UPSC CSE Prelims
Ecology and Ecosystem Previous Year Questions (PYQs)

Detailed Explanation:

Answer: Option 2 — Only three

Parasitoid species are organisms that live on or in a host organism, eventually killing it. Among the listed organisms, parasitoid species are found in Carabid beetles (some species are parasitoids of other insects), Flies (Tachinid flies and other Diptera families include numerous parasitoids), and Wasps (Hymenoptera has extensive parasitoid families). Centipedes are predators that directly hunt and kill prey, while termites are herbivorous social insects feeding on plant matter, neither being parasitoids.

📝 Short Notes: Parasitoids

• Definition: Parasitoids are organisms that spend a significant portion of their life attached to or within a single host organism, which they ultimately kill. They differ from true parasites (which usually don't kill the host) and predators (which kill multiple prey).
• Carabid Beetles: While most are predatory, some species (particularly in genera like Brachinus and Lebia) exhibit parasitoid behavior, especially targeting pupae of other insects.
• Flies (Diptera): Tachinidae family is the largest group of parasitoid flies, with over 10,000 species. Other families like Bombyliidae and Sarcophagidae also include parasitoid species.
• Wasps (Hymenoptera): The most diverse parasitoid group, including families like Ichneumonidae, Braconidae, Chalcidoidea, and many others. They parasitize various life stages of insects and other arthropods.
• Centipedes: Chilopoda are venomous predators that actively hunt arthropods and small invertebrates; they do not exhibit parasitoid behavior.
• Termites: Isoptera are eusocial insects primarily feeding on cellulose from wood and plant material; they are decomposers, not parasitoids.

Detailed Explanation:

Answer: Option 1 — Fig

Fig trees share a unique obligate mutualistic relationship with fig wasps, which are the only insects capable of pollinating fig flowers. The fig wasp enters the enclosed syconium (fig fruit structure) through a tiny opening called the ostiole to lay eggs, simultaneously pollinating the internal flowers. This highly specialized relationship is a classic example of coevolution, where both species have evolved together over millions of years, making them entirely dependent on each other for survival and reproduction.

Why other options are incorrect:
❌ Option 2 – Mahua: Mahua (Madhuca indica) is pollinated by various insects including bees, moths, and even bats, not a single specialized pollinator.
❌ Option 3 – Sandalwood: Sandalwood is primarily pollinated by bees and flies; it is a hemiparasitic plant that relies on host trees for nutrients but has no unique insect pollinator.
❌ Option 4 – Silk Cotton: Silk cotton trees are pollinated by bats and birds, not by a specialized insect species.

📝 Short Notes: Fig-Wasp Mutualism

• Obligate Mutualism: Both fig and fig wasp are entirely dependent on each other—figs cannot reproduce without fig wasps, and fig wasps cannot reproduce without figs.
• Syconium Structure: The fig is not a true fruit but a syconium—a hollow, fleshy structure with flowers enclosed inside.
• Pollination Process: Female fig wasps enter through the ostiole (small opening), lay eggs inside ovaries, and pollinate flowers in the process. Male wasps are wingless and mate inside the fig.
• Coevolution: This relationship has evolved over approximately 80 million years, with over 750 species of figs, each typically having its own specialized wasp species.
• Ecological Importance: Figs are keystone species in tropical ecosystems, providing food for numerous animals during lean periods when other fruits are scarce.

Detailed Explanation:

Answer: Option 4 — Aquatic plants absorb heavy metals and excess nutrients.

The analogy of wetlands as "kidneys of the Earth" is best reflected by their filtration function. Just as kidneys filter waste products and toxins from blood, wetlands act as natural filters by absorbing pollutants, heavy metals, and excess nutrients from water through aquatic plants and microbes. This phytoremediation and nutrient regulation process purifies water and prevents harmful substances from contaminating downstream ecosystems, paralleling the kidney's role in maintaining bodily health.

Why other options are less appropriate:
Option 1 describes the water cycle, which relates more to circulation than filtration. Option 2 explains the food web, not the purification function. Option 3 addresses sediment control, which is important but doesn't capture the filtering/cleansing aspect central to the kidney analogy.

📝 Short Notes: Wetland Functions

• Filtration & Purification: Wetlands remove pollutants, heavy metals, sediments, and excess nutrients through plant uptake and microbial action (phytoremediation and bioremediation).
• Nutrient Regulation: Absorb excess nitrogen and phosphorus, preventing eutrophication in water bodies downstream.
• Flood Control: Act as natural sponges, absorbing excess rainfall and reducing flood peaks.
• Groundwater Recharge: Facilitate percolation of water into aquifers, maintaining groundwater levels.
• Biodiversity Hotspots: Support diverse flora and fauna, including migratory birds, fish, and amphibians.
• Carbon Sequestration: Wetland vegetation and soils store significant amounts of carbon, helping mitigate climate change.
• Coastal Protection: Mangroves and coastal wetlands buffer against storms, tsunamis, and erosion.

Detailed Explanation:

Answer: Option 4 — 1, 2 and 3

All three groups—cnidarians, fungi, and protozoa—have species capable of establishing symbiotic relationships with other organisms. This demonstrates the widespread occurrence of symbiosis across different taxonomic groups in nature.

✅ Statement 1 – Correct: Cnidarians like corals form symbiotic relationships with zooxanthellae (photosynthetic algae), which is essential for coral reef ecosystems.
✅ Statement 2 – Correct: Fungi form diverse symbiotic associations including mycorrhizae with plant roots and lichens with algae or cyanobacteria.
✅ Statement 3 – Correct: Protozoa establish symbiotic relationships, such as those living in termite guts that help digest cellulose.

📝 Short Notes: Symbiotic Relationships in Different Organisms

• Mutualism: Both organisms benefit from the relationship
• Symbiosis: Close and long-term biological interaction between different species
• Zooxanthellae: Single-celled dinoflagellates crucial for coral bleaching studies
• Ecological importance: Symbiotic relationships are fundamental to ecosystem functioning and biodiversity

Detailed Explanation:

Ecosystem = Biotic community (living organisms) + Abiotic environment (non-living factors like soil, water, air, sunlight) functioning together.

❌ Option 1: Describes only a biological community (lacks abiotic factors).
❌ Option 2: Defines the biosphere (entire zone of life on Earth).
✅ Option 3: Correctly captures both organisms and their environment as an integrated functional unit.
❌ Option 4: Refers to biota/biodiversity of a region (only living components).

Detailed Explanation:

Ecological niche describes both the physical space occupied by an organism and its functional role in the community, including its interactions with biotic and abiotic factors.

Habitat refers only to the physical location where an organism lives, while ecotone is a transition zone between two ecosystems, and home range is the area an animal travels during normal activities.

Detailed Explanation:

Millennium Ecosystem Assessment (2005) classifies ecosystem services into four categories: Provisioning, Regulating, Supporting, and Cultural.

Supporting Services are foundational services necessary for production of all other ecosystem services, including nutrient cycling, soil formation, primary production, and photosynthesis.

Provisioning Services include food, water, timber, and fiber production (Option 1).

Regulating Services include climate regulation, disease control, water purification, and crop pollination (Options 2 and part of 3).

Cultural Services include spiritual, recreational, aesthetic, and educational benefits (Option 4's diversity maintenance also overlaps with supporting).

Option 3 is correct because nutrient cycling is the definitive supporting service listed, even though pollination is technically classified as a regulating service in the original MA framework.