Ecology, Ecosystem and Functions of Ecosystem: UPSC Previous Year Questions (Environment and Ecology)

Explanation

Decomposers are organisms that primarily feed on dead organisms or the waste from living organisms. Some organisms perform a similar function as decomposers, and are some-times called detritivores. The difference lies in the way decomposers and detritivores break down organic material. Detritivores must digest organic material within their bodies in order to break it down and gain nutrients from it. Decomposers do not need to digest organic material internally in order to break it down. Fungi and Bacteria are examples of decomposers. Scavengers are the one among the first to arrive at a dead organism’s remains. It includes jack-als, wolves, raccoons, and opossums.

Explanation

Ecological succession is the process by which the structure of a biological community evolves over time. In grasslands, the dominance of grasses over trees is maintained due to specific environmental factors.

Option (c) is correct: Grasslands are found in regions with seasonal rainfall or semi-arid conditions where water availability is limited. Grasses are more drought-resistant than trees and can survive with less water. Grasslands are often subject to frequent fires which prevent the establishment of trees. Grasses can quickly regenerate after a fire while trees are more vulnerable and less likely to survive. Thus these factors together maintain the dominance of grasses and prevent the succession to a forest ecosystem.

Option (a), (b) and (d) are incorrect:

Insects and fungi play roles in ecosystems but they are not the primary factors preventing trees from replacing grasses in grasslands. Insects and fungi can affect plant health but they do not determine the overall structure of grassland ecosystems. Limited Sunlight and Paucity of Nutrients are not the primary limiting factor for tree growth. In fact grasses are highly efficient at utilizing available nutrients and sunlight which allows them to dominate these ecosystems.

Explanation

Productivity is the rate of biomass production. It is measured in mass per unit volume per unit time. The quantity of biomass or organic matter created by plants during photosynthesis per unit area during a certain time is referred to as primary production. Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis. A considerable amount of GPP is utilized by plants in respiration.

Option (c) is correct: The correct sequence of ecosystems in decreasing order of productivity is Mangroves > Grasslands > Lakes > Oceans Mangroves have the highest productivity due to abundant nutrients, tidal action, and high photosynthetic rates making them crucial breeding grounds for marine life (NPP: ~2000 gC/m²/year). Grasslands follow, as they receive ample sunlight but have moderate water availability, supporting rapid grass growth (NPP: ~600-1500 gC/m²/year). Lakes are less productive than grasslands because nutrient availability varies with depth and type (eutrophic lakes are more productive than oligotrophic ones) (NPP: ~300-1000 gC/m²/year). Oceans have the lowest productivity, as vast open waters are nutrient-poor, and deep layers receive minimal sunlight, though coastal areas and coral reefs are exceptions (NPP: ~50-200 gC/m²/year).

Explanation

Food Chain is the successive transfer of nutrients and energy from one creature to another. A food chain shows a straightforward relationship and only one component of the food or energy flow. E.g. Grasses Grasshopper Frog Snake Hawk/Eagle.

Statement 1 is correct: A food chain is a linear flow of energy and nutrients from one organism to another. Primary producers primary consumers secondary consumers tertiary consumers. Statements 2 and 3 are incorrect:

Food chains are not limited to a single species or population. They involve multiple species across different trophic levels (e.g., producers, primary consumers, secondary consumers). A food chain represents interactions between different species, not within a single population. A food chain does not illustrate the numbers of organisms eaten by others. It shows the sequence of energy transfer and feeding relationships. The number of organisms at each trophic level is better represented by a food web or ecological pyramid (e.g., pyramid of numbers, pyramid of biomass).

Explanation

An ecological niche refers to both the physical space an organism occupies and its functional role in an ecosystem, including its interactions with other organisms, resource utilization, and contribution to energy flow and nutrient cycling. The concept was introduced by Joseph Grinnell (1917) and further developed by G. Evelyn Hutchinson (1957).

Option (a), (c) and (d) are incorrect:

Ecotone is transition zone between two different ecosystems such as a mangrove forest between land and sea. It does not define the functional role of an organism. Habitat is the physical location where an organism lives (e.g., a pond for a frog) but does not describe its interactions and role in the ecosystem. Home range is the area in which animal regularly moves within for feeding and other activities, but it does not account for ecological interactions.

Explanation

About 71% of the earth’s surface is covered with water. Out of the total water present on the planet earth, the majority is in the form of seas and oceans (more than 97%) and is termed as saline water. While the remaining water is termed as freshwater.

Option (c) is correct: The decreasing order of proportion of freshwater in different forms: Snow caps, icebergs and glaciers groundwater soil moistures freshwater lakes atmosphere rivers. Groundwater makes the largest portion of freshwater after freshwater that exists as ice caps and glaciers.