Mains Paper II · 4 Environment & Ecology · 4.1 Ecology and ecosystems
4.1.1 Ecology: levels of organisation, habitat and niche
Ecology studies how organisms interact with each other and with their physical surroundings, at levels that run from a single organism up to the whole biosphere.
- APPSC Group 2 · Mains Paper II
- Advanced level
- 8 min read
- Free
Core facts
- Ecology is the branch of biology that studies the interactions among organisms and between organisms and their physical (abiotic) environment.
- The word "ecology" (Oekologie) was coined by Ernst Haeckel in 1866. It comes from the Greek oikos (house) and logos (study).
- NCERT says ecology deals with four levels of biological organisation: organisms, populations, communities and biomes.
- Full order, smaller to larger: individual → population → community → ecosystem → biome → biosphere.
- Population: individuals of the same species living in a defined area at the same time.
- Community: populations of different species living and interacting in an area.
- Ecosystem: a community together with its abiotic environment. The term was coined by A.G. Tansley in 1935.
- Biosphere: the part of the Earth (land, water and air) where life exists.
- Habitat: the physical place where an organism lives (its "address").
- Niche: the functional role of a species, including what it eats, when and where it is active, and the range of conditions it tolerates (its "profession").
- Ecotone: a transition zone between two ecosystems, such as a mangrove between land and sea, or grassland between forest and desert.
- Edge effect: an ecotone often has more species, and higher density, than either neighbouring community.
Explained
Levels of organisation
| Level | Made of | Example |
|---|---|---|
| Organism | One individual | One tiger |
| Population | Same species, one area | All tigers in Nallamala forest |
| Community | All populations in an area | Tigers, deer, trees, fungi of that forest |
| Ecosystem | Community + abiotic factors | The forest with its soil, water, climate |
| Biome | Large region with similar climate and vegetation | Tropical deciduous forest |
| Biosphere | All ecosystems on Earth | The living layer of the planet |
Major abiotic factors
- Temperature. It affects enzyme activity and so the metabolism of organisms.
- Eurythermal organisms tolerate a wide range of temperature. NCERT notes that only a few organisms are like this.
- Stenothermal organisms tolerate only a narrow range (for example, many corals). The vast majority of organisms are stenothermal.
- Water. Salinity tolerance gives euryhaline (wide range) and stenohaline (narrow range) organisms. Many freshwater animals cannot live long in sea water, and the reverse.
- Light. Plants need it for photosynthesis. Many plants and animals use day length (photoperiod) to time flowering, breeding and migration.
- Soil. Its composition, grain size and water-holding capacity decide which plants can grow.
How organisms respond to stress
| Response | Meaning | Example |
|---|---|---|
| Regulate | Keep the body constant (homeostasis) | Birds and mammals keep body temperature constant |
| Conform | Body changes with the surroundings | Most animals and nearly all plants |
| Migrate | Move away for a while | Siberian cranes to Keoladeo (Bharatpur) in winter |
| Suspend | Lower activity until conditions improve | Hibernation, aestivation, diapause, spores, seed dormancy |
- Hibernation is winter sleep (bears).
- Aestivation is summer sleep, for example frogs, snails and some fish in burrows or mud during heat.
- Diapause is a stage of suspended development, as in zooplankton in lakes.
Deeper
Evolution of the niche concept
| Ecologist | Year | View of niche |
|---|---|---|
| Joseph Grinnell | 1917 | Spatial or habitat niche: the place and conditions a species needs |
| Charles Elton | 1927 | Functional niche: the role of a species in the community, especially in food relations |
| G.E. Hutchinson | 1957 | n-dimensional hypervolume: all the conditions and resources that let a species survive and reproduce |
- Fundamental niche: the full range a species could occupy with no competitors.
- Realised niche: the smaller range it actually occupies, because of competition and predation.
- Gause's competitive exclusion principle: two species with exactly the same niche cannot coexist indefinitely. One displaces the other. Coexistence happens through resource partitioning (see ENV-EC-06).
- Ecological equivalents: unrelated species that hold similar niches in different regions, such as grazing kangaroos in Australia and grazing bison in North America.
- Ecocline: a gradual change in community along an environmental gradient (for example, altitude). An ecotone, by contrast, is a sharper zone of transition.
Adaptations named in NCERT
- Kangaroo rat (North American desert) meets its water needs by internal fat oxidation, which yields water (metabolic water). It can also concentrate its urine.
- Desert plants have a thick cuticle and sunken stomata, which cut water loss. Many follow the CAM pathway: stomata stay closed in the day. In Opuntia, leaves become spines and the flattened stem (phylloclade) does photosynthesis.
- Allen's rule: mammals in cold climates tend to have shorter ears and limbs, which reduce heat loss.
- Altitude sickness: at high altitude, the body first breathes faster and raises heart rate, then makes more red blood cells over time.
- Seals in polar seas have a thick layer of fat (blubber) below the skin, which insulates them.
Common traps
- ✗ "Ecology was coined by Tansley." ✓ Haeckel (1866) coined ecology; Tansley (1935) coined ecosystem.
- ✗ "A population includes all species in an area." ✓ That is a community. A population is one species.
- ✗ "Habitat and niche mean the same thing." ✓ Habitat is the place; niche is the role and the range of conditions used.
- ✗ "Aestivation is winter sleep." ✓ Aestivation is summer sleep; hibernation is winter sleep.
- ✗ "An ecotone has fewer species than its neighbours." ✓ It often has more: this is the edge effect.
- ✗ "Elton gave the n-dimensional hypervolume." ✓ Hutchinson (1957) did; Elton gave the functional niche (1927).
Quick revision
- Ecology: Haeckel, 1866. Ecosystem: Tansley, 1935.
- NCERT's four levels: organisms, populations, communities, biomes.
- Order: individual → population → community → ecosystem → biome → biosphere.
- Habitat = address; niche = profession.
- Niche: Grinnell (spatial, 1917), Elton (functional, 1927), Hutchinson (hypervolume, 1957).
- Ecotone = transition zone; edge effect = more species there.
- Eurythermal (few) / stenothermal (most); euryhaline/stenohaline.
- Responses: regulate, conform, migrate, suspend.
- Hibernation = winter; aestivation = summer; diapause = suspended development.
Go deeper: Mains writing (beyond what APPSC Group 2 usually asks)
Mains writing Mains writing
- Frame: ecology is the scientific base of environmental policy. Laws on forests, wildlife and pollution protect habitats and the niches species occupy.
- Analysis points:
- Habitat loss is the main driver of species loss: when a habitat goes, every niche in it goes.
- Narrow-niche (specialist) species are most at risk. The great Indian bustard needs open grassland; the lion-tailed macaque needs evergreen canopy.
- Ecotones such as mangroves and wetland edges are rich in species and services, but they are often treated as "wasteland" and reclaimed.
- Climate change shifts habitats uphill and towards the poles, and stenothermal species (corals, alpine plants) cannot keep pace.
- Way forward:
- protect habitat connectivity through corridors
- legally protect ecotones such as wetlands and mangroves
- plan with landscape-level data, not project-by-project
- Example: Siberian cranes stopped arriving at Keoladeo after the winter of 2001–02. This shows how loss of a habitat far away on a migration route ends the use of a protected site too.
Practise this topic. Questions on Ecology & ecosystems, with answers explained.
All Ecology and ecosystems notes · APPSC Group 2 syllabus · APPSC G2 Prelims Mock 1 with answers · Start free
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