Topics to be Learn : 

  • Introduction
  • Ecosystem
  • Energy flow
  • Ecological pyramids
  • Nutrient cycles
  • Ecological succession
  • Ecosystem services

Ecosystem
  • Definition: Structural and functional unit of nature, self-regulating and self-sustaining.
  • Made up of biotic (living) and abiotic (non-living) elements.

Types of Ecosystems:

  1. Terrestrial Ecosystems:

    Forest, grassland, desert.

  2. Aquatic Ecosystems:

    Lakes, wetlands, rivers, estuaries.

  3. Natural Ecosystems:

    Operate under natural conditions. E.g., grasslands, forests, lakes.

  4. Artificial Ecosystems:

    Man-engineered, dependent on human maintenance. E.g., croplands, aquariums.

Dynamics of Ecosystem:

  • Input: Productivity.
  • Transfer of Energy: Food chain, food web, nutrient cycling.
  • Output: Degradation, energy loss.

Structure and Function:

  • Physical Structure: Result of biotic and abiotic interaction.
  • Species Composition: Identified by regional plant and animal species.
  • Spatial Patterns: Result from differences in space and time.

Stratification and Zonation:

  1. Stratification:

    • Vertical pattern based on organism height.
    • E.g., forest community.

    Examples:

    • Trees, herbs, shrubs (plants).
    • Epipelagic, mesopelagic, bathypelagic, benthic (aquatic).
     

  2. Zonation:

    • Horizontal distribution along ground or water.
    • Density and distribution vary along gradients.

    Examples:

    • Aquatic System:
      • Intertidal, littoral, sublittoral zones.
    • Wetlands:
      • Subtidal channels, mudflats, low marsh, high marsh.

Zonation in Wetlands:


Functional Aspects of Ecosystem:

(i) Productivity:

  • Conversion of inorganic substances into organic material by autotrophs using solar energy.
  • Autotrophs: Organisms that produce their own food.
  • Gross Primary Productivity (GPP):
    • Rate of organic matter production by photosynthesis.
    • Measure of total energy captured by autotrophs.
  • Net Primary Productivity (NPP):
    • NPP = GPP - respiratory losses.
    • Available biomass for heterotrophs.
  • Factors Affecting GPP:
    • Resident plant species
    • Nutrient availability
    • Photosynthetic capacity
    • Type of ecosystem
  • Secondary Productivity:
    • Rate of new organic matter formation by consumers.
    • Provides energy for next trophic levels.

(ii) Decomposition:

  • Breakdown of complex organic material into inorganic minerals.
  • Detritus: Raw material for decomposition.

 Steps of Decomposition:
  1. Fragmentation:
    • Break down detritus into smaller fragments or particles.
  2. Leaching:
    • Water-soluble inorganic nutrients percolate into soil.
  3. Catabolism:
    • Bacterial and fungal enzymes degrade detritus into simpler inorganic substances.
  4. Humification:
    • Accumulation of humus, partially decomposed organic material.
  5. Mineralization:
    • Humus further degraded, releasing inorganic nutrients.

Factors Regulating Decomposition:

  • Oxygen Availability:
    • Oxygen is essential for decomposition.
  • Detritus Chemical Composition:
    • Rich in lignin and chitin: Slower decomposition.
    • Rich in nitrogen and sugars: Faster decomposition.
  • Climatic Factors:
    • Temperature and soil moisture affect decomposition.
  • Temperature and Soil Moisture:
    • Warm and moist: Faster decomposition.
    • Low temperature, oxygen absence: Inhibited decomposition.

(iii) Nutrient Cycling:

  • Definition: Storage and transport of nutrients.

(iv) Energy Flow:

  • Definition: Unidirectional flow of energy from producer to consumer.
  • Energy dissipates as heat during flow.

Energy Flow:

  • Source of Energy: Sun for terrestrial ecosystems.
  • Solar Radiation: Less than 50% is photosynthetically active (PAR), 2-10% sustains life.
  • Producers: Convert solar energy into complex carbohydrates.
  • Unidirectional Flow: Sun → Producers → Consumers.
  • Second Law of Thermodynamics: Operates in ecosystems, countered by producers and consumers.
  • Organisms: Constant energy needed for survival and synthesis.
  • Primary Producers:
    • Terrestrial: Herbaceous and woody plants.
    • Aquatic: Phytoplankton and algae.
  • Food Chain/Food Web:
    • Interdependency among organisms.
    • Energy flows from producers to consumers.
    • Producer's death initiates detritus food chain/web.

Concept of Energy Flow:

  • Efficiency of Producers:

    • Absorption and conversion of solar energy.

  • Quantity of Converted Energy:

    • Used by consumers.

  • Total Input of Energy:

    • Food and its assimilation efficiency by consumers.

  • Energy Loss:

    • Through respiration, heat, excretion, etc.

  • Ultimate Gross Net Production.

  • Energy captured by autotrophs never returns to the sun, ensuring unidirectional flow.

  • Energy flow is progressive through trophic levels, with decreasing energy.

  • Shorter food chains have more available food energy.

  • Longer chains result in more energy loss.

Food Web:
  • Interconnections between multiple food chains.
  • Energy flow interconnected through numerous food chains.
  • One organism can feed on multiple types of organisms.
  • Difficult to calculate energy flow.
  • Increased stability due to complex food chains.
  • Not disturbed by removal of one group of organisms.
  • Higher trophic level organisms feed on various lower trophic level organisms.
  • Contains numerous trophic levels and species populations.
  • Competition occurs within and between trophic levels.
  • No distinct types in food web.

 Consumers:
  • Definition: Animals depending on plants for food; heterotrophs or consumers.
  • Primary Consumers:
    • Definition: Feed directly on producers.
    • Example: Herbivorous animals, insects, birds, some mammals.
  • Secondary Consumers:
    • Definition: Consume other animals.
    • Example: Carnivores.
  • Tertiary Consumers:
    • Definition: Feed on secondary consumers.
    • Example: In the food chain "Plant -> Insect -> Frog -> Snake", frog is a secondary consumer and snake is a tertiary consumer.

Food Chain:


  • Definition: Linear sequence of organisms for feeding.
  • Energy Flow: Single straight pathway from lower to higher trophic levels.
  • Members at Higher Trophic Level:
    • Feed on a single type of organism.
  • Calculation of Energy Flow: Easy.
  • Instability: Increases due to separate and confined food chains.
  • Impact of Disturbance: Affects the whole chain.
  • Members of Higher Trophic Level:
    • Depend on a single type of organism from lower trophic level.
  • Number of Trophic Levels: Typically 4-6.
  • Competition: Occurs among members of the same trophic level.

 Types of Food Chains and Energy Flow:

1. Grazing Food Chain (GFC):

  • Definition: Involves organisms that directly consume producers.
  • Example: Grass → Rabbit → Fox.
  • Energy Flow:
    • Starts with producers.
    • Transfers energy directly from one trophic level to the next.
    • Majority of energy flow occurs through this chain in terrestrial ecosystems.
  • Interconnections:
    • Some organisms from the detritus food chain serve as prey.
    • Omnivores like cockroaches, crows, pigs, and humans can be part of both chains.

2. Detritus Food Chain (DFC):

  • Definition: Comprised of decomposers starting with dead and decaying matter.
  • Example: Dead Leaves → Fungi → Bacteria.
  • Energy Flow:
    • Begins with dead organic matter.
    • Decomposers degrade dead material into simple inorganic materials.
    • Absorb these materials for energy.
  • Interconnections:
    • Some DFC organisms serve as prey for GFC animals.
    • Forms interconnections with grazing food chains.

Interconnections between GFC and DFC:

  • Some organisms from DFC serve as prey for GFC animals.
  • Omnivores bridge both chains.
  • Food Web: Natural interconnection of food chains.

Energy Flow in Food Chains:
  • Decrease in Energy:
    • Energy available reduces at each trophic level.
  • 10% Law (R. Lindermann, 1942):
    • Only 10% of energy is transferred to each trophic level as net energy.
  • Functionality of Trophic Levels:
    • Transfer energy when functional.
  • Interconnected Nature:
    • Food chains form a web to maintain ecosystem stability.
     

Ecological Pyramids:

  • Definition: Graphic representation of relationships between organisms at successive trophic levels regarding energy, biomass, and number.
  • Origin: Developed by C. Elton in 1927.

 Characteristics:
  • Each pyramid's base corresponds to producers (first trophic level), and its tip to tertiary consumers (top level).
  • Consideration of all organisms at each trophic level in calculations.
  • Trophic levels represent functional levels, not specific species.

Types of Ecological Pyramids:

  1. Pyramid of Biomass:

    • Represents the biomass (total mass of organisms) at each trophic level.
    • Biomass calculations include all organisms at that level.
    • Usually upright, with producers having the most biomass.
     

  2. Pyramid of Numbers:

    • Represents the number of organisms at each trophic level.
    • Includes all organisms regardless of size.
    • Generally upright, with producers having the highest number.

  3. Pyramid of Energy:

    • Represents the energy content at each trophic level.
    • Energy calculations consider energy available for consumption.
    • Always upright due to energy loss as heat at each step.

Observations:

  • Producers outnumber consumers, and biomass is greater for producers than herbivores.
  • Primary consumers outnumber carnivores.
  • Energy decreases as it moves up trophic levels due to energy loss as heat.
  • Energy pyramid shows the amount of energy per unit area over time.

Pyramid of Numbers:

  • Definition: Diagrammatic representation showing the relationship between producers, herbivores, and carnivores at successive trophic levels based on their numbers.
  • Relationship:
    • As trophic levels increase, the number of interdependent organisms decreases.
    • Example: Grasses > Herbivores (Rabbits) > Carnivores (Foxes).
  • Pattern:
    • Producers > Primary Consumers > Secondary Consumers > Tertiary Consumers.
    • Pyramid is upright, indicating more producers than consumers.

Pyramid of Biomass:

  • Definition: Represents biomass at each trophic level.
  • Construction: Considers biomass at every trophic level.
  • Exceptions:
    • In sea ecosystems, often inverted due to fish biomass exceeding that of phytoplankton.
    • Insects and birds thriving on a single huge tree may show inverted pyramid of numbers.

Differences between Upright and Inverted Pyramid of Biomass:

 

Limitations of Ecological Pyramids:

  • Overlap of Species: Same species may belong to multiple trophic levels, but pyramids don't account for this.
  • Simplicity: Based on simple food chains; doesn't reflect the complex trophic relationships of ecosystems, which are often in the form of food webs.
  • Exclusion of Saprophytes: Vital decomposers like saprophytes are not included in ecological pyramids, despite their significant role in ecosystems.

Nutrient Cycles:

Nutrient Cycling (Biogeochemical Cycle): Movement of nutrient elements through various components of an ecosystem.

Types of Nutrient Cycles:

  1. Gaseous Cycles: Nitrogen, Oxygen, and Carbon cycles with atmosphere as reservoir.
  2. Sedimentary Cycles: Phosphorus, Sulphur cycles with Earth's crust as reservoir.

Carbon Cycle (Gaseous Cycle):

  • Processes: Five basic processes drive the carbon cycle: Photosynthesis, respiration, decomposition, sedimentation, and combustion.

  • Main Component: Carbon is the main component of all organic compounds in protoplasm.

  • Organism Composition: Carbon constitutes 49% of the dry weight of organisms.

  • Global Distribution: 71% of global carbon is present in oceans.

  • Regulation: Oceanic reservoirs regulate atmospheric carbon dioxide.

  • Long-Term Storage: Carbon stored in rocks and fossil fuels acts as long-term storage.

  • Fossil Fuel Usage: Combustion of fossil fuels releases stored carbon dioxide into the atmosphere.

  • Elemental Carbon: Found in seawater, atmosphere, limestone, coal, soil, and living beings.

  • Movement: Carbon dioxide is absorbed by plants during photosynthesis and released during respiration.

  • Food Chains: Carbon moves along food chains.

  • Decomposition: Decomposers release carbon dioxide during the decomposition of organic matter.

  • Fossil Fuel Burning: Industrial and vehicular activities release carbon dioxide.

  • Carbon Release: Annually, 5.5 billion tonnes of carbon are released into the atmosphere through fossil fuel combustion, with 3.3 billion tonnes remaining.

  • Ocean Dissolution: Some carbon dissolves in seawater, forming calcium or magnesium carbonate compounds used by marine animals to make shells.

  • Natural Sources: Forest fires and volcanic activities are natural sources of carbon dioxide.

  • Human Impact:

    • Fossil Fuel Combustion: Transportation, industrial activities, and power plants release large amounts of carbon dioxide into the atmosphere.
    • Deforestation: Rapid deforestation disrupts the carbon balance by reducing the number of trees that absorb carbon dioxide during photosynthesis.

  • Consequences:

    • Global Warming: Increased carbon dioxide levels contribute to global warming and climate change.
    • Disturbed Equilibrium: Deforestation disturbs the natural carbon balance, leading to increased atmospheric carbon dioxide levels.
    • Massive Fossil Fuel Use: Increases the rate of carbon dioxide emissions, exacerbating global warming and climate change.

 Phosphorus Cycle (Sedimentary Cycle): 

  • Movement: Phosphorus cyclically moves through the hydrosphere, lithosphere, and biosphere.
  • Biological Importance: Phosphorus is a major constituent of biological membranes, nucleic acids, and cellular energy transfer systems.
  • Animal Requirement: Animals require phosphorus for the formation of shells, bones, hooves, and teeth.
  • Natural Reservoirs: Rocks containing phosphates act as natural reservoirs.
  • Weathering: Weathering of rocks releases minute amounts of phosphates into the soil solution, which are then absorbed by plants.
  • Herbivores and Animals: Herbivores and other animals obtain phosphorus by consuming plants.
  • Decomposition: Phosphorus is released during the decomposition of waste products and dead organisms by phosphate-solubilizing bacteria.
  • Limiting Factor: Phosphorus is often in short supply and acts as a limiting factor for plant growth.
  • Eutrophication: Eutrophication occurs due to the sudden influx of phosphorus into water bodies from agricultural runoff or industrial effluents rich in phosphate content.
    • Consequence: Eutrophication leads to the overgrowth of algae, which can harm or kill aquatic life.

Ecological Succession:

Definition: Ecological succession refers to the steady and often predictable shift in the species composition of a particular area over time, representing a long-term response by the community to environmental changes.

Climax Community: A climax community is a community that is in near equilibrium with the environment after ecological succession, where the change is sequential and environmentally regulated.

Process of Succession:

  1. Nudation: Succession begins with the development of a bare site due to disturbances.

  2. Migration: Tiny seeds or propagules arrive during this phase.

  3. Ecesis: Ecesis is the establishment and initial growth of vegetation.

  4. Competition: Well-formed vegetation competes with other species for space, light, and nutrients.

  5. Reaction: Autogenic changes such as the build-up of humus affect the habitat, leading to the replacement of one plant community by another.

  6. Stabilization: The better-adapted community becomes stable, forming a climax community.

Sere: A sere is the entire sequence of communities that successively change in a given area. Seral stages or seral communities are the individual transitional communities in this sere.

Changes in Seral Stages:

  • Change in Species Diversity: The diversity of species of organisms changes over time.

  • Increase in Number of Species: The number of species and organisms increases.

  • Increase in Total Biomass: The total biomass also increases as the succession progresses.

Additional Information:

  • Similar successions have occurred over millions of years, forming present-day global communities.

  • Succession and evolution were parallel processes in the past and continue to be so in the present.


Types of Succession:

1. Primary Succession: Primary succession refers to the initial development of life on a barren piece of land.

  • Occurrence: Primary succession occurs on newly cooled lava, rocks, and newly created ponds or reservoirs. It takes millions of years to develop the whole biomass on a newly formed volcanic island.

  • Changes in Seral Stages: There is a change in the diversity of species of organisms, an increase in the number of species and organisms, and an increase in the total biomass over successive seral stages.

  • Speed: The establishment of a new biotic community is generally slow and takes millions of years.

  • Factors: Primary succession depends on climatic conditions, soil characteristics, and natural processes.

2. Secondary Succession: Secondary succession occurs in areas where all existing life forms were lost.

  • Occurrence: It begins in places like abandoned farmlands, burned or cut forests, or lands that have been flooded. Secondary succession is faster as some abiotic factors such as soil or sediment are already present.

  • Impact of Vegetation Changes: Changes in vegetation also affect various types of animals and decomposers, as animals depend on plants for food and shelter.

  • Disturbances: Natural or human-induced disturbances, such as fire or deforestation, can convert a particular seral stage of succession to an earlier stage or create new conditions that encourage some species while eliminating others.

Succession of Plants:

  • Hydrarch and Xerarch: Succession of plants can be hydrarch (in wet areas) or xerarch (in very dry areas) based on the nature of the habitat.

  • Hydrarch Succession: Progresses from hydric to mesic conditions.

  • Xerarch Succession: Progresses from xeric to mesic conditions.

  • Result: Both hydrarch and xerarch successions lead to mesic conditions, neither too xeric nor too hydric.

 

Pioneer Species:

Pioneer species are the first to invade a bare area during primary succession.

  • Examples: Crustose lichens are often pioneer species, as they can secrete acids to dissolve rock, aiding in weathering and soil formation.

  • Succession Process: They are followed by bryophytes and mosses, which can take hold in the small amount of soil. Herbaceous plants come next, and after several more stages, a stable climax forest community is formed.

Ecosystem Services:

Ecosystem services are the byproducts of ecosystem processes, encompassing commodities and services in economics, the environment, and various human activities.

Definition:According to the Millennium Ecosystem Assessment (2005), ecosystem services are any advantages that people derive from an ecosystem.

Types of Ecosystem Services:

  1. Supporting Services:
    • Description: These services include nutrient cycling, primary production, soil formation, habitat provision, and pollination, all of which maintain the balance of the ecosystem.
  2. Provisioning Services:
    • Description: Provisioning services encompass food (including seafood), raw materials (like timber, skins, and fuelwood), genetic resources (including crop improvement genes), water, medicinal resources, and ornamental resources (such as furs, feathers, and orchids).
  3. Regulating Services:
    • Description: Regulating services involve carbon sequestration, predation to regulate prey populations, waste decomposition and detoxification, purification of water and air, and pest control.
  4. Cultural Services:
    • Description: Cultural services include spiritual and historical significance, recreational experiences, scientific and educational value, and therapeutic benefits (including animal-assisted therapy).

Main Ecological Services:

  1. Fixation of Atmospheric CO2 and Release of O2:
    • Description: Photosynthesis fixes atmospheric CO2 and releases O2, while respiration intakes oxygen and releases CO2. This balance is crucial for maintaining atmospheric composition.
  2. Pollination:
    • Description: Pollination, facilitated by wind, water, or biotic agents, is essential for plant reproduction and ecosystem health.
  3. Maintaining Biodiversity:
    • Description: Ecosystems maintain biodiversity, supporting a wide variety of species and genetic diversity, which is critical for ecological resilience and stability.

These services highlight the essential role of ecosystems in supporting human well-being, economic activities, and environmental health.