Ecology and Ecosystem Basics

1.Environment, Habitat and Ecosystem

• Meaning of EnvironmentImportance 2/5
  Be clear about the two senses of "environment", the ecological and the biological. What do living things draw from their environment? Know what interacts within it, so you can later separate it from habitat and ecosystem.
• Biotic and Abiotic Components (Soil, Humus, Fossil Fuels)Importance 3/5
  Remember which things count as biotic, including products of once-living organisms (bones, shells, coal, petroleum), and which count as abiotic. Is "biotic" the same as "living"? Understand why soil and humus are borderline cases and how they are classified.
• Organic and Inorganic CompoundsImportance 2/5
  What is the usual carbon-hydrogen bond test for telling organic compounds from inorganic ones? Learn examples of each. Urea is an exception to this rule. Why is it still treated as organic?
• Meaning of HabitatImportance 2/5
  What is a habitat, and why is it called an organism's "address"? How can many different species share one habitat? Know a few examples of habitats.
• Habitat and Environment ComparedImportance 2/5
  What are two differences between habitat and environment? Does a habitat always have life in it? Which of the two decides the properties of the other?
• Meaning and Characteristics of an EcosystemImportance 4/5UPSC 2015
  What is an ecosystem, and which living groups does it include? Understand its characteristics: its size, how its parts are linked, and how its species depend on each other. Is an ecosystem just a community of interacting organisms, or does it include more?
• Classification of EcosystemsImportance 2/5
  Know the main kinds of ecosystem, terrestrial, aquatic and human-made, with examples of each.
• Ecosystem, Environment, Habitat, Biosphere and Ecology ComparedImportance 3/5
  Be clear how these five terms nest within one another and how each differs from the others. Is ecology a place or a study? Also learn the related terms community and biodiversity.

2.Components of an Ecosystem

• Limiting Factors (Tropical Rainforest Regeneration)Importance 4/5UPSC 2003, 2011
  Understand what a limiting factor is, using the examples of seed germination and sapling survival in a rainforest. Why does a rainforest regenerate slowly after clearing? Understand how each of these explanations applies: nutrient-poor topsoil, short seed viability, slow-growing species, and invasion by exotic species. Remember how invasive grasses affect cleared areas of the Amazon.
• Major Abiotic Limiting FactorsImportance 3/5
  Remember the main abiotic limiting factors. Know the terms for wide and narrow tolerance of temperature and of salinity. Understand how altitude, soil and water pH, and nitrogen availability limit life. Know the main gases of the atmosphere, the current level of carbon dioxide and what is driving it.
• Effect of Light on PlantsImportance 2/5
  How do high and low light intensity change plant growth, and how do sun leaves differ from shade leaves? Remember which wavelengths work best and least for photosynthesis, and how blue, red and ultraviolet light affect growth. Why do plants stop growing below a minimum light level?
• Effects of Frost, Snow and High Temperature on PlantsImportance 2/5
  How does frost harm plants (drying out, tissue injury and canker)? Snow can also harm plants, so why does it protect them in frost-prone regions? Remember how high temperature affects plants, and where heat-loving bacteria (thermophiles) live.
• Primary Producers (Autotrophs)Importance 3/5UPSC 2021
  Which organisms are the primary producers on land and in water? Do bacteria and algae also count? Be clear why they are called autotrophs.
• Macro ConsumersImportance 3/5UPSC 2019, 2021
  Remember the classes of macro consumers (herbivores, secondary and tertiary consumers, omnivores) with an example of each. How does a secondary consumer differ from a tertiary one? Why can one animal appear in both?
• Micro Consumers, Decomposers and DetritivoresImportance 3/5UPSC 2013
  How does feeding by ingestion (phagotrophs, detritivores) differ from feeding by absorption (saprotrophs, osmotrophs)? Be able to distinguish decomposers (bacteria, fungi) from detritivores (earthworms, nematodes), and know how each gets its food.

3.Levels of Organisation in Ecology

• Meaning of EcologyImportance 2/5
  Learn the Greek roots of the word "ecology" and what each means. Understand what ecology studies: how organisms relate to each other and to their surroundings, including energy flow and mineral cycling.
• Levels of Ecological OrganisationImportance 3/5
  Remember the levels of ecological organisation in order, from the smallest to the largest.
• Organism and SpeciesImportance 2/5
  How does an organism differ from a species? Remember the test for belonging to one species, why species is the basic unit of naming, and how a Latin binomial is written. Also know roughly how close human and chimpanzee genes are.
• Population and Population GrowthImportance 2/5
  What is a population, and which four factors raise or lower its size?
• Pugmarks in Population StudiesImportance 2/5
  Remember what pugmarks can tell us about large mobile animals, and how the sex of a tiger is read from the shape of its pugmark. What role do pugmarks play in modern tiger estimation, and which method does it mainly depend on?
• Types of Ecological CommunitiesImportance 2/5
  How are communities named? Distinguish major communities from minor ones (societies), with an example of each. What makes a community stable?
• Ecological Niche and Its TypesImportance 4/5
  Understand the niche as the functional role and position of a species. Remember its types: habitat, food, reproductive, and physical and chemical niche. Why must conservation take a species' niche into account? Remember also how an ecosystem is made up of overlapping habitats.
• Niche and Habitat Compared (Home Range)Importance 3/5UPSC 2013
  Understand how a niche differs from a habitat (an "address" versus a "profession"). Can two species in one habitat share a niche? Think of many insects living on one plant. Also distinguish home range from habitat, and know which term describes both place and function.
• BiomeImportance 2/5
  Learn what a biome is and how it differs from a habitat. Remember taiga as an example of a biome spread across continents.
• Biosphere and Its LimitsImportance 2/5
  Remember which spheres the biosphere includes. Where is life sparse or only dormant, for example on polar ice caps and high peaks? Be clear about the limits of life, such as spores found at great heights. Does life persist even in the deepest ocean trenches?
• Ecotone (Mangroves, Estuaries, Grasslands)Importance 4/5
  Be clear what an ecotone is. Remember the standard examples (mangrove, grassland, estuary, riverbank and marshland) and which two systems each one lies between.
• Characteristics of an EcotoneImportance 3/5
  Understand why an ecotone can be narrow or wide, why it is called a zone of tension, and what happens to species as you move away from their home community. Remember the organisms unique to ecotones (such as mudskippers), and why ecotones are said to be more productive.
• Edge Effect and Edge SpeciesImportance 4/5
  What is the edge effect, and what are edge species? Remember examples, such as kingfishers and river turtles in an estuary, and birds and deer (chital, sambar) in grassland ecotones.
• Ecocline and Ecotone ComparedImportance 3/5
  What is an ecocline, and along what kinds of gradient does it occur (for example thermocline and halocline)? Distinguish it from an ecotone in boundary, species diversity and examples.

4.Principles of Ecology

• Meaning and Types of AdaptationImportance 3/5
  Understand adaptation as an inheritable trait that helps survival. Remember its three types, with the giraffe, the kangaroo rat and the Great Migration as examples. How does adaptation differ from evolution?
• Structural Adaptations of Plants and Animals (Allen's Rule, Dieback)Importance 3/5UPSC 2018
  Remember the features of desert plants. Understand dieback and the trees that show it. What does Allen's Rule say, and how does it explain the elephant's large ears? Also remember the typical vegetation features of taiga, desert and tropical forests.
• Extremophiles and ArchaeaImportance 4/5UPSC 2023
  Remember the main kinds of extremophile (hyperthermophiles, halophiles, thermoacidophiles, acidophiles). Know the examples Pyrolobus fumarii and the Antarctic nematode. Is the nematode a microbe? Can microbes live above boiling point, below freezing and below pH 3? Are extremophiles found only among archaea? Understand how archaea differ from bacteria, and that older and newer classification schemes place them differently.
• Acclimatisation and Behavioural AdaptationImportance 3/5UPSC 2021
  Understand how the body responds to high altitude and what haemoglobin does. How does acclimatisation differ from adaptation? Remember behavioural examples such as desert lizards basking and rodents burrowing.
• Hibernation and AestivationImportance 3/5
  How do hibernation and aestivation differ in cause and season? Remember examples of animals that show each, including the lungfish and its cocoon.
• Variation and RecombinationImportance 2/5
  Remember what causes variation within a species, with human examples. Understand recombination: does it create new genes, or only rearrange existing ones?
• Phenotypic PlasticityImportance 2/5
  Understand phenotypic plasticity as a change in traits caused by the environment, with no change in genes. Remember examples such as sun and shade leaves, tanning and seasonal fur colour.
• Adaptive Radiation (Darwin's Finches)Importance 3/5UPSC 2001
  Understand what adaptive radiation is and what drives it. Remember Darwin's finches on the Galapagos Islands and how their beaks became specialised. The number of finch species varies between sources, so know it as approximate.
• Speciation and Reproductive IsolationImportance 3/5UPSC 2002
  How do new species form when gene flow stops, and how does this link to evolution?
• Allopatric, Parapatric and Sympatric SpeciationImportance 3/5
  Distinguish the three modes by how far populations are separated. Remember the examples: red panda, California salamanders, Darwin's finches, Masai giraffe populations on either side of the Gregory Rift, and baboons. Are the rift-separated Masai populations separate species yet? Understand the role of disruptive selection in sympatric speciation.
• Polyploidy and HybridisationImportance 2/5
  Understand how polyploidy can isolate a new plant species at once, and remember some polyploid crops. What is hybridisation? Can hybrids such as the mule form a new species?
• MutationImportance 2/5
  What is a mutation, and what can cause it? Why is it called the raw material of evolution? How does it differ from recombination?
• Natural SelectionImportance 2/5
  Be clear how natural selection favours heritable traits that help survival and reproduction. Use the long-necked giraffe as the example.
• Evolution and Neo-DarwinismImportance 3/5UPSC 2014
  Remember what evolution is and which processes drive it. Who developed the theory of evolution by natural selection? Understand what Neo-Darwinism (the Modern Synthesis) adds to it.
• Extinction and the Five Mass ExtinctionsImportance 3/5
  Understand the main causes of extinction. Remember the five mass extinction events in order, with approximate dates (the last is now called the Cretaceous–Paleogene, or K–Pg, extinction) and how much life each wiped out. Which was the largest? Which let the dinosaurs flourish, and which ended them?
• Sixth Mass Extinction and the AnthropoceneImportance 4/5
  Remember the human activities behind the sixth mass extinction. Understand what the term Anthropocene means and what start marker was proposed for it. Is it an official geological epoch, or are we still in the Holocene? Know what the scientific bodies decided about it in March 2024.

1. 1.

   Consider the following statements regarding an ecosystem:
   1. It can be of any size.
   2. Its biotic and abiotic components are linked together through nutrient cycles and energy flows.
   3. If one part of an ecosystem is damaged or disappears, the other parts remain unaffected, because each species depends only on its own kind.
   How many of the above statements are correct?

   1. AOnly one
   2. BOnly two
   3. CAll three
   4. DNone
2. 2.

   In the study of environmental science, the term 'ecology' refers to which one of the following?

   1. AThe part of the Earth that is inhabited by living organisms
   2. BThe flora and fauna of a geographical area
   3. CThe physical and biological factors that affect an organism or a group of organisms
   4. DThe scientific study of interactions among organisms and between organisms and their physical surroundings
3. 3.

   Consider the following pairs:

   Ecotone	Lies between
   1. Mangrove forests	Marine and terrestrial ecosystems
   2. Estuary	Fresh water and saltwater
   3. Riverbank or marshland	Forest and desert

   Which of the pairs given above is/are correctly matched?

   1. A1 and 2 only
   2. B2 and 3 only
   3. C1 and 3 only
   4. D1, 2 and 3
4. 4.

   With reference to the edge effect in ecology, consider the following statements:
   1. It refers to greater species richness and population density of some species in an ecotone than in either of the adjoining communities.
   2. Kingfishers and river turtles are edge species of an estuarine ecotone.
   3. In the grassland ecotone between forest and desert, the density of birds and deer such as chital and sambar is lower than in the adjoining communities.
   Which of the statements given above is/are correct?

   1. A1 only
   2. B1 and 3 only
   3. C1 and 2 only
   4. D2 and 3 only
5. 5.

   Consider the following statements:
   Statement-I: Ecotones such as mangroves, wetlands and estuaries are generally more productive than a forest, pond or desert ecosystem.
   Statement-II: An ecotone contains diverse species from the adjacent ecosystems.
   Which one of the following is correct in respect of the above statements?

   1. ABoth Statement-I and Statement-II are correct and Statement-II explains Statement-I
   2. BBoth Statement-I and Statement-II are correct and Statement-II does not explain Statement-I
   3. CStatement-I is correct but Statement-II is incorrect
   4. DStatement-I is incorrect but Statement-II is correct
6. 6.

   Match List I with List II:

   List I (Type of niche)	List II (What it describes)
   A. Habitat niche	1. How and when a species reproduces
   B. Food niche	2. Temperature, soil, humidity and other requirements
   C. Reproductive niche	3. Where a species lives
   D. Physical and chemical niche	4. What it eats or decomposes and what species it competes with

   Select the correct answer using the code given below:

   1. AA-1, B-2, C-3, D-4
   2. BA-3, B-2, C-1, D-4
   3. CA-3, B-4, C-1, D-2
   4. DA-4, B-3, C-1, D-2
7. 7.

   With reference to the ecological niche and habitat of a species, consider the following statements:
   1. The habitat of a species is like its 'address', whereas its niche is like its 'lifestyle and profession'.
   2. A niche is unique for a species, while many species can share a habitat.
   3. Two species living in one habitat can occupy exactly the same niche indefinitely, because competition between them never displaces either species.
   How many of the above statements are correct?

   1. AOnly one
   2. BOnly two
   3. CAll three
   4. DNone
8. 8.

   Which one of the following best describes the 'ecological niche' of a species?

   1. AThe area in which an animal lives and moves on a daily or periodic basis
   2. BThe surroundings in which an organism lives
   3. CThe zone of transition between two ecosystems
   4. DThe unique functional role and position of a species in its habitat or ecosystem
9. 9.

   With reference to the regeneration of a tropical rainforest after it is cleared, consider the following statements:
   1. Heavy rain continuously washes nutrients out of the topsoil, so most seeds do not germinate for years and regeneration is very slow.
   2. Rainforest plant species are slow-growing because there is little competition among them for sunlight.
   3. In deforested areas of the Amazon, invasive African grasses have spread over pastures, increasing fire risk and biodiversity loss.
   Which of the statements given above is/are correct?

   1. A1 and 2 only
   2. B2 and 3 only
   3. C1 and 3 only
   4. D1, 2 and 3
10. 10.

    Consider the following pairs:

    Situation	Limiting factor
    1. Seed germination in an evergreen rainforest	Scarcity of rainfall
    2. Survival of saplings under a dense rainforest canopy	Absence of light (shade)
    3. Plant growth in natural and agricultural ecosystems	Nitrogen, a limiting nutrient

    Which of the pairs given above is/are correctly matched?

    1. A1 and 2 only
    2. B2 and 3 only
    3. C1 and 3 only
    4. D1, 2 and 3
11. 11.

    With reference to the Anthropocene, consider the following statements:
    1. It was proposed as a geological epoch marked by significant human impact on Earth's geology and ecosystems.
    2. The Subcommission on Quaternary Stratigraphy of the International Commission on Stratigraphy voted to reject the proposal to make it a formal Epoch of the Geologic Time Scale.
    3. Despite that decision, the term continues to be used by scientists and others as a descriptor of human impact on the Earth system.
    4. It is now a formal unit of the Geologic Time Scale that has replaced the Holocene.
    How many of the above statements are correct?

    1. AOnly one
    2. BOnly two
    3. COnly three
    4. DAll four
12. 12.

    Consider the following statements regarding organisms of extreme environments:
    1. The hyperthermophile Pyrolobus fumarii has been found growing at 113 °C.
    2. Extreme acidophiles dwell in environments with a pH value between 5 and 7.
    3. The Antarctic nematode Panagrolaimus davidi can survive temperatures above the boiling point of water.
    How many of the above statements are correct?

    1. AOnly one
    2. BOnly two
    3. CAll three
    4. DNone
13. 13.

    Consider the following statements regarding the mass extinction events in Earth's history:
    1. The Permian–Triassic extinction is regarded as the largest mass extinction event in Earth's history.
    2. The extinction of other vertebrate species on land at the end of the Triassic allowed dinosaurs to flourish.
    3. The extinction event that wiped out the dinosaurs occurred before the Triassic–Jurassic extinction.
    Which of the statements given above is/are correct?

    1. A1 only
    2. B2 and 3 only
    3. C1 and 3 only
    4. D1 and 2 only
14. 14.

    With reference to the biotic components of an ecosystem, consider the following statements:
    1. Decomposers are bacteria and fungi that obtain energy and nutrients from dead organic substances.
    2. Detritivores feed on detritus and facilitate the decomposition of organic matter; earthworms are an example.
    3. Mushrooms are detritivores, not decomposers.
    Which of the statements given above is/are correct?

    1. A1 and 2 only
    2. B2 and 3 only
    3. C1 and 3 only
    4. D1, 2 and 3
15. 15.

    Which one of the following best describes 'aestivation' in animals?

    1. AA prolonged, deep state of inactivity with a drastic slowdown of metabolism, to survive harsh winters
    2. BA summer-sleep survival strategy for extreme heat or drought, in which metabolic activity is reduced
    3. CSmall changes in the body over short periods to overcome minor challenges arising from environmental changes
    4. DAn inheritable trait that allows an organism to survive in a particular environment

1. 1.

   UPSC 2014

   Which of the following phenomena might have influenced the evolution of organisms?
   1. Continental drift
   2. Glacial cycles
   Select the correct answer using the code given below.

   1. A1 only
   2. B2 only
   3. CBoth 1 and 2
   4. DNeither 1 nor 2
2. 2.

   UPSC 2002

   Among living organisms, which one of the following is the most responsible factor for bringing about the origin of a new species?

   1. AIsolation
   2. BMutation
   3. CNatural Selection
   4. DSexual Reproduction
3. 3.

   UPSC 2023

   Consider the following statements :
   1. Some microorganisms can grow in environments with temperature above the boiling point of water.
   2. Some microorganisms can grow in environments with temperature below the freezing point of water.
   3. Some microorganisms can grow in highly acidic environment with a pH below 3.
   How many of the above statements are correct?

   1. AOnly one
   2. BOnly two
   3. CAll three
   4. DNone
4. 4.

   UPSC 2021

   Consider the following animals :
   1. Hedgehog
   2. Marmot
   3. Pangolin
   To reduce the chance of being captured by predators, which of the above organisms rolls up/roll up and protects/protect its/their vulnerable parts?

   1. A1 and 2
   2. B2 only
   3. C3 only
   4. D1 and 3
5. 5.

   UPSC 2021

   Which one of the following is a filter feeder?

   1. ACatfish
   2. BOctopus
   3. COyster
   4. DPelican
6. 6.

   UPSC 2019

   Consider the following statements :
   1. Some species of turtles are herbivores.
   2. Some species of fish are herbivores.
   3. Some species of marine mammals are herbivores.
   4. Some species of snakes are viviparous.
   Which of the statements given above are correct?

   1. A1 and 3 only
   2. B2, 3 and 4 only
   3. C2 and 4 only
   4. D1, 2, 3 and 4
7. 7.

   UPSC 2018

   Which of the following leaf modifications occur(s) in the desert areas to inhibit water loss ?
   1. Hard and waxy leaves
   2. Tiny leaves
   3. Thorns instead of leaves
   Select the correct answer using the code given below :

   1. A2 and 3 only
   2. B2 only
   3. C3 only
   4. D1, 2 and 3
8. 8.

   UPSC 2015

   Which one of the following is the best description of the term 'ecosystem'?

   1. AA community of organisms interacting with one another
   2. BThat part of the Earth which is inhabited by living organisms
   3. CA community of organisms together with the environment in which they live
   4. DThe flora and fauna of a geographical area
9. 9.

   UPSC 2013

   Which one of the following terms describes not only the physical space occupied by an organism, but also its functional role in the community of organisms?

   1. AEcotone
   2. BEcological niche
   3. CHabitat
   4. DHome range
10. 10.

    UPSC 2013

    With reference to the food chains in ecosystems, which of the following kinds of organism is/are known as decomposer organism/organisms?
    1. Virus
    2. Fungi
    3. Bacteria
    Select the correct answer using the codes given below.

    1. A1 only
    2. B2 and 3 only
    3. C1 and 3 only
    4. D1, 2 and 3
11. 11.

    UPSC 2011

    If a tropical rain forest is removed, it does not regenerate quickly as compared to a tropical deciduous forest. This is because

    1. Athe soil of rain forest is deficient in nutrients
    2. Bpropagules of the trees in a rain forest have poor viability
    3. Cthe rain forest species are slow-growing
    4. Dexotic species invade the fertile soil of rain forest
12. 12.

    UPSC 2003

    Assertion (A): Unlike temperate forests, the tropical rain forests, if cleared, can yield productive farm-land that can support intensive agriculture for several years even without chemical fertilizers.
    Reason (R): The primary productivity of the tropical rain forest is very high when compared to that of the temperate forests.

    1. ABoth A and R are individually true and R is the correct explanation of A
    2. BBoth A and R are individually true but R is NOT the correct explanation of A
    3. CA is true but R is false
    4. DA is false but R is true
13. 13.

    UPSC 2001

    A class of animals known as Marsupials is a characteristic feature of

    1. AAfrica
    2. BAustralia
    3. CSouth America
    4. DSouth-east Asia
14. 14.

    UPSC 2021

    Consider the following kinds of organisms :
    1. Copepods
    2. Cyanobacteria
    3. Diatoms
    4. Foraminifera
    Which of the above are primary producers in the food chains of oceans?

    1. A1 and 2
    2. B2 and 3
    3. C3 and 4
    4. D1 and 4