Ecology

11. Which of the following are detritivores? Earthworms Jellyfish Mill

Which of the following are detritivores?

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  1. Earthworms
  2. Jellyfish
  3. Millipedes
  4. Seahorses
  5. Woodlice

Select the correct answer using the code given below.

1, 2 and 4 only
2, 3, 4 and 5 only
1, 3 and 5 only
1, 2, 3, 4 and 5
This question was previously asked in
UPSC IAS – 2021
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Option C is the correct answer. Detritivores are organisms that feed on dead organic matter. Earthworms, Millipedes, and Woodlice are well-known detritivores.
Detritivores play a crucial role in ecosystems by breaking down dead plant and animal material, thus recycling nutrients.
Earthworms consume decaying plant matter in soil. Millipedes feed on decaying leaves and wood. Woodlice (also known as roly-polies or pill bugs) feed on dead plant material. Jellyfish are carnivorous predators. Seahorses are predatory fish that feed on small crustaceans.

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12. In case of which one of the following biogeochemical cycles, the weath

In case of which one of the following biogeochemical cycles, the weathering of rocks is the main source of release of nutrient to enter the cycle?

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Carbon cycle
Nitrogen cycle
Phosphorus cycle
Sulphur cycle
This question was previously asked in
UPSC IAS – 2021
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Option C is the correct answer. In the phosphorus cycle, the main reservoir of phosphorus is in rocks and minerals. Weathering of these rocks releases phosphorus into the soil and water.
The phosphorus cycle is unique among major biogeochemical cycles in that it does not have a significant atmospheric gaseous phase. The primary source of phosphorus for ecosystems is the slow weathering of phosphate-bearing rocks.
The carbon cycle involves atmospheric CO2, oceans, biomass, and fossil fuels. The nitrogen cycle primarily involves atmospheric nitrogen (N2) fixed by microbes, as well as organic matter decomposition. The sulphur cycle involves minerals (sulfates), atmospheric gases (SO2, H2S), and biological processes. While rocks can be a source in other cycles (e.g., sulfates in gypsum), rock weathering is the fundamental initial step that makes phosphorus available in most ecosystems.

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13. Due to some reasons, if there is a huge fall in the population of spec

Due to some reasons, if there is a huge fall in the population of species of butterflies, what could be its likely consequence/consequences ?

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  • 1. Pollination of some plants could be adversely affected.
  • 2. There could be a drastic increase in the fungal infections of some cultivated plants.
  • 3. It could lead to a fall in the population of some species of wasps, spiders and birds.

Select the correct answer using the code given below :

1 only
2 and 3 only
1 and 3 only
1, 2 and 3
This question was previously asked in
UPSC IAS – 2017
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Statement 1 is correct. Butterflies are important pollinators for many flowering plants. A significant decline in their population would directly reduce the pollination services they provide, adversely affecting the reproduction of plants that rely on them.
Statement 2 is incorrect. A fall in the butterfly population is unlikely to cause a drastic increase in fungal infections of cultivated plants. Fungal infections are typically influenced by factors like weather conditions, soil health, plant susceptibility, and the presence of fungal spores, not directly by butterfly populations. While butterfly larvae are herbivores, their impact on plant health is different from fungal pathogens.
Statement 3 is correct. Butterflies, in their various life stages (egg, larva/caterpillar, pupa, adult), serve as a food source for a variety of predators, including insects like wasps and spiders, and numerous bird species. A substantial decrease in the butterfly population would reduce the food availability for these predators, potentially leading to a decline in their populations due to starvation or reduced reproductive success.
– Butterflies act as pollinators and are part of the food chain.
– Changes in prey population can impact predator populations.
Butterflies are often considered indicators of ecosystem health. Their decline can signal broader environmental issues such as habitat loss, pesticide use, and climate change. Conserving butterfly populations is important for biodiversity and ecosystem services like pollination.

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14. Which one of the following is the best description of the term

Which one of the following is the best description of the term ‘ecosystem’?

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A community of organisms interacting with one another
That part of the Earth which is inhabited by living organisms
A community of organisms together with the environment in which they live
The flora and fauna of a geographical area
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UPSC IAS – 2015
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The correct option is C (A community of organisms together with the environment in which they live). This is the standard definition of an ecosystem.
– An ecosystem comprises both biotic (living organisms) and abiotic (physical environment like soil, water, air, sunlight, temperature) components.
– The organisms within an ecosystem interact with each other (biotic interactions) and also with their physical environment (biotic-abiotic interactions).
– Option A describes only the biotic community.
– Option B describes the biosphere or habitable part of the Earth.
– Option D describes flora and fauna, which are only parts of the biotic community.
The term ‘ecosystem’ was coined by A.G. Tansley in 1935. Ecosystems can vary greatly in size, from a small pond to a large forest or ocean. Energy flows through the ecosystem, typically originating from the sun and transferred through trophic levels, while nutrients are cycled within the ecosystem.

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15. Which of the following adds/add carbon dioxide to the carbon cycle on

Which of the following adds/add carbon dioxide to the carbon cycle on the planet Earth?

  • 1. Volcanic action
  • 2. Respiration
  • 3. Photosynthesis
  • 4. Decay of organic matter

Select the correct answer using the code given below.

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1 and 3 only
2 only
1, 2 and 4 only
1, 2, 3 and 4
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UPSC IAS – 2014
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Volcanic action, respiration, and decay of organic matter all release carbon dioxide into the atmosphere, thus adding to the carbon cycle.
Volcanic eruptions release gases, including CO2, from the Earth’s interior. Respiration is the process by which living organisms convert organic matter into energy, releasing CO2 as a byproduct. Decomposers break down dead organic matter, releasing CO2 through respiration and decomposition processes. Photosynthesis, however, is the process by which plants and other organisms use sunlight, water, and CO2 to create energy-rich organic molecules, thus *removing* CO2 from the atmosphere.
The carbon cycle is a biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Human activities, particularly the burning of fossil fuels and deforestation, have significantly increased the amount of CO2 in the atmosphere, leading to concerns about climate change.

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16. Which one of the following terms describes not only the physical space

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?

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Ecotone
Ecological niche
Habitat
Home range
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UPSC IAS – 2013
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The term that describes both the physical space occupied by an organism and its functional role in the community is “Ecological niche”.
– **Habitat:** Refers primarily to the physical environment or location where an organism lives.
– **Ecotone:** Is a transition zone between two different ecosystems.
– **Home range:** Is the area an animal traverses in its activities, but it doesn’t define its functional role.
– **Ecological niche:** Encompasses not just the physical space (like habitat) but also the organism’s role, including how it interacts with other organisms (predators, prey, competitors), what it consumes, how it reproduces, and how it is affected by its environment. It is often described as the organism’s “profession” or “address + profession” within the ecosystem.
The concept of the ecological niche was first described by Joseph Grinnell (focused on habitat) and later refined by Charles Elton (focused on the functional role) and G. Evelyn Hutchinson (mathematical definition of the ‘n-dimensional hypervolume’). The principle of competitive exclusion states that no two species can occupy exactly the same niche in the same habitat for a prolonged period.

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17. Which of the following adds/add nitrogen to the soil? 1. Excretion o

Which of the following adds/add nitrogen to the soil?

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  • 1. Excretion of urea by animals
  • 2. Burning of coal by man
  • 3. Death of vegetation

Select the correct answer using the codes given below.

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1 only
2 only
1 and 3 only
1, 2 and 3
This question was previously asked in
UPSC IAS – 2013
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Statements 1, 2, and 3 all describe processes that add nitrogen to the soil.
1. Excretion of urea by animals: Urea is a nitrogen-rich organic compound. When animals excrete urea onto the soil, decomposers convert it into inorganic forms like ammonium, which plants can absorb. This is a direct addition of nitrogen to the soil through the nitrogen cycle.
2. Burning of coal by man: Combustion of fossil fuels like coal releases nitrogen oxides (NOx) into the atmosphere. These atmospheric nitrogen compounds can be deposited onto the soil through dry deposition (particles) or wet deposition (acid rain). This process, known as atmospheric nitrogen deposition, adds nitrogen to ecosystems, including soil.
3. Death of vegetation: When plants and other organisms die, their organic matter is decomposed by microorganisms in the soil. This process, called mineralization, breaks down organic nitrogen compounds into inorganic forms (like ammonium), making nitrogen available in the soil for uptake by plants. This is a crucial part of the nitrogen cycle.
Nitrogen is a vital nutrient for plant growth. Nitrogen is added to the soil through various natural processes (like biological nitrogen fixation, atmospheric deposition, decomposition) and human activities (like application of fertilizers, burning fossil fuels leading to deposition). While decomposition and biological fixation are primary natural inputs, anthropogenic activities have significantly altered the global nitrogen cycle, increasing deposition rates in many areas.

18. With reference to food chains in ecosystems, consider the following st

With reference to food chains in ecosystems, consider the following statements:

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  • 1. A food chain illustrates the order in which a chain of organisms feed upon each other.
  • 2. Food chains are found within the populations of a species.
  • 3. A food chain illustrates the numbers of each organism which are eaten by others.

Which of the statements given above is/are correct?

1 only
1 and 2 only
1, 2 and 3
None
This question was previously asked in
UPSC IAS – 2013
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Statement 1 is correct. A food chain shows the linear sequence of organisms where nutrients and energy are transferred as one organism eats another. Statements 2 and 3 are incorrect.
A food chain illustrates the trophic relationships between different species in an ecosystem, showing the flow of energy from producers to consumers of various levels. Food chains involve interactions *between* different species at different trophic levels, not typically *within* the population of a single species (unless referring to cannibalism, which isn’t the primary representation). While the number of organisms at each level can be represented in an ecological pyramid (like the pyramid of numbers), a simple food chain diagram does not illustrate the *numbers* of organisms eaten.
Ecosystems consist of multiple interconnected food chains, forming a food web. Food chains help understand the flow of energy and the impact of changes in one trophic level on others.

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19. Which one of the following is the correct sequence of ecosystems in th

Which one of the following is the correct sequence of ecosystems in the order of decreasing productivity?

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Oceans, lakes, grasslands, mangroves
Mangroves, oceans, grasslands, lakes
Mangroves, grasslands, lakes, oceans
Oceans, mangroves, lakes, grasslands
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UPSC IAS – 2013
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The correct answer is C) Mangroves, grasslands, lakes, oceans.
Primary productivity refers to the rate at which energy is converted by photosynthetic organisms into organic substances. Among the given options, mangrove ecosystems, being highly productive coastal environments rich in nutrients and sunlight, generally exhibit the highest net primary productivity. Grasslands have moderate productivity, varying significantly based on rainfall and soil fertility. Lakes vary widely from oligotrophic (low productivity) to eutrophic (high productivity), but generally have lower average productivity than highly productive terrestrial or coastal systems. Open oceans, especially the vast pelagic zones, are often nutrient-limited and have relatively low average productivity, although coastal upwelling zones can be highly productive.
The generalized order of decreasing productivity among major ecosystems is often cited as: Tropical rainforests, Swamps and Marshes (including Mangroves), Estuaries > Temperate forests, Cultivated land > Grasslands, Lakes and Streams > Tundra, Open Ocean > Deserts. Comparing the specific options given, mangroves are known for very high productivity, followed by grasslands (moderate), then lakes (variable but often moderate to low), and finally open oceans (generally low). Thus, the sequence of decreasing productivity is typically Mangroves > Grasslands > Lakes > Oceans.

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20. In the grasslands, trees do not replace the grasses as a part of an ec

In the grasslands, trees do not replace the grasses as a part of an ecological succession because of

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insects and fungi
limited sunlight and paucity of nutrients
water limits and fire
None of the above
This question was previously asked in
UPSC IAS – 2013
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The correct answer is C) water limits and fire.
In many grassland ecosystems, the primary environmental factors that prevent the establishment and growth of trees, thus maintaining the dominance of grasses in ecological succession, are limited water availability (seasonal droughts, low rainfall) and frequent fires (natural or human-caused). Grasses are well-adapted to these conditions, with deep root systems that survive drought and ability to quickly regrow after fire, whereas young trees are often killed by lack of water or fire.
Ecological succession is the process by which the mix of species and habitat in an area changes over time. In a typical succession sequence in a region capable of supporting forests, grassland might be a transitional stage before shrubland and then forest. However, specific environmental regimes like drought and fire can create “climax communities” like grasslands where forest does not develop. While other factors like grazing can also influence grasslands, water limits and fire are fundamental abiotic factors that often define this biome.

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