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

Explanation

An ecosystem can be defined as a functional unit of nature, where living organisms (producers, consumers, and decomposers) interact among themselves and also with the surrounding physical environment. Ecosystems can be of any size and usually encompasses a diverse range of species. E.g. Aquatic Ecosystem. In the ecosystem, biotic and abiotic components are linked together through nutrient cycles and energy flows. Everything that lives in an ecosystem is dependent on the other species and elements that are also part of that ecological community. A damaged or extinct component of an ecosystem has an effect on the entire system.

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.

Explanation

Millennium Ecosystem Assessment (MA) was initiated in 2001 by the United Nations. The objective of the MA was to evaluate how changing ecosystems might affect human well-being as well as the scientific foundation for any necessary action to improve the systems’ conservation and sustainable us-age, as well as their contribution to human well-being. Ecosystem services to the society are in the form of:

1. Provisioning services: food, raw materials, genetic resources, water, etc

2. Regulating services: carbon sequestration and climate regulation

3. Cultural services: tourism and religion

4. Supporting services: that are necessary for the production of all other ecosystem services such as nutrient recycling, crop pollination and soil formation, etc.

Explanation

Phytoplanktons are the primary producers in the marine food chain and hence they are called the ‘grass of the sea’. They contribute more than half of the oxygen in the environment and help in reducing global warming by absorbing human-in-duced carbon dioxide. They are important bioindicators regulating life in oceAns:

Statements 1 is correct: If phytoplankton are destroyed then less CO₂ will be absorbed thereby increasing atmospheric carbon and contributing to global warming. Phytoplankton are responsible for carbon fixation through photosynthesis. They absorb CO₂ from the atmosphere and convert it into organic matter. When phytoplankton die, some of this carbon sinks to the ocean floor, sequestering it for long periods. Statements 2 is correct: Phytoplankton are the primary producers in marine ecosystems forming the base of the food web. They are consumed by zooplankton which in turn are eaten by larger organisms like fish, marine mammals, and seabirds. The destruction of phytoplankton would disrupt the entire marine food chain and can lead to the collapse of fisheries and the decline of marine biodiversity.

Statement 3 is incorrect: The density of ocean water is primarily determined by temperature and salinity and not by the presence of phytoplankton. While phytoplankton can slightly affect water properties through their metabolic activities but their destruction would not cause a drastic decrease in ocean water density.

Explanation

Upwelling is a process in which deep, cold water of the ocean rises toward the surface. Winds blowing across the ocean surface push water away. Water then rises up from beneath the surface to replace the water that was pushed away. This process is known as "upwelling."

Statement 1 is incorrect: Decomposer microorganisms primarily reside in the deep ocean and play a role in breaking down organic matter. Upwelling does not bring decomposers to the surface. Most decomposition occurs at depth and decomposer microbes are not significantly transported to the surface by upwelling.

Statement 2 is correct: Upwelling regions bring nutrients like nitrogen, phosphorus, and iron from deep waters to the surface. These nutrients enhance phytoplankton growth which supports higher trophic levels such as fish and marine mammals. Major upwelling zones include the coasts of Peru, California, and West Africa. These regions contribute to high fishery productivity (Ex: Peru-vian anchovy fishery).

Statement 3 is incorrect: Bottom-dwelling (benthic) organisms such as crustaceans and mollusks are not brought to the surface by upwelling. Upwelling affects water movement but does not displace benthic creatures from the ocean floor.