Class 11 Biology – Ecosystem Ecology Notes
Complete notes on ecology, ecological factors, food chains, food webs, ecological pyramids, pond and grassland ecosystems, community and ecological succession.
Ecology
Ecology is the study of the reciprocal relationship between living organisms and their environment.
The notes divide ecology into:
- Autecology
- Synecology
1. Autecology
The study of an individual animal or plant species, or its population throughout its life history in relation to the habitat in which it grows, is called autecology.
2. Synecology
The major causes of distribution of communities and their structure, nature and development are studied under synecology.
Important Ecological Terms
Biome
Major terrestrial ecosystems of distinctive terrestrial areas, together with their climax plants and associated animals, are known as biomes.
Ecological Niche
The specific part of a habitat occupied by individuals of a species, characterized by its range of tolerance, range of movement, types of food, availability, microclimate, shelter, activity timing and related features, is called an ecological niche.
Ecotype
Species having a wide range of distribution may develop genetically adapted local populations. Such populations are called ecotypes.
Ecotone
The zone where two or more different communities meet and integrate is called a transition zone or ecotone.
Productivity
Productivity can be defined as the amount of energy produced or synthesized by producers of an ecosystem in a given area at a given time.
Ecological Factors (Ecofactors)
The various things, substances or factors affecting an ecosystem are known as ecological factors or ecofactors.
These factors determine the growth and survival of living organisms in an ecosystem.
They are divided into:
- Biotic factors
- Abiotic factors
Food Chain
The energy or nutrients in the form of food pass from one trophic level to another trophic level of an ecosystem through the repeated process of eating and being eaten. This process is called a food chain.
Food Chain in Pond Ecosystem
Food Chain in Grassland Ecosystem
Types of Food Chain
1. Grazing Food Chain
A food chain found in grassland which starts from a producer and ends with a tertiary consumer is known as a grazing food chain.
2. Detritus Food Chain
Detritus is decomposed organic matter. A food chain beginning with detritus and continuing through organisms feeding upon detritus is called a detritus food chain.
3. Parasitic Food Chain
The food chain which begins from a host and continues through parasites and hyperparasites is known as a parasitic food chain.
Food Web
In an ecosystem, more than one food chain operates. Different food chains remain interconnected with one another and form a complex network-like structure.
Such an interconnected network of different food chains is called a food web.
Ecological Pyramid
Different aspects of an ecosystem can be represented graphically in a pyramidal form. Such a representation is called an ecological pyramid.
An ecological pyramid may be:
- Upright – broad base and narrow top.
- Inverted – narrow base and broad top.
Types of Ecological Pyramid
1. Pyramid of Number
The graphical representation of the total number of individuals occupying a particular trophic level of an ecosystem in pyramidal form is called the pyramid of number.
| Ecosystem | Sequence Shown in Source | Form |
|---|---|---|
| Pond | Phytoplankton → Zooplankton → Small Fish → Large Fish | Upright |
| Grassland | Grass → Herbivores → Carnivores → Top Carnivores | Upright |
| Parasitic Food Chain | Tree → Birds → Lice / Hyperparasites | Inverted |
2. Pyramid of Biomass
The total dry weight of organisms is known as biomass.
The graphical representation of the total dry weight of organisms occupying particular trophic levels in pyramidal form is called the pyramid of biomass.
The source illustrates biomass pyramids for grassland, pond and parasitic systems.
3. Pyramid of Energy
The graphical representation of energy flow between different trophic levels of an ecosystem in pyramidal form is called the pyramid of energy.
The source diagrams show upright energy pyramids for pond, grassland and parasitic food chains.
Pond Ecosystem
A pond ecosystem is a freshwater ecosystem.
Pond water is ecologically described in the notes as lentic water. Therefore, a pond represents a lentic-water ecosystem.
Zones of Pond Water
| Zone | Depth According to Source |
|---|---|
| Littoral Zone | Up to approximately 6 metres depth |
| Limnetic Zone | Approximately 6–10 metres depth |
| Profound Zone | Below approximately 10 metres depth |
Structure of Pond Ecosystem
The pond ecosystem consists of:
- Abiotic components
- Biotic components
Abiotic Components of Pond Ecosystem
Non-living components of an ecosystem are called abiotic components.
1. Organic Substances
Organic substances include carbohydrates, proteins, lipids and nucleic acids synthesized by plants and essential for growth, development and maintenance of life.
2. Inorganic Substances
Inorganic substances include nitrates, sulphates and phosphates, which are necessary for the growth and development of living organisms.
3. Ecological Factors
Examples include:
- Sunlight
- Air
- Water
- Soil
Biotic Components of Pond Ecosystem
Living components of an ecosystem are called biotic components.
They include:
- Producers
- Consumers
- Decomposers
A. Producers
Living organisms which can synthesize their own food through photosynthesis are called producers.
Phytoplankton
Phytoplankton are rootless lower plants found floating on or near the surface of pond water.
Examples mentioned in the notes:
- Spirogyra
- Zygnema
- Volvox
Macrophytes
Macrophytes are rooted plants found growing in the pond. They are also called hydrophytes.
Floating Hydrophytes
Their leaves float on the water surface.
Example: Nymphaea.
Submerged Hydrophytes
The entire plant body remains inside pond water.
Example: Hydrilla.
Emergent Hydrophytes
These are rooted plants growing in the pond, but much of the plant body extends above the water.
Examples: Sagittaria, Ranunculus.
Consumers of Pond Ecosystem
Living organisms that cannot prepare their own food and obtain food from producers or other organisms are called consumers.
1. Primary Consumers
Primary consumers obtain food directly from producers.
Zooplankton
Zooplankton are lower animals floating in pond water. They are generally microscopic and may occur in colonies.
Examples:
- Daphnia
- Diaptus
Benthos
Benthos are comparatively larger animals found in pond water. They may feed on phytoplankton and hydrophytes.
Examples mentioned include:
- Water insects
- Molluscs
- Larvae
2. Secondary Consumers
Secondary consumers obtain food from primary consumers.
Examples:
- Frog
- Water snake
- Small fish
3. Tertiary Consumers
Organisms obtaining food from secondary consumers are called tertiary consumers.
Example: Large fish.
C. Decomposers
Decomposers are also called mineralizers. They act upon dead producers and consumers and convert complex organic matter into simpler forms.
They include saprophytic fungi and bacteria.
Examples mentioned in the notes include Mucor and Rhizopus.
Grassland Ecosystem
A grassland ecosystem is a terrestrial ecosystem.
According to the notes, grasslands are commonly found in subtropical regions of the world with moderate rainfall.
The source mentions:
- Koshi Tappu
- Shuklaphanta Wildlife Reserve
as examples associated with grassland ecosystems.
Structure of Grassland Ecosystem
Like the pond ecosystem, it consists of:
- Abiotic components
- Biotic components
Components of Grassland Ecosystem
A. Abiotic Components
Abiotic components include:
- Organic substances
- Inorganic substances
- Sunlight
- Air
- Water
- Soil
B. Biotic Components
1. Producers
Green plants capable of synthesizing food through photosynthesis are producers.
Examples mentioned in the notes include:
- Imperata
- Cynodon
- Trees
2. Primary Consumers
Grass-eating animals or herbivores and plant-feeding insects act as primary consumers.
Examples mentioned include:
- Grasshopper
- Millipede
- Centipede
- Other herbivorous animals
3. Secondary Consumers
Secondary consumers obtain food from primary consumers.
Examples listed in the source include:
- Fox
- Jackal
- Frog
- Lizards
- Snakes
4. Tertiary Consumers
These are top carnivores that obtain food from secondary consumers.
Examples:
- Eagle
- Hawks
5. Decomposers
Saprophytic fungi and bacteria decompose dead organic matter and return minerals to the environment.
Community
A community can be defined as the total living organisms, including plants, animals and microorganisms, occupying a natural habitat and maintaining relationships among themselves.
A population is the total number of individuals of a species occupying a particular habitat.
Thus, a community represents an assembly or group of different populations occupying a natural habitat.
Characteristics of Community
- Species diversity
- Dominance
- Growth form and structure
- Trophic structure or self-sufficiency
- Succession
Ecological Succession
Succession is the process of establishment of a community replacing an existing community in a natural habitat during the course of time.
It is a gradual process occurring slowly and continuously.
Succession begins with the establishment of a pioneer community and ends with the establishment of a climax community.
Pioneer Community
The community that initially occupies a natural habitat is called the pioneer community.
Climax Community
The community which finally occupies the natural habitat during the course of succession is called the climax community.
Types of Succession
Depending upon the nature of the bare area on which succession develops, succession is divided into:
- Primary succession
- Secondary succession
1. Primary Succession
Succession starting from a bare and sterile area, or from an area which has not previously been altered physically by organisms, is called primary succession.
Examples mentioned in the notes:
- Succession in a pond – Hydrosere
- Succession on bare rock – Lithosere
- Succession in desert – Xerosere
2. Secondary Succession
Succession beginning in an area that was previously colonized but has been cleared is known as secondary succession.
It may occur when the major species of a community are destroyed by:
- Fire
- Erosion
- Wind
- Flood
- Human activities
General Process of Succession
The general process of succession is carried out through sequential steps.
Nudation
Nudation is the development of a nude or bare area without any form of life on it.
A nude area may be formed due to:
- Landslide
- Erosion
- Fire
- Human activities
Invasion
The successful establishment of species in a nude area is called invasion.
Coaction and Competition
Competition for food and space develops among individual species due to an increase in the number of different species.
Species that cannot compete may be replaced from the community. However, according to the notes, species having high productivity and a broad ecological amplitude may continue to be maintained in the area.
Reaction
Reaction is the process of modification of the environment due to the influence of living organisms on it.
Environmental conditions such as:
- Soil
- Water
- Light
- Temperature
may change as a result of reaction.
Stabilization of Climax
The climax community becomes more or less stable for a longer period of time and is not readily replaced by other communities.
Succession at a Glance
Quick Revision
- Ecology studies relationships between organisms and their environment.
- Ecology is divided into autecology and synecology.
- Major terrestrial ecosystems are called biomes.
- An ecological niche describes the particular role and position of a species in its habitat.
- A locally adapted population is called an ecotype.
- The transition zone between communities is called an ecotone.
- Ecological factors are biotic and abiotic.
- Biotic factors include producers, consumers and decomposers.
- Abiotic factors include topographic, climatic and edaphic factors.
- Transfer of food and energy through trophic levels forms a food chain.
- Grazing, detritus and parasitic food chains are described in the notes.
- Interconnected food chains form a food web.
- Ecological pyramids may be upright or inverted.
- The three ecological pyramids are pyramid of number, biomass and energy.
- A pond ecosystem is a freshwater lentic ecosystem.
- The notes divide pond water into littoral, limnetic and profound zones.
- Producers in a pond include phytoplankton and macrophytes.
- Primary consumers include zooplankton and benthos.
- Small fish, frogs and water snakes may act as secondary consumers.
- Large fish are described as tertiary consumers.
- Fungi and bacteria function as decomposers.
- Grassland is a terrestrial ecosystem.
- A community consists of different populations occupying the same natural habitat.
- Community characteristics include diversity, dominance, structure, trophic structure and succession.
- Succession begins with a pioneer community and ends with a climax community.
- Succession may be primary or secondary.
- Hydrosere occurs in water, lithosere on bare rock and xerosere in desert according to the notes.
- The succession sequence given is nudation → invasion → coaction and competition → reaction → stabilization of climax.
Important Questions
- Define ecology.
- Differentiate between autecology and synecology.
- What is a biome?
- Define ecological niche.
- What are ecotypes?
- What is an ecotone?
- Define productivity.
- What are ecological factors?
- Classify ecological factors.
- Differentiate between biotic and abiotic factors.
- What are topographic, climatic and edaphic factors?
- Define food chain with examples.
- Describe the types of food chains.
- What is a grazing food chain?
- What is a detritus food chain?
- What is a parasitic food chain?
- Define food web.
- What is an ecological pyramid?
- Differentiate between upright and inverted ecological pyramids.
- Describe the pyramid of number.
- Describe the pyramid of biomass.
- Describe the pyramid of energy.
- What is a pond ecosystem?
- Describe the different zones of pond water.
- Describe the abiotic components of a pond ecosystem.
- Describe the biotic components of a pond ecosystem.
- What are phytoplankton?
- What are macrophytes?
- Differentiate between floating, submerged and emergent hydrophytes.
- What are zooplankton?
- What are benthos?
- Explain primary, secondary and tertiary consumers in a pond.
- Write a short note on decomposers.
- Describe the grassland ecosystem.
- Describe the structure of a grassland ecosystem.
- Define community.
- Differentiate between population and community.
- Write the characteristics of a community.
- Define ecological succession.
- What are pioneer and climax communities?
- Differentiate between primary and secondary succession.
- What are hydrosere, lithosere and xerosere?
- Explain the general process of succession.
- What is nudation?
- What is invasion?
- Explain coaction and competition during succession.
- What is reaction in ecological succession?
- Explain stabilization of climax.
Discussion
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