Exploring Ecosystems: Terrestrial & Aquatic Worlds

Dive into the diverse and intricate tapestry of life on Earth, from the highest mountains to the deepest oceans.

2.7 Introduction to Ecosystems

Ecosystems are incredibly diverse, varying in size, climate, dominant species, and complexity. They are broadly classified into Terrestrial (land-based) and Aquatic (water-based) ecosystems, each with numerous sub-types. Understanding these systems is crucial for appreciating the interconnectedness of life and the environmental challenges we face.

Basis of Classification:

  • Primary Medium: Land or water.
  • Climatic Conditions: Temperature, precipitation, sunlight availability.
  • Dominant Vegetation/Organisms: The types of plants and animals that characterize the ecosystem.
  • Salinity: Crucial for aquatic ecosystems (freshwater, marine, brackish).

A. Terrestrial Ecosystems

These are ecosystems found on land. Their nature is primarily determined by temperature, rainfall, soil type, and topography.

Forest Ecosystems

Characterized by a dominance of trees and other woody vegetation, forming a closed or nearly closed canopy. They are among the most productive and biodiverse terrestrial ecosystems.

Forest Structure

Forests exhibit clear vertical stratification (emergent layer, canopy, understory, shrub layer, forest floor/litter layer, soil), which creates diverse niches.

Forest Functions

Crucial for carbon sequestration, oxygen production, regulation of hydrological cycles, soil conservation, habitat provision, timber and non-timber forest products.

Location: Equatorial regions (e.g., Amazon basin, Congo basin, Southeast Asia).

Climate: High temperatures (20-30°C) and high rainfall (>200 cm/year) throughout the year.

Vegetation: Evergreen broadleaf trees, exceptionally high species diversity (e.g., mahogany, ebony), epiphytes, lianas. Extremely dense.

Soil: Often nutrient-poor (lateritic soils) due to rapid recycling. Decomposition is very fast.

Biodiversity Hotspots: Contain more than half of the world's terrestrial species.

Threats: Deforestation for agriculture, logging, mining, road construction.

Case Study: The Amazon Rainforest

The world's largest tropical rainforest, crucial for global climate regulation ("lungs of the planet" - a simplification, more about carbon cycling). Facing severe deforestation pressures. Indigenous communities hold vast traditional knowledge.

Location: Regions with distinct wet and dry seasons (e.g., India, Southeast Asia).

Climate: Warm temperatures year-round, seasonal rainfall (100-200 cm/year).

Vegetation: Broadleaf trees that shed leaves in dry season (e.g., Teak, Sal). Less dense than rainforests.

Soil: Generally more fertile than rainforest soils.

Significance: Important for timber, subject to human pressures for agriculture.

Location: Mid-latitudes with mild, wet winters and warm, dry summers or oceanic influence.

Vegetation:

  • Broadleaf Evergreen: (e.g., Eucalyptus in Australia, Live Oaks in SE USA).
  • Coniferous Evergreen (Temperate Rainforests): (e.g., Pacific Northwest – Douglas fir, Redwood). High rainfall, large trees.

Location: Mid-latitudes with distinct seasons (e.g., Eastern North America, Western Europe).

Climate: Moderate rainfall (75-150 cm/year) distributed evenly.

Vegetation: Broadleaf trees that shed leaves in autumn (e.g., Oak, Maple). Rich herbaceous layer.

Soil: Fertile (brown earths) due to annual leaf fall.

Significance: Historically cleared for agriculture, now often in secondary growth.

Location: High northern latitudes (e.g., Canada, Scandinavia, Russia).

Climate: Long, very cold winters; short, cool summers. Low precipitation (40-100 cm/year), mostly snow.

Vegetation: Cold-tolerant coniferous evergreens (e.g., Spruce, Fir, Pine). Low species diversity.

Soil: Acidic, nutrient-poor (podzols). Permafrost may be present.

Significance: World's largest terrestrial biome. Important for timber and carbon storage.

Occur at different altitudes on mountains, exhibiting altitudinal zonation similar to latitudinal biomes.

Climate and vegetation change rapidly with increasing elevation. Often rich in endemic species.

Example: The Himalayas show distinct vegetation zones from tropical at foothills to alpine meadows.

Grassland Ecosystems

Characterized by a dominance of grasses and herbaceous plants. Occur where rainfall is insufficient for forests but too much for deserts.

Tropical Grasslands (Savannas)

Location: Equatorial/sub-equatorial regions (e.g., Africa, Australia).

Climate: Warm year-round, seasonal rainfall (50-150 cm/year).

Vegetation: Tall grasses, scattered drought/fire-resistant trees (e.g., Acacia).

Fauna: Large herbivores (zebras, wildebeest) and predators.

Fire Ecology: Crucial for maintaining grassland structure.

Temperate Grasslands

Location: Mid-latitudes, continental interiors (e.g., Prairies, Steppes).

Climate: Cold winters, hot/dry summers. Moderate rainfall (25-75 cm/year).

Vegetation: Shorter grasses, rich herbaceous diversity.

Soil: Very fertile (Mollisols), prime agricultural lands ("breadbaskets").

Threats: Conversion to agriculture, overgrazing, desertification.

Desert Ecosystems

Arid regions with very low precipitation (<25 cm/year), high evaporation, and sparse, adapted vegetation.

Hot and Dry Deserts

Location: Subtropical regions (e.g., Sahara, Arabian Desert).

Climate: Very hot summers, mild winters, low/erratic rainfall. Large diurnal temperature range.

Vegetation: Xerophytes (cacti, succulents), ephemeral annuals.

Fauna: Nocturnal animals, burrowers, water-conserving adaptations (e.g., kangaroo rat).

Cold Deserts

Location: High altitudes or mid-latitudes in rain shadows (e.g., Gobi Desert, Ladakh).

Climate: Hot, dry summers; very cold winters. Low precipitation, often snow.

Vegetation: Sparse, low-growing shrubs and grasses.

Desertification

The process by which fertile land becomes desert, due to drought, deforestation, or inappropriate agriculture. A major environmental concern, especially in semi-arid regions (e.g., Sahel in Africa).

Tundra Ecosystems

Treeless regions in the coldest parts of the world, characterized by permafrost (permanently frozen subsoil).

Arctic Tundra

Location: High northern latitudes (e.g., northern Canada, Siberia).

Climate: Extremely cold, long winters; short, cool summers. Low precipitation (15-25 cm/year).

Vegetation: Mosses, lichens, sedges, dwarf shrubs. No trees (permafrost).

Soil: Thin, nutrient-poor, permafrost layer. Waterlogged in summer.

Fauna: Migratory birds, caribou, arctic fox, polar bears (coastal).

Threats: Climate change (permafrost thaw), oil/gas exploration.

Alpine Tundra

Location: High altitudes on mountains worldwide, above treeline.

Climate: Cold, windy, high solar radiation. Permafrost may be patchy/absent.

Vegetation: Similar to Arctic tundra, more flowering plants.

Fauna: Mountain goats, sheep, marmots, pikas.

B. Aquatic Ecosystems

These are ecosystems found in bodies of water, primarily determined by salinity, depth, water flow, and nutrient availability.

Freshwater Ecosystems (Salinity < 0.5 ppt)

Examples: Lakes, ponds, swamps, bogs, marshes.

Lakes and Ponds Structure (Zonation):

  • Littoral Zone: Shallow, near-shore, rooted plants, high biodiversity.
  • Limnetic Zone: Open, sunlit surface water, phytoplankton/zooplankton. (Photic zone)
  • Profundal Zone: Deep, aphotic water, decomposers.
  • Benthic Zone: Bottom sediments, benthos.

Thermal Stratification (deeper temperate lakes):

  • Epilimnion: Warm, upper, mixed layer.
  • Thermocline: Zone of rapid temperature decrease.
  • Hypolimnion: Cold, dense, bottom layer.
  • Seasonal Turnover: Mixing in spring/fall, redistributes oxygen/nutrients.

Classification by Nutrient Content:

  • Oligotrophic: Nutrient-poor, clear, low productivity.
  • Mesotrophic: Moderate nutrients/productivity.
  • Eutrophic: Nutrient-rich, high productivity (algal blooms), murky.
  • Dystrophic: Rich in humic substances, acidic, brown water.

Wetlands are covered in detail in a spotlight section.

Examples: Rivers, streams, springs.

Characteristics:

  • Unidirectional flow of water.
  • Continuous physical/chemical change from source to mouth.
  • Organisms adapted to currents.

River Continuum Concept: Describes longitudinal changes in conditions, organisms, energy sources from headwaters to larger rivers.

Floodplains: Adjacent low-lying areas, periodically inundated, very fertile.

Threats: Pollution, dam construction, channelization, water over-extraction.

Marine Ecosystems (Salinity ~35 ppt)

Cover about 71% of the Earth's surface.

Marine Zonation (Depth & Light)
  • Intertidal Zone (Littoral): Between high/low tide.
  • Neritic Zone (Coastal): Shallow water over continental shelf (~200m depth). High productivity.
  • Oceanic Zone (Pelagic - Open Ocean):
    • Photic Zone (Epipelagic): Surface (0-200m), photosynthesis.
    • Aphotic Zone: Below photic zone. (Mesopelagic, Bathypelagic, Abyssopelagic, Hadopelagic).

Deep aphotic zones depend on detritus ("marine snow") or chemosynthesis (hydrothermal vents).

Specialized Marine Ecosystems

Semi-enclosed coastal bodies where freshwater mixes with saltwater. Fluctuating salinity, temperature, water levels.

High Productivity: Nutrient-rich, trap sediments.

Ecological Importance: "Nurseries of the sea," critical breeding/feeding grounds, coastal buffers, filter pollutants.

Vegetation: Salt-tolerant plants (salt marshes, mangroves).

Threats: Pollution, land reclamation, dredging, overfishing.

Salt-tolerant forests along sheltered tropical/subtropical coastlines.

Dominant Vegetation: Mangrove trees (Rhizophora, Avicennia) with specialized roots (pneumatophores, prop roots).

Ecological Importance: Coastal protection, habitat/nursery, high productivity, carbon sequestration (blue carbon).

Distribution in India: Sundarbans, Pichavaram, Bhitarkanika, Gulf of Kutch, A&N Islands.

Threats: Coastal development, pollution, deforestation, sea-level rise.

Case Study: 2004 Tsunami & Mangroves

Areas with intact mangroves experienced significantly less damage and loss of life, highlighting their protective role.

Coral Reefs

Underwater ecosystems built by corals. "Rainforests of the sea." (Detailed in Spotlight section)

Seagrass Beds

Underwater "meadows" of flowering plants. High productivity, habitat, stabilize sediments.

Threats: Pollution, dredging.

Kelp Forests

Underwater forests of large brown algae (kelp) in cool, nutrient-rich waters. Highly productive, complex habitat.

Threats: Overgrazing, pollution, warming waters.

Hydrothermal Vents

Deep-sea ecosystems near geothermally active areas. Support unique communities based on chemosynthesis.

Brackish Water Ecosystems

Transitional zones where freshwater and saltwater mix (salinity 0.5 - 30 ppt). Examples include estuaries, mangrove forests, some coastal lagoons and salt marshes (already discussed under their primary ecosystem type).

Spotlight on Key Ecosystems

I. Coral Reefs: Rainforests of the Sea

Vibrant coral reef

Underwater ecosystems built by reef-building corals (tiny colonial polyps secreting calcium carbonate skeletons). Exceptionally high biodiversity.

Structure & Symbiosis:

Complex 3D structures providing habitat. Crucial mutualistic relationship with zooxanthellae (algae) living in coral tissues. Algae provide energy via photosynthesis; corals provide protection and nutrients.

Conditions for Growth:

  • Warm Water: 23-29°C (Optimum 25-27°C).
  • Clear, Shallow Water: Sunlight for zooxanthellae (photic zone, <50m).
  • Clean Water: Low turbidity and nutrients.
  • Normal Salinity: ~32-40 ppt.
  • Hard Substrate: For larval attachment.

Types of Coral Reefs:

  • Fringing Reefs: Grow directly from shore.
  • Barrier Reefs: Separated from shore by a lagoon (e.g., Great Barrier Reef).
  • Atolls: Ring-shaped reefs enclosing a lagoon.

Ecological Importance:

  • Highest marine biodiversity (support ~25% of marine species).
  • Coastal protection from storms/erosion.
  • Source of food/livelihood (fisheries, tourism).
  • Potential source of new medicines.

Distribution in India: Gulf of Kutch, Gulf of Mannar, Palk Bay, Andaman & Nicobar Islands, Lakshadweep Islands.

Major Threats

Climate Change (Coral Bleaching due to rising sea temperatures, Ocean Acidification), Pollution, Overfishing, Destructive Fishing, Coastal Development, Diseases, Invasive Species.

Case Study: The Great Barrier Reef, Australia

World's largest coral reef system. Experienced severe mass bleaching events (2016, 2017, 2020, 2022) due to marine heatwaves. Faces threats from agricultural runoff, coastal development, and crown-of-thorns starfish. Significant conservation efforts are underway, but global warming remains the primary threat.

Historical Context & Conservation:

Charles Darwin (1842) proposed atoll formation theory. Awareness of threats grew from 1980s/90s. Conservation includes MPAs, artificial reefs, restoration, reducing CO₂ emissions, managing local stressors.

II. Wetlands: Kidneys of the Earth

Serene wetland landscape

Definition (Ramsar Convention, 1971): "Areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres." India is a signatory.

Characteristics:

  • Presence of water at surface or root zone.
  • Hydric soils (anaerobic conditions).
  • Hydrophytic vegetation (adapted to wet conditions).

Types of Wetlands:

  • Inland: Marshes, Swamps, Bogs, Fens, Lakes, Rivers, Floodplains.
  • Coastal: Estuaries, Mangroves, Salt Marshes, Lagoons, Coral Reefs (<6m).

Distribution in India: Rich diversity from Himalayan lakes to coastal mangroves. Numerous Ramsar sites (e.g., Chilika Lake, Keoladeo NP, Vembanad-Kol, Sundarbans).

Ecological Importance (Ecosystem Services):

  • Water Purification: Filter pollutants, nutrients.
  • Flood Control: Act as natural sponges.
  • Groundwater Recharge/Discharge.
  • Shoreline Stabilization & Erosion Control.
  • Habitat for Biodiversity: Especially waterfowl, migratory birds.
  • Nutrient Cycling & Carbon Sequestration (Peatlands).
  • Provisioning Services: Fish, fuelwood, timber, recreation.
Threats to Wetlands

Drainage/conversion for agriculture & development, Pollution, Hydrological alterations (dams), Overexploitation, Invasive species, Climate change.

Case Study: Chilika Lake, Odisha, India

Largest coastal lagoon in India, a Ramsar site. Faced siltation, salinity changes, pollution, overfishing, invasive weeds. Chilika Development Authority (CDA) undertook restoration (new sea mouth, weed control, community management), leading to some recovery in biodiversity and fisheries.

Conservation Efforts: Ramsar Convention, National Wetland Conservation Programme (India), integrated management plans.

UPSC Relevance

This topic is highly relevant for both Prelims and Mains examinations.

Prelims Focus

Very high importance. Expect questions on:

  • Types of ecosystems (forests, grasslands, deserts, tundra characteristics, locations).
  • Detailed questions on coral reefs (growth conditions, bleaching, threats, Indian locations).
  • Wetlands (Ramsar Convention, ecological importance, threats, Indian examples).
  • Specific terms: permafrost, xerophytes, pneumatophores etc.
Mains (GS Paper III) Focus

Potential questions:

  • Causes and consequences of desertification; mitigation measures.
  • Threats to coral reefs and conservation measures. (Highly probable)
  • Importance of wetlands and challenges in their conservation in India. (Highly probable)
  • Deforestation, biodiversity loss in specific ecosystems.
  • Impact of climate change on different ecosystem types.

Related Previous Year Questions (PYQs)

  • "Which of the following is/are unique characteristic/characteristics of equatorial forests?" (UPSC Prelims 2013)
  • "Which one of the following is the correct sequence of ecosystems in the order of decreasing productivity?" (UPSC Prelims 2013)
  • "Which of the following have coral reefs? (Andaman and Nicobar Islands, Gulf of Kutch, Gulf of Mannar, Sunderbans)" (UPSC Prelims 2014)
  • "What is the Ramsar Convention primarily related to?" (Direct question)
  • "Consider the following statements: Most of the world’s coral reefs are in tropical waters. More than one-third of the world’s coral reefs are located in the territories of Australia, Indonesia and Philippines. Coral reefs host far more animal phyla than those hosted by tropical rainforests. Which of the statements given above is/are correct?" (UPSC Prelims 2018)
  • "What are the consequences of spreading of ‘Dead Zones’ on marine ecosystem?" (UPSC Mains 2018, GS Paper III)
  • "Coastal sand mining, whether legal or illegal, poses one of the biggest threats to our environment. Analyse the impact of sand mining along the Indian coasts, citing specific examples." (UPSC Mains 2019, GS Paper III)

Note: For actual PYQ links, you would need to search the UPSC website or other reliable sources. These are representative examples.