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Q21 (IAS/2017) Environment & Ecology › Ecology & Ecosystem Basics › Plant–animal interactions Official Key

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

Result
Your answer: —  ·  Correct: C
Explanation

The correct answer is option C (statements 1 and 3 only).

**Statement 1 is correct:** Bees and butterflies are pollinators that transfer pollen and seeds from one flower to another, fertilizing plants so they can grow and produce food.[1] These insects help pollinate flowers from nearby areas moving pollen from one flower to another, which helps plants produce seeds.[2] Therefore, a huge fall in butterfly populations would adversely affect pollination of some plants.

**Statement 2 is incorrect:** There is no direct ecological connection between butterfly populations and control of fungal infections.[3] Butterflies are not known to control fungal infections in cultivated plants, so their decline would not lead to an increase in such infections.

**Statement 3 is correct:** Dragonflies usually eat flies, bees and butterflies.[4] This demonstrates that butterflies serve as prey in food chains. When butterfly populations fall drastically, predators that feed on them—including certain species of wasps, spiders, and birds—would face reduced food availability, potentially leading to declines in their populations as well.

Sources
  1. [1] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 6: Environmental Issues > 6.4. COLONY COLLAPSE DISORDER > p. 119
  2. [2] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 12: How Nature Works in Harmony > Activity 12.3: Let us read > p. 195
  3. [4] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 12: How Nature Works in Harmony > Activity 12.3: Let us read > p. 195
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Don’t just practise – reverse-engineer the question. This panel shows where this PYQ came from (books / web), how the examiner broke it into hidden statements, and which nearby micro-concepts you were supposed to learn from it. Treat it like an autopsy of the question: what might have triggered it, which exact lines in the book matter, and what linked ideas you should carry forward to future questions.
Q. Due to some reasons, if there is a huge fall in the population of species of butterflies, what could be its likely consequence/consequenc…
At a glance
Origin: Books + Current Affairs Fairness: Moderate fairness Books / CA: 6.7/10 · 3.3/10

A classic 'Common Sense Ecology' question solvable via NCERT basics. Statements 1 and 3 are direct applications of Food Chains and Pollination. Statement 2 is an 'Extreme Exaggeration' trap designed to test your ability to filter out scientifically weak correlations.

How this question is built

This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.

Statement 1
Would a large decline in butterfly populations adversely affect the pollination of some plant species?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 6: Environmental Issues > 6.4. COLONY COLLAPSE DISORDER > p. 119
Presence: 5/5
“Bees are one of a myriad of other animals, including birds, bats, beetles, and butterflies, called pollinators. Pollinators transfer pollen and seeds from one flower to another, fertilizing the plant so it can grow and produce food. Cross-pollination helps at least 30 percent of the world's crops and go percent of our wild-plants to thrive. Without bees to spread seeds, many plants - including food crops - would die off. Bees are not summertime nuisance, they are small and hard-working insects actually make it possible for many of your favorite foods to reach your table. From apples to almonds to the pumpkin in our pumpkin pies, we have bees to thank.”
Why this source?
  • Explicitly lists butterflies among the animals called pollinators.
  • Explains pollinators transfer pollen and seeds, enabling plant fertilization and production.
  • Notes pollination by such animals is essential for a substantial fraction of crops and wild plants, implying loss of pollinators reduces plant reproduction.
Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 12: How Nature Works in Harmony > Activity 12.3: Let us read > p. 195
Presence: 4/5
“These insects help pollinate flowers from nearby areas moving pollen from one flower to another, which helps plants produce seeds. So, flowers near ponds with fish may produce more seeds than those near ponds without fish. • z What does this study show? How does the population of fish in a pond affect the seed production in nearby plants?• z This study shows how biotic components (fish, dragonflies, pollinators, plants) and abiotic components (temperature, water, nutrients) interact with and affect each other (Fig. 12.4). Similarly, can overfishing by humans change this balance? How do you think it may affect the living and non-living parts of the habitat?”
Why this source?
  • States insects move pollen between flowers and thereby increase seed production nearby.
  • Connects variation in insect (biotic) populations to measurable changes in plant seed output, supporting that insect declines can reduce pollination success.
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > 2.6.r. Tlpes of biotic interaction > p. 16
Presence: 4/5
“r Mutualism: both species benefit. Example; in pollination mutualisms, the pollinator gets food (pollen, nectar), and the plant All Rights Reserved. No part of this material may be reproduced in any form or by any means, without permission in writing,”
Why this source?
  • Identifies pollination as a mutualism where both pollinator and plant benefit.
  • Provides the ecological mechanism (mutual dependence) linking declines in pollinators to adverse effects on plant reproduction.
Statement 2
Would a large decline in butterfly populations cause an increase in fungal infections of cultivated plants?
Origin: Web / Current Affairs Fairness: CA heavy Web-answerable

Web source
Presence: 5/5
"There is no direct ecological connection between butterfly populations and control of fungal infections."
Why this source?
  • Passage explicitly states there is no direct ecological connection between butterfly populations and control of fungal infections.
  • That statement directly addresses causality between butterfly declines and fungal infections of plants, arguing no direct causal link.

Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 10: Locational Factors of Economic Activities > Demerits of Social and Agroforestry > p. 27
Strength: 3/5
“Bacterial and fungal diseases may increase in shaded, more humid environments. For example, the incidence of diseases increases greatly under conditions of heavy shading. Te main reasons for this are probably greater relative humidity and decreased wind both of which tend to favour fungal growth. Source: Vyas, A.K., 2011, Introduction to Agriculture, 5th ed. New Delhi,Jain Brothers, p.202.”
Why relevant

Fungal diseases increase under more humid, shaded conditions which favour fungal growth.

How to extend

A student could ask whether loss of butterflies (and associated changes in vegetation structure or insect communities) might alter shading or humidity locally, thereby creating conditions more favourable to fungi.

Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 13: Plant Diversity of India > 13.2.4. Effect of temperature on plants > p. 197
Strength: 4/5
“• R Excessive high temperature results in death of plant due to coagulation of protoplasmic proteins. It disturbs the balance between respiration and photo synthesis thereby causes depletion of food resulting in greater susceptibility to fungal and bacterial attack. • R It also results in desiccation of plant tissues and depletion of moisture.”
Why relevant

Stressed or weakened plants (e.g., from temperature extremes) become more susceptible to fungal and bacterial attack.

How to extend

Combine this with the idea that loss of pollinators or changes in herbivory (connected to butterfly decline) can reduce plant vigour or reproduction, potentially increasing susceptibility to fungal infection.

Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 9: Agriculture > Environmental and Ecological Implications of Green Revolution > p. 66
Strength: 4/5
“Some of the environmental and ecological problems that emerged out of the cultivation of the High Yielding Varieties are depletion of forests, reduction in pastures, salination, water-logging, depletion of underground water-table, soil erosion, change in the soil chemistry, reduction in biodiversity, decline in soil fertility, silting of rivers, increase in weeds, emergence of numerous new plant diseases, and health hazards. An overview of these environmental and ecological problems has been given here.”
Why relevant

Reduction in biodiversity is listed among causes associated with emergence of numerous new plant diseases.

How to extend

Use the general rule that biodiversity loss can change disease dynamics to hypothesise that a major decline in butterflies (a component of biodiversity) could shift ecological balances and influence fungal disease incidence.

Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 12: How Nature Works in Harmony > Activity 12.3: Let us read > p. 195
Strength: 3/5
“Chapter 12 — How Nature Works in Harmony 195 two ponds—A with fish and large number of flowering plants around it; B without fish and fewer flowering plants around it (Fig. 12.3). Think of a reason for these observations. • z Compare the number of dragonflies, bees, and butterflies in both the ponds. Do you find any relationship between the number of dragonflies and bees/butterflies? We observed that in Pond A (with fish) the number of dragonflies were less as compared to Pond B. Why?• z Fish eat dragonfly larvae, so ponds with fish had fewer dragonflies. Dragonflies usually eat flies, bees and butterflies With fewer dragonflies, more bees, flies, and butterflies were found.”
Why relevant

Butterflies are part of food-web observations tying presence/absence of consumers to differences in community composition (pond example showing links among predators and insect abundances).

How to extend

Extend this by considering that reducing butterfly populations may alter food-web interactions (e.g., predator/prey numbers) and thereby indirectly change pressures on plants or microclimates that affect fungal growth.

Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 26: Agriculture > Factors Influencing Agriculture > p. 240
Strength: 3/5
“Many fungus diseases and insect pests do great damage to crops. The boll-weevil is a dreaded pest in the Cotton Belt of the U.S.A. and has completely annihilated the Sea Island species of cotton in southeastern U.S.A. since the 1890s. The Coffee Blishts. of Sri Lanka destroyed practically all the coffee trees in the Central Highlands in 1878 and farmers had to turn to tea growing instead. Even greater havoc was created by the fungus parasite Phytophthora infestans in Ireland between 1845 and 1848. It attacked the potatoes and caused the Potato Famine which drove many Irish farmers to leave their homes and migrate to England and the United States of America.”
Why relevant

Many fungal diseases can cause severe damage to crops, showing that changes which favour fungi have important agricultural consequences.

How to extend

A student might combine this with rules about biodiversity and plant stress to evaluate whether butterfly declines could plausibly lead to conditions that increase crop fungal disease and thus be agriculturally significant.

Statement 3
Can a significant decline in butterfly populations lead to population declines in predators or species that feed on butterflies, such as some wasps, spiders, and birds?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 12: Animal Diversity of India > I2.8. SPECIES EXTINCTION > p. 194
Presence: 5/5
“weather patterns, decreased food supply, disease, increase of competitors, predators or parasites, etc. that may act independently or add to determinist effects. • The impact of these processes will of course depend on the size and degree of genetic diversity and resilience of populations. • Traits that adversely affect or increase a species vulnerability to extinction due to habitat fragmentation have been identified. These are: • rarity or low abundance • poor dispersal ability • ecological specialization • unstable populations • high trophic status * as animals occupying a higher trophic level (i.e.”
Why this source?
  • Lists 'decreased food supply' as a driver of species extinction, implying that loss of prey can cause declines in predators reliant on that food.
  • Mentions vulnerability factors and trophic relationships that make species susceptible when their food resources diminish.
Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 12: How Nature Works in Harmony > Activity 12.3: Let us read > p. 195
Presence: 4/5
“Chapter 12 — How Nature Works in Harmony 195 two ponds—A with fish and large number of flowering plants around it; B without fish and fewer flowering plants around it (Fig. 12.3). Think of a reason for these observations. • z Compare the number of dragonflies, bees, and butterflies in both the ponds. Do you find any relationship between the number of dragonflies and bees/butterflies? We observed that in Pond A (with fish) the number of dragonflies were less as compared to Pond B. Why?• z Fish eat dragonfly larvae, so ponds with fish had fewer dragonflies. Dragonflies usually eat flies, bees and butterflies With fewer dragonflies, more bees, flies, and butterflies were found.”
Why this source?
  • Describes direct predator–prey links (dragonflies eat butterflies) and shows how changes in one trophic level alter abundances in others.
  • Provides an observed example of cascading population changes linked to predator–prey interactions.
Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 12: How Nature Works in Harmony > Keep the curiosity alive > p. 208
Presence: 4/5
“4. Look at this food chain: Grass Grasshopper Frog Snake If frogs disappear from this ecosystem, what will happen to the population of grasshoppers and snakes? Why? • 5. In a school garden, students noticed fewer butterflies the previous season. What could be the possible reasons? What steps can students take to have more butterflies on campus?• 6. Why is it not possible to have an ecosystem with only producers and no consumers or decomposers?• 7. Observe two different places near your home or school (e.g., a park and a roadside). List the living and non-living components you see. How are the two ecosystems different?• 8.”
Why this source?
  • Contains a classic food chain example and asks what happens when a species (frog) is removed, highlighting interdependence of trophic levels.
  • Directly prompts consideration of fewer butterflies and asks for possible causes and remedial steps, indicating ecological consequences of butterfly declines.
Pattern takeaway: UPSC Environment questions often mix two 'General Truths' (Pollination, Food Chain) with one 'Specific Fabrication' (Fungal infection). If a statement implies a complex, indirect causality with extreme adjectives ('Drastic'), it is likely false.
How you should have studied
  1. [THE VERDICT]: Sitter. Solvable using Class VIII/XII NCERT Science basics + Logic. Statement 2 is the only hurdle.
  2. [THE CONCEPTUAL TRIGGER]: Ecosystem Functions: Trophic Levels (Food Web) and Biotic Interactions (Mutualism/Pollination).
  3. [THE HORIZONTAL EXPANSION]: Memorize other non-insect pollinators (Bats, Birds, Lemurs, Lizards). Understand 'Co-extinction' (e.g., Yucca Moth & Yucca Plant). Review 'Keystone Species' (Fig trees) vs 'Indicator Species' (Lichens, Frogs).
  4. [THE STRATEGIC METACOGNITION]: When asked for 'Consequences' of a species loss, prioritize DIRECT functional loss (Pollination) and DIRECT trophic impact (Predators starving). Reject indirect, speculative, or extreme outcomes ('Drastic fungal increase') unless it's a famous specific case.
Concept hooks from this question
📌 Adjacent topic to master
S1
👉 Pollinators include butterflies and sustain plant reproduction
💡 The insight

References explicitly name butterflies as pollinators and describe pollinators' role in transferring pollen and enabling seed production.

High-yield for ecology and environment questions: links biodiversity (insect groups) to ecosystem services and food security. Helps answer questions on impacts of species declines, conservation priorities, and agro-ecology. Useful for questions on causes/effects of pollinator loss and policy responses.

📚 Reading List :
  • Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 6: Environmental Issues > 6.4. COLONY COLLAPSE DISORDER > p. 119
  • Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 12: How Nature Works in Harmony > Activity 12.3: Let us read > p. 195
🔗 Anchor: "Would a large decline in butterfly populations adversely affect the pollination ..."
📌 Adjacent topic to master
S1
👉 Pollination as a mutualism (plant–pollinator interaction)
💡 The insight

Evidence frames pollination as mutualism—pollinators obtain food while plants gain fertilization—showing the ecological dependence involved.

Conceptual for ecosystem functions and interspecific interactions in GS ecology segments. Enables explanation of cascading effects (e.g., pollinator decline → reduced plant reproduction → impacts on food webs and livelihoods). Useful for both descriptive and analytical UPSC questions.

📚 Reading List :
  • Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > 2.6.r. Tlpes of biotic interaction > p. 16
  • Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 12: How Nature Works in Harmony > Activity 12.3: Let us read > p. 195
🔗 Anchor: "Would a large decline in butterfly populations adversely affect the pollination ..."
📌 Adjacent topic to master
S1
👉 Consequences of pollinator decline for crops and wild plants
💡 The insight

Sources link pollinator activity to a measurable share of crop and wild-plant reproduction, implying declines harm plant productivity.

Directly relevant to questions on agriculture, food security, and conservation policy. Mastering this helps tackle questions about pesticide impacts, habitat loss, and mitigation strategies (e.g., protecting pollinators).

📚 Reading List :
  • Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 6: Environmental Issues > 6.4. COLONY COLLAPSE DISORDER > p. 119
  • Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 6: Environmental Issues > Against > p. 123
🔗 Anchor: "Would a large decline in butterfly populations adversely affect the pollination ..."
📌 Adjacent topic to master
S2
👉 Biodiversity loss and plant disease emergence
💡 The insight

The references link reduction in biodiversity to the emergence of new plant diseases, which is the closest evidence for a link between loss of insects (butterflies) and plant disease risk.

High-yield for UPSC: biodiversity–disease relationships recur in questions on ecology, agriculture and environmental policy. Mastering this helps answer questions on impacts of species loss, agroecology and conservation measures. Enables analysis-style answers on cascading effects of biodiversity change.

📚 Reading List :
  • Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 9: Agriculture > Environmental and Ecological Implications of Green Revolution > p. 66
🔗 Anchor: "Would a large decline in butterfly populations cause an increase in fungal infec..."
📌 Adjacent topic to master
S2
👉 Environmental conditions that favour fungal pathogens
💡 The insight

References describe microclimatic and chemical conditions (shade, humidity, pH) that promote fungal proliferation—key proximate drivers of fungal outbreaks in crops.

High utility for questions on plant pathology, agroecology and pollution impacts (e.g., acid rain). Helps link environmental change to disease risk and design mitigation measures (crop spacing, drainage, soil chemistry management).

📚 Reading List :
  • Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 10: Locational Factors of Economic Activities > Demerits of Social and Agroforestry > p. 27
  • Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 5: Environmental Pollution > b) Vegetation > p. 104
🔗 Anchor: "Would a large decline in butterfly populations cause an increase in fungal infec..."
📌 Adjacent topic to master
S2
👉 Plant stress increases susceptibility to fungal infection
💡 The insight

Evidence shows stressed plants (e.g., from temperature extremes or other stressors) become more vulnerable to fungal and bacterial attack, providing a mechanism by which ecosystem change can raise disease incidence.

Important for answering questions on crop vulnerability and adaptation: links abiotic stressors to biotic disease outcomes and supports policy discussion on climate resilience, irrigation and crop management.

📚 Reading List :
  • Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 13: Plant Diversity of India > 13.2.4. Effect of temperature on plants > p. 197
🔗 Anchor: "Would a large decline in butterfly populations cause an increase in fungal infec..."
📌 Adjacent topic to master
S3
👉 Predator–prey relationships and food chains
💡 The insight

The statement concerns how changes in a prey population (butterflies) affect predators; references include explicit food-chain examples and predator–prey links.

High-yield for ecology questions: explains basic population interdependence, helps answer questions on cascading effects and conservation measures; connects to biodiversity, ecosystem services and species interactions. Master via chain diagrams and case examples.

📚 Reading List :
  • Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 12: How Nature Works in Harmony > Keep the curiosity alive > p. 208
  • Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 12: How Nature Works in Harmony > Activity 12.3: Let us read > p. 195
🔗 Anchor: "Can a significant decline in butterfly populations lead to population declines i..."
🌑 The Hidden Trap

The 'Yucca Moth and Yucca Plant' relationship. This is an example of Obligate Mutualism where the extinction of one guarantees the extinction of the other. UPSC loves asking about specific symbiotic pairs.

⚡ Elimination Cheat Code

The 'Intensity Mismatch' Rule. Statement 1 uses 'adversely affected' (Moderate). Statement 3 uses 'fall in population' (Moderate). Statement 2 uses 'Drastic increase' (Extreme). In Ecology, extreme outcomes from a single variable change are rare. Eliminate the extreme.

🔗 Mains Connection

Mains GS-3 (Agriculture/Food Security): Pollinator decline is a direct threat to 'Nutritional Security' (fruits/vegetables depend on them) vs 'Calorific Security' (wheat/rice are wind-pollinated). Use this distinction in answers.

✓ Thank you! We'll review this.

SIMILAR QUESTIONS

IAS · 2012 · Q75 Relevance score: -2.85

The acdification of oceans is increasing. Why is this phenomenon a cause of concern? 1. The growth and survival of calcareous phytoplankton will be adversely affected. 2. The growth and survival of coral reefs will be adversely affected. 3. The survival of some animals that have phytoplanktonic larvae will be adversely affected. 4. The cloud seeding and formation of clouds will be adversely affected. Which of the statements given above is /are correct?

IAS · 2010 · Q90 Relevance score: -2.87

Due to their extensive rice cultivation, some regions may be contributing to global warming. To what possible reason/reasons is this attributable? 1. The anaerobic conditions associated with rice cultivation cause the emission of methane. 2. When nitrogen based fertilizers are used, nitrous oxide is emitted from the cultivated soil. Which of the statements given above is/are correct?

IAS · 2011 · Q4 Relevance score: -3.60

India has experienced persistent and high food inflation in the recent past. What could be the reasons ? 1. Due to a gradual switchover to the cultivation of commercial crops, the area under the cultivation of food grains has steadily decreased in the last five years by about 30% 2. As a consequence of increasing incomes, the consumption patterns of the people have undergone a significant change. 3. The food supply chain has structural constraints. Which of the statements given above are correct ?

IAS · 2024 · Q29 Relevance score: -3.68

Consider the following : 1. Butterflies 2. Fish 3. Frogs How many of the above have poisonous species among them ?

IAS · 2012 · Q24 Relevance score: -3.79

What would happen if phytoplankton of an ocean is completely destroyed for some reason ? 1. The ocean as a carbon sink would be adversely affected. 2. The food chains in the ocean would be adversely affected. 3. The density of ocean water would drastically decrease. Select the correct answer using the codes given below :