Ecology

Ecology is part of Environment and Ecology. Below are notes on 13 sub-topics, followed by practice MCQs from State PSC and UPSC papers.

Aquatic Ecosystems: Freshwater, Marine, Estuaries, Wetlands

• Aquatic Ecosystem Classification:
• Lotic: Flowing water (e.g., rivers, streams).
• Lentic: Still/standing water (e.g., lakes, ponds, bogs, swamps, marshes).
• Aquatic Organism Categories:
• Plankton: Microscopic floating organisms (phytoplankton - plants, zooplankton - animals).
• Nekton: Actively swimming organisms.
• Benthos: Organisms (plants and animals) living on the ocean/lake floor.
• First Asian beach to receive Blue Flag certification: Chandrabhaga beach (Odisha).
• Initial 8 Indian beaches to receive Blue Flag in 2020: Shivrajpur (Gujarat), Ghoghla (Diu), Kasarkod & Padubidri (Karnataka), Kappad (Kerala), Rushikonda (Andhra Pradesh), Golden (Odisha), Radhanagar (Andaman & Nicobar).
• Thundi Beach and Kadmat Beach (Lakshadweep) received Blue Flag certification later, bringing India's total to 10 in 2021. As of recent updates, India has 12 Blue Flag certified beaches.
• BEAMS (Beach Environment & Aesthetic Management Services): India’s own eco-label for beaches, launched in 2020.
• Lisbon Declaration: Associated with ocean conservation.
• Important Environmental Days:
• World Wetlands Day: 2 February
• World Water Day: 22 March
• International Mother Earth Day: 22 April
• International Tiger Day: 29 July
• Lake Ecosystems:
• Trophic States:
• Oligotrophic: Low nutrient, high oxygen, clear water.
• Mesotrophic: Moderate nutrient.
• Eutrophic: High nutrient, high productivity, low dissolved oxygen (shallow lakes with rich organic products).
• Zones (Vertical):
• Littoral Zone: Shallow water zone around the lake edge, welllit, rooted plants.
• Limnetic Zone: Open, offshore surface water zone, well-lit, abundant phytoplankton.
• Profundal Zone: Deep, dark zone where light cannot reach, least light penetration, low oxygen.
• Eutrophication: Nutrient enrichment of a water body (often from runoff), leading to excessive algal growth and subsequent depletion of dissolved oxygen upon decomposition.
• Wetlands:
• Definition: Land covered by slowmoving or stagnant water, or waterlogged wet ground.
• Types:
• Bogs: Peat-producing wetlands, receive water only from rain (ombrotrophic), characterized by stagnant water, low temperature, and acidic pH. Permeable soil is NOT an essential factor for bog development.
• Marshes: Highly productive natural environments, transform mineral matter into organic matter, function as physico-chemical sinks. (Are NOT least productive).
• Swamps: Forested wetlands.
• Functions: Nutrient recovery and cycling, reducing siltation of rivers by retaining sediments, absorption of heavy metals (phytoremediation).
• Marine Ecosystems:
• Halophytes: Plants adapted to grow in saline soils/seashores.
• Coral Reefs:
• Living organisms; Corallite is their house.
• Reefs are cemented and hard structures of calcium carbonate.
• Require warm water (23-25°C), shallow saltwater (not deeper than 50m), and plenty of sunlight (for symbiotic algae photosynthesis).
• Cannot grow in freshwater.
• Oldest living communities, high biomass producers, rich floral and faunal diversity, shallow water tropical ecosystems.
• Red Tide: Caused by the rapid proliferation of Dinoflagellates.
• Pycnocline: Zone of rapid density change in seawater.
• Thermocline: Zone of rapid temperature change in water.
• Halocline: Zone of rapid salinity change in water.
• Estuaries:
• Definition: Transitional region where river freshwater meets ocean saltwater.
• Highly productive ecosystems.
• Other Concepts:
• Ecotone: A transitional region between two ecosystems, often exhibiting characteristics of both and high biodiversity.
• Artificial Ecosystem: E.g., Rice field.
• World's most problematic aquatic weed: Eichhornia (Water Hyacinth).
• Alkaline soils improvement: By the use of gypsum.

Biogeochemical Cycles: Carbon, Nitrogen, Phosphorus, Sulphur, Water

• Biogeochemical Cycles (Nutrient Cycles): Natural pathways by which chemical elements or molecules move through the biotic (living) and abiotic (non-living) components of an ecosystem.
• Movement of nutrients in an ecosystem is always cyclic.
• Types: Gaseous cycles (reservoir in atmosphere/oceans; e.g., Carbon, Nitrogen, Oxygen) and Sedimentary cycles (reservoir in Earth's crust/rocks/soil; e.g., Phosphorus, Sulphur, Calcium).
• Role of bacteria/microorganisms in ecosystems is primarily to recycle nutrients.
• Deep Carbon Observatory (DCO): A global research program investigating the role of carbon on Earth, including field observations of deep microbial ecosystems.
• Carbon Cycle:
• Primary reservoirs: Atmosphere (CO₂), Oceans (dissolved CO₂), Lithosphere (fossil fuels, carbonate rocks), Biosphere (organic matter).
• Processes increasing atmospheric CO₂: Respiration (by living organisms), Decomposition/decay of organic matter, Combustion (burning fossil fuels, biomass), Volcanic action.
• Photosynthesis (by plants/algae) removes CO₂ from the atmosphere, thus it is not a contributor to CO₂ release.
• At night, plants respire, releasing CO₂; hence, it's advised not to sleep under trees.
• Deforestation leads to increased atmospheric CO₂ as forests act as carbon sinks (utilize CO₂ for photosynthesis).
• Nitrogen Cycle:
• A gaseous cycle; main reservoir is the atmosphere (~78% N₂). Its main reservoir is not the soil.
• Hydrogen sulphide (H₂S) is not a part of the nitrogen cycle.
• Key Processes:
• Nitrogen Fixation: Atmospheric N₂ is converted into ammonia (NH₃) or ammonium (NH₄⁺) by bacteria (e.g., Rhizobium in legumes, cyanobacteria in aquatic environments) or lightning. This is not the oxidation of NH₃ to NO₃⁻.
• Nitrification: Ammonia/ammonium (NH₃/NH₄⁺) is oxidized by bacteria (e.g., Nitrosomonas, Nitrobacter) into nitrites (NO₂⁻), then into nitrates (NO₃⁻). This is not the reduction of NO₃⁻ to N₂.
• Assimilation: Plants absorb nitrates (NO₃⁻) and ammonium (NH₄⁺) to synthesize organic nitrogen compounds.
• Ammonification: Decomposers convert organic nitrogen from dead organisms/waste into ammonia (NH₃).
• Denitrification: Nitrates (NO₃⁻) are reduced back to gaseous nitrogen (N₂) by denitrifying bacteria (e.g., Pseudomonas) under anaerobic conditions, returning N₂ to the atmosphere. This does not convert molecular N₂ into a fixed organic form.
• Cyanobacteria are significant nitrogen fixers in aquatic ecosystems.
• Phosphorus Cycle:
• A sedimentary (sedentary) cycle; main reservoir is Earth's crust (rocks, soil, sediments, ocean floor).
• Phosphorus is predominantly found as orthophosphate in soil (PO₄³⁻).
• Dolomite powder is applied to agricultural lands to increase the pH of the soil (acts as a liming agent), not primarily to increase phosphorus or nitrogen content directly.
• Sulphur Cycle:
• A sedimentary cycle with significant atmospheric components (e.g., H₂S, SO₂).
• Main reservoirs include rocks, sediments, oceans, and the atmosphere. Its main reservoir is not solely the soil.
• Hydrogen sulphide (H₂S) is a component of the sulphur cycle.
• Water Cycle (Hydrological Cycle):
• Processes include: Evaporation, Condensation, Precipitation, Transpiration, Infiltration, Runoff, Melting, Freezing.
• "Composition" is not a process in the water cycle.
• Loss of water (via transpiration) is maximum from the leaf surface.

Community Ecology: Species Diversity, Edge Effect, Keystone Species

• Amphibians are generally most sensitive to environmental changes.
• Ecotone is a transitional zone/area/frontier between two distinct ecosystems or biological communities.
• The 'edge effect' between cold and warm ocean waters often results in the development of dense phytoplankton (rich in diatoms), indicating high primary productivity.
• Keystone species are those whose elimination seriously affects the ecosystem and the ability of many other species to persist in the community.
• Expansion of starfish (e.g., Crown-ofThorns) can cause severe coral bleaching, as seen in cases like Keppel Island.
• Bathua (Chenopodium album) is typically a weed of winter (Rabi) crops, not paddy (Kharif crop).

Ecological Niche and Habitat

• Habitat: The actual location or place where an organism lives; its physical address.
• Ecological Niche:
• Describes not only the physical space occupied but also the functional role an organism plays in its community.
• Encompasses the range of conditions an organism can tolerate, the resources it utilizes, and its interactions with other organisms (biotic and abiotic).
• Each species has a distinct niche.
• Concept enunciated by Joseph Grinnell.
• Gause's Competitive Exclusion Principle: States that two species cannot coexist indefinitely if they occupy exactly the same ecological niche in the same habitat, as one will outcompete the other.
• Ecological Amplitude: The range of demands and consequent range of tolerance of a species to fluctuations in environmental conditions.
• Biotope: A homogeneous set of physical and chemical conditions in a given geographic area at a particular time, forming a uniform environment for a certain type of biological assemblage.
• Ecesis: The successful establishment of a new organism or species in a new habitat.
• Edaphic Factors: Pertaining to or influenced by soil conditions (e.g., soil composition, pH, water content).
• Halophytes: Plants adapted to grow in saline soil conditions.
• Eurythermal: Organisms (e.g., plants or animals) that can tolerate a wide range of temperatures.
• Stenothermal: Organisms that can tolerate only a narrow range of temperatures.
• Eucalyptus: Considered dangerous for the environment due to high water consumption and allelopathic effects.
• Fig Tree (Ficus): Shows a unique obligate mutualistic relationship with a specific fig wasp that is the only insect capable of pollinating it.
• Eco-Sensitive Area (ESA): An area designated as having a very diverse yet fragile ecosystem, often surrounding protected areas, to regulate activities that could harm the environment.
• Ecological Niche and Species Diversity:
• Dominant species may occupy more extensive or broader ecological niches.
• In a natural ecosystem, if resources are sufficient and equitably distributed, a larger number of species can coexist due to niche partitioning, leading to less dominance by a single species.

Ecological Principles: Carrying Capacity, Limiting Factors

• Carrying Capacity: The maximum number of individuals of a particular species that a specific environment can sustainably support indefinitely, given available resources and waste absorption capacity.
• Limiting Factors: Environmental conditions or resources (e.g., food, water, space, light, nutrients, temperature) that restrict population growth or distribution.
• Logistic Growth: A type of population growth where the growth rate slows down as the population size approaches the environment's carrying capacity, resulting in an Sshaped curve.
• Biotic Potential: The maximum rate at which a population can increase under ideal environmental conditions (without any limiting factors).
• Environmental Resistance: All the limiting factors that restrict the biotic potential of a population.
• Shelford's Law of Tolerance: States that organisms with a wide tolerance range for a particular environmental factor tend to have a wide geographical distribution and high population size.
• Ecological Footprint: The minimum productive land and water area required to continuously sustain the life of one person (or a population) and assimilate their waste.
• Hedgerows: Used by farmers during high insolation periods to reduce evapotranspiration and prevent wilting of plants.
• Environmental Hazard Tree: Eucalyptus is considered an environmental hazard due to its high water consumption, which can deplete groundwater.
• Main Cause of Ecological Imbalance in India: Deforestation.
• Overgrazing: A direct cause of soil erosion.
• Optimal Soil pH for Cultivation: Generally,

cultivation.

• Carrying Capacity of Environment (Sustainability Principles):
• The rate of resource extraction should not exceed the rate of resource generation.
• Generation of waste should remain within the absorption capacity of the environment.
• Integrated Pest Management (IPM) Stages:
• Avoid: Improve sanitation (e.g., preventing pest breeding).
• Block: Isolate (e.g., using physical barriers).
• Detect: Inspect (e.g., monitoring for pest presence).
• Respond: Implement targeted control measures (e.g., fumigation).
• Ecological Farming Principles:
• Production from nature should be within its regenerative capacity.
• Minimum interference in natural ecological processes.
• Replenishment of exhausted soil nutrients using natural methods.

Ecological Resilience and Stability

• Ecological Stability: The ability of an ecosystem to resist disturbance and return to its original state (resilience) or maintain its structure and function in the face of disturbance (resistance).
• Most Stable Ecosystem: Marine (Ocean) ecosystem.
• Reasons for Marine Ecosystem Stability: Large volume, high specific heat capacity of water (thermal inertia, leading to slow temperature changes), high biodiversity, and continuous interconnectedness.
• Ecological Balance: A state of dynamic equilibrium within an ecosystem, where interactions between living organisms and their environment result in a stable and functional system.
• Factors Maintaining Ecological Balance: Afforestation, water management, wildlife protection, pollution control, sustainable resource use.
• Tree's Cooling Effect:
• Shade: Blocks direct solar radiation, preventing its conversion to heat on the ground/surfaces.
• Evaporative Cooling (Transpiration): Water evaporates from leaf surfaces, using latent heat from the surrounding air, thereby reducing ambient temperature.
• Photosynthesis: Absorbs light energy (solar radiation) for energy conversion, slightly reducing the amount of energy that would otherwise contribute to heating the immediate environment.

Ecological Succession: Types and Stages

• Ecological Succession: Gradual, predictable process of change in species composition of an ecological community over time, leading to a stable climax community.
• Sere: The entire sequence of communities that successively change in a given area during ecological succession.
• Serai Stages: The transitional communities that appear during a sere.
• Pioneer Community: The first community to colonize a bare or disturbed area.
• Climax Community: The final, stable, mature, self-perpetuating community in an ecosystem, in equilibrium with the environment.
• Types of Succession:
• Primary Succession: Begins in a barren area where no life previously existed (e.g., bare rock, lava flows, new islands, retreating glaciers). No existing soil.
• Secondary Succession: Occurs in areas where a pre-existing community has been removed but the soil or substrate remains intact (e.g., abandoned fields, clear-cut forests, areas after fire/ flood). Faster than primary succession.
• Autogenic Succession: Changes in environmental conditions brought about by the inhabiting organisms themselves.
• Allogenic Succession: Changes in environmental conditions brought about by external, non-biological factors (e.g., volcanic eruptions, climate change).
• Progressive Succession: Leads to increased diversity and complexity, typical succession towards climax.
• Retrogressive Succession: Leads to a reduction in diversity and complexity, often due to increasing environmental stress or human impact.
• Stages (Phases) of Succession (Clementsian): Nudation: Creation of a bare or de1. nuded area (e.g., landslide, volcanic eruption, fire). Invasion: Arrival of new species into 2. the bare area. Comprises three substages:
• Migration: Arrival of propagules (seeds, spores, larvae) from other areas.
• Ecesis: Establishment and initial growth of the new species in the habitat.
• Aggregation: Individuals of the same species multiply and cluster together. Competition and Coaction: As popu3. lation grows, competition for resources (light, space, nutrients) occurs within and between species (intraspecific & interspecific). Coactions are various interactions among species. Reaction: Organisms modify their 4. own environment (e.g., adding organic matter, changing soil pH, shading), making it less suitable for themselves and more suitable for subsequent species. This is considered the most important stage. Stabilization (Climax): The relatively 5. stable community that becomes established and remains in equilibrium with the local climate and environment.
• Key Figures: The idea of Ecological Succession was first formally coined by F.E. Clements. He also propounded the Monoclimax Theory.
• Juvenile Ecosystem: Early successional stages characterized by energy usage primarily directed towards multiplication and growth of organisms. High production-tobiomass ratio.
• Tropical Rainforest Regeneration: Does not regenerate quickly after removal due to the soil being deficient in nutrients (most nutrients are tied up in the biomass, not the soil, and leached quickly by heavy rains).
• Grasslands & Tree Replacement: Trees generally do not replace grasses in grasslands due to limiting factors like water availability (droughts) and frequent fires.
• Pyrophilous Organism: An organism that thrives in habitats created by fire, such as fungi growing in soils of burnt terrains or plants whose seeds germinate after fire.
• Ecotone: A transition zone of varied natural vegetation occupying the boundary between two adjacent and differing plant communities (e.g., mangrove forests between marine and terrestrial ecosystems).

Ecology: Definition, Principles, and Levels of Organization

• Ecology: Study of interrelationships between organisms and their environment.
• Term "Ecology" coined by Ernst Heinrich Haeckel.
• E.P. Odum (1969) defined ecology as the study of the structure and function of the ecosystem.
• Concept of Ecosystem: Proposed by A.G. Tansley (1935).
• Levels of Organization (increasing complexity): Organism → Population → Community → Ecosystem → Landscape → Biosphere/ Ecosphere.
• Organism: An individual living being.
• Population: Group of individuals of the same species in a given area.
• Community: Assemblage of different species (populations) interacting in an area.
• Ecosystem: Interaction between a community and its physical (abiotic) environment; its components are interdependent.
• Landscape: Heterogeneous land area composed of interacting ecosystems.
• Biome: A large regional unit of ecosystem, characterized by dominant vegetation and climate. A biome is an ecosystem.
• Biosphere/Ecosphere: The life-supporting zone of Earth; global sum of all ecosystems; Earth and its atmosphere inhabited by living organisms.
• Earth's Spheres:
• Lithosphere: Solid component of Earth.
• Hydrosphere: All water on Earth (oceans, seas, rivers, lakes, etc.).
• Atmosphere: Thick gaseous cover surrounding Earth.
• Biosphere: Zone where living organisms interact with litho-, hydro-, and atmosphere.
• Phenology: Study of periodic plant phenomena (e.g., flowering) in relation to climate.
• Deep Ecology: Philosophy advocating a radical change in human-nature relationship; coined by Arne Naess.
• Ecological Transition: Concept first used by Bennett.
• Pedology: Study of soil (soil science).
• Biogeography: Study of the distribution of the world's species (past and present).
• Ecological Footprint: Measured in global hectares (gha).
• Coprophagic: Decomposers that specifically act on fecal matter.
• Ramdeo Mishra: Known as the Father of Indian Ecology.
• Human activities significantly impact the environment.
• Related Studies/Practices:
• Cosmology: Study of the universe.
• Anthology: Study of flowers (in this specific context).
• Pomology: Study of fruits.
• Neurology: Study of neurons.
• Viticulture: Grapes farming.
• Vegeculture: Tree farming (or cultivation of root/tuber crops).
• Pisciculture: Fish farming.
• Olericulture: Vegetable farming.
• Plant Macronutrients: K, Ca, Mg. Micronutrient: Fe.
• Endosymbiont: Anabaena (e.g., in Azolla for nitrogen fixation).
• Bioluminescence: Photobacterium phosphoreum is an example.
• Palaeoclimatic studies: Utilize tree rings, ice cores, and lacustrine deposits.
• Chlorofluorocarbons (CFCs): Widely used as refrigerants (super coolants) and propellants in aerosols.

Ecosystem Functions: Productivity, Energy Flow, Trophic Levels

• Ecosystem Function Components: Productivity, decomposition, nutrient cycling, and energy flow are fundamental processes that link biotic and abiotic components.
• Ecosystem Definition: A self-regulatory, selfsustained structural and functional unit of nature. It is not a closed system.
• Driving Force: Solar energy is the primary driving force and source of energy for an ecosystem.
• Producers (Autotrophs): Organisms that produce their own food.
• Terrestrial Producers: Herbaceous and woody plants.
• Aquatic Producers: Phytoplankton (major producers of organic carbon in oceans) and algae.
• Chemoautotrophs: Some producers (e.g., Archaea) use chemical compounds as an energy source.
• Green plants absorb approximately 1% (or 1-3%) of incident solar radiation for photosynthesis.
• Productivity: The rate of biomass production.
• Gross Primary Productivity (GPP): Total rate of photosynthesis.
• Net Primary Productivity (NPP): GPP minus respiration losses; biomass available to consumers.
• Highest NPP Ecosystems: Tropical rainforests, mangroves, swamps, coral reefs.
• Decreasing Productivity Order (General): Mangroves > Grasslands > Lakes > Oceans. (Tropical forests have very high NPP, but their soils are often nutrient-poor, making long-term intensive agriculture difficult after clearing.)
• Trophic Levels: Steps in a food chain/web, representing feeding relationships.
• Primary Producers: Autotrophs (e.g., green plants).
• Primary Consumers (Herbivores): Feed directly on producers (e.g., deer, ants). Producers are generally more numerous and have greater biomass than primary consumers.
• Secondary Consumers: Feed on primary consumers.
• Tertiary Consumers: Feed on secondary consumers.
• Energy Flow:
• Direction: Unidirectional, from producers to consumers.
• Energy Loss: Energy decreases at each successive trophic level as organisms use it for survival, growth, and development.
• Ten Percent Law (Lindeman's Law): Only about 10% of the energy from one trophic level is transferred to the next higher trophic level; the rest is lost, primarily as heat, during metabolic processes.
• Limitation of Trophic Levels: The number of trophic levels is limited by the significant decrease in available energy at higher levels.
• Second Law of Thermodynamics: Explains the decline of energy at higher trophic levels due to energy loss as heat.
• All solar energy entering the living system eventually returns to the atmosphere as heat.
• Energy Transfer Efficiency: Carnivores tend to be more efficient in assimilation than herbivores. Birds and mammals have low production efficiency due to high metabolic rates. A trophic level can support more herbivores than carnivores.
• Nutrient Flow:
• Direction: Cyclic, nutrients are recycled within the ecosystem.
• Decomposition: An essential process for nutrient cycling.
• Decomposers: Organisms (e.g., fungi, bacteria) that break down dead organic matter (detritus), releasing nutrients back into the ecosystem.
• Detritivores: Consumers of detritus (e.g., earthworms, millipedes, woodlice).
• Biological Equilibrium: A balance maintained between producers, consumers, and decomposers in an ecosystem.
• Bioenergetic Approach: The study of similarities and differences in food relationships among living organisms and various forms of energy supporting life.
• Biomagnification: The increase in concentration of persistent toxins (e.g., DDT) at successive trophic levels in a food chain.
• Ecosystem Services: Benefits provided by ecosystems to human society (e.g., clean air, water, pollination); their degradation represents a major loss to humankind.
• Specific Fauna Roles: Insects are crop-pollinators; snakes protect crops from rodents; frogs consume insects; earthworms improve soil fertility.

Ecosystem: Structure and Components

• An Ecosystem is the functional unit of nature, comprising a biological community interacting with its physical (abiotic) environment.
• It consists of two main components: Biotic (living organisms) and Abiotic (non-living physical and chemical factors).
• Biotic Components include:
• Producers (Autotrophs): Organisms like green plants that synthesize their own food (e.g., Green Plants).
• Consumers (Heterotrophs): Organisms that feed on other organisms (e.g., Animals).
• Decomposers (Saprotrophs): Organisms that break down dead organic matter, recycling nutrients (e.g., Fungi, Bacteria, Flagellates).
• Abiotic Components include non-living elements such as soil, air, water, light, temperature, and minerals.
• Fresh water is an abiotic resource. Air is an abiotic component.
• Soil: A crucial abiotic component that supports plant growth by providing nutrients, holding water, and serving as anchorage.
• Soil Impoverishment: Occurs when soil becomes very deficient in plant nutrients.
• Vegetation (grass, tree cover, forests) prevents soil degradation and desertification by stabilizing soil and maintaining water and nutrient cycling; grass protects soil against erosion and supports biological activities.
• Duff: Refers to partially decomposed organic litter found on the forest floor.
• Humus: The well-decomposed organic component of soil, derived from plant materials, significantly contributes to soil fertility.
• The Forest Canopy is the boundary layer of a forest where significant energy exchange occurs, including insolation and its reflection back to space.
• Standing Crop: Represents the total living biomass present in an ecosystem at a given time. Forest plantations typically exhibit a high standing crop among managed ecosystems.
• Managed Ecosystems: Are ecosystems significantly influenced and altered by human activities; examples include agricultural lands and forest plantations.
• Shifting Cultivation: An agricultural system that can be considered an ecosystem metric or an ecosystem-based approach, due to its interaction with natural cycles.
• Oceans are generally considered the most stable ecosystems due to their vastness and relatively constant conditions.
• Biotic Resources: Include living organisms and products derived from them; Coal and Petroleum are biotic resources formed from ancient organic matter.

Food Chains, Food Webs, and Ecological Pyramids

• Food Chain:
• Passage of food (and thus energy) from one organism to another in a specific sequence.
• Illustrates the feeding relationships between organisms.
• Example: Grass (Producer) → Goat (Primary Consumer/Herbivore) → Human (Secondary Consumer/Omnivore).
• Impact of missing link: In Grass – Deer – Tiger chain, if deer are missing, tiger population decreases (due to lack of food), and grass population increases (due to lack of grazing).
• Trophic Levels: Formed by organisms linked in a food chain, representing their feeding positions (e.g., producers, primary consumers, secondary consumers, tertiary consumers).
• Types of Food Chains:
• Grazing Food Chain (GFC): Starts with producers (autotrophs like green plants) → herbivores → carnivores.
• Detritus Food Chain (DFC): Begins with dead organic matter (detritus) → microorganisms (decomposers) → detritivores.
• Food Web:
• A complex network of interconnected food chains within an ecosystem.
• Shows the multiple feeding relationships among different organisms.
• Ecological Pyramids:
• Graphical representations showing the relationship between different trophic levels in terms of number, biomass, or energy.
• The base represents producers, and successive layers represent primary, secondary, and tertiary consumers.
• Types of Ecological Pyramids:
• 1. Pyramid of Energy:
• Represents the total amount of energy present at each trophic level.
• Always upright. It can never be inverted.
• Energy decreases at successive trophic levels due to metabolic losses and incomplete consumption. Only about 10% of energy is transferred from one trophic level to the next (10% Law).
• 2. Pyramid of Number:
• Represents the number of individual organisms at each trophic level.
• Can be upright: e.g., Grassland ecosystem (many grass plants → fewer herbivores → even fewer carnivores).
• Can be inverted: e.g., Parasitic food chain (a single large producer like a tree → supports many herbivores → which support many parasites).
• Can be spindle-shaped: e.g., A single large tree → many herbivores (birds/ insects) → fewer secondary carnivores.
• 3. Pyramid of Biomass:
• Represents the total dry weight (biomass) of organisms at each trophic level.
• Can be upright: e.g., Grassland and Forest ecosystems (large biomass of producers at the base → decreasing biomass at higher levels).
• Can be inverted: e.g., Marine/Pond ecosystem (small standing crop biomass of phytoplankton (producers) but rapid turnover, supporting a larger biomass of zooplankton and fish).

Major Terrestrial Biomes

• Biome Definition: A large regional unit characterized by major vegetation type and associated fauna, determined by climate and geology; encompasses similar biotic and abiotic components.
• Components of Biome: Consists of both plant communities and animal communities.
• Anthropogenic Biome: Cropland is an example of a human-modified biome.
• Tropical Rain Forest:
• Climate: High rainfall and high temperatures.
• Vegetation: Evergreen, enabling photosynthesis year-round.
• Soils: Generally infertile due to rapid nutrient cycling; often described as 'deserts covered by trees' due to quick nutrient depletion from soil.
• Productivity: Has maximum plant biomass and is the most productive landbased ecosystem.
• Plant Adaptations: Abundant creepers/ climbers and epiphytes (plants that grow on other plants, not rooted in ground; not all epiphytes are creepers).
• Tree Adaptations: Buttress roots help bear the mechanical load of hardwoods and provide stability in shallow soils.
• Decomposition: High temperature and moisture cause dead organic matter (leaf litter) to decompose very quickly, resulting in an often almost bare soil surface.
• Global Impact: Amazon rainforest is known as the "lungs of the planet earth," estimated to produce 20% of Earth's oxygen through photosynthesis.
• Temperate Deciduous Forest:
• Climate: High rainfall and temperatures varying from cold to mild.
• Vegetation: Primarily broad-leaved deciduous trees (e.g., maple, oak, hickory, beechwood).
• Typical Region: Found in temperate regions.
• Fauna: Raccoons, opossums, bats, and squirrels are common.
• Temperate Coniferous Forest:
• Undergrowth: Characterized by very little undergrowth.
• Growing Period: Short, typically 50 to 100 days in a year.
• Temperature: Characterized by significant variation in annual temperature.
• Taiga (Boreal Forest):
• Climate: Characterized by long, severe winters and few months of summer, constituting the only growing season for plants.
• Vegetation: Dominated by coniferous trees.
• Tundra Ecosystem: Characterized by long, severe winters and a very short growing season; treeless, with permafrost.
• Savanna Ecosystem:
• Vegetation: Consists of grassland with scattered small trees; extensive areas have no trees.
• Factors Checking Forest Development: Forest development is generally kept in check by fire, grazing herbivores, seasonal rainfall, and soil properties.
• Desert Biome:
• Animals: Desert dwelling animals are called Xericoles.
• Plant Adaptations: Phreatophytes are plants adapted to grow in arid environments by having deep roots to reach groundwater. Psammophytes are plants adapted to sandy soils.
• Non-Terrestrial Ecosystem: Marine ecosystem is an aquatic ecosystem, not a sub-category of terrestrial ecosystem.

Population Ecology: Characteristics and Interactions

• Zoonosis: disease/infection naturally transmissible from animals to humans.
• Neutralism: ecological interaction where two species ignore each other, causing no advantage or inconvenience.
• Juvenile ecosystem zoocenoses (animal communities) are often polyphagous (generalist feeders).
• Dormancy ecological adaptations include Hibernation (winter sleep), Aestivation (summer sleep), and Diapause (suspended development).
• Cyclomorphosis is not dormancy; it is a cyclical change in morphology due to environmental changes.
• Quadrat: sampling unit used to enumerate plants and sessile/slow animals in a unit area for population density/distribution estimation.
• Autecology: study of a single species and its environmental factors in its habitat.
• Synecology: study of groups of organisms (communities) in relation to their environment.
• Butterfly population decline consequences:
• Pollination of some plants could be adversely affected.
• Fall in population of some species of wasps, spiders, and birds (predators).
• No direct drastic increase in fungal infections of cultivated plants.
• Allelopathy: one species produces toxins/ chemicals that inhibit the growth or development of another species.
• Common crop-weed associations:
• Wheat - Phalaris minor (Gulli Danda)
• Pea - Piyazi (Asphodelus tenuifolius)
• Berseem - Kasni (Chicory)
• Bathua (Chenopodium album) is a weed of Rabi crops (e.g., wheat, mustard), not typically paddy (Kharif).
• Crop-Season associations:
• Kharif (Rainy season, June-October): Cotton, Paddy.
• Rabi (Winter season, October-March): Linseed, Wheat, Gram.
• Zaid (Summer season, March-June): Muskmelon, Watermelon.

3. Biodiversity

Practice MCQs: Ecology

Aquatic Ecosystems: Freshwater, Marine, Estuaries, Wetlands

1. Plants that grow in seashores are called as :

   Asked in: APPSC Group 1 Prelims 2010

   1. Halophytes
   2. Hydrophytes
   3. Xerophytes
   4. Psammophytes
   Show answer

   Answer: A. Halophytes

   Halophytes are plants adapted to grow in salty conditions, commonly found in coastal areas, salt marshes, and mangrove swamps.

2. Which one of the following statements with regard to growth of coral reefs is not correct?

   Asked in: UPSC CDS 2 2018

   1. Coral can grow abundantly in fresh water.
   2. It requires warm water between 23 °C-25 °C.
   3. It requires shallow saltwater, not deeper than 50 metres.
   4. It requires plenty of sunlight to aid photosyn‐ thesis.
   Show answer

   Answer: A. Coral can grow abundantly in fresh water.

   Chandrabhaga beach received this certification in 2018.

3. Wetland day is observed on

   Asked in: UPPSC Upper Mains 2008

   1. 2nd February
   2. 2nd April
   3. 2nd May
   4. 2nd March
   Show answer

   Answer: A. 2nd February

   World Wetlands Day is celebrated on February 2nd each year to raise global awareness about the vital role of wetlands for people and planet. Corals are marine invertebrates that primarily inhabit shallow, warm, clear saltwater environments. They are sensitive to changes in salinity and cannot survive or grow abundantly in freshwater. The statement that coral can grow abundantly in freshwater is factually incorrect.

4. The term wetland implies:

   Asked in: UPSC Geoscientist 2020

   1. land covered by rain water only.
   2. slow moving water covered wet ground.
   3. water logged wet ground.
   4. fast moving water covered wet ground.
   Show answer

   Answer: C. water logged wet ground.

   The defining characteristic of a wetland is the presence of water, which leads to saturated or waterlogged soil conditions that influence the types of plants and animals that can live there.

5. Bog ecosystem wetland receives water only from:

   Asked in: UPSC Geoscientist 2020

   1. Rain
   2. Streams
   3. Rivers
   4. Groundwater
   Show answer

   Answer: A. Rain

   - Bogs are typically acidic and nutrient-poor because rain is naturally acidic and low in nutrients compared to groundwater or surface water. - They are dominated by Sphagnum moss, which contributes to the acidic conditions and peat formation. - Unlike fens, marshes, or swamps, bogs are typically isolated from mineral-rich groundwater and surface water flow.

6. Which one among the following is a peat- producing wetland?

   Asked in: UPSC Geoscientist 2021

   1. Swamps
   2. Marshes
   3. Bogs
   4. Lakes
   Show answer

   Answer: C. Bogs

   Bogs are a type of freshwater wetland characterized by spongy peat deposits, acidic waters, and a floor covered by a thick carpet of sphagnum moss. Peat is accumulated partially decayed vegetation or organic matter that develops in wetlands where waterlogged conditions inhibit decomposition, which is a defining feature of bogs.

7. Which one among the following is NOT a characteristic feature of Mangrove?

   Asked in: UPSC Geoscientist 2021

   1. They are intertidal forested wetlands
   2. Mangrove habitat obstructs the growth and es‐ tablishment of other organisms
   3. They dominate river deltas, lagoons and estu‐ aries
   4. They are highly salt tolerant
   Show answer

   Answer: B. Mangrove habitat obstructs the growth and es‐ tablishment of other organisms

   Mangroves are a group of trees and shrubs that live in the intertidal zone of tropical and subtropical coastlines. They are halophytes (salt-tolerant) and possess unique adaptations like prop roots, pneumatophores, and salt-excreting leaves to survive in challenging conditions.

Biogeochemical Cycles: Carbon, Nitrogen, Phosphorus, Sulphur, Water

8. In the nighttime, it is advised not to sleep under trees because

   Asked in: BPSC Prelims Exam 67th Cancelled

   1. they liberate less amount of oxygen
   2. they liberate harmful gases at night
   3. they liberate carbon dioxide
   4. they liberate carbon monoxide
   Show answer

   Answer: C. they liberate carbon dioxide

   Plants respire continuously, consuming oxygen and releasing carbon dioxide, while photosynthesis (consuming carbon dioxide and releasing oxygen) only occurs in the presence of light.

9. Dolomite powder is applied in some agricultural lands. The purpose of applying it is to

   Asked in: UPSC CDS 2 2016

   1. increase the pH of the soil
   2. lower the pH of the soil
   3. increase the phosphorus content of the soil
   4. increase the nitrogen content of the soil
   Show answer

   Answer: A. increase the pH of the soil

   Applying dolomite to soil increases the soil's pH, making it less acidic. This is often done in agricultural lands where the soil is too acidic for optimal plant growth. Dolomite acts as a liming agent and also provides essential nutrients, calcium and magnesium, to the soil.

10. Which is not gaseous cycle ?

    Asked in: CGPSC Prelims Exam 2014

    1. N₂
    2. O₂
    3. Carbon
    4. H₂
    Show answer

    Answer: D. H₂

    Biogeochemical cycles are typically classified into gaseous cycles and sedimentary cycles. Gaseous cycles involve elements that primarily exist in the atmosphere in gaseous form. Major gaseous cycles include the Carbon cycle (as CO₂), Nitrogen cycle (as N₂), Oxygen cycle (as O₂), and Water cycle (as H₂O). While Hydrogen is a key element in many compounds involved in these cycles (like water and organic matter), the elemental form H₂ is not considered a primary component of a major atmospheric gaseous biogeochemical cycle in the same way as N₂, O₂, or CO₂. Therefore, H₂ does not represent a gaseous cycle in the common ecological classification.

11. Nitrogen cycle is one of the most important microorganisms-mediated chemical reactions in aquatic and soil environments. In this context consider the following statements : 1. Nitrogen fixation is the process of oxidising NH₃ to NO₃⁻. 2. Nitrification process causes reduction of NO₃ and NO₂⁻ to NO₂, followed by recycling of N₂ to the atmosphere. 3. Denitrification converts molecular N₂ into a fixed form as an organic nitrogen. How many of the statements given above is/are correct ?

    Asked in: UPSC Geoscientist 2024

    1. 1
    2. 2
    3. 3
    4. None
    Show answer

    Answer: D. None

    - Statement 1 is incorrect: Nitrogen fixation is the process where atmospheric nitrogen (N₂) is converted into ammonia (NH₃) or other nitrogenous compounds. The process described (oxidising NH₃ to NO₃⁻) is nitrification, which involves the oxidation of ammonia first to nitrite (NO₂⁻) and then to nitrate (NO₃⁻). - Statement 2 is incorrect: The process described (reduction of NO₃⁻ and NO₂⁻ to NO₂, followed by recycling of N₂ to the atmosphere) is denitrification, which is the conversion of nitrates and nitrites back into nitrogen gas (N₂) under anaerobic conditions. Nitrification is the oxidation of ammonia compounds. - Statement 3 is incorrect: Denitrification converts fixed nitrogen (like nitrates and nitrites) back into atmospheric molecular nitrogen (N₂). The process that converts molecular N₂ into a fixed form as organic nitrogen (via ammonia) is nitrogen fixation.

12. The natural cycle that circulates elements between the earth and the environment (particularly between living and non-living matter) is called

    Asked in: GPSC Prelims CSP 2 2017

    1. Biogeochemical cycle
    2. Chemical cycle
    3. Biological cycle
    4. Bioorganic cycle
    Show answer

    Answer: A. Biogeochemical cycle

    A biogeochemical cycle is a pathway by which a chemical element or molecule moves through both biotic (living) and abiotic (non-living) components of Earth. Examples include the water cycle, carbon cycle, nitrogen cycle, phosphorus cycle, and sulfur cycle.

13. In which form is phosphorus predominantly found in soil ?

    Asked in: HPPSC HPAS Prelims 2010

    1. Orthophosphate
    2. Phosphorus oxide
    3. Phosphorus sulphide
    4. Phosphoric acid
    Show answer

    Answer: A. Orthophosphate

    Phosphorus in soil exists in both organic and inorganic forms. The inorganic forms, which are the ones plants primarily take up, are various orthophosphate ions (H₂PO₄⁻, HPO₄²⁻, PO₄³⁻) depending on the soil pH. These ions are derived from the weathering of minerals containing phosphate and the mineralization of organic phosphorus compounds.

14. Which of the following processes does not occur in the water cycle ?

    Asked in: HPPSC HPAS Prelims 2018

    1. condensation
    2. infiltration
    3. evaporation
    4. composition
    Show answer

    Answer: D. composition

    The water cycle (hydrologic cycle) is the continuous movement of water on, above, and below the surface of the Earth. Key processes include evaporation (liquid water changing to vapor), condensation (water vapor changing to liquid or solid), precipitation (water falling from clouds as rain, snow, etc.), infiltration (water soaking into the ground), runoff (water flowing over the land surface), and transpiration (water released by plants). Composition refers to the make-up of something (e.g., water's composition is H₂O); it is not a process within the water cycle.

Community Ecology: Species Diversity, Edge Effect, Keystone Species

15. Which one of the following is most sensitive to environmental change?

    Asked in: UPSC CDS 2 2016

    1. Amphibian
    2. Reptile
    3. Mammal
    4. Insect
    Show answer

    Answer: A. Amphibian

    Amphibians are particularly vulnerable to environmental changes due to several factors: their permeable skin readily absorbs substances from the environment (water and air), they often rely on both aquatic and terrestrial habitats during their life cycle, and many have specific requirements for reproduction and development. These characteristics make them highly susceptible to changes in water quality, habitat destruction, pollution, and climate change, serving as important bioindicators.

16. An ecotone generally refers to the:

    Asked in: UPSC Geoscientist 2021

    1. frontier between two ecosystems of different evolutionary levels.
    2. frontier between two ecosystems of same evolutionary levels.
    3. integration of two ecosystems of different evolutionary levels.
    4. integration of two ecosystems of graded evolutionary levels.
    Show answer

    Answer: C. integration of two ecosystems of different evolutionary levels.

    The core concept of an ecotone is the 'frontier' or 'transition zone' between two different ecological communities or ecosystems.

17. Which one of the following results due to the 'edge effect' between cold and warm ocean waters?

    Asked in: UPSC Geoscientist 2022

    1. Development of dense phyto- planktons rich in diatoms
    2. Decrease in fish population in the area
    3. Decrease in mussel population in the area
    4. Decrease in primary productivity of the area
    Show answer

    Answer: A. Development of dense phyto- planktons rich in diatoms

    - 'Edge effect' between distinct water masses (like cold and warm currents) causes mixing and/or upwelling. - Upwelling brings nutrients from the deep ocean to the surface. - Increased surface nutrients fuel phytoplankton growth (primary productivity). - Diatoms are common and abundant phytoplankton in nutrient-rich waters.

18. The transitional area between two living organisms is known as

    Asked in: MPSC CS Prelims 2018

    1. Ecozone
    2. Ecophos
    3. Ecotone
    4. Ecotype
    Show answer

    Answer: C. Ecotone

    An ecotone is a transition zone between two ecological communities or ecosystems.

19. Some species if eliminated seriously affect the ecosystem. These are called

    Asked in: MPSC CS Prelims 2023

    1. Blue stone
    2. Red stone
    3. Yellow stone
    4. Keystone
    Show answer

    Answer: D. Keystone

    The definition provided perfectly matches the concept of a keystone species. Examples include the sea otter (predator that controls sea urchin populations, preventing kelp forest destruction) or the star fish Pisaster ochraceus (predator that prevents mussels from dominating intertidal zones).

20. Keppel Island is completely bleached mainly due to the expansion of

    Asked in: UPSC NDA 1 2021

    1. Starfish.
    2. Blue whale.
    3. Octopus.
    4. Sea horse.
    Show answer

    Answer: A. Starfish.

    Coral bleaching is primarily caused by environmental stress, most notably elevated sea temperatures. However, biological factors can also contribute. Outbreaks of predatory starfish, specifically the Crown-of-Thorns starfish (Acanthaster planci), are known to cause significant damage to coral reefs by feeding on polyps. Severe predation can weaken the coral, making it more susceptible to bleaching, or cause direct mortality that appears as whitening (tissue loss revealing the white skeleton). Keppel Island, being part of the Great Barrier Reef ecosystem which experiences COTS outbreaks, is susceptible to such damage. While climate change and rising temperatures are the main driver of widespread bleaching events, localised stress from predators like starfish can exacerbate or cause bleaching in specific areas. Given the options, Starfish (Crown-of-Thorns) is the only organism listed that is a known significant predator of coral and contributes to coral damage and bleaching.

21. Transition zone between two ecosystems is called

    Asked in: PPSC CS Prelims 2015

    1. Eco-cline
    2. Eco-tone
    3. E-cad
    4. Eco-barrier
    Show answer

    Answer: B. Eco-tone

    Ecotones can be sharp or gradual and can vary in size from local to regional. They often contain species from both bordering communities and may also contain unique species not found in either community. They are often areas of high biodiversity.

Ecological Niche and Habitat

22. The actual location or place where an organism lives is called

    Asked in: BPSC Prelims Exam 65th

    1. habitat
    2. ecosystem
    3. niche
    4. biome
    Show answer

    Answer: A. habitat

    Habitat refers to the physical location or environment where an organism lives.

23. Halophytes are the plants that grow on which one, among the following categories of soil ?

    Asked in: UPSC CDS 2 2024

    1. Acidic soil
    2. Saline soil
    3. Black soil
    4. Sandy soil
    Show answer

    Answer: B. Saline soil

    - Halophytes possess specific physiological adaptations (like salt excretion, succulence, or accumulating salts in specific tissues) to tolerate saline conditions. - Saline soils are characterized by excessive amounts of soluble salts, mainly sodium chloride, sodium sulfate, magnesium chloride, and magnesium sulfate.

24. Gause`s competitive exclusion principle states that two species:

    Asked in: UPSC Geoscientist 2020

    1. can coexist if they occupy the same niche.
    2. cannot coexist if they occupy the same niche.
    3. cannot coexist if they occupy the adjacent niches.
    4. can coexist if they occupy similar niches.
    Show answer

    Answer: B. cannot coexist if they occupy the same niche.

    Also known as the principle of competitive exclusion, it posits that if two species compete for the identical set of resources (occupy the same niche), one will inevitably outcompete the other, leading to the local extinction of the less competitive species.

25. The term 'biotope' refers to

    Asked in: UPSC Geoscientist 2022

    1. a set of general physical conditions excluding chemical and biological conditions in a given geographic area
    2. a homogeneous set of physical and chemical conditions in a given geographic area at a particular time
    3. a homogeneous set of both biological and chemical conditions in a given geographic area
    4. a particular type of biological assemblage in a given geographic area
    Show answer

    Answer: B. a homogeneous set of physical and chemical conditions in a given geographic area at a particular time

    - Biotope refers to the non-living environment or habitat. - It is characterized by homogeneous physical and chemical conditions (e.g., temperature, humidity, soil type, pH, salinity). - The living community inhabiting a biotope is called a biocenose or biotic assemblage. - An ecosystem comprises both the biotope and the biocenose.

26. An ecological “Niche” can be defined as __________.

    Asked in: KPSC KAS Prelims 2017

    1. The various habitats an organism may inhabit
    2. The specific environment an organism inhabits
    3. The role an organism plays in its community
    4. The inorganic, non-living aspects of a given area
    Show answer

    Answer: C. The role an organism plays in its community

    An ecological niche is a fundamental concept in ecology that describes the functional role of an organism within its community and ecosystem.

27. What is ecological amplitude?

    Asked in: UPSC Geoscientist 2023

    1. The range of demands and consequent range of tolerance of a species to the fluctuations in environmental conditions
    2. The range of tolerance of a species in constant environmental conditions
    3. The range of demands of a species in constant environmental conditions
    4. The range of ecological conditions found in a biome
    Show answer

    Answer: A. The range of demands and consequent range of tolerance of a species to the fluctuations in environmental conditions

    Ecological amplitude refers to the range of environmental conditions (such as temperature, moisture, salinity, pH, etc.) within which a species can survive, grow, and reproduce. It is determined by the physiological tolerance limits of the species to fluctuations in these conditions and its specific resource requirements (demands).

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

    Asked in: OPSC CS Prelims 2023 · UPSC IAS 2013

    1. Ecotone
    2. Ecological niche
    3. Habitat
    4. Home range
    Show answer

    Answer: B. Ecological niche

    Habitat is the physical place where an organism lives. Ecological niche is a more comprehensive concept that includes the habitat as well as the organism's 'profession' or 'role' in the ecosystem – how it interacts with biotic and abiotic factors, its feeding habits, reproductive strategies, and its impact on the environment. Ecotone is a transitional area between ecosystems. Home range is the area an animal uses for its regular activities.

Ecological Principles: Carrying Capacity, Limiting Factors

29. The maximum number of individuals that can be supported by a given environment is called

    Asked in: APSC CCE Prelims Exam 2020

    1. carrying capacity
    2. population size
    3. biotic potential
    4. environmental resistance
    Show answer

    Answer: A. carrying capacity

    Carrying capacity is the maximum population size of a species that an environment can sustain indefinitely, given the available resources like food, water, habitat, and other necessities.

30. Farmers surround the fields with hedgerows during high insolation period to:

    Asked in: UPSC Geoscientist 2020

    1. prevent the reduction in photosynthetic activ‐ ity.
    2. reduce evapotranspiration.
    3. create conditions for plants to close their sto‐ mata.
    4. prevent wilting of plants.
    Show answer

    Answer: B. reduce evapotranspiration.

    - Evapotranspiration is the combined loss of water from the soil surface by evaporation and from plants by transpiration. - High wind speed increases the rate of both evaporation and transpiration. - By reducing wind speed, hedgerows decrease the rate of water loss from the field, helping to conserve soil moisture and reduce plant water stress.

31. A growing population cannot increase indefinitely at a geometric rate because a given habitat has a carrying capacity. This type of growth is known as:

    Asked in: UPSC Geoscientist 2021

    1. Exponential growth
    2. Sinusoidal growth
    3. Logistic growth
    4. Chaotic growth
    Show answer

    Answer: C. Logistic growth

    Logistic growth describes a population's growth when it is limited by the carrying capacity (K) of its environment. As the population size approaches K, the growth rate slows down due to resource scarcity, increased competition, predation, or disease, resulting in an S-shaped curve.

32. According to Shelford's Law of Tolerance, the organisms wide environmental factor tolerance limit show :

    Asked in: OPSC CS Prelims 2021

    1. Narrow distribution with low population size
    2. Wide distribution with high population size
    3. Narrow distribution with high population size
    4. Wide distribution with low population size
    Show answer

    Answer: B. Wide distribution with high population size

    Shelford's Law of Tolerance states that an organism's distribution and abundance are limited by the environmental factor(s) for which it has the narrowest range of tolerance. Conversely, organisms with a wide range of tolerance for environmental factors are called euryoecious species. - Organisms with a wide tolerance range can survive and reproduce across a broader spectrum of environmental conditions. - This ability allows them to inhabit a greater variety of locations and habitats, leading to a wide geographical distribution. - Within the wide range of conditions they can tolerate, there is likely an optimal range where the organism thrives, potentially leading to a high population density in suitable areas within their broad distribution. - Therefore, a wide environmental factor tolerance limit generally correlates with a wide distribution and the potential for high population size where conditions are favorable within that range.

33. The ability of a population to increase under ideal environmental conditions is called

    Asked in: OPSC CS Prelims 2023

    1. Natality
    2. Carrying capacity
    3. Biotic potential
    4. Absolute natality
    Show answer

    Answer: C. Biotic potential

    - Biotic potential is the maximum rate of population increase. - Occurs under ideal environmental conditions (no limiting factors). - Represents the inherent ability of a species to reproduce.

34. The number of organisms that can be supported by the environment in a given area is known as :

    Asked in: UKPSC CS Prelims 2012

    1. Population
    2. Carrying Capacity
    3. Pyramid of number or biomass
    4. None of the above
    Show answer

    Answer: B. Carrying Capacity

    It represents the environmental limit to population growth in a particular area or ecosystem. When a population exceeds its carrying capacity, resource depletion, disease, and increased mortality often follow.

35. The minimum area of the land required To completely sustain the life of one person is called his

    Asked in: UPPCS Prelims 2012

    1. Biota
    2. Ecological foot print
    3. Biome
    4. Niche
    Show answer

    Answer: B. Ecological foot print

    The Ecological Footprint is a measure of the demand placed by a person or population on the environment, expressed as the area of productive land and water required to produce the resources consumed and absorb the waste produced.

Ecological Resilience and Stability

36. During a hot sunny day people feel cool in the shadow under a big tree (a) because the tree blocks direct sunlight. (b) because heat from the air is used in evaporation of water by tree leaves reducing the temperature. (c) because photosynthesis by tree leaves absorbs energy from sunlight. (d) because tree leaves absorb water vapour from air which is an endothermic process. The correct answer is

    Asked in: KPSC KAS Prelims 2024

    1. only (a)
    2. only (a) and (b)
    3. only (a), (b) and (c)
    4. all (a), (b), (c) and (d)
    Show answer

    Answer: B. only (a) and (b)

    Let's analyze each statement: (a) because the tree blocks direct sunlight: TRUE. Blocking direct solar radiation significantly reduces the heat load on the person and the ground, making the shade feel cooler. (b) because heat from the air is used in evaporation of water by tree leaves reducing the temperature: TRUE. Trees undergo transpiration, where water evaporates from their leaves. This evaporation is an endothermic process, absorbing latent heat from the leaves and the surrounding air, leading to a cooling effect. (c) because photosynthesis by tree leaves absorbs energy from sunlight: Partially true, photosynthesis does absorb light energy, but the amount of energy absorbed for photosynthesis is relatively small compared to the total solar radiation, and this absorbed energy is converted into chemical energy (sugars), not dissipated as a cooling effect on the environment. The primary way trees dissipate excess heat absorbed from sunlight is through transpiration. (d) because tree leaves absorb water vapour from air which is an endothermic process: FALSE. Trees release water vapor into the air through transpiration. While plants can absorb some atmospheric moisture, it's not a primary cooling mechanism, and absorbing water vapor (condensation) is an exothermic process, releasing heat.

37. Which is the most stable ecosystem ?

    Asked in: UPPCS Prelims 2018

    1. Marine (ocean)
    2. Forest
    3. Mountain
    4. Desert
    Show answer

    Answer: A. Marine (ocean)

    Stability in an ecosystem refers to its ability to resist disturbance and return to its original state after being disturbed. Large, complex, and ancient ecosystems tend to be more stable.

38. Which one of the following is not related with ecological balance?

    Asked in: UPPCS Prelims 2005

    1. Water management
    2. Afforestation
    3. Industrial Management
    4. Wild life protection
    Show answer

    Answer: C. Industrial Management

    Activities that conserve resources, habitats, and biodiversity contribute to ecological balance; activities that cause pollution, depletion, or destruction disrupt it.

39. Most stable ecosystem is:

    Asked in: RPSC RAS Prelims 2008

    1. Forest
    2. Grassland
    3. Desert
    4. Marine
    Show answer

    Answer: D. Marine

    Stability is attributed to their vastness, relatively constant physical and chemical conditions (temperature, salinity), high biodiversity, and interconnectedness which provides resilience against disturbances.

40. Which among the following is the most stable ecosystem?

    Asked in: MPPSC CS Prelims 2023

    1. Forest ecosystem
    2. Desert ecosystem
    3. Marine ecosystem
    4. Grassland ecosystem
    Show answer

    Answer: C. Marine ecosystem

    Large marine ecosystems, particularly the open ocean, are generally considered the most stable ecosystems. This is due to several factors: their vast size, relatively uniform and stable environmental conditions (temperature, salinity) over large areas and depths, and high species diversity which contributes to resilience. Terrestrial ecosystems (forests, deserts, grasslands) are subject to greater fluctuations in temperature, precipitation, and human impact, making them generally less stable than large marine systems.

Ecological Succession: Types and Stages

41. Which one of the following is the correct sequential phase in the successional development of vegetation community in a habitat ?

    Asked in: UPSC CDS 2 2019

    1. Migration, Reaction, Stabilization and Nuda‐ tion
    2. Migration, Nudation
    3. Nudation, Migration, Reaction and Stabiliza‐ tion
    4. Reaction, Migration, Stabilization and Nuda‐ tion
    Show answer

    Answer: C. Nudation, Migration, Reaction and Stabiliza‐ tion

    - Ecological succession is the process of change in the species structure of an ecological community over time. It is a directional process, leading to a relatively stable state called the climax community. - The typical sequential stages of succession (sometimes presented with slightly varying terminology) are: 1. Nudation Creation of a bare area, devoid of any life. This can be caused by natural events like volcanic eruptions, floods, erosion, or human activities like deforestation. 2. Invasion (or Migration) Arrival of propagules (seeds, spores, etc.) of plants in the bare area. This involves three steps: migration (dispersal to the area), ecesis (establishment and initial growth), and aggregation (increase in number through reproduction). 3. Competition and Co-action As populations grow and species interact, competition for resources (light, water, nutrients, space) occurs. Co-actions (like facilitation or inhibition) also play a role in modifying the environment. 4. Reaction The organisms living in the area modify the environment (e.g., change soil composition, light availability, temperature, humidity). These changes make the habitat less suitable for the existing community but more suitable for new species. This stage drives the succession forward. 5. Stabilization (or Climax) Eventually, a relatively stable community develops that is in equilibrium with the environment and can reproduce itself. This is called the climax community. - The sequence presented in option C follows the logical progression: a bare area is formed (Nudation), species arrive and establish (Migration/Invasion), organisms interact and modify the environment (Reaction), leading towards a stable state (Stabilization/Climax).

42. A juvenile ecosystem is characterized by energy usage which is primarily directed towards

    Asked in: UPSC Geoscientist 2022

    1. multiplication and growth of organisms
    2. maintenance of biocenose
    3. conservation of biocenose
    4. reduced growth of plants
    Show answer

    Answer: A. multiplication and growth of organisms

    - Juvenile ecosystems (early successional stages) focus on production and growth. - Energy is channeled into accumulating biomass and increasing population size. - Net primary productivity is often high, but respiration (maintenance cost) is relatively low per unit biomass compared to mature systems. - Mature ecosystems focus more on maintenance, diversity, and efficient nutrient cycling.

43. Which one of the following is the most important stage in the process of ecological succession?

    Asked in: UPSC Geoscientist 2023

    1. Claim
    2. Acceptance by community members
    3. Reaction
    4. Settlement
    Show answer

    Answer: C. Reaction

    In ecological succession, 'Reaction' refers to the modifications made by organisms to their physical habitat. These changes, such as altering soil composition, light availability, or nutrient levels, significantly influence the suitability of the environment for the existing community and pave the way for the establishment of subsequent communities. It is a crucial feedback mechanism that drives the process of succession forward.

44. Which one of the following is the appropriate sequential order of ecological succession ?

    Asked in: UPSC Geoscientist 2024

    1. Invasion – Nudation – Competition and coac‐ tion – Reaction – Stabilization
    2. Nudation – Invasion – Competition and coac‐ tion – Reaction – Stabilization
    3. Nudation – Invasion – Reaction – Competition and coaction – Stabilization
    4. Invasion – Nudation – Competition and coac‐ tion – Reaction – Stabilization
    Show answer

    Answer: B. Nudation – Invasion – Competition and coac‐ tion – Reaction – Stabilization

    The classic sequence of ecological succession (particularly primary succession on bare ground) involves several steps: 1. Nudation The creation of a bare area devoid of life (e.g., by volcanic eruption, glacier retreat, landslide). 2. Invasion The arrival of organisms (propagules like seeds, spores, or larvae) into the bare area. This includes migration and ecesis (establishment and growth). 3. Competition and Coaction Interactions between the established organisms and with the environment, including competition for resources and modifications of the environment. 4. Reaction The established organisms modify the environment (e.g., adding organic matter, changing soil pH, altering light levels), making it more or less suitable for themselves and often creating conditions favorable for the invasion and growth of new species. 5. Stabilization The community reaches a relatively stable state, often referred to as a climax community, where the species composition changes little over time.

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

    Asked in: GPSC Prelims CSP 2 2022

    1. The soil of rain forest is deficient in nutrients.
    2. Propagules of trees in a rain forest have poor viability.
    3. The rain forest species are slow growing.
    4. Exotic species invade the fertile soil of rain forest
    Show answer

    Answer: A. The soil of rain forest is deficient in nutrients.

    - Nutrients in tropical rainforests are primarily stored in vegetation biomass and rapid litter decomposition. - High rainfall causes rapid leaching of nutrients from the soil. - Clearing the forest removes the main nutrient store and exposes the often nutrient-deficient soil, hindering quick regeneration.

46. What is 'pyrophilous organism'?

    Asked in: UPSC Geoscientist 2023

    1. Fresh grass growing after ground fire
    2. Fungi growing in soils of burnt terrains
    3. Seeds germinating after clear felling of forest
    4. Organisms with capacity to regenerate the tail after it was lost due to damage
    Show answer

    Answer: B. Fungi growing in soils of burnt terrains

    'Pyrophilous' means 'fire-loving'. Pyrophilous organisms are those that are either dependent on fire for part of their life cycle or thrive in environments recently affected by fire. Fungi that specifically colonize or grow best on burnt organic matter or in fire-affected soil are classic examples of pyrophilous organisms.

47. The introduction of new life forms in a denuded habitat is initiated by the process of :

    Asked in: OPSC CS Prelims 2017

    1. Ecesis
    2. Aggregation
    3. Migration
    4. Coactions
    Show answer

    Answer: A. Ecesis

    Ecological succession is the process of change in the species structure of an ecological community over time. In a denuded habitat (bare ground), the process begins with invasion, which includes migration (arrival of propagules like seeds or spores) and ecesis (establishment of these propagules). Ecesis involves germination of seeds, growth, and reproduction of the pioneer species, allowing them to survive and multiply in the new environment.

Ecology: Definition, Principles, and Levels of Organization

48. The definition of biosphere is :

    Asked in: HPPSC HPAS Prelims 2010

    1. The earth and its atmosphere which is inhabited by living organisms
    2. All living organisms on earth
    3. All the plants on earth
    4. All the animals on earth
    Show answer

    Answer: A. The earth and its atmosphere which is inhabited by living organisms

    The biosphere is the part of the Earth where life exists, including the interactions between living organisms and their environment.

49. Ecology takes into account of :

    Asked in: HPPSC HPAS Prelims 2011

    1. Environmental factors only
    2. Effects of plants on environment
    3. Plant adaptation
    4. Relationship between organism and their en‐ vironment
    Show answer

    Answer: D. Relationship between organism and their en‐ vironment

    Ecology studies the interrelationships between organisms and their environment.

50. Q. 19-21 : Fill in the blanks in the given sentence/paragraph logically using the appropriate set of words from the four options given below the question. 20 Nature is ________ and unchangeable, and it is ________ as to whether its hidden reasons and ________ are ________ to man or not.

    Asked in: HAS Prelims 2023

    1. relentless, indifferent, actions, understandable
    2. persistent, heartless, actions, comprehensible
    3. inexorable, apathetic, activities, explicable
    4. harsh, indifferent, actions, understandable
    Show answer

    Answer: C. inexorable, apathetic, activities, explicable

    - Choosing vocabulary that fits the meaning and tone of the sentence. - Understanding synonyms and their nuances (e.g., relentless vs inexorable, indifferent vs apathetic, understandable vs explicable). - Ensuring grammatical correctness and logical flow.

51. In relation to Environment match the following. (a) Bio‐ (i) Oceans, Seas, River, Lakes etc. sphere (b) Litho‐ (ii) Plants, Animals, Microbes etc. sphere (c) Hydro‐ (iii) Thick gaseous cover sursphere rounding the Earth (d) Atmo‐ (iv) Solid Component of Earth sphere

    Asked in: MPSC CS Prelims 2020

    1. (a)-(iii), (b)-(ii), (c)-(i), (d)-(iv)
    2. (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)
    3. (a)-(ii), (b)-(iv), (c)-(i), (d)-(iii)
    4. (a)-(iii), (b)-(ii), (c)-(iv), (d)-(i)
    Show answer

    Answer: C. (a)-(ii), (b)-(iv), (c)-(i), (d)-(iii)

    - Biosphere: Region on Earth where life exists. - Lithosphere: Earth's solid, rocky outer layer. - Hydrosphere: All water on Earth's surface and underground. - Atmosphere: The gaseous envelope surrounding Earth.

52. "Ecology is the study of structure and function of ecosystem" who defined in 1969?

    Asked in: MPSC CS Prelims 2021

    1. Krebs
    2. Andrewartha
    3. Taylor
    4. Odum
    Show answer

    Answer: D. Odum

    - Eugene Odum, often considered the father of modern ecology, particularly ecosystem ecology, emphasized the study of structure and function of ecosystems. - His definition of ecology as "the study of the structure and function of nature" appeared in his seminal work "Fundamentals of Ecology", first published in 1953, with later editions in 1959 and 1971. The phrasing "structure and function of ecosystem" is closely associated with his ecosystem-centric approach. - While other ecologists like Krebs have made significant contributions and written textbooks, Odum is most strongly linked to this specific definition and the development of the ecosystem concept.

53. Who among the following Scientists coined the term "Ecology" ?

    Asked in: MPSC CS Prelims 2021

    1. Charles Krebs
    2. Emst Heinrich Haeckel
    3. A.G. Tansley
    4. Victor Shelford
    Show answer

    Answer: B. Emst Heinrich Haeckel

    Ernst Haeckel established ecology as a distinct field of study and gave it its name ("Ökologie" in German, derived from Greek "oikos" meaning house or dwelling, and "logos" meaning study).

54. Which one of the following is the correct sequence about various levels of organization of Biosphere?

    Asked in: UPSC NDA 2 2015

    1. Ecosystem—Biosphere — Community — Population
    2. Population — Organism — Eco system — Biosphere
    3. Organism — Community — Population — Biosphere
    4. Organism — Population — Eco system — Biosphere
    Show answer

    Answer: D. Organism — Population — Eco system — Biosphere

    Understanding the hierarchical levels of organization in ecology, from individual organisms to the entire biosphere, is fundamental.

Ecosystem Functions: Productivity, Energy Flow, Trophic Levels

55. In ecosystem terminology, who are the major producers in a terrestrial ecosystem ?

    Asked in: APPSC Group 1 Prelims 2016

    1. Human beings
    2. Phytoplankton
    3. Herbaceous and woody plants
    4. All the given options
    Show answer

    Answer: C. Herbaceous and woody plants

    Herbaceous and woody plants are the fundamental producers in terrestrial ecosystems because they photosynthesize, creating organic matter.

56. Which of the following limits the number of trophic levels in a food chain ?

    Asked in: UPSC CDS 2 2021

    1. Deficient food supply
    2. Polluted air
    3. Decrease in the available energy at higher trophic levels
    4. Parasitic organisms
    Show answer

    Answer: C. Decrease in the available energy at higher trophic levels

    - Energy transfer between trophic levels is inefficient. - Approximately 90% of energy is lost at each step. - The decrease in available energy limits the length of food chains.

57. Energy and nutrients flow from one trophic level to another in an ecosystem. Which one of the following statements correctly describes the direction of flow of energy and nutrients in an ecosystem ?

    Asked in: UPSC CDS 2 2023

    1. Energy flow is cyclic and nutrient flow is uni‐ directional.
    2. Energy flow is unidirectional and nutrient flow is cyclic.
    3. Both energy and nutrient flow are unidirec‐ tional.
    4. Both energy and nutrient flow are cyclic.
    Show answer

    Answer: B. Energy flow is unidirectional and nutrient flow is cyclic.

    Energy enters an ecosystem primarily from the sun (for producers) and is transferred from one trophic level to the next (producers to consumers, etc.). At each transfer, a significant amount of energy is lost as heat, and this energy cannot be reused by organisms in lower trophic levels. Therefore, energy flow is unidirectional and non-cyclic. Nutrients, such as carbon, nitrogen, phosphorus, etc., are continuously cycled within the ecosystem, moving from the environment to organisms and back to the environment through processes like decomposition.

58. 10 percent law is related with

    Asked in: CGPSC Prelims Exam 2016

    1. Transfer of energy as food from one tropic level to other
    2. Transfer of heat from one matter to another
    3. Transfer of Birds from one zone to another
    4. Transfer of water from one zone to another
    Show answer

    Answer: A. Transfer of energy as food from one tropic level to other

    According to the 10 percent law, only about 10% of the energy from one trophic level is transferred to the next trophic level when organisms are consumed. The rest of the energy is lost primarily as heat through metabolic activities or is not consumed.

59. Green Plants in Ecosystem are

    Asked in: CGPSC Prelims Exam 2024

    1. Primary Producer
    2. Primary Consumer
    3. Secondary Consumer
    4. Decomposer
    Show answer

    Answer: A. Primary Producer

    cgpsc 2025-2025 Producers are organisms that create their own food, supporting all other life forms in the ecosystem. Consumers obtain energy by feeding on other organisms (primary consumers eat producers, secondary consumers eat primary consumers, etc.). Decomposers break down dead organic matter.

60. The amount of sun energy trapped by plants is:

    Asked in: UPSC Geoscientist 2020

    1. 1 % - 3 %
    2. 12 % - 15 %
    3. 17 % - 20 %
    4. 23 % - 26 %
    Show answer

    Answer: A. 1 % - 3 %

    Most of the solar energy incident on a plant is not used for photosynthesis; it is reflected, transmitted, or dissipated as heat. Only a small fraction is converted into biomass.

61. Which one of the following ecosystems has the highest net primary productivity?

    Asked in: UPSC Geoscientist 2020

    1. Rainforest
    2. Extreme desert
    3. Lakes and streams
    4. Mid-latitude grassland
    Show answer

    Answer: A. Rainforest

    - Net Primary Productivity (NPP) is the rate at which producers (plants) accumulate biomass or store energy, calculated as Gross Primary Productivity (GPP) minus the energy used in respiration. - Tropical rainforests have ideal conditions for plant growth: high temperatures, abundant rainfall, and high light intensity throughout the year, leading to very high rates of photosynthesis and biomass accumulation.

Ecosystem: Structure and Components

62. A biological community in its environment such as a pond, an ocean, a forest, even an aquarium is known as

    Asked in: UPSC CDS 2 2017

    1. biome
    2. community
    3. abiotic environment
    4. ecosystem
    Show answer

    Answer: D. ecosystem

    An ecosystem is defined as a community of living organisms (biotic components) interacting with the nonliving components (abiotic components) of their environment. The examples given (pond, ocean, forest, aquarium) all represent systems where plants, animals, and other organisms live and interact with physical and chemical factors like water, soil, air, and sunlight.

63. The term soil impoverishment relates to which one of the following ?

    Asked in: UPSC CDS 2 2019

    1. Soil erosion
    2. Soil deposition
    3. Soil getting very deficient in plant nutrients
    4. Soil getting enriched with plant nutrients
    Show answer

    Answer: C. Soil getting very deficient in plant nutrients

    - Impoverishment generally means the process of making something poor or deficient. - In the context of soil, impoverishment refers to the depletion of essential nutrients required for plant growth, such as nitrogen, phosphorus, potassium, etc. - This can occur due to various factors including continuous cropping without replenishment, soil erosion removing fertile topsoil, leaching of nutrients by excessive rainfall, or nutrient imbalance.

64. Which one of the following managed ecosystems has the highest amount of standing crop?

    Asked in: UPSC Geoscientist 2023

    1. Agricultural land
    2. Grazing land
    3. Human habitation
    4. Forest plantation
    Show answer

    Answer: D. Forest plantation

    Standing crop refers to the total biomass present in an ecosystem at a given time. Among the managed ecosystems listed, a forest plantation, especially as it matures, accumulates a very large amount of biomass in the form of trees. This biomass per unit area is significantly higher than that typically found in agricultural land (which is often harvested frequently), grazing land, or areas of human habitation.

65. Which one of the following agricultural systems is an ecosystem metric?

    Asked in: HPPSC HPAS Prelims 2014

    1. Organic farming
    2. Shifting cultivation
    3. High-yielding varieties farming
    4. Growing plants in a greenhouse
    Show answer

    Answer: B. Shifting cultivation

    Shifting cultivation is an agricultural system where forest land is cleared, cultivated for a few years, and then abandoned to allow forest regeneration, with the cultivators moving to a new plot. This system is intimately tied to the forest ecosystem cycle. While the term "ecosystem metric" is unusual phrasing in this context, shifting cultivation is often studied as a specific type of agro-ecosystem, and its characteristics (such as soil fertility decline, forest regeneration time, biodiversity changes) are inherently ecological "metrics" related to the sustainability and impact of the system on the environment. Among the given options, it is the system most fundamentally defined by its interaction with and reliance on natural ecological processes and succession.

66. Which of the following is a biotic component ?

    Asked in: HPPSC HPAS Prelims 2023

    1. Soil
    2. Air
    3. Animal
    4. Water
    Show answer

    Answer: C. Animal

    - Abiotic components are the non-living parts of an ecosystem, such as soil, air, water, sunlight, temperature, etc. - Biotic components include all living organisms, such as plants (producers), animals (consumers), and microorganisms (decomposers).

67. Which of the following statements regarding Soil is/are FALSE? 1. Fertile soil supports plant growth by providing plants with nutrients, acting as a water holding body and serving as the substrate to which plants anchor their roots. 2. Vegetation, tree cover and forest prevents soil degradation and desertification by stabilizing the soil, maintaining water and nutrient cycling. 3. Grass found on pasture lands cannot protect the soil against soil erosion and also inhibits the soil biological activities. Choose the correct answer from the options given below:

    Asked in: HAS Prelims 2022

    1. 1 and 3 only
    2. 2 and 3 only
    3. 2 only
    4. 3 only
    Show answer

    Answer: D. 3 only

    Soil health and stability are heavily influenced by vegetation cover. Grasslands are crucial for preventing soil erosion and supporting soil biological activity.

68. What is 'duff'?

    Asked in: UPSC Geoscientist 2023

    1. Partially decomposed litter
    2. Weathered rock
    3. Muddy puddle
    4. Carcass of a dead animal
    Show answer

    Answer: A. Partially decomposed litter

    'Duff' is an ecological term referring to the layer of organic matter on the floor of a forest or wooded area, consisting of fallen leaves, twigs, and other plant debris in various stages of decomposition. It is the layer above the mineral soil but below the fresh litter.

Food Chains, Food Webs, and Ecological Pyramids

69. Food chain is

    Asked in: UPSC CDS 2 2019

    1. relationship between autotrophic organisms
    2. exchange of genetic material between two or‐ ganisms
    3. passage of food (and thus energy) from one organism to another
    4. modern entrepreneur establishment providing food outlets
    Show answer

    Answer: C. passage of food (and thus energy) from one organism to another

    The essence of a food chain is the transfer of energy and nutrients from one organism to the next through consumption.

70. Which of the following constitute a food- chain ?

    Asked in: CGPSC Prelims Exam 2015 · OPSC CS Prelims 2015

    1. Grass, wheat and mango
    2. Grass, goat and human
    3. Goat, cow and elephant
    4. Grass, fish and goat
    Show answer

    Answer: B. Grass, goat and human

    A food chain depicts the flow of energy from one organism to another. It starts with producers (organisms that make their own food, like plants), followed by consumers. In option B, Grass is a producer, the goat is a primary consumer (herbivore) that eats grass, and a human is a secondary or tertiary consumer (omnivore) that can eat the goat. This represents a valid sequence of energy transfer.

71. What will happen if deer are missing in the foodchain of Grass - Deer - Tiger?

    Asked in: GPSC Prelims CSP 2 2022

    1. The population of both the tiger and grass in‐ creases.
    2. The population of both the tiger and grass de‐ creases.
    3. There will be no impact on the population of both the tiger and grass.
    4. The population of tiger decreases and the grass increases.
    Show answer

    Answer: D. The population of tiger decreases and the grass increases.

    - In the food chain Grass - Deer - Tiger, the deer are the primary consumers (herbivores) that feed on grass (producers), and the tigers are secondary consumers (carnivores) that feed on deer. - If deer are removed from this food chain: - The tigers lose their primary food source. Without deer, the tiger population will decline due to starvation and lack of food. - The grass is no longer consumed by deer. With the removal of this predation pressure, the grass population will likely increase and grow unchecked (assuming no other significant herbivores are present).

72. Inverted Pyramid of Numbers and Biomass, are found in

    Asked in: KPSC KAS Prelims 2014

    1. Parasitic food-chain and forest eco-system re‐ spectively.
    2. Grassland Ecosystem and forest eco-system respectively.
    3. Parasitic food-chain and Pond eco-system re‐ spectively.
    4. Pond eco system and forest eco-system re‐ spectively.
    Show answer

    Answer: C. Parasitic food-chain and Pond eco-system re‐ spectively.

    Ecological pyramids (pyramids of numbers, biomass, and energy) graphically represent the trophic structure of an ecosystem. While pyramids of energy are always upright, pyramids of numbers and biomass can be inverted in certain ecosystems or food chains.

73. The pyramid of energy in any ecosystem is

    Asked in: MPPSC CS Prelims 2020

    1. Always upright
    2. May be upright and inverted
    3. Always inverted
    4. None of the above
    Show answer

    Answer: A. Always upright

    The flow of energy in an ecosystem is unidirectional and follows the 10% law (approximately 10% of the energy from one trophic level is transferred to the next). This fundamental principle ensures that energy pyramids are never inverted.

74. What is Grass-Grasshopper-Frog-Snake- Eagle, foodchain called ?

    Asked in: MPSC CS Prelims 2012

    1. Marshy Ecosystem
    2. Grassland Ecosystem
    3. Agro Ecosystem
    4. Forest Ecosystem
    Show answer

    Answer: B. Grassland Ecosystem

    A food chain starts with the primary producer, which is usually a plant. In the given food chain (Grass-Grasshopper-Frog-Snake-Eagle), 'Grass' is the primary producer. Ecosystems are named based on the dominant type of vegetation or the primary environment. An ecosystem dominated by grass is called a grassland ecosystem. The subsequent organisms in the chain represent different trophic levels within this ecosystem.

75. Which of the following is not the type of Ecological pyramid ?

    Asked in: MPSC CS Prelims 2023

    1. Pyramid of number
    2. Pyramid of biomass
    3. Pyramid of food web
    4. Pyramid of energy
    Show answer

    Answer: C. Pyramid of food web

    The three main types of ecological pyramids are the Pyramid of Number (representing the count of organisms at each level), the Pyramid of Biomass (representing the total mass of organisms), and the Pyramid of Energy (representing the energy flow). A food web is a concept describing the feeding relationships within an ecosystem, not a type of pyramid used to quantitatively represent trophic levels in a hierarchical structure.

Major Terrestrial Biomes

76. Which one of the following statements regarding temperate coniferous forest biome is not correct ?

    Asked in: UPSC CDS 2 2019

    1. They are characterized by very little under‐ growth.
    2. They have a growing period of 50 to 100 days in a year.
    3. There is low variation in annual temperature.
    4. There is high range in spatial distribution of annual precipitation.
    Show answer

    Answer: C. There is low variation in annual temperature.

    Temperate coniferous forests (like Boreal forests or Taiga) are found in high latitudes or on high mountains in temperate regions. These areas are characterized by very cold, long winters and relatively short, mild to warm summers. Therefore, there is a high variation in annual temperature between the extreme seasons, not a low variation.

77. Identify the land biome on the basis of the given characteristics: 1. Their climates are characterised by high rainfall and temperatures that vary from cold to mild. 2. These forests contain primarily deciduous trees – including maple, oak, hickory and beechwood. 3. Raccoons, opossums, bats and squirrels are found in the trees. Select the correct land biome from the options given below:

    Asked in: UPSC NDA 1 2024

    1. Tropical forest
    2. Temperate forest
    3. Boreal forest
    4. Mediterranean forest
    Show answer

    Answer: B. Temperate forest

    Temperate forests are characterized by moderate to high rainfall and distinct seasons, leading to temperature variations from cold in winter to mild in other seasons. They are predominantly composed of deciduous trees (trees that shed their leaves seasonally) like maple, oak, hickory, and beechwood. The fauna described, such as raccoons, opossums, bats, and squirrels, are commonly found in these forests.

78. Broad leaved deciduous forests are typical of :

    Asked in: OPSC CS Prelims 2015

    1. Monsoon region
    2. Mediterranean region
    3. Temperate region
    4. Alpine region
    Show answer

    Answer: C. Temperate region

    Temperate deciduous forests are characterized by trees that shed their leaves annually, typically in autumn, before the cold winter season. This biome is found in regions with distinct warm and cold seasons and moderate precipitation, common in parts of North America, Europe, and Asia within the temperate zones.

79. A habitat of long severe winters and few months of summer constituting the only growing season for plants are the characteristics of :

    Asked in: OPSC CS Prelims 2015

    1. Savannah ecosystem
    2. Tundra ecosystem
    3. Coniferous ecosystem
    4. Taiga ecosystem
    Show answer

    Answer: B. Tundra ecosystem

    - Tundra ecosystems are treeless due to permafrost and harsh conditions. - The growing season is very short (often only a few weeks to months) and occurs during the relatively warmer summer. - Savannahs are tropical/subtropical grasslands. Coniferous forests (Taiga) are found south of the Tundra and have longer growing seasons and dominated by trees.

80. Which of the following forests is known as the "lungs of the planet earth" ?

    Asked in: RPSC RAS Prelims 2013

    1. Taiga forest
    2. Tundra forest
    3. Amazon rain forest
    4. Rain forests of North-East India
    Show answer

    Answer: C. Amazon rain forest

    The Amazon rainforest is the world's largest rainforest and plays a crucial role in regulating the global climate and producing oxygen, leading to it being popularly referred to as the "lungs of the planet earth."

81. Out of total Oxygen present in the earth's atmosphere, the estimated production of oxygen by Amazon forest through photosynthesis is

    Asked in: RPSC RAS Prelims 2023

    1. 40 percent
    2. 50 percent
    3. 70 percent
    4. 20 percent
    Show answer

    Answer: D. 20 percent

    Forests produce oxygen through photosynthesis but also consume it through respiration and decomposition. The net contribution to atmospheric oxygen is not as straightforward as gross production numbers suggest.

82. Which of the following is an example of anthropoogenic biome?

    Asked in: UPPCS Prelims 2018

    1. Fresh water
    2. Crassland
    3. Rain forest
    4. Cropland
    Show answer

    Answer: D. Cropland

    An anthropogenic biome is a biome that is primarily created and maintained by human activities. Croplands are areas of land devoted to agriculture, which are entirely artificial ecosystems shaped and managed by humans for food production.

Population Ecology: Characteristics and Interactions

83. 'Zoonosis' refers to any disease or infection that is naturally transmissible from: (i) human to human (ii) animal to human (iii) animal to animal (iv) bird to animal Select the correct answer using the codes given below.

    Asked in: APSC CCE Prelims Exam 2022

    1. Only (i) and (iii)
    2. Both (i) and (ii)
    3. Both (iii) and (iv)
    4. Only (ii)
    Show answer

    Answer: D. Only (ii)

    The World Health Organization (WHO) defines a zoonosis as "an infectious disease that has jumped from a non-human animal to humans."

84. When two species can very well ignore each other totally, each remaining perfectly neutral and causing no advantage or inconvenience to its neighbour, the relationship is termed as

    Asked in: UPSC Geoscientist 2022

    1. commensalism
    2. amensalism
    3. symbiosis
    4. mutualism
    Show answer

    Answer: C. symbiosis

    - The described relationship (0/0 effect) is called Neutralism. - Neutralism is not listed as an option. - Commensalism (+/0), Amensalism (0/-), and Mutualism (+/+) describe specific interactive effects, none of which are neutral for both parties. - Symbiosis refers to a close and long-term relationship of "living together".

85. In a juvenile ecosystem, the zoocenoses are often

    Asked in: UPSC Geoscientist 2022

    1. monophagous
    2. polyphagous
    3. oligophagous
    4. carnivorous
    Show answer

    Answer: A. monophagous

    - Juvenile ecosystems are characterized by high growth rates and potentially fluctuating resource availability. - Generalist feeding strategies (polyphagy) can be advantageous in such environments, providing resilience to changes in the abundance of specific food items. - Mature ecosystems tend to have more complex food webs and a higher degree of specialization (monophagy, oligophagy) among consumers, as niches become more defined.

86. Which one of the following ecological adaptations is not 'dormancy'?

    Asked in: UPSC Geoscientist 2023

    1. Hibernation
    2. Aestivation
    3. Diapause
    4. Cyclomorphosis
    Show answer

    Answer: D. Cyclomorphosis

    Dormancy is a state of reduced metabolic activity and physiological inactivity in response to unfavorable environmental conditions. Hibernation (winter dormancy), Aestivation (summer dormancy), and Diapause (dormancy in insects, often cued by photoperiod) are all examples of dormancy. Cyclomorphosis refers to seasonal or cyclical changes in the morphology of organisms, particularly plankton, in response to environmental factors like predation pressure or water turbulence, rather than a state of inactivity.

87. Quadrat is generally used to enumerate the number of

    Asked in: UPSC Geoscientist 2023

    1. animals breeding in a pond
    2. burrows present in an anthill
    3. plants present in a unit area
    4. epiphytes on a tree
    Show answer

    Answer: C. plants present in a unit area

    - A quadrat is a sampling frame defining a unit area. - Used in ecological surveys. - Most commonly applied to enumerate sessile or slow-moving organisms. - Ideal for sampling plant populations in a defined area.

88. Study of a single species and the environmental factors in its habitat is called

    Asked in: UPSC CAPF 2017

    1. Genecology
    2. Synecology
    3. Autecology
    4. Ethology
    Show answer

    Answer: C. Autecology

    Autecology is the branch of ecology concerned with the study of the ecological relationships of a single species or population with its environment. It focuses on how an individual species interacts with the biotic and abiotic factors in its habitat, including its adaptations, physiological responses, life cycle, and population dynamics.

89. 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 :

    Asked in: UPSC IAS 2017

    1. 1 only
    2. 2 and 3 only
    3. 1 and 3 only
    4. 1, 2 and 3
    Show answer

    Answer: C. 1 and 3 only

    - Butterflies act as pollinators and are part of the food chain. - Changes in prey population can impact predator populations.