Ecology

Ecosystem energetics, trophic dynamics, and the laws of thermodynamics governing biotic-abiotic interactions.

• Ecosystem term coined by A.G. Tansley in 1935, representing a self-regulating functional unit of biosphere.
• Biotic components include producers (autotrophs), consumers (heterotrophs), and decomposers (saprotrophs).
• Abiotic components encompass climatic factors (solar radiation, temperature, precipitation) and edaphic factors (soil structure, pH, nutrients).
• Lindeman's 10% Law: Only about 10% of energy is transferred from one trophic level to the next; 90% is lost as metabolic heat.
• Ecological pyramids (Eltonian pyramids) of number, biomass, and energy can be upright or inverted depending on the biome.

• Energy flow is unidirectional (Sun to Producers to Consumers to Decomposers).
• Nutrient cycling is cyclic/biogeochemical (Carbon, Nitrogen, Phosphorus cycles).

The circulation of chemical elements between living organisms and their geological environment.

• Gaseous cycles include Nitrogen, Carbon, and Oxygen, characterized by atmospheric reservoirs.
• Sedimentary cycles include Phosphorus, Calcium, and Sulphur, where the Earth's crust is the primary reservoir.
• Nitrogen Fixation converts inert atmospheric N2 into ammonia via Rhizobium bacteria, lightning, and industrial Haber-Bosch process.
• Carbon cycle operates via photosynthesis, respiration, oceanic absorption, and lithospheric fossilization.
• Eutrophication occurs due to excessive nutrient loading (Nitrates and Phosphates), causing algal blooms and oxygen depletion.

• Nutrients are conserved and recycled endlessly within the biosphere.
• Anthropogenic interventions severely disrupt natural carbon and nitrogen stoichiometric ratios.

Directional change in ecosystem structure over time culminating in a stable climax community.

• Primary succession begins on lifeless substrates (e.g., bare rock, cooled lava) starting with pioneer species like lichens.
• Secondary succession occurs in areas where natural vegetation has been removed but soil remains (e.g., abandoned agricultural fields, post-wildfire forests).
• Clementsian Monoclimax theory emphasizes climate as the sole determining factor of the climax community.
• Polyclimax theory (Tansley) argues that multiple factors including soil, topography, and fire determine local climax states.
• Major global biomes (Tundra, Taiga, Temperate Deciduous, Tropical Rainforest, Desert, Savanna) are dictated by temperature and precipitation gradients (Whittaker's Biome Classification).

• Succession increases species diversity and biomass up to the climax stage.
• Whittaker's diagram using moisture and temperature is a high-frequency question area in UGC-NET.

Human-environment interactions, biodiversity conservation, and ecological footprints.

• Biodiversity hotspots concept introduced by Norman Myers (1988); requires >1,500 endemic vascular plants and <30% primary vegetation remaining.
• In-situ conservation includes National Parks, Wildlife Sanctuaries, and Biosphere Reserves (e.g., Nilgiri, Nanda Devi).
• Ex-situ conservation includes botanical gardens, gene banks, seed vaults, and zoological parks.
• Ecological Niche (Grinnellian vs. Eltonian) defines an organism's functional role and space within a community.
• Edge effect and Ecotone: Transitional zones between two biomes exhibit high species richness and density.

• India hosts 4 out of 36 global biodiversity hotspots (Himalaya, Indo-Burma, Western Ghats, Sundaland).
• Ecotones feature high biodiversity known as the edge effect.