Unit 2: Ecosystem and biodiversity

1. Concept of an Ecosystem

An ecosystem is a functional unit of nature, where living organisms (biotic components) interact among themselves and with their surrounding physical environment (abiotic components). The term was coined by A.G. Tansley in 1935.

1.1. Structure and Function of an Ecosystem

A. Structure of an Ecosystem

The structure of an ecosystem is characterized by the organization of both biotic and abiotic components.

• Abiotic (Non-living) Components: These are the physical and chemical factors of the environment.

  • Physical Factors: Sunlight, temperature, rainfall, humidity, soil texture, water availability.
  • Chemical Factors: Nutrients (carbon, nitrogen, phosphorus), pH, salinity, soil composition.

• Biotic (Living) Components: These include all living organisms, categorized based on their nutritional (trophic) level.

  • Producers (Autotrophs): Organisms that synthesize their own food, typically through photosynthesis. They form the base of the food chain.
    • Examples: Green plants, algae, cyanobacteria.
  • Consumers (Heterotrophs): Organisms that obtain energy by feeding on other organisms.
    • Primary Consumers (Herbivores): Feed directly on producers. Examples: Grasshopper, deer, cow, rabbit.
    • Secondary Consumers (Carnivores): Feed on primary consumers. Examples: Frog, fox, snake.
    • Tertiary Consumers (Top Carnivores): Feed on secondary consumers. Examples: Lion, hawk, tiger.
    • Omnivores: Feed on both plants and animals. Examples: Humans, bears, crows.
  • Decomposers (Saprotrophs): Organisms that break down dead organic matter (dead plants, animals, and waste products) and return nutrients to the soil, making them available for producers. They are essential for nutrient cycling.
    • Examples: Bacteria, fungi.

B. Function of an Ecosystem

The function of an ecosystem is a result of the interactions between its components and involves:

• Energy Flow: The unidirectional flow of energy from the sun to producers and then to consumers.
• Nutrient Cycling (Biogeochemical Cycles): The cyclic movement of nutrients like carbon, nitrogen, and phosphorus between biotic and abiotic components.
• Ecological Succession: The process of change in the species structure of an ecological community over time.
• Homeostasis (Self-regulation): The ability of an ecosystem to maintain its structure and function in a stable state.

1.2. Food Chains and Food Webs

• Food Chain: A linear sequence of organisms where nutrients and energy are transferred from one organism to another. It shows "who eats whom".

  • Example: Grass → Grasshopper → Frog → Snake → Hawk
  • Types of Food Chains:
    1. Grazing Food Chain (GFC): Starts with green plants (producers) and moves to herbivores and then to carnivores. This is the major food chain in most aquatic and terrestrial ecosystems.
    2. Detritus Food Chain (DFC): Starts with dead organic matter (detritus), which is consumed by decomposers (like bacteria and fungi), and then by detritivores (like earthworms), which are in turn eaten by smaller carnivores.

• Food Web: An interconnected network of multiple food chains in an ecosystem. It represents all the possible energy pathways and is a more realistic representation of trophic relationships than a simple food chain.

                  Hawk (Tertiary/Quaternary Consumer)
                 /     \
                /       \
      Snake (Tertiary Consumer)   Fox (Secondary Consumer)
            |                   /       \
           Frog (Secondary)    Rabbit (Primary)   Mouse (Primary)
             |                 |               /
        Grasshopper (Primary)    |              /
              \                /             /
               \              /             /
                 Grass / Plants (Producer)

1.3. Ecological Pyramids

An ecological pyramid is a graphical representation designed to show the biomass or productivity at each trophic level in a given ecosystem. The base is always the producers.

• Pyramid of Numbers: Represents the total number of individual organisms at each trophic level.

  • Upright: In most ecosystems (e.g., grassland, pond), the number of individuals decreases at successive trophic levels.
  • Inverted: In a tree ecosystem, one large tree (producer) can support thousands of insects (primary consumers).

• Pyramid of Biomass: Represents the total dry weight (biomass) of organisms at each trophic level.

  • Upright: In most terrestrial ecosystems, the biomass of producers is greater than that of consumers.
  • Inverted: In some aquatic ecosystems (e.g., ocean), the biomass of producers (phytoplankton) is much less than the biomass of consumers (zooplankton and fish) because phytoplankton have a very short lifespan and reproduce rapidly.

• Pyramid of Energy: Represents the total amount of energy at each trophic level.

  • Always Upright: This pyramid can never be inverted because there is always a progressive loss of energy at each successive trophic level, according to the second law of thermodynamics.

1.4. Energy Flow in the Ecosystem

• Unidirectional Flow: Energy flows in one direction: from the sun to producers, then to consumers, and is eventually lost as heat. It does not cycle back.
• The 10% Law (Lindeman's Law): During the transfer of energy from one trophic level to the next, only about 10% of the energy is stored as biomass and becomes available to the next level. The remaining 90% is lost during metabolic processes (respiration, digestion) or remains in uneaten parts.

1.5. Ecological Succession

Ecological succession is the gradual and fairly predictable change in the species composition of a given area over time.

• Primary Succession: Occurs in a lifeless area where no soil exists, such as on a bare rock after a volcanic eruption or a newly formed sand dune.

  • Pioneer Species: The first species to colonize the barren area (e.g., lichens, mosses).
  • Climax Community: The final, stable, and mature community that is in equilibrium with its environment. This process is very slow, taking hundreds or thousands of years.

• Secondary Succession: Occurs in an area that previously supported life but has undergone a disturbance, such as a forest fire, flood, or abandoned farmland. Soil is already present.

  • This process is much faster than primary succession because the starting point (soil, some seeds) already exists.

2. Types, Features, Structure and Function of Ecosystems

2.1. Forest Ecosystem

• Characteristic Features: Dominated by trees and woody vegetation. High rainfall, rich soil, and a wide variety of flora and fauna.
• Structure:
  • Abiotic: Soil, water, sunlight, temperature.
  • Biotic:
    • Producers: Trees (e.g., Teak, Sal), shrubs, herbs.
    • Consumers: Herbivores (deer, elephants), carnivores (tigers, leopards), omnivores (bears).
    • Decomposers: Bacteria, fungi.
  • Stratification: Vertical layers are distinct: Forest floor, herb layer, shrub layer, understory, and canopy.
• Function:
  • Major carbon sinks, regulating the climate.
  • Provide timber, fuel, and other forest products.
  • Support immense biodiversity.
  • Regulate hydrological cycles and prevent soil erosion.

2.2. Grassland Ecosystem

• Characteristic Features: Dominated by grasses with few or no trees. Occur in regions of moderate rainfall.
• Structure:
  • Abiotic: Soil rich in organic matter, limited rainfall, high evaporation rates.
  • Biotic:
    • Producers: Grasses (e.g., Cynodon, Dicanthium), forbs.
    • Consumers: Grazing herbivores (cows, deer, zebra), carnivores (foxes, snakes, hawks).
    • Decomposers: Bacteria, fungi.
• Function:
  • Support large populations of grazing animals and livestock.
  • Help in soil formation and conservation.
  • Used for agriculture and animal husbandry.

2.3. Desert Ecosystem

• Characteristic Features: Extremely low rainfall (less than 25 cm/year), high temperature fluctuations, and sparse vegetation. Can be hot (e.g., Thar) or cold (e.g., Ladakh).
• Structure:
  • Abiotic: Sandy or rocky soil, high sunlight, extreme temperatures, lack of water.
  • Biotic:
    • Producers: Cacti, succulents, shrubs (plants with adaptations like deep roots, waxy cuticles, and thorns).
    • Consumers: Animals adapted to conserve water (nocturnal, burrowing) like camels, reptiles, rodents.
    • Decomposers: Thermophilic bacteria and fungi.
• Function:
  • Rich source of minerals.
  • Home to specialized species adapted to xeric conditions.

2.4. Aquatic Ecosystems

A. Ponds/Lakes (Lentic or Still Water)

• Characteristic Features: Standing body of water.
• Structure:
  • Zones:
    1. Littoral Zone: Shallow, near-shore area where light penetrates to the bottom. Rooted plants are found here.
    2. Limnetic Zone: Open water zone with effective light penetration. Main producers are phytoplankton.
    3. Profundal Zone: Deep water region below the limnetic zone where light does not penetrate.
    4. Benthic Zone: The bottom of the lake, inhabited by decomposers and detritivores.
  • Biotic: Phytoplankton, zooplankton, aquatic plants, fish, insects, amphibians.

B. Streams/Rivers (Lotic or Flowing Water)

• Characteristic Features: Unidirectional flow of water. Higher dissolved oxygen content than lentic systems.
• Structure: Organisms are adapted to resist water currents (e.g., streamlined bodies, attachment organs).
• Function: Essential for water supply, irrigation, and transportation.

C. Oceans (Marine Ecosystem)

• Characteristic Features: Largest and most stable ecosystem. High salinity.
• Structure:
  • Zones:
    1. Intertidal Zone: Area between high and low tide.
    2. Neritic Zone: Shallow region over the continental shelf.
    3. Oceanic Zone: The vast open ocean beyond the continental shelf.
    4. Photic Zone: Upper layer where sunlight penetrates (photosynthesis occurs).
    5. Aphotic Zone: Lower layer with no sunlight.
  • Biotic: Phytoplankton (diatoms), zooplankton, coral reefs, fish, whales, deep-sea organisms.

D. Estuaries

• Characteristic Features: A transition zone where a river meets the sea. Water is brackish (a mix of fresh and saltwater).
• Structure: Subject to tidal action. High nutrient levels.
• Function:
  • Among the most productive ecosystems in the world.
  • Act as a nursery ground for many species of fish and shellfish.
  • Filter pollutants from river water before it enters the ocean.

3. Introduction to Biodiversity

Biodiversity or Biological Diversity refers to the variety and variability of life on Earth. It encompasses all living organisms, their genetic differences, and the ecosystems they form. The term was popularized by sociologist Edward O. Wilson.

3.1. Levels of Biodiversity

• Genetic Diversity: The variation in genes within a single species.

  • High genetic diversity allows a species to adapt to changing environments.
  • Example: Different varieties of rice (e.g., Basmati, Sona Masuri) or mangoes. The medicinal plant Rauwolfia vomitoria growing in different Himalayan ranges shows genetic variation in the potency of the chemical reserpine it produces.

• Species Diversity: The variety of different species (number and abundance) within a region.

  • It is measured by species richness (the number of different species) and species evenness (the relative abundance of different species).
  • Example: The Western Ghats have a greater diversity of amphibian species than the Eastern Ghats.

• Ecosystem (or Ecological) Diversity: The variety of habitats, biological communities, and ecological processes in the biosphere.

  • It refers to the diversity of different ecosystems within a geographical location.
  • Example: India has a greater ecosystem diversity (deserts, rainforests, mangroves, coral reefs, wetlands) than a Scandinavian country like Norway.

3.2. Biodiversity at Global, National, and Local Levels

• Global Level: The tropics are the richest in biodiversity. Scientists have recorded more than 1.5 million species, but estimates of the total number of species range from 5 to 30 million.
• National Level (India): India is one of the 17 mega-diverse countries in the world. With only 2.4% of the world's land area, India accounts for about 7-8% of all recorded species.
• Local Level: Biodiversity can be assessed at a community or ecosystem level, such as the number of species in a particular forest, lake, or village.

3.3. Hotspots of Biodiversity

A biodiversity hotspot is a biogeographic region with significant levels of biodiversity that is threatened by human habitation.

• Criteria (as defined by Norman Myers):

  1. It must have at least 1,500 species of vascular plants as endemics (>0.5% of the world’s total).
  2. It has to have lost at least 70% of its original habitat.

• Global Hotspots: There are currently 36 recognized biodiversity hotspots.

• Hotspots in India: India has four biodiversity hotspots:

  1. The Himalayas: Includes the entire Indian Himalayan region.
  2. The Western Ghats & Sri Lanka: A chain of mountains running along the western coast of India.
  3. Indo-Burma Region: Includes northeastern India (except Assam), Andaman Islands, and parts of Southeast Asia.
  4. Sundaland: Includes the Nicobar Islands.

4. Value of Biodiversity

The value of biodiversity can be categorized into direct and indirect values.

• Consumptive Use Value (Direct): Goods harvested and consumed directly without passing through a market.

  • Examples: Firewood, fodder, food (fruits, vegetables, meat), water.

• Productive Use Value (Direct): Products that are commercially harvested and marketed.

  • Examples: Timber from forests, silk from silkworms, wool from sheep, medicinal drugs derived from plants (e.g., quinine from Cinchona tree, taxol from Yew tree).

• Social Value: Values associated with social life, customs, religion, and psycho-spiritual aspects.

  • Examples: The reverence for certain plants and animals in Indian culture (e.g., Tulsi, Peepal tree, cow).

• Ethical Value: The belief that all forms of life have a right to exist, regardless of their value to humans. It is based on the principle of "live and let live".

• Aesthetic Value: The beauty of nature that provides pleasure, inspiration, and contributes to ecotourism.

  • Examples: Bird-watching, trekking, wildlife photography, visiting national parks.

• Option Values: The potential of biodiversity to provide economic benefits to human society in the future.

  • Examples: A plant species that is not currently used might contain a cure for a future disease. Exploring species for genes that can be used in genetic engineering.

5. Threats to Biodiversity

The accelerated rate of species extinction is largely due to human activities. This is often called "The Evil Quartet".

• Habitat Loss and Fragmentation: This is the primary driver of biodiversity loss.

  • Habitat Loss: Complete destruction of natural habitats for agriculture, urbanization, mining, and dam construction. (e.g., Deforestation of tropical rainforests).
  • Habitat Fragmentation: Breaking up a large, continuous habitat into smaller, isolated patches, which harms species with large territories (e.g., tigers, elephants).

• Poaching of Wildlife: Illegal hunting, killing, or capturing of wild animals.

  • Animals are poached for their valuable products like horns (rhinoceros), ivory (elephants), skin (tigers), and for use in traditional medicine. This has driven many species to the brink of extinction.

• Man-Wildlife Conflicts: Struggles that arise when the presence or behavior of wildlife poses a direct and recurring threat to human interests or needs, leading to a negative impact on both humans and their resources as well as the wildlife.

  • Causes: Habitat encroachment by humans, crop raiding by animals (e.g., elephants, monkeys), livestock predation by carnivores (e.g., leopards, tigers).
  • Consequences: Retaliatory killings of animals, financial loss to farmers, human injury or death.

• Endangered and Endemic Species of India

  • Endangered Species: A species that is at a very high risk of extinction in the wild.
    • Examples: Bengal Tiger, Asiatic Lion, Snow Leopard, One-horned Rhinoceros, Gangetic Dolphin.
  • Endemic Species: Species that are found only in a particular geographical region and nowhere else in the world.
    • Examples: Lion-tailed Macaque (Western Ghats), Nilgiri Tahr (Western Ghats), Sangai Deer (Loktak Lake, Manipur).

6. Biogeographical Classification of India

India is divided into 10 major biogeographic zones based on its climate, geography, and species distribution.

1. Trans-Himalayan Zone: High-altitude, cold, and arid region (e.g., Ladakh).
2. Himalayan Zone: Mountainous region with diverse forests and alpine meadows.
3. Desert Zone: Arid and semi-arid regions (e.g., Thar Desert).
4. Semi-Arid Zone: A transition zone between the desert and the denser forests of the Western Ghats.
5. Western Ghats Zone: A mountain range along the western coast with high rainfall and rich biodiversity.
6. Deccan Peninsula Zone: A large plateau in southern India, the most extensive zone.
7. Gangetic Plain Zone: A fertile plain formed by the Ganges river system.
8. North-East India Zone: A region with high rainfall and dense forests, part of the Indo-Burma hotspot.
9. Coastal Zone: The coastline of mainland India.
10. Islands Zone: The Andaman and Nicobar Islands and the Lakshadweep Islands.

7. Conservation of Biodiversity

Biodiversity conservation aims to protect, maintain, and manage biological diversity to derive sustainable benefits for present and future generations.

7.1. In-situ (On-site) Conservation

Conservation of species in their natural habitats. This is the most appropriate method for biodiversity conservation.

• National Parks: Areas strictly reserved for the welfare of wildlife where private ownership, grazing, and cultivation are prohibited. They are established for the protection of an entire ecosystem.

  • Example: Jim Corbett National Park (Uttarakhand), Kaziranga National Park (Assam).

• Wildlife Sanctuaries: Areas where protection is given only to wild animals. Certain human activities like timber harvesting and collection of minor forest products are allowed, as long as they do not interfere with the well-being of the animals.

  • Example: Periyar Wildlife Sanctuary (Kerala).

• Biosphere Reserves: Large, multi-purpose protected areas that include natural ecosystems and are meant to conserve biodiversity, promote sustainable development, and facilitate research and education. They have three zones:

  1. Core Zone: Strictly protected, no human activity allowed.
  2. Buffer Zone: Limited human activity (research, education) is permitted.
  3. Transition Zone: Sustainable human settlements and activities are allowed.
     • Example: Nilgiri Biosphere Reserve, Nanda Devi Biosphere Reserve.

• Sacred Groves: Tracts of forest set aside by local communities and protected due to religious beliefs. They are rich in biodiversity and often harbor rare species.

7.2. Ex-situ (Off-site) Conservation

Conservation of threatened plants and animals outside their natural habitats.

• Botanical Gardens and Zoos (Zoological Parks):

  • Botanical Gardens: Maintain collections of living plants for scientific research, conservation, and education.
  • Zoos: Maintain wild animals in captivity for public display, research, and captive breeding programs to reintroduce them into the wild.

• Gene Banks: Facilities that preserve genetic material.

  • Seed Banks: Seeds are stored at low temperatures and humidity to preserve their viability for long periods.
  • Cryopreservation: Preservation of seeds, pollen, tissues, or embryos at very low temperatures (-196°C) in liquid nitrogen. This technique is useful for preserving the genetic material of threatened species for long durations.