Elaborate Notes
Ecosystems: A Comparative Overview
An ecosystem, a term coined by the British ecologist Arthur Tansley in 1935, refers to a community of living organisms (biotic components) in conjunction with the non-living components (abiotic components) of their environment, interacting as a system. Ecosystems can be broadly classified based on their habitat into terrestrial (land-based) and aquatic (water-based) types.
- Terrestrial vs. Aquatic Ecosystems: A Detailed Comparison
- Sunlight Penetration: In aquatic ecosystems, sunlight is a major limiting factor. Its penetration is restricted to the upper layer, known as the photic or euphotic zone, which typically extends to about 200 meters in clear ocean water. Below this depth lies the aphotic zone, where photosynthesis is not possible. In contrast, terrestrial ecosystems receive abundant sunlight, with availability primarily varying due to latitude, season, time of day, and canopy cover, but it is not limited by the medium itself.
- Oxygen Availability: Dissolved oxygen (DO) is a critical factor in aquatic environments. It is more abundant in the surface layers due to atmospheric diffusion and photosynthesis by phytoplankton. In deeper layers, oxygen can become scarce (hypoxic or anoxic zones), especially in stratified lakes or oceans. Terrestrial ecosystems have a relatively uniform and high concentration of oxygen in the atmosphere (approx. 21%), making it readily available for respiration.
- Temperature Fluctuation: Water has a high specific heat capacity, which means it heats up and cools down much more slowly than land or air. Consequently, aquatic ecosystems exhibit a narrow and more stable range of temperatures. Terrestrial ecosystems, particularly in continental interiors and deserts, experience significant temperature fluctuations, both diurnally (day-night) and seasonally.
- Water Availability: For aquatic organisms, water is the surrounding medium and is not a limiting factor. For terrestrial organisms, water availability is a primary determinant of survival, distribution, and adaptation. It is a scarce resource in arid and semi-arid regions, profoundly influencing the types of flora and fauna found there.
Understanding Biomes
A biome is a large, naturally occurring community of flora and fauna occupying a major habitat. The concept was developed by ecologists like Frederic E. Clements and Victor E. Shelford in the early 20th century. Biomes are defined by their dominant vegetation and are primarily determined by climate, specifically temperature and precipitation.
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Tundra Biome
- Etymology and Location: The word ‘Tundra’ comes from the Kildin Sami word tūndâr, meaning “uplands” or “treeless mountain tract.” It is found in regions poleward of the Arctic Circle (Arctic Tundra) and at very high elevations on mountains (Alpine Tundra). Examples include the vast plains of northern Siberia and Canada, and high-altitude areas like the Tibetan Plateau.
- Climate and Soil: Characterised by extremely cold temperatures, with long, harsh winters and short, cool summers. Precipitation is very low, typically less than 25 cm annually, mostly in the form of snow. A defining feature is permafrost—a layer of permanently frozen subsoil. This frozen layer impedes water drainage and root penetration, preventing the growth of large trees.
- Biodiversity and Vegetation: The summary’s claim of “high biodiversity” is factually incorrect; the Tundra has very low biodiversity due to its extreme environmental conditions. The growing season is brief (6-10 weeks). Vegetation consists of hardy, low-growing plants like lichens (e.g., reindeer moss), mosses, sedges, dwarf shrubs (dwarf birch, arctic willow), and various grasses.
- Fauna and Adaptations: Animals are adapted to survive the cold. Key adaptations include:
- Physiological: Thick fur or feathers for insulation (polar bear, arctic fox), layers of blubber (walrus, seal), large body size to conserve heat (Bergmann’s Rule), and shorter extremities like ears and tails to reduce heat loss (Allen’s Rule).
- Behavioural: Hibernation (e.g., arctic ground squirrel), migration (caribou/reindeer, many bird species), camouflage (arctic fox and hare change fur colour seasonally), and huddling for warmth (emperor penguins).
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Taiga (Boreal Forest) Biome
- Location and Scale: The Taiga is the world’s largest terrestrial biome, forming a circumpolar belt across North America (Canada, Alaska) and Eurasia (Scandinavia, Siberia). It is found only in the Northern Hemisphere as there are no large landmasses at the equivalent latitudes in the Southern Hemisphere.
- Climate and Soil: Characterised by long, severe winters and short, mild summers. It experiences a wide annual temperature range. Precipitation (40-100 cm annually) is higher than in the Tundra, with snowfall in winter and convectional rain in summer. The characteristic soil is Podzol, an acidic, nutrient-poor soil formed through a process called podzolization, where minerals are leached from the upper layers by acidic water from decomposing conifer needles.
- Vegetation and Productivity: Dominated by coniferous trees like pine, spruce, fir, and larch. These are evergreen, allowing them to photosynthesise whenever temperatures are favourable, without expending energy on regrowing leaves. The forest floor has limited undergrowth due to the dense canopy and acidic soil. Ecological productivity is higher than the Tundra. These forests are a massive carbon sink, playing a crucial role in global carbon cycles, as highlighted by numerous IPCC reports.
- Biodiversity and Fauna: Biodiversity is low compared to temperate or tropical forests but higher than the Tundra. Fauna includes large herbivores like moose and reindeer, and predators such as wolves, lynx, bears, and the Siberian tiger. Adaptations include thick fur, hibernation, and food storage.
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Temperate Grassland Biome
- Global Distribution: Known by various regional names: Prairies in North America, Pampas in South America, Steppes in Eurasia, Veld in South Africa, and Downs in Australia.
- Climate and Soil: Experiences moderate temperatures with cold winters and hot summers. Precipitation is moderate, often insufficient to support forests but adequate for grasses. The summary’s claim that rainfall is higher than in tropical grasslands is generally inaccurate; Savannas typically receive higher, though more seasonal, rainfall. A key feature is the highly fertile soil, known as Chernozem or Mollisol (e.g., Prairie soil), often called “black earth.” Its fertility is due to the process of calcification in these semi-arid conditions, where calcium carbonate accumulates in the lower soil layers, preventing leaching and enriching the topsoil with organic matter from decaying grass roots.
- Vegetation and Fauna: Dominated by grasses, which are short and green. Trees are rare and are usually found only along riverbanks. Historically, these grasslands supported vast herds of large grazing animals like the American Bison and pronghorn. Predators include coyotes and wolves. Burrowing animals like prairie dogs are also characteristic.
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Savannah (Tropical Grassland) Biome
- Location and Climate: Found in transitional zones between tropical rainforests and deserts, primarily in Africa (e.g., Serengeti), South America (Llanos, Campos), India, and Australia. Characterised by consistently high temperatures throughout the year. Rainfall is seasonal, with a distinct and prolonged dry season and a wet season.
- Controlling Factors and Vegetation: The ecosystem is shaped by the interplay of water availability, frequent fires (often natural or human-induced), and grazing pressure from large herbivores. This prevents the establishment of a closed-canopy forest. Vegetation consists of tall, coarse grasses that turn yellow/brown in the dry season and green in the wet season, interspersed with scattered, drought-resistant and fire-resistant trees like Acacia, Baobab, and palms.
- Fauna and Adaptations: Famous for its high diversity of large herbivores (‘megafauna’) like elephants, giraffes, zebras, and wildebeest, which often undertake vast migrations in search of water and pasture. A diverse community of predators, including lions, cheetahs, leopards, and hyenas, coexists with them. Adaptations for animals include speed for escaping predation, camouflage, migration, and nocturnal behaviour to avoid midday heat.
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Desert Biome
- Defining Characteristic: The primary defining feature is aridity, with average annual rainfall of less than 25 cm. Deserts can be hot (e.g., Sahara, Thar) or cold (e.g., Gobi, Patagonia).
- Climate: Hot deserts are characterised by extremely high daytime temperatures and a very high diurnal temperature range, as the clear skies and low humidity allow for rapid heat gain during the day and rapid heat loss at night.
- Vegetation and Adaptations (Xerophytes): Plants are adapted to conserve water, a condition known as xerophytism.
- Structural Adaptations: Leaves are reduced to spines or thorns to minimize water loss through transpiration (e.g., Cactus). Some plants have waxy coatings on leaves. Stems may be green and fleshy (succulents) to store water and carry out photosynthesis.
- Root System: Extensive and deep root systems to tap into groundwater.
- Physiological Adaptations: Some plants, like cacti, use a special photosynthetic pathway called Crassulacean Acid Metabolism (CAM), where they open their stomata at night to take in CO₂ to reduce water loss.
- Flora examples: Cacti, date palms, Acacia, and hardy shrubs like Prosopis juliflora.
- Fauna and Adaptations: Animals have evolved remarkable adaptations to cope with heat and water scarcity.
- Water Conservation: Many obtain water from their food (seeds, insects). The camel is famous for its physiological adaptations to tolerate dehydration.
- Behavioural Adaptations: Many are nocturnal, active only during the cooler night. Burrowing underground provides an escape from the extreme surface heat.
- Physiological Adaptations: Large ears (e.g., Fennec fox) act as radiators to dissipate body heat. Efficient kidneys produce highly concentrated urine to conserve water.
Prelims Pointers
- Photic Zone: The upper layer of a body of water into which sunlight penetrates, enabling photosynthesis. Typically extends to 200m.
- Aphotic Zone: The portion of a lake or ocean where there is little or no sunlight.
- Biome: A large community of vegetation and wildlife adapted to a specific climate.
- Permafrost: A thick subsurface layer of soil that remains frozen throughout the year, characteristic of the Tundra biome.
- Podzol: Acidic, infertile soil found in Taiga (boreal forest) biomes.
- Calcification: Soil-forming process in arid/semi-arid regions leading to an accumulation of calcium carbonate; creates highly fertile soils.
- Chernozem/Mollisol (Prairie Soil): Extremely fertile, dark-coloured soil rich in organic matter, found in temperate grasslands. It is considered the most fertile soil on Earth.
- Xerophytes: Plants adapted for life in a dry or physiologically dry habitat (e.g., Cactus).
- CAM Photosynthesis: Crassulacean Acid Metabolism, a carbon fixation pathway in some plants (like cacti) that allows them to reduce water loss.
Biome-Specific Facts:
- Tundra:
- Location: Arctic regions (circumpolar) and high mountains (Alpine).
- Precipitation: < 25 cm per year.
- Key Feature: Permafrost, treeless landscape.
- Biodiversity: Very low.
- Fauna: Polar bear, reindeer, arctic fox, walrus.
- Taiga (Boreal Forest):
- Location: Northern Hemisphere only (Canada, Scandinavia, Siberia).
- Distinction: World’s largest terrestrial biome.
- Vegetation: Coniferous evergreen trees (pine, spruce, fir).
- Soil: Podzol (acidic, nutrient-poor).
- Fauna: Moose, wolf, Siberian tiger, lynx.
- Temperate Grasslands (Regional Names):
- Prairies: North America
- Pampas: South America
- Steppes: Eurasia
- Veld: South Africa
- Downs: Australia
- Soil: Chernozem (highly fertile).
- Fauna: Bison, coyote, prairie dog.
- Savannah (Tropical Grassland):
- Climate: High temperatures year-round with distinct wet and dry seasons.
- Controlling Factors: Fire, water availability, and grazing.
- Vegetation: Tall grasses with scattered drought-resistant trees (Acacia, Baobab).
- Fauna: High diversity of megafauna like elephants, giraffes, zebras, lions, cheetahs. Tigers are not naturally found in African Savannas.
- Desert:
- Precipitation: < 25 cm per year.
- Key Feature: High diurnal range of temperature in hot deserts.
- Vegetation: Xerophytes (Cactus, Acacia, Date Palm).
- Animal Behaviour: Many are nocturnal and/or burrowing.
Mains Insights
1. Climate as the Master Determinant of Biome Distribution
- Cause and Effect: The global distribution of biomes is a direct consequence of climatic patterns, primarily temperature and precipitation, which are in turn influenced by latitude, altitude, and proximity to oceans. For instance, the transition from the Equator to the Poles demonstrates a clear succession: Tropical Rainforest → Savannah → Desert → Temperate Grassland/Forest → Taiga → Tundra. This latitudinal zonation is mirrored in altitudinal zonation on high mountains.
- Analytical Perspective: Understanding this relationship is crucial for predicting the impacts of climate change. A warming planet could cause biome shifts, such as the northward expansion of the Taiga into the Tundra, or the desertification of Savannah and Temperate Grasslands. This has profound implications for biodiversity, ecosystem services, and human livelihoods dependent on these biomes.
2. The Anthropocene and Biome Degradation: A Critical Analysis
- Human Impact: No biome remains pristine. Human activities are the primary drivers of degradation across all biomes.
- Tundra: Threatened by climate change (melting permafrost releasing methane, a potent greenhouse gas), oil and gas exploration, and mineral extraction.
- Taiga: Faces threats from large-scale logging for timber and paper, mining, and hydroelectric projects, leading to deforestation and habitat fragmentation.
- Temperate Grasslands: Most have been converted into agricultural land (“breadbaskets of the world”) due to their fertile soils. This has led to massive habitat loss, soil degradation from intensive farming, and loss of iconic species like the bison.
- Savannah: Threatened by conversion to agriculture and pastureland, poaching of wildlife, desertification due to overgrazing, and altered fire regimes.
- Deserts: Expanding due to desertification of adjacent biomes. Also threatened by unsustainable water extraction, urbanization, and use for military testing or waste disposal.
- Policy Implication (GS-III): This necessitates a shift from a purely protectionist conservation model to an integrated landscape management approach. Policies must address the drivers of degradation, promote sustainable land use, restore degraded ecosystems (e.g., Great Green Wall initiative for the Sahel), and ensure the well-being of local communities.
3. Soil Formation and its Link to Agricultural Potential (GS-I & GS-III)
- Interconnection: There is a direct link between the climate of a biome, its vegetation, the resulting soil type, and its agricultural productivity.
- Highly Fertile: Temperate grasslands, with their calcification process and rich organic matter from grass roots, produce Chernozem soils, making them the world’s most productive agricultural regions.
- Moderately/Poorly Fertile: Taiga’s Podzols are acidic and nutrient-poor, making them unsuitable for large-scale agriculture. Tropical rainforest soils (Latosols) are also surprisingly infertile due to rapid nutrient cycling and intense leaching by heavy rainfall.
- Savannah & Desert: Savannah soils are often leached and less fertile than Chernozems, while desert soils (Aridisols) lack organic matter and water, limiting agriculture to oases or irrigated areas.
- Socio-Economic Significance: This geographical distribution of soil fertility has shaped patterns of human settlement, agricultural development, and global food trade. Regions with fertile soils have historically become centres of civilization and economic power. However, over-exploitation of these soils now poses a significant threat to global food security.
4. Biodiversity Patterns: A Tale of Two Extremes
- Debate/Analysis: Why do biomes like Tropical Rainforests teem with life, while others like the Tundra and Deserts have low biodiversity? The key factors are energy availability, water availability, and climatic stability.
- High Biodiversity (e.g., Tropical Rainforest): High, consistent solar energy input, abundant rainfall, and stable temperatures year-round support high primary productivity and allow for complex, multi-layered ecosystems with numerous ecological niches, fostering speciation.
- Low Biodiversity (e.g., Tundra/Desert): Life is constrained by a primary limiting factor—extreme cold and a short growing season in the Tundra, and lack of water in the Desert. Only a few species with highly specialized adaptations can survive, leading to simpler food webs and lower overall species richness. This challenges the erroneous statement in the summary about Tundra having high biodiversity.
- Conservation Perspective (GS-III): This understanding helps prioritize conservation efforts. While all biomes are important, those with high biodiversity and high threat levels are designated as “biodiversity hotspots” (a concept by Norman Myers, 1988), requiring urgent conservation action.