Ecology

Part III · Common Biology · Chapter Fifteen

Expect 8–12 questions: population growth equations (J vs S curve), Lindeman's 10% law, ecological pyramids (which inverts?), types of ecological succession, biome characteristics, India's four biodiversity hotspots, HP National Parks and their flagship species, Ramsar wetlands (Pong Dam, Chandratal, Renuka), protected-area categories (NP vs WLS vs BR), greenhouse gases vs ozone-depleting substances, and biomagnification. HP-angle items — Great Himalayan NP UNESCO status, snow leopard and Western tragopan, altitudinal vegetation zones, cold desert biome of Lahaul-Spiti — are reliably tested.

Read · 75 min
Revise · 20 min
MCQs · 26

Syllabus Coverage

Population ecology (growth, interactions, niche) • Community and ecosystem structure • Energy flow and biogeochemical cycles • Ecological succession • Biogeography and major biomes including HP altitudinal zones • Biodiversity — levels, patterns and India's hotspots • Conservation — protected areas of India and Himachal Pradesh • Pollution — air, water, soil, noise • Global environmental change — climate change, ozone depletion, biodiversity crisis.

Term ecology — Haeckel 1866 · Ecosystem — Tansley 1935 · 10% energy law — Lindeman 1942 · Modern ecosystem ecology — Odum brothers 1953–1971 · Island biogeography — MacArthur & Wilson 1967 · α/β/γ diversity — Whittaker 1972 · Term biodiversity — E. O. Wilson 1986 · IPCC established 1988 · CBD adopted at Rio Earth Summit 1992 · Montreal Protocol (ozone) 1987 — Kyoto 1997 — Paris 2015

15.1 Population Ecology — Density, Growth and Interactions

Ecology (Gr. oikos = house; logos = study) was coined by Ernst Haeckel in 1866 as the study of organisms in relation to their environment. It operates across four levels of biological organisation: population, community, ecosystem and biosphere. A population is a group of individuals of the same species occupying the same area at the same time.

Population

A group of conspecific individuals (same species) living in a defined area at a given time, capable of interbreeding and sharing a common gene pool. Distinguished from a community (multiple species) and from a metapopulation (network of subpopulations linked by dispersal).

15.1.1 Population Parameters

Population density (N/area or N/volume) is the fundamental measurement. It changes through four processes: natality (births, increases N), mortality (deaths, decreases N), immigration (in-movement, increases N) and emigration (out-movement, decreases N). Formally: ΔN = (births + immigration) − (deaths + emigration).

Age structure — the relative proportions of pre-reproductive, reproductive and post-reproductive individuals — predicts future population trajectory. A pyramid with a broad base (many young) indicates a growing population; a column indicates stability; an inverted pyramid (few young) indicates decline. Sex ratio (number of males per female) affects reproductive output. The intrinsic rate of natural increase (r) = birth rate − death rate under unlimited resources; it summarises a species' reproductive potential.

15.1.2 Exponential (J-curve) Growth

When resources are unlimited (food, space, no predators), populations grow geometrically. The instantaneous rate is dN/dt = rN, where r is the intrinsic growth rate and N is current population size. Integrating gives N(t) = N₀ e^rt. The curve is J-shaped; growth accelerates without bound. Doubling time = ln 2 / r ≈ 0.693 / r. Real populations can approximate this briefly: introduced species, bacterial cultures, human populations in the industrial era.

Worked example — calculating doubling time

"A bacterial population has r = 0.35 h⁻¹. How long before it doubles?"

Solution: t_double = ln 2 / r = 0.693 / 0.35 ≈ 1.98 hours. Note that r here is per hour; if r were given as per year the doubling time would be in years. The equation also applies to human populations: India had r ≈ 0.022 yr⁻¹ in 1980, giving t_double ≈ 31 years.

15.1.3 Logistic (S-curve) Growth

Real populations face environmental resistance (resource depletion, predation, disease). The logistic model adds a braking term: dN/dt = rN(K − N)/K. When N is small, (K − N)/K ≈ 1 so growth resembles exponential; as N approaches K, the term approaches zero and growth slows; at N = K (carrying capacity) dN/dt = 0. The plot is sigmoidal (S-shaped). Maximum growth rate (inflection point) occurs at N = K/2. Fisheries management targets harvesting at K/2 for maximum sustainable yield.

Figure 15.1 Population growth curves. Left: exponential (J-curve) — unlimited resources, dN/dt = rN. Right: logistic (S-curve) — density-dependent limiting factors, dN/dt = rN(K−N)/K; growth is maximal at the inflection point N = K/2 and tapers to zero as N approaches the carrying capacity K.

15.1.4 r-strategists and K-strategists

MacArthur and Wilson (1967) formalised the r/K selection continuum. r-strategists evolve in unpredictable, resource-rich environments: high reproductive rate (r), small body size, short generation time, many small offspring with little parental care, opportunistic. Examples: Drosophila, annual weeds, mice, cockroaches, algae. K-strategists evolve in stable, resource-limited environments near carrying capacity: low r, large body, long generation time, few offspring with intensive parental care. Examples: elephants, oaks, humans, whales, snow leopard.

Easy to confuse — r-strategist vs K-strategist

r-strategist

High r, low or no K-proximity. Small body, many offspring, short life, early maturity, high mortality, boom-bust dynamics. Opportunistic. Eg: Drosophila, weeds, mice, annual plants, algae, bacteria.

K-strategist

Low r, population density near K. Large body, few offspring, long life, late maturity, low mortality, stable populations. Equilibrium species. Eg: elephants, humans, oaks, whales, snow leopard, condors.

Exam Tip: The logistic equation dN/dt = rN(K−N)/K is the single most-tested formula in ecology MCQs. Note the components: r = intrinsic rate, N = current population, K = carrying capacity. When N = K, growth = 0. When N = K/2, growth is maximum. The term (K−N)/K is called the unutilised growth factor or damping term.

15.1.5 Population Interactions

Two species interact in various ways, summarised by the sign convention (+, −, 0) indicating benefit, harm or neutrality to each partner.

**Table 15.1**Population interactions — sign convention and examples
Interaction	Signs	Effect	Examples
Predation	+/−	Predator benefits; prey harmed	Tiger–deer; hawk–mouse; Nepenthes–insect
Competition	−/−	Both harmed; resource limitation	Two grass spp. competing for soil; lions & hyenas
Mutualism	+/+	Both benefit; often obligate	Anabaena–Azolla; lichen; mycorrhiza; pollination
Commensalism	+/0	One benefits; other unaffected	Barnacle on whale; orchid on tree (epiphyte); remora on shark
Amensalism	−/0	One harmed; other unaffected	Allelopathy: Juglans nigra secretes juglone; Parthenium weed
Parasitism	+/−	Parasite benefits; host harmed (rarely killed immediately)	Cuscuta on host; mistletoe; tapeworm; Plasmodium–human

Easy to confuse — Mutualism vs Commensalism vs Parasitism

Mutualism (+/+)

Both species benefit; often obligate (cannot survive apart). Lichen = alga + fungus. Mycorrhiza = fungus + plant roots. Rhizobium in root nodules. Pollinator–flower.

Commensalism (+/0)

One benefits; the other is unaffected (not harmed). Barnacle on whale: barnacle gets transport; whale is neither helped nor harmed. Epiphytic orchids on a tree.

15.1.6 Ecological Niche

The niche is the functional role of a species in the community — what it does, not just where it lives. Grinnell (1917) described niche as habitat requirements; Elton (1927) stressed functional role in the food web (who eats what); Hutchinson (1957) formalised it as an n-dimensional hypervolume defined by all the environmental axes (temperature, humidity, food size, pH…) within which a species can survive and reproduce. The fundamental niche is the full hypervolume possible in the absence of competitors; the realised niche is the actual smaller one occupied due to competition.

Easy to confuse — Habitat vs Niche

Habitat

The place where an organism lives — its address. Oak woodland, alpine meadow, river bend. One habitat can house many niches.

Niche

The functional role — its profession. What it eats, what eats it, what it needs. Two species cannot occupy the same niche in the same place (Gause's exclusion principle).

Easy to confuse — Gause's Competitive Exclusion Principle

The Principle (Gause 1934)

Two species with identical niches cannot stably coexist. The better competitor drives the other to local extinction — demonstrated with Paramecium aurelia vs P. caudatum in same culture. Result: one excluded.

Coexistence via niche differentiation

Species can coexist if niches differ even slightly. Character displacement — competing species evolve to reduce niche overlap (Darwin's finches, beak sizes). MacArthur's warblers in spruce: each exploits different canopy zone.

HP Angle: The snow leopard (Panthera uncia) is HP's state animal and a K-strategist adapted to the cold desert and sub-alpine zones of Lahaul, Spiti and upper Kinnaur. Low r, few cubs (1–3 per litter every 2 years), long generation time. Its prey base includes blue sheep (Bharal) and Himalayan ibex. Pin Valley National Park (Lahaul-Spiti) is the primary snow leopard reserve in HP.

15.2 Community & Ecosystem Structure

A community (biotic community) is the assemblage of all populations of different species in the same area at the same time. An ecosystem (Tansley, 1935) is the community together with its abiotic environment — it is the basic functional unit of ecology because it includes both living organisms and non-living factors and the interactions between them.

Ecosystem (Tansley 1935)

A system comprising the biotic community (all living organisms) and its abiotic environment (soil, water, air, nutrients, energy) interacting as a functional unit. Energy flows through it (one-directional, non-cyclic); nutrients cycle within it. Examples: a pond, a forest patch, the entire biosphere.

15.2.1 Community Properties

Species richness = total number of species in a defined area. Species evenness = how equally individuals are distributed among species. A community can be species-rich but low in evenness (one dominant species with many rare ones). Diversity indices combine both:

Shannon-Wiener index (H') = −Σ p_i ln p_i, where p_i = proportion of species i. Higher H' = more diverse. (Shannon 1948)
Simpson's diversity index (D) = 1 − Σ (n_i/N)². Ranges 0–1; higher = more diverse.

Ecotone — the transition zone between two adjacent communities (e.g., forest–grassland edge). Edge effect: ecotones often have higher species diversity than either community alone because they support species from both. Ecocline is a gradual, clinally varying transition over a geographic gradient (e.g., increasing altitude).

Easy to confuse — Ecotone vs Ecocline

Ecotone

A sharp transitional zone between two clearly distinct communities. Forest – savanna edge; mangrove – sea. Supports edge-adapted species; often higher biodiversity (edge effect).

Ecocline

A gradual, continuous gradient of environmental change across geography. The altitudinal gradient from subtropical to alpine in HP is an ecocline — species replace each other progressively.

15.2.2 Biotic and Abiotic Components

Abiotic components — non-living: light, temperature, precipitation, soil type, pH, salinity, topography, nutrients (macronutrients N, P, K; micronutrients Fe, Mn, Zn…). Biotic components — living: producers (autotrophs), consumers (heterotrophs), decomposers (saprotrophs: bacteria and fungi that break down dead organic matter into inorganic form). In HP, harsh abiotic factors (thin air at >3000 m, intense UV, frost, low soil organic matter) strongly control which species can persist.

Easy to confuse — Biotic vs Abiotic factors

Abiotic

Non-living physical and chemical factors: temperature, light, water, pH, soil texture, wind, altitude, atmospheric gases. They set limits on which species can live where.

Biotic

Living factors: competitors, predators, prey, mutualists, parasites, pathogens, pollinators. They modulate abundance within abiotic limits. In HP forests, deodar–mycorrhiza is a crucial biotic interaction.

15.2.3 Productivity

Gross Primary Productivity (GPP) = total rate of photosynthesis (energy fixed by producers per unit area per unit time). Net Primary Productivity (NPP) = GPP − Respiration loss of producers. NPP is the energy available to consumers. Standing crop (biomass) = total dry weight of living matter at a given instant; it is a snapshot, not a rate. Tropical rainforests have the highest NPP (~20 t/ha/yr); deserts and tundra are lowest. In HP, alpine meadows have low but seasonally intense NPP.

15.3 Energy Flow & Biogeochemical Cycles

15.3.1 Trophic Levels and the 10% Law

Energy enters the ecosystem through producers (T1, autotrophs) that fix solar energy via photosynthesis. It passes to primary consumers (T2, herbivores), secondary consumers (T3, carnivores), tertiary consumers (T4), and finally decomposers (bacteria, fungi — act at every level). Lindeman's 10% law (1942): only approximately 10% of energy stored at one trophic level is available to the next; the remaining ~90% is lost as heat, used in respiration, or unassimilated. This limits most food chains to 4–5 trophic levels.

Worked example — energy transfer through trophic levels

"Grass fixes 10,000 kcal at T1. How much energy is available at T3 (secondary consumers)?"

Solution: T2 (herbivores) = 10,000 × 10% = 1,000 kcal. T3 = 1,000 × 10% = 100 kcal. At T4 only 10 kcal would remain. This is why long food chains are energetically inefficient and why large carnivores are always numerically rarer than their prey.

15.3.2 Food Chains and Food Webs

A food chain is a linear sequence of feeding relationships (grass → grasshopper → frog → snake → hawk). A food web is the network of interconnected food chains in an ecosystem; it reflects reality more accurately because most species eat and are eaten by multiple species. Grazing food chains begin with living plants; detritus food chains begin with dead organic matter (detritus) and are quantitatively more important in most terrestrial ecosystems.

15.3.3 Ecological Pyramids

An ecological pyramid is a graphic representation of the number, biomass or energy at successive trophic levels. Three types:

Pyramid of Numbers — number of individuals at each trophic level. Usually upright (many plants → fewer herbivores → fewer carnivores). Inverted when a single large producer (one oak tree) supports many herbivores (caterpillars).
Pyramid of Biomass — total dry weight at each level. Upright in terrestrial ecosystems (more plant biomass than herbivore biomass). Inverted in pelagic (open ocean) ecosystems where tiny phytoplankton (low standing crop) support large zooplankton biomass because phytoplankton turn over very rapidly.
Pyramid of Energy — energy content at each level. Always upright — thermodynamic laws prevent energy from increasing up the trophic ladder. This is the most fundamental pyramid.

Figure 15.2 Ecological pyramids. Left: Energy pyramid is always upright (Lindeman's 10% law, 1942). Right: Biomass pyramid is inverted in pelagic ocean ecosystems because phytoplankton have very high turnover rates; their standing biomass is low even though total energy produced is high.

15.3.4 Biogeochemical Cycles

Biogeochemical cycles describe the movement of chemical elements between the living (bio) and non-living (geo, chemical) components. Unlike energy, matter is recycled. Major cycles: water, carbon, nitrogen, phosphorus, sulphur.

Carbon cycle. Carbon is fixed from atmospheric CO₂ by photosynthesis (terrestrial plants, marine phytoplankton). It enters food webs and returns to atmosphere via respiration, decomposition and combustion. Oceans are the largest reservoir (~38,000 Gt C), followed by fossil fuel deposits (~3,700 Gt), soil (~2,500 Gt), atmosphere (~850 Gt) and living biomass (~600 Gt). Anthropogenic combustion of fossil fuels releases ~10 Gt C/yr, disrupting the natural balance.

Nitrogen cycle. Atmosphere is 78% N₂ but it is metabolically inert unless “fixed”. Nitrogen fixation: biological (symbiotic Rhizobium in legume nodules; free-living Azotobacter, Anabaena, Clostridium) or industrial (Haber-Bosch: N₂ + 3H₂ → 2NH₃) or lightning. Fixed N enters soil as NH₄⁺ (ammonium). Nitrification: Nitrosomonas oxidises NH₃ → NO₂⁻; Nitrobacter oxidises NO₂⁻ → NO₃⁻ (nitrate, plant-available). Denitrification: Pseudomonas and Thiobacillus reduce NO₃⁻ back to N₂ under anaerobic conditions. Ammonification: decomposers release NH₄⁺ from organic N.

Phosphorus cycle. Sedimentary cycle — no atmospheric phase. Phosphate weathers from rocks into soil solution; plants absorb it as H₂PO₄⁻; passes through food web; decomposers return it to soil; some lost to ocean sediment. Often the limiting nutrient in freshwater and terrestrial ecosystems. No gaseous form — slow cycle.

Sulphur cycle. Reservoirs: rocks (pyrite), soil, ocean, atmosphere. Enters atmosphere as SO₂ from volcanoes, industrial combustion and decomposition. Oxidised to SO₄²⁻ (sulphate); dissolved in rain as H₂SO₄ (acid rain). Desulfovibrio reduces sulphate under anaerobic conditions.

Figure 15.3 Simplified carbon and nitrogen cycles. In the carbon cycle (left) photosynthesis is the entry point; combustion and respiration release CO₂. In the nitrogen cycle (right) biological N fixation by Rhizobium and Azotobacter, nitrification by Nitrosomonas/Nitrobacter, and denitrification by Pseudomonas are the key microbial processes.

Mnemonic — Nitrogen cycle microbes in order

“Fixers Need Numbers Back” — Fixation (Rhizobium) → Nitrification step 1 (Nitrosomonas: NH₃→NO₂⁻) → Nitrification step 2 (Nitrobacter: NO₂⁻→NO₃⁻) → Back to N₂ by denitrification (Pseudomonas).

**Table 15.2**Ecological pyramids — upright vs inverted
Pyramid type	Usually upright?	Inverted case	Example of inverted
Numbers	Yes	Yes — when one large plant supports many herbivores	Single oak tree → thousands of caterpillars → few birds
Biomass	Yes (terrestrial)	Yes — in pelagic ocean	Phytoplankton (low standing crop) → large zooplankton biomass
Energy	Always upright	Never inverted	Thermodynamic impossibility (2nd law)

Exam Tip: “Which ecological pyramid is always upright?” — the Energy pyramid. This is a guaranteed 1-mark question. The energy pyramid is always upright because of the second law of thermodynamics: entropy always increases, so energy can only decrease up the chain. Biomass and number pyramids can invert.

15.4 Ecological Succession

Ecological succession is the predictable, directional, sequential change in community composition and structure over time at a particular location, driven by the modification of the abiotic environment by existing species (“facilitation”), until a relatively stable climax community is reached. Each stage is called a sere (or serial stage); the entire sequence from bare substrate to climax is a sere (pl. seres) or prisere.

Easy to confuse — Primary vs Secondary Succession

Primary Succession

Begins on a bare, lifeless substrate with no soil — bare rock after glacial retreat, fresh lava flow, new volcanic island, sand dune. Pioneers are lichens (rock face) and mosses. Very slow; may take thousands of years. Examples: succession on Krakatoa island after 1883 eruption.

Secondary Succession

Begins on a substrate that previously supported a community; soil is intact. After fire, flood, forest clearance, abandoned farmland. Faster than primary because soil, seed bank and vegetative propagules remain. Examples: regrowth after forest fire in HP chir pine forests; abandoned agricultural fields in Kangra valley.

15.4.1 Stages of Primary Succession on Rock (Lithosere / Xerosere)

Nudation — formation of bare area by physical agency (glaciation, erosion).
Pioneer stage — crustose lichens colonise bare rock; produce acids that weather rock; die and add humus. Then foliose and fruticose lichens.
Moss stage — mosses take over; trap more soil; organic matter accumulates.
Herb stage — annual and biennial herbs enter; nitrogen-fixers enrich soil.
Shrub stage — shrubs shade out herbs; soil deepens.
Climax forest — canopy trees (oak, deodar, etc. depending on climate) form self-perpetuating community. Composition depends on regional climate (monoclimax theory of Clements; polyclimax theory of Tansley).

15.4.2 Hydrarch Succession (Hydrosere)

Begins in open water body (pond or shallow lake) and proceeds through aquatic to terrestrial climax: Phytoplankton → submerged plants (Hydrilla, Vallisneria) → floating plants (Nymphaea, water lily) → reed swamp (Typha, Phragmites) → marsh/meadow → shrubs → climax forest. Each stage fills in the water body with organic matter, making it shallower until land forms.

Easy to confuse — Hydrosere vs Xerosere

Hydrosere (Hydrarch)

Starts in water; proceeds towards mesic (moist) conditions. Ponds → bog → marsh → woodland. Pioneer = phytoplankton. Filled in by sediment and organic matter accumulation.

Xerosere (Xerarch)

Starts on dry bare rock or desert; also proceeds towards mesic climax. Pioneer = crustose lichens. Sub-types: lithosere (bare rock), psammosere (sand dunes), halosere (salt flats).

Exam Tip: Both hydrosere and xerosere converge towards a mesic climax forest for a given climate. This is the key concept — succession is directional and convergent (Clementsian monoclimax) or site-specific (polyclimax). Examiners love asking: “What is the pioneer in xerosere?” Answer: lichens. “What is the pioneer in hydrosere?” Answer: phytoplankton.

Mnemonic — Xerosere stages

“Lichens Make Herbs Smell Climatic” — Lichens (pioneer) → Mosses → Herbs → Shrubs → Climax forest. Remember: each stage modifies the environment to make conditions suitable for the next (facilitation model).

15.5 Biogeography & Major Biomes (with HP Altitudinal Zones)

Biogeography studies the distribution of species and communities across space and through time. At the broadest scale, climate-determined biotic communities form biomes. Within a biome, local topography creates gradients; in mountainous regions like Himachal Pradesh, altitude compresses multiple biomes into a single mountain, creating stacked altitudinal vegetation zones.

15.5.1 Major Biomes of the World

**Table 15.3**Major biomes — climate, vegetation and animal characteristics
Biome	Climate	Dominant vegetation	Characteristic fauna
Tropical rainforest	High rainfall (>2000 mm), warm (>25°C), no dry season	Tall evergreen trees; high stratification; lianas, epiphytes	Howler monkeys, sloths, toucans, jaguars
Tropical savanna	Distinct wet & dry seasons; 500–1500 mm rain	Grassland with scattered trees (Acacia, Baobab)	Wildebeest, elephants, lions, zebra
Desert (hot)	<250 mm rain; extreme temperature range	CAM succulents (Cactus), sparse xerophytes	Camel, fennec fox, monitor lizard, rattlesnake
Temperate grassland	Low, irregular rainfall; hot summers, cold winters	Grasses (no trees); deep rich soil (mollisol)	Bison (prairies), wild horse (steppes), prairie dog
Temperate deciduous forest	Moderate rain; warm summers, cold winters; 4 seasons	Broad-leaved deciduous trees (oak, maple, beech)	Deer, bears, squirrels, woodpeckers
Temperate rainforest	High rainfall; mild, foggy; Pacific coast	Conifers (coast redwood, Douglas fir), ferns	Spotted owl, banana slug, Roosevelt elk
Taiga (Boreal forest)	Short cool summer; long cold winter; low precipitation	Coniferous (spruce, fir, larch, pine); needle leaves	Moose, wolf, lynx, Siberian tiger
Tundra (Arctic & Alpine)	Very cold; low precipitation (<250 mm); permafrost	Mosses, lichens, grasses, dwarf shrubs; no trees	Polar bear (arctic), caribou, snowy owl, musk ox

15.5.2 Indian Biogeographic Zones (Rodgers-Panwar 1988)

India is divided into 10 biogeographic zones: (1) Trans-Himalaya, (2) Himalaya, (3) Indian Desert, (4) Semi-arid, (5) Western Ghats, (6) Deccan Peninsula, (7) Gangetic Plain, (8) North-East India, (9) Coasts, (10) Islands. Himachal Pradesh spans zones 1 (Trans-Himalaya — Lahaul-Spiti, Kinnaur highlands) and 2 (Himalaya — most of the state).

15.5.3 HP Altitudinal Vegetation Zones

The Himalayas compress the equivalent of a latitudinal transect from tropics to arctic within a vertical span of <5000 m. Himachal Pradesh, spanning from ~300 m (Shivalik foothills) to >6000 m (Spiti peaks), displays all major altitudinal belts.

Figure 15.4 Altitudinal vegetation zones of Himachal Pradesh. Each zone stacks like a latitudinal biome compressed by altitude. The cold desert of Lahaul-Spiti (Transhimalayan zone) lies in the rain shadow of the Greater Himalayas and resembles the Tibetan plateau floristically.

**Table 15.4**HP altitudinal vegetation zones — elevation, districts, vegetation and fauna
Zone	Elevation (m)	Districts	Key plants	Key fauna
Subtropical	300–1500	Una, Bilaspur, lower Sirmaur, lower Kangra	Chir pine (Pinus roxburghii), sal (Shorea robusta), mango, ber, khair (Acacia catechu)	Spotted deer, sambar, common leopard
Temperate	1500–3000	Shimla, Mandi, Kullu, Chamba, Kangra (upper)	Deodar (Cedrus deodara), blue pine (Pinus wallichiana), oak (Quercus spp.), walnut, rhododendron	Himalayan black bear, barking deer, goral, monal, Western tragopan
Sub-alpine	3000–3500	Upper Kullu, Kinnaur, Chamba (high)	Birch (Betula utilis), juniper (Juniperus spp.), silver fir (Abies pindrow), spruce (Picea smithiana)	Himalayan tahr, musk deer, snow partridge
Alpine meadow	3500–5000	Spiti, Kinnaur, Rohru, Chamba highland	Aconitum heterophyllum (atees), Saussurea lappa (kuth), Picrorhiza kurroa (kutki), Rhododendron campanulatum	Snow leopard, blue sheep (bharal), ibex, Himalayan red panda
Cold desert / Trans-Himalayan	>3500 (rain shadow)	Lahaul, Spiti, parts of Kinnaur	Sea buckthorn (Hippophae rhamnoides), Caragana spp., Artemisia, drought-adapted cushion plants	Snow leopard, Tibetan wolf, kiang (Tibetan wild ass), bar-headed goose (migratory)

HP Angle: The state tree is deodar (Cedrus deodara), the state flower is pink rhododendron (Rhododendron campanulatum), the state bird is Western tragopan or Jujurana (Tragopan melanocephalus), and the state animal is the snow leopard (Panthera uncia). All four are temperate-to-alpine zone denizens of Himachal Pradesh and appear regularly in HPRCA exams. Hippophae rhamnoides (sea buckthorn) of Lahaul-Spiti is a cold desert pioneer and a commercially important source of vitamin C and omega fatty acids.

15.6 Biodiversity — Levels, Patterns and India’s Hotspots

The term biodiversity was popularised by E. O. Wilson in 1986 (building on Thomas Lovejoy's 1980 use). It encompasses three levels: genetic diversity (variety of alleles and genotypes within a species), species diversity (number and relative abundance of species in a community), and ecosystem diversity (variety of ecosystems and habitats in a region). Worldwide, ~8.7 million eukaryotic species are estimated; only ~1.5–1.8 million are formally described. India harbours ~45,000 plant species (~12% of world's plant biodiversity) and ~90,000 animal species (~7% of known).

15.6.1 Levels of Biodiversity

Genetic diversity — variation at the gene level within a species. Essential for adaptation and evolution. Eg: 50,000+ traditional varieties of rice in India; genetic erosion from modern monocultures.
Species diversity — commonly measured as species richness (number) + evenness (relative abundance). Tropical regions are richer than temperate; the latitudinal diversity gradient is one of ecology's most robust patterns (more species nearer the equator).
Ecosystem diversity — variety of habitats, biotic communities and ecological processes. India has deserts, grasslands, mangroves, coral reefs, alpine meadows, wetlands — exceptionally high ecosystem diversity.

15.6.2 Whittaker's Diversity Indices

Robert Whittaker (1972) formalised three levels of species diversity measurement:

α (alpha) diversity — species richness within a single community or habitat (local diversity).
β (beta) diversity — change in species composition between habitats (turnover between communities). High β diversity means communities differ greatly from each other.
γ (gamma) diversity — total species richness over a large geographic area (landscape diversity = α × β broadly).

Mnemonic — Diversity levels

“Alpha lives At home, Beta lives Between habitats, Gamma is Geographic” — α = within one site; β = between sites; γ = over the whole landscape. Also remember: Whittaker 1972 coined these terms.

15.6.3 Biodiversity Patterns

Latitudinal gradient — species richness increases from poles to equator; most prominent in plants and vertebrates. Tropical rainforests cover <6% of land surface but house >50% of species. Explanations include: longer evolutionary time in tropics, higher productivity, niche diversification, greater habitat heterogeneity.

Species–area relationship (MacArthur & Wilson, 1967) — log S = log C + z log A, where S = species richness, A = area, C and z are constants. On larger islands or habitat patches, more species persist. z ≈ 0.1–0.2 for islands within the same region; z ≈ 0.6–1.2 across continents. Applied in conservation: smaller habitat fragments support fewer species.

15.6.4 Biodiversity Hotspots

Norman Myers (1988) introduced the hotspot concept: regions of exceptional plant endemism (≥1500 endemic plant species) that have lost ≥70% of their original vegetation. Currently 36 hotspots worldwide (updated 2023). India falls within 4 hotspots:

Figure 15.5 India's four biodiversity hotspots as identified under the Myers/CEPF framework. The Himalaya hotspot (including Western Himalaya and Himachal Pradesh) is among the world's richest for endemic alpine and sub-alpine species.

**Table 15.5**India's four biodiversity hotspots — area, key species and threats
Hotspot	States/region	Key endemic plants	Key endemic/flagship fauna	Major threats
Himalaya	HP, Uttarakhand, J&K, Sikkim, NE states, Nepal, Bhutan	Rhododendron (1000+ spp.), Saussurea, Picrorhiza kurroa, Aconitum	Snow leopard, Western tragopan, Himalayan monal, red panda, clouded leopard	Climate change, over-grazing, illegal collection of medicinal plants
Western Ghats	Kerala, Karnataka, Maharashtra, Tamil Nadu, Goa	~5000 endemic plant species; Myristica, Garcinia	Lion-tailed macaque, Nilgiri tahr, purple frog, Malabar tree toad	Deforestation, agriculture expansion, quarrying
Indo-Burma	NE India, Myanmar, Yunnan, Indochina	Dipterocarpus spp., wild banana, many orchids	Hoolock gibbon, Irrawaddy dolphin, green peacock, giant Mekong catfish	Shifting cultivation, hunting, logging
Sundaland (Nicobar)	Andaman & Nicobar Islands (Indian part)	Dipterocarp forest species, mangroves	Nicobar megapode, leatherback sea turtle, dugong, saltwater crocodile	Development, tsunami impact, invasive species

India is one of 17 megadiverse countries (Mittermeier 1988): those that together harbour more than 70% of the world's species despite occupying only ~10% of land. Others include Brazil, Indonesia, Australia, China, Mexico, Colombia.

HP Angle: Himachal Pradesh has ~67% forest cover, among the highest of any Indian state, placing it as a critical component of the Himalayan hotspot. The Great Himalayan National Park (Kullu) was designated a UNESCO World Heritage Site in 2014 specifically for its role in conserving the upper Beas and Tirthan river catchment biodiversity, including 375 plant species, 31 mammal species and over 180 bird species. HPRCA-pat.

15.7 Conservation — Protected Areas of India & Himachal Pradesh

Conservation is the management of natural resources to prevent depletion, degradation and extinction. It falls into two broad strategies: in situ (on-site, in natural habitat) and ex situ (off-site, away from natural habitat).

Easy to confuse — In situ vs Ex situ Conservation

In situ Conservation

Protecting species within their natural habitat, where they continue to evolve. Methods: National Parks, Wildlife Sanctuaries, Biosphere Reserves, Tiger Reserves, Conservation Reserves, Sacred Groves, Ramsar wetlands. Most effective for maintaining ecological interactions and evolutionary processes.

Ex situ Conservation

Protecting species outside natural habitats. Zoos, botanical gardens, seed banks (NBPGR, New Delhi; Svalbard Global Seed Vault), gene banks, cryopreservation, tissue culture, IVF & embryo transfer. Used for critically endangered species or genetic stock preservation.

Easy to confuse — National Park vs Wildlife Sanctuary vs Biosphere Reserve vs Tiger Reserve

National Park

Highest legal protection. No human habitation, grazing, forestry or any extractive use permitted. Boundaries fixed by legislation. Cannot be altered without Parliament approval. Eg: Great Himalayan NP, Corbett NP. India has 106 NPs (as of 2023).

Wildlife Sanctuary

Species-focused protection. Some controlled human activities permitted (grazing, regulated harvesting). Boundaries can be altered by State Government. India has ~565 WLSs. Eg: Kalatop-Khajjiar WLS (Chamba).

Easy to confuse — Biosphere Reserve vs Tiger Reserve

Biosphere Reserve (UNESCO MAB)

Largest category; encompass NPs and WLSs. Three zones: Core (strictly protected), Buffer (limited research/education), Transition/Manipulation (sustainable human use). India has 18 BRs; 12 in UNESCO World Network. Eg: Cold Desert BR (Lahaul-Spiti, HP) — one of India's 18 BRs.

Tiger Reserve (Project Tiger)

Designated under Project Tiger (1973) for tiger conservation. Managed by NTCA (National Tiger Conservation Authority). India has 54 Tiger Reserves (2023). Core + buffer zone structure. Eg: Sariska, Ranthambore, Corbett. HP has no official Tiger Reserve.

15.7.1 HP National Parks (5)

**Table 15.6**National Parks of Himachal Pradesh
National Park	Year est.	Area (km²)	District	Key species / notes
Great Himalayan NP	1984	754	Kullu	Snow leopard, Himalayan tahr, blue sheep, western tragopan, Himalayan monal; UNESCO World Heritage Site 2014; also GHNP Conservation Area (1171 km²) as buffer
Pin Valley NP	1987	675	Lahaul-Spiti	Snow leopard, ibex (Capra ibex), Tibetan wolf, Himalayan snowcock; cold desert ecosystem
Khirganga NP	2010	710	Kullu	Brown bear, snow leopard, Hippophae; adjoins Great Himalayan NP
Inderkilla NP	2010	104	Kullu	Monal, western tragopan, Himalayan black bear; part of Kullu biogeographic complex
Simbalbara NP	2010	27.88	Sirmaur	Sal forest; hog deer, barking deer, leopard; smallest NP in HP; adjoins Kalesar NP (Haryana)

15.7.2 Notable HP Wildlife Sanctuaries

**Table 15.7**Notable Wildlife Sanctuaries of Himachal Pradesh
Sanctuary	District	Notable features
Kalatop-Khajjiar	Chamba	Deodar forest; Himalayan black bear, leopard; near Khajjiar ‘mini-Switzerland’
Daranghati	Shimla	Monal, snow leopard; mixed conifer forest
Kanawar	Kullu	Western tragopan; oak-deodar forest
Manali	Kullu	Snow leopard, ibex; Great Himalayan NP buffer
Sechu Tuan Nala	Chamba	High altitude; Himalayan ibex, snow leopard
Bandli	Mandi	Mixed forest; leopard, goral
Lippa Asrang	Kinnaur	Cold desert; snow leopard, Siberian ibex
Rupi Bhaba	Kinnaur	Snow leopard, Himalayan tahr; connects Pin Valley NP

15.7.3 Ramsar Wetlands of HP (3)

The Ramsar Convention (1971, Iran) is the international treaty for conservation and sustainable use of wetlands. India has 80 Ramsar sites (2024). Himachal Pradesh has three:

**Table 15.8**Ramsar wetlands of Himachal Pradesh
Wetland	District	Ramsar year	Significance
Pong Dam Lake	Kangra	1994	Largest Ramsar site of HP; wintering ground for bar-headed goose (Anser indicus), northern pintail and >220 bird species; also called Maharana Pratap Sagar
Renuka Lake	Sirmaur	2005	Sacred lake; dolphin-shaped; Renuka ji pilgrim site; freshwater ecosystem
Chandratal	Lahaul-Spiti	2005	High-altitude lake (~4200 m); moon-shaped; no permanent human habitation; bar-headed goose and Brahminy duck stopover; part of Spiti cold desert landscape

15.7.4 Biosphere Reserves with HP Component

Cold Desert Biosphere Reserve (established 1992) covers 7770 km² of Lahaul-Spiti — the largest BR by area in HP. Nanda Devi Biosphere Reserve (UNESCO WH; established 1988) spans Uttarakhand but its buffer touches the HP boundary. HP is a biodiversity corridor connecting the trans-Himalayan cold desert to the temperate and subtropical zones of the Shivaliks.

HP Angle: Pong Dam Lake (1994) is the oldest Ramsar site in HP. The bar-headed goose (Anser indicus) crosses the Himalayas at altitudes up to 7000 m — the highest altitude migration of any bird — and winters at Pong Dam. Great Himalayan NP became a UNESCO World Heritage Site on 23 June 2014 — the first in HP. Pin Valley NP is India's only cold desert National Park within the trans-Himalayan biogeographic zone. HPRCA-pat.

15.8 Pollution — Air, Water, Soil and Noise

A pollutant is any substance introduced into the environment that causes adverse effects on living organisms or the abiotic environment. Pollution may be natural (volcanic SO₂) or anthropogenic (industrial effluents, vehicle exhaust). Major categories: air, water, soil and noise.

15.8.1 Air Pollution

Major air pollutants and their sources:

Sulphur dioxide (SO₂) — combustion of coal and petroleum, smelting. Causes acid rain (H₂SO₄), respiratory irritant, damages deodar forests in Himachal (bio-indicator: lichen disappears near SO₂ sources).
Nitrogen oxides (NO_x) — vehicle exhaust, thermal power plants. React with hydrocarbons + UV light to form photochemical smog (ozone, PAN — peroxyacetyl nitrate).
Carbon monoxide (CO) — incomplete combustion. Bonds to haemoglobin (250× more than O₂), causing asphyxia.
Particulates (PM_2.5, PM₁₀) — dust, soot, smoke. PM_2.5 penetrates deep lung alveoli; causes cardiovascular and respiratory disease.
CFCs (chlorofluorocarbons) — refrigerants, aerosols. Destroy stratospheric ozone (see 15.9).
Lead (Pb) — leaded fuel (phased out), paint. Neurological damage especially in children.

Lichen (crustose) are excellent bio-indicators of SO₂ pollution: their absence near industrial zones is an early warning sign. Acid rain (pH <5.6) forms when SO₂ and NO_x dissolve in atmospheric moisture; damages forests, acidifies lakes, corrodes limestone monuments (Taj Mahal affected by Mathura refinery fumes).

15.8.2 Water Pollution

Biological Oxygen Demand (BOD) = amount of oxygen (mg/L) consumed by microbes to decompose organic matter in water at 20°C for 5 days. Clean water has BOD <5 mg/L; polluted river may have BOD >17 mg/L; raw sewage >200 mg/L. High BOD = high organic pollution.

Eutrophication — excessive nutrient enrichment (mainly N and P from agricultural runoff and sewage) of water bodies leads to algal blooms. Decomposition of algae consumes O₂, creating hypoxic/anoxic zones (dead zones). Fish and invertebrates suffocate. Examples: Lake Victoria (Africa), Dal Lake (Kashmir), many HP hill lakes threatened by nutrient runoff from horticulture.

Biomagnification (bioaccumulation) — concentration of a persistent pollutant increases at each trophic level because it is not metabolised and accumulates in fat tissues. Classic example: DDT in aquatic food chains — water (0.003 ppm) → zooplankton (0.04 ppm) → small fish (0.5 ppm) → large fish (2 ppm) → osprey (25 ppm). High DDT causes eggshell thinning in raptors (Carson's Silent Spring, 1962). Mercury — Minamata disease (Japan 1956): industrial methylmercury in Minamata Bay concentrated up food chain to fish and then to humans causing neurological damage.

Easy to confuse — Eutrophication vs Biomagnification

Eutrophication

Nutrient overload (↑ N, P) → algal bloom → O₂ depletion → fish death. The nutrient itself does not accumulate through trophic levels; it triggers biological overgrowth. Affects lakes and slow-moving rivers. BOD rises dramatically.

Biomagnification

Persistent toxic chemicals (DDT, mercury, PCBs) accumulate in fat tissue at each trophic level. Concentration increases up the food chain. Top predators most affected. Does NOT require a water body — occurs in any food chain.

**Table 15.9**Pollution types — major pollutants, indicators and health effects
Type	Key pollutants	Indicators / monitors	Health / ecosystem effects
Air	SO₂, NO_x, CO, PM_2.5, O₃, CFCs, Pb	Lichen absence, conifer needle necrosis, RSPM monitors	Acid rain, smog, asthma, lung cancer, cardiovascular disease
Water	Sewage BOD, nitrates, phosphates, heavy metals, pesticides, plastics	BOD, COD, DO (dissolved oxygen), coliform count, turbidity	Eutrophication, methemoglobinemia (blue baby from nitrates), Minamata (Hg), biomagnification
Soil	Pesticides (organochlorines, organophosphates), heavy metals, plastics, excess fertilisers, salts	Earthworm and nematode populations decline; nitrifier enzyme activity	Loss of soil fertility, contamination of groundwater, food-chain entry of toxins
Noise	Industrial noise, traffic, construction, firecrackers	dB(A) measurement; WHO standard: 45 dB (day), 35 dB (night) outdoor	Hearing loss (>85 dB prolonged), stress hormones, hypertension, wildlife disruption (birds, dolphins)

Worked example — identifying pollution type from symptoms

"A river shows: (i) green-brown scum on surface; (ii) dead fish; (iii) no aquatic invertebrates; (iv) high BOD. What type of pollution is indicated?"

Analysis: Green-brown scum = algal bloom; dead fish and no invertebrates = oxygen depletion; high BOD = high organic decomposition demand. This is classic eutrophication due to nutrient (N/P) loading, most likely from agricultural runoff or sewage discharge. Action indicator: reduce nutrient input, restore riparian buffer strips, treat sewage before discharge.

Exam Tip: Examiners often ask: “BOD of a sample is 4 mg/L and another is 22 mg/L — which is more polluted?” Answer: 22 mg/L is far more polluted (high BOD = high organic pollution). Also note: high DO (dissolved oxygen) = clean water; low DO = polluted water. These two are inversely related via eutrophication.

15.9 Global Environmental Change — Climate, Ozone and Biodiversity Loss

15.9.1 Greenhouse Effect and Climate Change

The natural greenhouse effect is essential for life: greenhouse gases (GHGs) in the troposphere trap outgoing longwave radiation and keep Earth's mean temperature at ~15°C instead of −18°C. The problem is enhanced greenhouse effect from anthropogenic GHG emissions raising global mean temperature.

Greenhouse gases (GHGs) in order of contribution to anthropogenic forcing:

CO₂ (~66% of enhanced forcing) — fossil fuel combustion, deforestation, cement. Pre-industrial: 280 ppm; 2024: ~422 ppm.
Methane (CH₄) (~16%) — rice paddies, cattle ruminants, landfills, natural gas leaks. GWP₁₀₀ = 25× CO₂. Lifetime ~12 years.
Nitrous oxide (N₂O) (~6%) — nitrogenous fertilisers, livestock. GWP₁₀₀ = 298× CO₂.
Water vapour (H₂O) — largest natural GHG but not directly driven by humans; acts as amplifying feedback.
CFCs — strongest per-molecule GHGs (GWP up to 22,800) but phased out under Montreal Protocol; also ozone destroyers.
Ozone (O₃) in troposphere — GHG and smog component.

Easy to confuse — Greenhouse gases vs Ozone-depleting substances

Greenhouse gases (GHGs)

Trap longwave radiation from Earth's surface, warming troposphere. CO₂, CH₄, N₂O, H₂O, CFCs, tropospheric O₃. Protocol: Kyoto 1997 (binding targets for Annex I countries); Paris Agreement 2015 (1.5°C limit).

Ozone-depleting substances (ODS)

Destroy stratospheric ozone (15–35 km), which shields life from UV-B. CFCs (Freon), HCFCs, halons, methyl bromide. Each Cl radical destroys 100,000 ozone molecules. Protocol: Montreal 1987 — most successful environmental treaty; CFC production essentially phased out. Antarctic ozone hole (spring maximum). Note: CFCs are both GHGs and ODS.

Consequences of climate change: rising sea levels (thermal expansion + ice melt), increased frequency of extreme weather, glacier retreat (HP's Himalayan glaciers shrinking — Rohtang Pass is a documented case), shifts in species ranges, disrupted monsoon, coral bleaching (ocean warming), phenological mismatches (pollinator timing vs flower timing), increased wildfire risk.

Mitigation: renewable energy, energy efficiency, reforestation, carbon capture, reduced deforestation. Adaptation: drought-resistant crops, flood barriers, altered agricultural calendars.

15.9.2 Ozone Depletion

The ozone layer (stratosphere, 15–35 km) absorbs UV-B and UV-C radiation, preventing DNA damage, skin cancer, cataracts and disruption of phytoplankton photosynthesis. CFCs release chlorine radicals (Cl•) on polar stratospheric ice crystals, which catalytically destroy ozone: Cl• + O₃ → ClO + O₂; ClO + O → Cl• + O₂. Each Cl• destroys ~100,000 ozone molecules. The Antarctic ozone hole was discovered by Farman et al. in 1985; largest in September–October. The Montreal Protocol (1987) mandated CFC phase-out; the ozone layer is projected to recover to pre-1980 levels by 2065 — the one confirmed environmental success story of global cooperation.

Exam Tip: A very common exam trap: ozone in the stratosphere is beneficial (protects against UV); ozone in the troposphere is harmful (smog, respiratory irritant). The CFCs that harm the stratospheric ozone layer are the same substances that are also powerful greenhouse gases. Montreal Protocol 1987 (ozone) and Kyoto 1997 (climate) are the two most-tested environmental treaties.

15.9.3 Biodiversity Loss — The Sixth Mass Extinction

Current extinction rates are estimated at 100–1000 times above natural background rates, earning the designation Sixth Mass Extinction (Wilson; Ceballos et al. 2017). The five previous were geological events (e.g., K-Pg boundary asteroid 66 Ma ago). The current crisis is entirely anthropogenic.

HIPPO framework (Wilson): the five major drivers of biodiversity loss:

Habitat loss and fragmentation — the single largest driver; tropical deforestation, wetland draining, grassland conversion.
Invasive alien species — compete with, prey on or parasitise native species. Eg: Parthenium hysterophorus (Congress weed) in Indian grasslands; Lantana camara in Indian forests and HP hill slopes.
Pollution — chemical, noise, light, plastic.
Population growth (human) — resource demand, land conversion.
Over-exploitation — hunting, poaching, over-harvesting. Snow leopard poaching for fur in HP/Spiti; illegal collection of medicinal plants (Aconitum, Picrorhiza).
(+Climate change) — increasingly added as sixth driver.

Key international frameworks:

Convention on Biological Diversity (CBD) — adopted Rio de Janeiro, 1992. Three objectives: conservation, sustainable use, fair sharing of benefits from genetic resources (Access and Benefit Sharing, ABS — Nagoya Protocol 2010).
CITES — Convention on International Trade in Endangered Species (1963/1975). Three appendices (I = no trade; II = regulated; III = country-specific). Snow leopard is CITES Appendix I.
Aichi Biodiversity Targets (CBD COP10, 2010, Nagoya, Japan) — 20 targets by 2020; largely unmet.
Kunming-Montreal Global Biodiversity Framework (GBF) 2022 — “30×30”: protect 30% of land and oceans by 2030. Agreed at CBD COP15, Montreal.
IUCN Red List — global standard for species threat assessment: Extinct (EX), Extinct in Wild (EW), Critically Endangered (CR), Endangered (EN), Vulnerable (VU), Near Threatened (NT), Least Concern (LC).

HP Angle: The snow leopard (Panthera uncia) is classified as Vulnerable on IUCN Red List (downlisted from Endangered in 2017). The Western tragopan (Tragopan melanocephalus) is Vulnerable. Himalayan red panda (Ailurus fulgens) is Endangered. The Himalayan monal (Lophophorus impejanus), though the national bird of Nepal and state bird of Uttarakhand, is also found in HP's Great Himalayan NP. Western tragopan is HP's state bird and among the most endangered pheasants in the world. HPRCA-pat.

15.10 Quick-Reference Tables

**Table 15.10**Population growth — equations and parameters
Model	Equation	Key parameters	Curve shape	When applicable
Exponential	dN/dt = rN	r = intrinsic rate; N = population size	J-shaped	Unlimited resources; early colonisation; pest outbreaks
Logistic	dN/dt = rN(K−N)/K	K = carrying capacity; inflection at N = K/2	S-shaped (sigmoid)	Limited resources; most real populations
Doubling time	t_d = 0.693 / r	—	Single value	Applies to exponential phase only

**Table 15.11**Biogeochemical cycles — key processes and organisms
Cycle	Type	Key processes	Key organisms	Main reservoir
Carbon	Gaseous	Photosynthesis (in), respiration + combustion (out)	Plants/algae (fixation); decomposers	Ocean (~38,000 Gt C)
Nitrogen	Gaseous	Fixation, nitrification, denitrification, ammonification	Rhizobium, Nitrosomonas, Nitrobacter, Pseudomonas	Atmosphere (78% N₂)
Phosphorus	Sedimentary (no gas phase)	Weathering, uptake, decomposition, sedimentation	Plants (uptake); decomposers (mineralisation)	Rocks (apatite)
Sulphur	Mixed (gas + sediment)	Volcanic emission, oxidation to SO₄²⁻, plant uptake, H₂S from anaerobic decomp.	Desulfovibrio (reduction); Thiobacillus (oxidation)	Rocks (pyrite) + ocean

Mnemonic — “PCBR” for ecological organisation levels

Population (one species, one area) → Community (many species, one area) → Biome (climate-defined vegetation zone) → Region / Biosphere (entire Earth's life zone). Remember: each level adds one more dimension of complexity. The ecosystem sits between community and biome — it adds the abiotic components to a community.

**Table 15.12**Greenhouse gases vs ozone-depleting substances — comparison
Parameter	GHGs (climate change)	ODS (ozone depletion)
Effect	Trap IR radiation in troposphere; warm Earth	Destroy O₃ in stratosphere; allow UV-B through
Main chemicals	CO₂, CH₄, N₂O, H₂O, CFCs, O₃ (troposphere)	CFCs, HCFCs, halons, CH₃Br
Governing treaty	UNFCCC / Kyoto 1997 / Paris 2015	Vienna Convention 1985 / Montreal Protocol 1987
Health effect	Heat waves, vector-borne diseases, food insecurity	Skin cancer, cataracts, suppressed immunity, phytoplankton decline
Overlap	CFCs are simultaneously potent GHGs and ODS; phasing them out via Montreal also mitigates climate change

Chapter 15 Recap

Ecology (Haeckel 1866) operates at population, community, ecosystem and biosphere levels. Ecosystem coined by Tansley 1935.
Exponential growth: dN/dt = rN (J-curve; unlimited resources). Logistic growth: dN/dt = rN(K−N)/K (S-curve; K = carrying capacity; max growth at N = K/2).
r-strategists: high r, small body, many offspring (mice, weeds). K-strategists: low r, large body, few offspring (elephants, snow leopard, humans).
Population interactions: predation (+/−), competition (−/−), mutualism (+/+), commensalism (+/0), amensalism (−/0), parasitism (+/−). Gause's exclusion: identical niches cannot coexist.
Lindeman's 10% law (1942): only ~10% of energy transfers to next trophic level. Energy pyramid is always upright; biomass can invert (pelagic); numbers can invert (single tree + many insects).
Ecological succession: primary (bare rock; pioneer = lichens) vs secondary (soil present; faster). Hydrosere (phytoplankton → climax forest); xerosere (lichens → climax forest).
HP altitudinal zones: subtropical (chir pine) → temperate (deodar) → sub-alpine (birch) → alpine (<em>Saussurea</em>) → cold desert (Hippophae). State animal: snow leopard; state bird: Western tragopan; state tree: deodar; state flower: pink rhododendron.
HP's 3 Ramsar sites: Pong Dam Lake (1994; bar-headed goose), Chandratal (2005; 4200 m), Renuka Lake (2005). HP has 5 National Parks; Great Himalayan NP = UNESCO World Heritage 2014; Pin Valley NP = India's only cold-desert NP.
India's 4 biodiversity hotspots: Himalaya, Western Ghats, Indo-Burma, Sundaland-Nicobar. India is one of 17 megadiverse countries. Hotspot criteria (Myers): ≥1500 endemic plant species + ≥70% original habitat lost.
In situ: NP, WLS, BR, Tiger Reserve. Ex situ: zoo, botanical garden, NBPGR seed bank, gene bank, cryopreservation.
BOD: high = polluted. Eutrophication: nutrient overload → algal bloom → O₂ depletion. Biomagnification: DDT/Hg concentrated up food chain.
GHGs: CO₂ (66%), CH₄ (25× CO₂), N₂O (298×), CFCs; Paris 2015 (1.5°C target). ODS: CFCs destroy stratospheric O₃; Montreal 1987; Antarctic ozone hole (Farman 1985).
6th mass extinction: HIPPO drivers (Habitat loss, Invasive species, Pollution, Population growth, Over-exploitation). CBD 1992 (Rio); Kunming-Montreal GBF 2022 (“30×30”).

Ecology Cheatsheet

Population equations

Exponential: dN/dt = rN
Logistic: dN/dt = rN(K−N)/K
Doubling time: t = 0.693/r
Max logistic growth: N = K/2

Ecology landmarks

Ecology — Haeckel 1866
Ecosystem — Tansley 1935
10% law — Lindeman 1942
α/β/γ diversity — Whittaker 1972
Biodiversity — Wilson 1986

HP protected areas

NPs: Great Himalayan (UNESCO WH), Pin Valley, Khirganga, Inderkilla, Simbalbara
Ramsar: Pong Dam (1994), Chandratal (2005), Renuka (2005)
BR: Cold Desert (Lahaul-Spiti)

Succession pioneers

Xerosere (rock): crustose lichens
Hydrosere (water): phytoplankton
Psammosere (sand): marram grass
Halosere (salt): glasswort (Salicornia)

Nitrogen cycle microbes

Fixation: Rhizobium, Azotobacter, Anabaena
Nitrification: Nitrosomonas → Nitrobacter
Denitrification: Pseudomonas
Ammonification: general decomposers

Pollution indicators

High BOD = organic water pollution
Lichen absence = SO₂ air pollution
Algal bloom = eutrophication
Thinning eggshell = DDT biomagnification
Minamata disease = methylmercury

India's 4 biodiversity hotspots

1. Himalaya (incl. HP)
2. Western Ghats
3. Indo-Burma (NE India)
4. Sundaland–Nicobar
Criteria: ≥1500 endemic plants + ≥70% habitat lost (Myers 1988)

Env. treaties

Montreal 1987 (ozone / CFCs)
CBD 1992 Rio (biodiversity)
Kyoto 1997 (GHGs / climate)
Paris 2015 (1.5°C)
Kunming-Montreal 2022 (30×30)

Cross-references

Chapter 2 (Economic Botany): HP medicinal plants — Picrorhiza kurroa, Aconitum, Hippophae — also feature in biodiversity and in situ conservation discussions here.
Chapter 1 (Plant Diversity): Lichens as pioneers in primary succession; mycorrhiza as mutualistic interaction; Azolla–Anabaena mutualism; nitrogen fixation by cyanobacteria.
Cell Biology & Physiology chapters: photosynthesis and respiration underpin NPP calculation and energy flow through trophic levels.
Genetics chapter: genetic diversity (one of three levels of biodiversity); genetic erosion from agricultural monocultures; NBPGR seed bank and gene conservation.
Human Welfare / Applied Biology: pollution and health effects, biomagnification (DDT, Hg), eutrophication, biodiversity conservation policies, Project Tiger, IUCN Red List categories.

Practice Questions — Chapter 15: Ecology

1. Which equation correctly represents logistic population growth?

dN/dt = rN
dN/dt = rN(K − N)/K
N(t) = N₀ e^rt
dN/dt = bN − dN

Answer: B

The logistic model introduces the braking term (K − N)/K. Option A is exponential; Option C is the integrated exponential; Option D is birth-rate minus death-rate, the basic difference equation without density dependence.

2. At what population size does logistic growth rate reach its maximum? HPRCA-pat.

N = K
N = K/4
N = K/2
N = 2K

Answer: C

The inflection point of the logistic S-curve is at N = K/2. This is the point of maximum rate of increase and the target for maximum sustainable yield in fisheries management.

3. Lindeman's 10% law states that during energy transfer from one trophic level to the next, the amount of energy:

Increases tenfold
Remains constant
Decreases to approximately 10%
Decreases to exactly 50%

Answer: C

Lindeman (1942) showed that only ~10% of energy stored at one trophic level is available to the next. The remaining 90% is dissipated as heat during metabolism, used for growth maintenance and lost as undigested matter to decomposers.

4. Which ecological pyramid is ALWAYS upright and can NEVER be inverted? HPRCA-pat.

Pyramid of numbers
Pyramid of biomass
Pyramid of energy
Both A and B

Answer: C

The energy pyramid is always upright because energy is lost (as heat) at each trophic level per the second law of thermodynamics. Numbers and biomass pyramids can be inverted under certain conditions.

5. The term ‘ecosystem’ was coined by:

Ernst Haeckel (1866)
Arthur Tansley (1935)
Raymond Lindeman (1942)
E. O. Wilson (1986)

Answer: B

Arthur George Tansley introduced the term ‘ecosystem’ in 1935 in the journal Ecology. Haeckel coined ‘ecology’ in 1866; Lindeman proposed the 10% law in 1942; Wilson popularised ‘biodiversity’ in 1986.

6. The UNESCO World Heritage Site status was conferred on Great Himalayan National Park (HP) in: HPRCA-pat.

1984
1994
2010
2014

Answer: D

Great Himalayan National Park was established in 1984 but received UNESCO World Heritage Site designation on 23 June 2014 — the first natural World Heritage Site in Himachal Pradesh.

7. Pong Dam Lake (Kangra, HP) was declared a Ramsar site in: HPRCA-pat.

1971
1994
2005
2010

Answer: B

Pong Dam Lake was listed as a Ramsar wetland in 1994 — the first and oldest Ramsar site in HP. Chandratal and Renuka Lake were both listed in 2005. The Ramsar Convention itself was signed in Ramsar, Iran, in 1971.

8. Which bird species is famous for wintering at Pong Dam Lake, HP, and is known to cross the Himalayas at altitudes above 7000 m? HPRCA-pat.

Western tragopan (Tragopan melanocephalus)
Himalayan monal (Lophophorus impejanus)
Bar-headed goose (Anser indicus)
Siberian crane (Grus leucogeranus)

Answer: C

The bar-headed goose migrates over the Himalayas between its breeding grounds in Tibet/Central Asia and wintering grounds in the Indian subcontinent, including Pong Dam Lake. It holds the record for the highest-altitude bird migration.

9. Pin Valley National Park (Lahaul-Spiti) is significant because it is: HPRCA-pat.

The largest National Park in India
India's only cold desert National Park in the trans-Himalayan biogeographic zone
India's first National Park established under Project Tiger
A UNESCO World Heritage Site since 1994

Answer: B

Pin Valley NP (est. 1987) lies in the Spiti valley, entirely within the trans-Himalayan cold desert biogeographic zone — making it unique among Indian National Parks. Its flagship species include snow leopard, Siberian ibex and Tibetan wolf.

10. The pioneer organisms in primary succession on bare rock (xerosere) are:

Mosses
Grasses
Crustose lichens
Phytoplankton

Answer: C

Crustose lichens are the true pioneers on bare rock. They secrete carbonic acid that weathers the rock, and on their death add organic matter that begins soil formation, enabling mosses to colonise next.

11. Biological Oxygen Demand (BOD) is a measure of:

Dissolved oxygen content of water
Amount of oxygen consumed by microbes to decompose organic matter in water
Photosynthetic rate of aquatic plants
Concentration of nitrate in water

Answer: B

BOD (mg/L) quantifies the oxygen demand of microbial decomposition of organic matter at 20°C over 5 days. High BOD indicates high organic pollution. Clean water has BOD <5 mg/L.

12. Which of the following is a K-strategist? HPRCA-pat.

Drosophila melanogaster
Annual weed plants
Snow leopard (Panthera uncia)
Housefly (Musca domestica)

Answer: C

Snow leopards are classic K-strategists: large body, low reproductive rate (1–3 cubs per litter, breeding every 2 years), long life span, high parental investment. Options A, B and D are r-strategists with high reproductive rates and short generation times.

13. Which interaction is represented by barnacles living on whale skin (barnacle benefits; whale is unaffected)?

Mutualism
Parasitism
Commensalism
Amensalism

Answer: C

Commensalism (+/0): barnacle gains transport and access to food-rich oceanic currents; whale is neither benefited nor harmed. This contrasts with parasitism (+/−) where the host is harmed.

14. The state bird of Himachal Pradesh is: HPRCA-pat.

Himalayan monal (Lophophorus impejanus)
Western tragopan (Tragopan melanocephalus)
Bar-headed goose (Anser indicus)
Satyr tragopan (Tragopan satyra)

Answer: B

Western tragopan (Tragopan melanocephalus), locally called Jujurana or ‘king of birds’, is the state bird of HP. It is classified as Vulnerable (IUCN) and is one of the most endangered pheasants in the world, found in the temperate forests of the Great Himalayan NP corridor.

15. Assertion (A): The biomass pyramid is inverted in a pelagic ocean ecosystem.
Reason (R): Phytoplankton have a very high rate of reproduction and turnover, so their standing crop biomass at any instant is low even though they produce large amounts of organic matter. HPRCA-pat.

Both A and R are true; R is the correct explanation of A
Both A and R are true; R is NOT the correct explanation of A
A is true but R is false
A is false but R is true

Answer: A

Both statements are correct and causally linked. The inverted biomass pyramid in pelagic ecosystems occurs precisely because phytoplankton divide rapidly, keeping standing biomass low relative to the total energy produced, while zooplankton accumulate more biomass at any given moment.

16. Assertion (A): Ozone in the stratosphere is beneficial, but ozone in the troposphere is harmful.
Reason (R): Stratospheric ozone absorbs UV-B radiation; tropospheric ozone is a component of photochemical smog and an irritant.

Both A and R are true; R is the correct explanation of A
Both A and R are true; R is NOT the correct explanation of A
A is true but R is false
A is false but R is true

Answer: A

Stratospheric ozone (15–35 km) shields the biosphere from UV-B/UV-C radiation that causes DNA damage, skin cancer and cataracts. Tropospheric ozone forms as a secondary pollutant from NO_x + VOC reactions in sunlight; it is a respiratory irritant and damages plant tissues.

17. Assertion (A): Two species occupying identical ecological niches cannot coexist indefinitely in the same area.
Reason (R): The better competitor will displace the other through competitive exclusion (Gause's Principle, 1934). HPRCA-pat.

Both A and R are true; R is the correct explanation of A
Both A and R are true; R is NOT the correct explanation of A
A is true but R is false
A is false but R is true

Answer: A

Gause's Competitive Exclusion Principle (demonstrated with Paramecium, 1934) states that two species with identical niches cannot stably coexist — one will outcompete the other. Coexistence requires niche differentiation.

18. Assertion (A): The Montreal Protocol is considered the most successful international environmental treaty.
Reason (R): Under the Montreal Protocol, production of CFCs has been essentially eliminated, and the stratospheric ozone layer is projected to recover by 2065.

Both A and R are true; R is the correct explanation of A
Both A and R are true; R is NOT the correct explanation of A
A is true but R is false
A is false but R is true

Answer: A

The Montreal Protocol (1987) achieved near-universal ratification and measurable phase-out of CFCs, halons and other ODS. The ozone layer is recovering and projected to reach pre-1980 levels by ~2065, making it the one confirmed global environmental recovery success story.

19. Assertion (A): Eutrophication leads to a decrease in dissolved oxygen in water bodies.
Reason (R): Decomposition of the algal bloom by microorganisms consumes large amounts of dissolved oxygen.

Both A and R are true; R is the correct explanation of A
Both A and R are true; R is NOT the correct explanation of A
A is true but R is false
A is false but R is true

Answer: A

Nutrient loading → algal bloom → massive algal die-off → microbial decomposition consumes dissolved O₂ → hypoxic/anoxic conditions → fish kills. Both A and R are true and causally linked.

20. Match the HP National Parks (Column I) with their districts and key features (Column II): HPRCA-pat.
Column I: (a) Great Himalayan NP (b) Pin Valley NP (c) Simbalbara NP (d) Khirganga NP
Column II: (1) Lahaul-Spiti; cold desert; snow leopard (2) Kullu; UNESCO WH 2014 (3) Sirmaur; sal forest; hog deer (4) Kullu; adjoins Great Himalayan NP

a-2, b-1, c-3, d-4
a-1, b-2, c-4, d-3
a-2, b-3, c-1, d-4
a-3, b-1, c-2, d-4

Answer: A

Great Himalayan NP = Kullu, UNESCO WH 2014 (a-2). Pin Valley = Lahaul-Spiti, cold desert (b-1). Simbalbara = Sirmaur, sal + hog deer (c-3). Khirganga = Kullu, adjoins GHNP (d-4).

21. Match the scientists (Column I) with their contributions (Column II): HPRCA-pat.
Column I: (a) Haeckel (b) Tansley (c) Lindeman (d) Whittaker
Column II: (1) 10% energy law (2) ecosystem (3) term ecology (4) α/β/γ diversity

a-3, b-2, c-1, d-4
a-2, b-3, c-4, d-1
a-1, b-2, c-3, d-4
a-3, b-4, c-1, d-2

Answer: A

Haeckel 1866 — term ecology; Tansley 1935 — ecosystem; Lindeman 1942 — 10% law; Whittaker 1972 — alpha/beta/gamma diversity. A classic discovery-year combination that appears in almost every HPRCA biology paper.

22. Match the environmental convention (Column I) with its focus and year (Column II):
Column I: (a) Montreal Protocol (b) Ramsar Convention (c) CBD (d) Paris Agreement
Column II: (1) Biodiversity conservation; Rio 1992 (2) Ozone-depleting substances; 1987 (3) Climate change, 1.5°C target; 2015 (4) Wetland conservation; 1971

a-2, b-4, c-1, d-3
a-1, b-2, c-4, d-3
a-2, b-1, c-3, d-4
a-4, b-2, c-1, d-3

Answer: A

Montreal Protocol 1987 — CFCs/ODS (a-2). Ramsar Convention 1971 — wetlands (b-4). CBD 1992 Rio — biodiversity (c-1). Paris Agreement 2015 — 1.5°C climate target (d-3).

23. Match the interaction type with the correct sign convention and example: HPRCA-pat.
Column I: (a) Amensalism (b) Mutualism (c) Parasitism (d) Commensalism
Column II: (1) +/0; barnacle on whale (2) −/0; allelopathy (3) +/−; Cuscuta on host (4) +/+; Rhizobium in legume nodule

a-2, b-4, c-3, d-1
a-1, b-3, c-2, d-4
a-2, b-1, c-4, d-3
a-3, b-4, c-2, d-1

Answer: A

Amensalism (−/0): one harmed, other unaffected — allelopathy (a-2). Mutualism (+/+): both benefit — Rhizobium (b-4). Parasitism (+/−): parasite benefits, host harmed — Cuscuta (c-3). Commensalism (+/0): one benefits, other unaffected — barnacle (d-1).

24. Consider the following statements about biodiversity hotspots and select the incorrect one: HPRCA-pat.

Criteria include ≥1500 endemic plant species and ≥70% original habitat loss
India contains 4 biodiversity hotspots
The Western Himalaya, including Himachal Pradesh, is part of the Himalayan hotspot
Biodiversity hotspot concept was introduced by E. O. Wilson in 1986

Answer: D

The biodiversity hotspot concept was introduced by Norman Myers in 1988, not E. O. Wilson. Wilson popularised the term ‘biodiversity’ in 1986 but the hotspot framework came from Myers' analysis of endemism and habitat loss. Options A, B and C are all correct.

25. Which of the following statements about the nitrogen cycle is incorrect?

Nitrosomonas converts NH₃ to NO₂⁻
Nitrobacter converts NO₂⁻ to NO₃⁻
Pseudomonas denitrifies NO₃⁻ back to N₂
Rhizobium converts atmospheric N₂ to NO₃⁻ directly

Answer: D

Rhizobium fixes N₂ to NH₃/NH₄⁺ (ammonium), NOT directly to NO₃⁻. Conversion to nitrate requires the nitrification steps by Nitrosomonas and Nitrobacter separately. Options A, B and C are all accurate descriptions of nitrification and denitrification.

26. Arrange the following events in the correct chronological order: HPRCA-pat.
(i) Tansley coins ‘ecosystem’
(ii) Lindeman proposes 10% energy law
(iii) E. O. Wilson popularises ‘biodiversity’
(iv) CBD adopted at Rio Earth Summit
(v) Haeckel coins ‘ecology’

v → i → ii → iii → iv
i → v → ii → iv → iii
v → ii → i → iii → iv
iii → v → i → ii → iv

Answer: A

Haeckel 1866 (ecology) → Tansley 1935 (ecosystem) → Lindeman 1942 (10% law) → Wilson 1986 (biodiversity) → CBD 1992 (Rio). Memorising these five dates in order covers a large fraction of ecology discovery-timeline questions.

27. Which of the following is the odd one out with respect to HP state symbols? HPRCA-pat.

Deodar (Cedrus deodara) — state tree
Snow leopard (Panthera uncia) — state animal
Western tragopan (Tragopan melanocephalus) — state bird
Blue pine (Pinus wallichiana) — state flower

Answer: D

The state flower of HP is the pink rhododendron (Rhododendron campanulatum), not blue pine. Blue pine is an important timber tree of the temperate zone but is not the state flower. Options A, B and C are all correct HP state symbols.

28. Consider the following statements about in situ and ex situ conservation and identify which is/are correct: HPRCA-pat.
(i) National Parks provide the highest legal protection among protected area categories in India
(ii) Biosphere Reserves have three zones: core, buffer and transition
(iii) NBPGR (National Bureau of Plant Genetic Resources) in New Delhi is an ex situ conservation facility
(iv) Wildlife Sanctuaries allow no human activity whatsoever

Only (i)
(i), (ii) and (iii)
(ii) and (iv)
All four

Answer: B

Statements (i), (ii) and (iii) are correct. Statement (iv) is incorrect: Wildlife Sanctuaries allow some controlled human activities including regulated grazing, research and limited tourism. Only National Parks forbid all human habitation and extractive activities without legislative approval.

End of Chapter 15 · Ecology. HPRCA-pat. indicates HPRCA / state-TGT pattern questions; literal past-paper items will be flagged with year when official papers are sourced.

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