Ecology and Environment
Ecology and Environment tests quantitative ecology - population growth, energy flow, species–area relationships - alongside named Indian examples and conservation categories. Expect calculations plus short notes on interactions and pollution.
Populations
- Attributes: density, natality, mortality, sex ratio, age pyramid.
- Exponential growth: dN/dt = rN, giving N_t = N_0 e^{rt}. Logistic growth: dN/dt = rN(K − N)/K, the S-curve. r-selected species versus K-selected species.
- Interactions: mutualism (+,+; lichen, mycorrhiza), commensalism (+,0; cattle egret), parasitism, predation, competition. Gause's Paramecium and Connell's barnacle experiments demonstrate competitive exclusion.
Ecosystem
- GPP − R = NPP; roughly 10% of energy passes to the next trophic level.
- Pyramids of number, biomass and energy; the energy pyramid is always upright.
- Decomposition steps: fragmentation, leaching, catabolism, humification, mineralisation.
- Succession: hydrarch and xerarch, pioneer community to climax; primary versus secondary.
Biodiversity and conservation
- Latitudinal gradient; species–area relationship log S = log C + Z log A, with Z about 0.1–0.2 for small areas and 0.6–1.2 for continents.
- In situ: biosphere reserves, national parks, sanctuaries, sacred groves. Ex situ: zoos, botanical gardens, seed and gene banks, cryopreservation.
- Indian hotspots: Western Ghats–Sri Lanka and Indo-Burma; the Himalaya is also listed.
Worked example
Producers fix 20,000 kcal. Applying the 10% law: herbivores 2,000 kcal, primary carnivores 200 kcal, secondary carnivores 20 kcal. Reasoning: take 10% of the preceding level each time, not 10% of the original at every level.
Traps that cost marks
- Measuring the ozone hole in Dobson units but blaming the greenhouse effect; stratospheric CFCs cause it.
- Claiming the phosphorus cycle has a gaseous phase; it is sedimentary.
- Confusing biomagnification (concentration rises up the chain) with energy flow (energy falls).