosis inhibit decomposition.
3. ENERGY FLOW
► SUN- Main Source of energy
► 50% of incident light is PHOTOSYNTHETICALLY ACTIVE RADIATION (PAR)
► 2- 10 % of PAR is captured by plants.
► Only a small fraction of this (stored as organic compounds) is transferred to consumers; the rest is used up in respiration and other life-supporting activities of the plants.
► As energy is transferred as food, most part is lost as heat at each stage (10% LAW)
Unidirectional flow of Energy:
Sun -> Producers -> Consumers
Transfer of energy / food from the producer through a series of organisms is known as FOOD CHAINS.
FOOD CHAINS
- Food chains represent energy flow through ecosystems.
- Different steps in a food chain are TROPHIC LEVELS
- Basic terms:
Producers, Herbivores, Carnivores, Omnivores.
1.GRAZING FOOD CHAIN (GFC)
- Primary source of energy – Solar radiations.
- First trophic level includes – All Herbivores.
- -GFCs are Long-sized chains
2) DETRITUS FOOD CHAIN (DFC)
· Primary source of energy is Detritus.
· First trophic level includes Detritivores.
· Detritus Food Chains are small-sized chains.
SAPROPHYTES:These include decomposers (fungi, bacteria) which feed on detritus.
FOOD WEBS
• The Natural Interconnection of Several Food Chains forms a FOOD WEB.
• Provides alternate pathways for food availability.
• Unlike food chains, food webs are never straight.
• Help in ecosystem development and stability.
TEN PERCENT LAW:
Ø By Lindemann in 1942
Ø States that : during transfer of energy from one trophic level to another, only about 10% is stored at higher levels; remaining 90% is lost in respiration (heat)
4. ECOLOGICAL PYRAMIDS
- Developed by Charles Elton in 1927.
- Pyramids are an expression of the relationship between organisms at different trophic levels in terms of their number, biomass or energy.
- Three types of pyramids:
1. Pyramid of Number
2. Pyramid of Biomass
3. Pyramid of energy
- Pyramid of Number: The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid in terms of number called pyramid of number.
- Pyramid of Biomass: The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid in terms of biomass called pyramid of biomass. It can be of two types:
a) Upright (in case of grassland ecosystem)
b) Inverted (in case of pond ecosystem)
3. Pyramid of energy: The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid in terms of flow of energy called pyramid of energy. It is always upright.
Learn more from your teachers in class along with diagram
Limitations of Ecological Pyramids:
- ž It does NOT consider the same species belonging to two or more trophic levels.
- ž It is based on simple food chains, which hardly exist. It does NOT accommodate food webs.
- ž Saprophytes (decomposers) are NOT given any place in the ecosystem.
Climax Community:
- Changes that lead finally to a community that is in near equilibrium with the environment.
- It remains stable as long as the environment remains unchanged.
The Rainforest is an example of climax community ecosystem.
Ecological Succession:
- Refers to predictable and orderly change in the composition or structure of a community.
- May be initiated either by formation of new, unoccupied habitat or by some form of disturbance of an existing community.
- Sere – entire sequence of community that successively change in a given area.
- Seral stages – individual transitional communities.
Seral Communities:
Hydrosere – Community in freshwater
Lithosere – Community on rock
Pssamosere – Community on sand
Halosere – Community in saline body
Xerosere – Community in dry area
Primary Succession
- If the development begins on an area that has not been previously occupied by a community.
- Pioneer species – lichens, phytoplankton, etc.
- Examples:
– newly exposed rock or sand surface
– a lava flow
– glacial tills
– newly formed lake,
Secondary Succession
- If the community development is proceeding in an area from which a community was removed.
- Pioneer species – grasses, wildflowers, algae.
- Examples:
– an abandoned crop field
– cut-over forest
– natural forces such as wind storms and floods
Succession in Plants:
Hydrarch succession
- It takes place in wetter areas and the successional series progress from hydric to the mesic conditions.
Phytoplankton in pond -> Submerged plant stage-> Submerged free floating plant stage -> Reed – swamp stage -> Marsh – meadow stage – scrub stage -> Forest
Xerarch succession
- It takes place in dry areas and the series progress from xeric to mesic condition.
Bare rock -> Lichens and mosses -> Annual grasses -> Perennial grasses -> Shrubs -> Tall Trees
The Nutrient Cycle
- Also known as biogeochemical cycle.
- Environmental factors like soil, moisture, temperature, etc. regulate the rate of release of nutrients into the atmosphere.
- Standing state – amount of nutrients, such as C, N, P, Ca, etc. present in the soil at any given time.
- Nutrients are never lost from the ecosystem; they are recycled time an again indefinitely.
- There are two types:
– Gaseous cycle
– Sedimentary cycle
Ecosystem Services
- Humankind benefits from a multitude of resources and processes that are supplied by natural ecosystems. Collectively, these benefits are known as ecosystem services.
- Purify air and water
- Decomposition of waste materials
- Cycle nutrients
- Pollinate crops
- Maintain biodiversity
- Researchers have put an average price tag of US $33 trillion a year on these fundamental ecosystems services, which is largely taken for granted because they are free.