These notes cover environment and ecology for OPSC/OAS prelims and mains in depth: the meaning and scope of environment, the determinism–possibilism debate, ecosystem structure and function, ecological pyramids, biogeochemical cycles, succession, biome types, India’s environmental movements and laws, and Odisha-specific data on Ramsar wetlands, forest cover and mining-related environmental issues. Each section combines conceptual explanation with concrete facts, examples and practice questions.
Environment and Ecology: Basic Concepts, Scope and Thought
Environment is the sum total of conditions surrounding an organism at a given point of time, including physical, biological and cultural elements. UPPSC 2006 The word derives from the French environner, “to surround.” The physical environment includes landforms, soils, water, air and minerals; settlements belong to the cultural environment, not the physical one. MPPSC 2001 Environment is not merely a store of physical resources; it includes biological resources and possesses self-enrichment capacity. IAS (Pre) 1997
Ecology is the study of the relationship between organisms and their environment; the term was coined by Ernst Haeckel in 1866. UPPSC 2003 UPRO/ARO 2014 Environment is the broader set of surrounding conditions, while ecology is the scientific study of interactions within it.
Determinism, Possibilism and Neo-Determinism
Environmental determinism holds that nature is all-powerful and humans are “toys in the hands of nature”; it is associated with Friedrich Ratzel. Possibilism, associated with Vidal de La Blache, argues that humans can choose among the possibilities nature offers. Neo-determinism, or stop-and-go determinism, is the middle path: humans can modify nature but within limits, and it underpins sustainable development. The developmental sequence is determinism → possibilism → neo-determinism.
OPSC frequently asks: Ratzel = determinism, La Blache = possibilism, Haeckel = ecology, Tansley = ecosystem, Arne Naess = deep ecology, Charles Elton = ecological pyramids, Lindeman = 10% law.
Ecosystem: Structure, Components and Function
An ecosystem is a community of organisms together with the environment in which they live; the term was proposed by A.G. Tansley in 1935. UKPSC 2005 IAS (Pre) 2015 It comprises abiotic components (air, water, soil, minerals) and biotic components (producers, consumers, decomposers). Air is abiotic, not biotic. RAS 2013 An ecosystem is an open system, not a closed one. UPPSC 2015
| Component | Function and example |
|---|---|
| Producers (autotrophs) | Prepare food by photosynthesis; green plants, phytoplankton in marine ecosystems UPPSC 2013 UPPSC 2005 |
| Primary consumers | Herbivores; caterpillar, deer, goat NDA 2019 |
| Secondary consumers | Carnivores that eat herbivores; frog, fish |
| Tertiary / top consumers | Snake, eagle; humans can be primary and secondary consumers UPPSC 2016 |
| Decomposers | Fungi and bacteria; convert organic matter to inorganic nutrients IAS (Pre) 2013 |
The functioning of an ecosystem involves energy flow and nutrient circulation. Energy flow is unidirectional, from the sun through producers to consumers, and is lost as heat at each transfer. UPPSC 2015 Nutrients, unlike energy, cycle through biotic and abiotic components. A food chain is the passage of food and energy from one organism to another; trophic level I is occupied by green plants. IAS (Pre) 2013 MPPSC 2016 Raymond Lindeman proposed the 10% law: only about 10% of energy at one trophic level is transferred to the next. CGPSC 2016 Plants utilise only about 1% of incident solar energy. SSC 2011 A correct terrestrial chain is grass → grasshopper → frog → snake. UPPSC 2010 A marine chain is diatoms → crustaceans → herring. IAS (Pre) 2014
Marine upwelling and productivity
Marine upwelling zones are highly productive because they bring nutrients to the surface, not decomposers or bottom-dwelling organisms. IAS (Pre) 2011 Net primary productivity (NPP) is highest in tropical forests and in swamps and marshes among wetland types. Astt. Comm. 2017
Ecological Pyramids: Types and Rules
Charles Elton enunciated ecological pyramids in 1927. CDS 2013 There are three types: numbers, biomass and energy.
| Pyramid | Shape rule and exception |
|---|---|
| Energy | Always upright; energy is lost as heat at each trophic transfer |
| Biomass | Upright in forests and grasslands; inverted in ponds and oceans because phytoplankton biomass is small but supports a large fish biomass UPPSC 2010 |
| Numbers | Upright in grasslands; inverted in a single-tree ecosystem or parasitic chains |
- “Pyramid of numbers is always upright” is false; it can be inverted where a few large producers support many small consumers.
- “Pyramid of biomass is always upright” is also false; it is inverted in aquatic ecosystems. Only the energy pyramid is always upright.
Biogeochemical Cycles: Gaseous vs Sedimentary
The cycling of elements through the biotic and abiotic components of an ecosystem is a biogeochemical cycle. UPPSC 2012 Gaseous cycles (carbon, nitrogen, oxygen) have the atmosphere or ocean as reservoir; sedimentary cycles (phosphorus, sulphur, calcium) have the Earth’s crust as reservoir.
Nitrogen cycle
Nitrogen fixation is the conversion of atmospheric nitrogen into useful compounds. UPPSC 2011 Ammonification produces ammonia from organic matter; nitrification converts ammonia to nitrite and then nitrate; denitrification returns nitrogen to the atmosphere.
Phosphorus cycle
Phosphorus is essential for plants and animals and is naturally found in rocks and minerals. Unlike carbon and nitrogen, there is no respiratory release of phosphorus into the atmosphere; plants absorb it from the soil, and it enters the cycle mainly through erosion and mining.
Bioaccumulation and biomagnification
| Term | Meaning |
|---|---|
| Bioaccumulation | Increase in pollutant concentration from the environment to the first organism in a food chain |
| Biomagnification | Increase in pollutant concentration from one trophic level to the next; top carnivores show the highest concentration IAS (Pre) 1997 |
In a DDT-contaminated ecosystem, the snake shows the highest concentration among grasshopper, toad, snake and cattle because it occupies the highest trophic level in that chain. IAS (Pre) 1997
Ecological Succession: Primary, Secondary and Seral Stages
Succession is the gradual change in community composition over time. The basic process is nudation → invasion → competition and coaction → reaction → stabilisation. Primary succession starts on a bare area with no previous vegetation; secondary succession starts where vegetation has been removed by a disaster, and it reaches climax faster because soil already exists.
| Type | Starting condition and trajectory |
|---|---|
| Hydrarch (hydrosere) | Wet area; progresses from hydric to mesic conditions |
| Xerarch (xerosere) | Dry area or bare rock; progresses from xeric to mesic conditions; pioneers are lichens |
| Autogenic | Community itself modifies the environment |
| Allogenic | External factors such as fire or flood drive change |
The final stable community is the climax community. In an ecotone, the transition zone between two communities, species diversity is often greater than in adjacent zones; species abundant there are edge species. UPPSC 2012
Biomes, Habitat, Niche and Related Terms
A biome is a large ecological area characterised by climate, soil and dominant plants and animals. Major biome types are forest, grassland, tundra, desert and aquatic. The tropical evergreen biome extends roughly between 10°N and 10°S. The ocean is the largest and most stable ecosystem and covers the largest area of the Earth’s surface. UPPSC 2018 UP Lower 2003 Freshwater ecosystems are classified as lentic (still water: ponds, lakes, swamps) and lotic (running water: rivers, streams). MPPSC 2014 An aquarium and a field are artificial ecosystems. JPSC 2013
| Term | Meaning |
|---|---|
| Habitat | The actual place where an organism lives |
| Ecological niche | The physical space plus the functional role of an organism in the community; concept developed by Grinnell IAS (Pre) 2013 |
| Ecotone | Transition zone between two communities; has edge species UPPSC 2012 |
| Ecological footprint | Minimum area of land needed to sustain one person’s life; measured in global hectares UPRO/ARO 2016 |
| Autecology | Study of a single species and its environment Astt. Comm. 2017 |
Environmental Movements and Environmental Justice in India
India’s environmental movement is rooted in grassroots resistance. The Chipko movement began in 1973 in Gopeshwar, Chamoli district (Uttarakhand), when villagers led by Gaura Devi hugged trees to prevent felling; it is often credited as India’s first environmental justice movement. 2024 The Appiko movement (1983) in Karnataka, led by Pandurang Hegde, was its southern counterpart. The Silent Valley movement in Kerala saved a tropical rainforest from a hydroelectric project, and the Narmada Bachao Andolan (from 1985) opposed the Sardar Sarovar Dam. 2024
According to the Environmental Justice Atlas, India has the largest number of reported environmental justice conflicts (about 300 cases), and more than 57% of these involve Adivasi communities mobilising to protect jal, jungle, jameen (water, forest, land). The Forest Rights Act, 2006 emerged as a legislative response to these movements. In Odisha, the Niyamgiri movement against Vedanta’s bauxite mining is a prominent example of an environmental justice struggle with significant Adivasi participation.
The Niyamgiri hills in Odisha are sacred to the Dongria Kondh tribe; their resistance led to the rejection of a bauxite mining project, making it a landmark case in environmental justice and tribal rights.
Environmental Laws and International Conventions
India’s environmental legal framework includes the Water (Prevention and Control of Pollution) Act, 1974; the Air (Prevention and Control of Pollution) Act, 1981; the Environment (Protection) Act, 1986; the Forest (Conservation) Act, 1980; the Wildlife (Protection) Act, 1972; the Biological Diversity Act, 2002; and the National Green Tribunal Act, 2010. The Constitution obligates the state (Article 48A) and citizens (Article 51A(g)) to protect the environment.
| Convention / Agreement | Core focus |
|---|---|
| Ramsar Convention (1971) | Conservation and wise use of wetlands |
| Stockholm Conference (1972) | First UN conference on the human environment |
| Montreal Protocol (1987) | Phase-out of ozone-depleting substances |
| Basel Convention (1989) | Control of transboundary movements of hazardous wastes |
| Convention on Biological Diversity (1992) | Conservation of biodiversity and sustainable use |
| UNFCCC (1992) and Paris Agreement (2015) | Climate change mitigation and adaptation |
Odisha Angle: Wetlands, Forest Cover and Environmental Challenges
Odisha has six Ramsar sites as of early 2026: Chilika Lake (1981, India’s first Ramsar site and Asia’s largest brackish-water lagoon), Bhitarkanika Mangroves (2002, known for saltwater crocodiles), and four sites added in 2021—Satkosia Gorge, Tampara Lake, Hirakud Reservoir and Ansupa Lake. 2026 Chilika supports the rare Irrawaddy dolphin and is a major wintering ground for migratory birds. 2026
| Odisha environmental indicator | Latest data |
|---|---|
| Forest cover (ISFR 2023) | 52,433.56 sq km; increased by 814.56 sq km compared with ISFR 2019 2024 |
| Forest and tree cover (2026) | 58,597 sq km, or 37.63% of the state’s geographical area; an addition of 558 sq km in two years 2026 |
| Ramsar sites | 6 (Chilika, Bhitarkanika, Satkosia, Tampara, Hirakud, Ansupa) 2026 |
| Coastline | About 574.71 km along the Bay of Bengal |
Odisha’s mining belt faces significant environmental stress. A 2025 study of the Sukinda Valley found that around 50–60% of groundwater samples were contaminated with heavy metals, and surface water was close to critical condition due to leaching from chromite mines. 2025 Coal mining around Talcher has been linked to heavy-metal contamination of groundwater. 2025 Open-cast mining in Joda has caused soil erosion, air and water pollution, and vegetation loss. 2025 These issues are directly relevant to OAS questions on environmental degradation and sustainable development.
On the policy side, Odisha’s forest and tree cover increased by 558 sq km in two years, reaching 37.63% of geographical area, as announced on World Forest Day 2026. 2026 The state government has also approved a five-year integrated plan for the ecological restoration of Chilika Lake, including reopening its mouth to the sea and desiltation. 2026
IMAGE (Map): Map of Odisha marking the six Ramsar sites and major mining belts.
Labels: Chilika (Puri–Khurda–Ganjam), Bhitarkanika (Kendrapara), Satkosia Gorge (Mahanadi), Tampara Lake, Hirakud Reservoir, Ansupa Lake; Sukinda Valley (chromite), Talcher (coal), Joda (iron ore).
Caption: Odisha’s Ramsar wetlands and major mining-related environmental stress zones.
Find it: Odisha Forest and Environment Department map or Ramsar Sites Information Service; or draw from the names in these notes.
Practice Questions
Environment is a composite state of
- Biotic factors
- Physiographic factors
- Abiotic factors
- All of the above
Show answer
(d) – Environment includes biotic, abiotic and physiographic factors. BPSC 2011
Who among the following proposed the deterministic concept in the context of the man–environment relationship?
- Ratzel
- Vidal de La Blache
- Ernst Haeckel
- Tansley
Show answer
(a) – Ratzel is associated with environmental determinism.
The term ‘ecosystem’ was proposed by
- G. Taylor
- E. Hartigan
- D.R. Stoddart
- Tansley
Show answer
(d) – A.G. Tansley proposed the term ‘ecosystem’ in 1935. UKPSC 2005
Consider the following statements:
- The pyramid of energy is always upright.
- The pyramid of biomass in a pond ecosystem is inverted.
- The pyramid of numbers is always upright.
How many of the statements given above are correct?
- Only one
- Only two
- All three
- None
Show answer
(b) – Statements 1 and 2 are correct. The pyramid of numbers can be inverted, so statement 3 is incorrect.
10 per cent Law is related with
- Transfer of energy as food from one trophic level to another
- Transfer of heat from one matter to another
- Transfer of birds from one zone to another
- Transfer of water from one zone to another
Show answer
(a) – Lindeman’s 10% law deals with energy transfer between trophic levels. CGPSC 2016
The cycling of elements in an ecosystem is called
- Chemical cycle
- Biogeochemical cycle
- Geological cycle
- Geochemical cycle
Show answer
(b) – The movement of nutrient elements through biotic and abiotic components is the biogeochemical cycle. UPPSC 2012
In ecological succession, the final stable community is known as
- Climax community
- Ultimate community
- Final community
- Seral community
Show answer
(a) – The climax community is the stable end-stage of succession.
Consider the following statements regarding Odisha’s Ramsar sites:
- Chilika Lake was India’s first Ramsar site, designated in 1981.
- Bhitarkanika Mangroves are known for saltwater crocodiles.
- Odisha had six Ramsar sites as of early 2026.
How many of the statements given above are correct?
- Only one
- Only two
- All three
- None
Show answer
(c) – All three statements are correct. Chilika (1981) was India’s first Ramsar site; Bhitarkanika is famous for saltwater crocodiles; Odisha has six Ramsar sites as of early 2026. 2026