Learning Objectives
- Understand organisms and their environment
- Learn about populations, communities, and ecosystems
- Study biodiversity, conservation, and environmental issues
- Understand energy flow, nutrient cycling, and ecological succession
Key Concepts
Organisms and Environment
Abiotic factors: Temperature, light, water, soil. Organisms respond through: Regulate (maintain homeostasis โ thermoregulation in mammals), Conform (body temperature changes with environment โ poikilotherms/ectotherms), Migrate (move to favourable habitat โ Siberian cranes to India), Suspend (dormancy โ hibernation in winter, aestivation in summer, diapause in zooplankton). Allen's rule: Mammals in cold climates have shorter ears and limbs. Bergmann's rule: Larger body size in colder climates (less surface area to volume ratio).
Population Ecology
Population attributes: Birth rate, death rate, sex ratio, age distribution. Age pyramid: Expanding (growing โ broad base), Stable, Declining (inverted โ narrow base). Population growth models: (1) Exponential growth: dN/dt = rN (unlimited resources); J-shaped curve. r = intrinsic rate of natural increase. Nt = N0ert. (2) Logistic growth: dN/dt = rN(K-N)/K (limited resources); S-shaped (sigmoid) curve. K = carrying capacity. Population stabilizes at K.
Population interactions: Mutualism (+, +): lichens, mycorrhiza. Predation (+, -): tiger eats deer. Parasitism (+, -): Cuscuta on host plant, ticks on dogs. Competition (-, -): between species for same resource (competitive exclusion principle โ Gause). Commensalism (+, 0): orchid on mango tree, barnacles on whale. Amensalism (-, 0): Penicillium inhibits bacteria.
Ecosystem
Components: Abiotic (non-living) + Biotic (living). Productivity: GPP (Gross Primary Productivity) = total organic matter produced by photosynthesis. NPP (Net Primary Productivity) = GPP - Respiration. Highest productivity: tropical rainforests and coral reefs. Lowest: deep ocean.
Energy flow: Unidirectional. 10% law (Lindeman): Only 10% of energy is transferred from one trophic level to the next. Food chain: Grazing food chain (starts with producers โ most ecosystems) and Detritus food chain (starts with dead organic matter โ more energy flow in forests). Food web: Interconnected food chains. Ecological pyramids: Pyramid of energy โ always upright. Pyramid of biomass โ upright (terrestrial), inverted (aquatic โ phytoplankton biomass less than zooplankton). Pyramid of numbers โ varies (grassland: upright; tree ecosystem: inverted at producer level).
Nutrient Cycling
Carbon cycle: CO2 fixed by photosynthesis โ organic matter โ respiration/decomposition releases CO2. Fossil fuels release CO2 on burning โ greenhouse effect. Phosphorus cycle: Sedimentary cycle (no gaseous phase). Rocks โ weathering โ soil โ plants โ animals โ decomposition โ soil. Slowest cycling element.
Ecological Succession
Sequential change in community structure over time. Primary succession: On bare/lifeless area (newly cooled lava, bare rock). Pioneer species: lichens (on rock), phytoplankton (in water). Stages on rock: Lichens โ Mosses โ Herbs โ Shrubs โ Trees (climax community). Secondary succession: On previously inhabited but disturbed area (burnt forest, abandoned farmland). Faster than primary. Climax community: Final stable community in equilibrium.
Biodiversity and Conservation
Biodiversity: Term by Edward Wilson. Levels: Genetic, Species, Ecological (ecosystem). India: one of 12 mega-biodiversity countries. Species-Area relationship: log S = log C + Z log A (Alexander von Humboldt). Z value: ~0.1-0.2 for small areas; ~0.6-0.7 for large areas (entire continents).
Biodiversity loss causes: HIPPO โ Habitat loss (most important), Invasive species, Pollution, Population growth (human), Overexploitation. Evil quartet (Jared Diamond): habitat destruction, overkill, invasive species, co-extinctions.
Conservation: In-situ: Protection in natural habitat โ National Parks (Silent Valley, Kaziranga), Wildlife Sanctuaries, Biosphere Reserves, Sacred Groves, Biodiversity Hotspots (34 worldwide; India has 4: Himalayas, Western Ghats, Indo-Burma, Sundaland). Ex-situ: Protection outside natural habitat โ Zoos, Botanical gardens, Seed banks, Gene banks, Cryopreservation.
Environmental Issues
Air pollution: Greenhouse effect (CO2, CH4, N2O, CFCs). Ozone depletion by CFCs (Montreal Protocol). Water pollution: BOD, eutrophication (algal bloom due to nutrient enrichment), biomagnification (DDT concentration increases at higher trophic levels). Solid waste: Biodegradable and non-biodegradable. Radioactive waste is most hazardous. Deforestation: Slash and burn agriculture (Jhum cultivation). Chipko Movement โ tree conservation.
Summary
Ecology encompasses organism-environment interactions at population, community, and ecosystem levels. Energy flows unidirectionally with only 10% transfer between trophic levels. Nutrient cycling maintains element availability. Ecological succession leads to climax communities. Biodiversity conservation through in-situ and ex-situ methods is critical. Environmental issues include pollution, climate change, and habitat loss.
Important Terms
- Carrying capacity (K): Maximum population size an environment can sustain
- Ecological pyramid: Graphical representation of trophic levels
- 10% law: Only 10% energy transfers to next trophic level (Lindeman)
- Biodiversity hotspot: Region with high endemism and significant habitat loss
- Biomagnification: Increase in toxin concentration at successive trophic levels
- Eutrophication: Nutrient enrichment of water bodies causing algal bloom
- Climax community: Final stable community in ecological succession
- Species-Area relationship: log S = log C + Z log A (more area = more species)
Quick Revision
- Exponential growth: J-curve (dN/dt = rN); Logistic: S-curve (dN/dt = rN(K-N)/K)
- 10% law by Lindeman; energy pyramid always upright
- Pyramid of biomass: inverted in aquatic ecosystems
- Primary succession on rock: Lichen โ Moss โ Herbs โ Shrubs โ Trees
- India: 4 biodiversity hotspots (Himalayas, Western Ghats, Indo-Burma, Sundaland)
- In-situ: National parks, sanctuaries; Ex-situ: zoos, seed banks
- Biomagnification: DDT increases up food chain
- Evil quartet: habitat loss, overexploitation, invasive species, co-extinction