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Course Code: MEV-011

Course Title: Fundamentals of Environmental Science and Ecology

Assignment Code: MEV-011/TMA-01/January 2025 to July 2026 session

  1. Explain the key principles of the ecosystem approach to conserving natural resources.
Ans Key Principles of the Ecosystem Approach to Conserving Natural Resources

The ecosystem approach is a strategy for the integrated management of land, water, and living resources that promotes conservation and sustainable use in an equitable way. It was strongly endorsed by the Convention on Biological Diversity (CBD) as the primary framework for action. The approach focuses on maintaining ecosystems in a healthy, productive, and resilient state, so they can continue to provide essential goods and services to humans and other living beings.

Key Principles

  1. Holistic and Integrated Management
    1. Natural resources should be managed as parts of a larger system, rather than in isolation.
    1. Land, water, and biodiversity are interconnected, so decisions should consider ecological, social, and economic linkages.
  2. Sustainability of Use
    1. The use of resources should not compromise the ability of ecosystems to regenerate and continue supporting future generations.
    1. Both consumptive (e.g., timber, fisheries) and non-consumptive (e.g., recreation, cultural values) uses must be sustainable.
  3. Decentralized Decision-Making
    1. Resource management should occur at the lowest possible level, involving local communities and indigenous groups who directly depend on and interact with the ecosystem.
  4. Balance between Conservation and Use
    1. The approach emphasizes conserving ecosystem structure and functions while allowing for sustainable use of resources.
    1. Trade-offs may be necessary but should be managed carefully to maintain ecological integrity.
  5. Adaptive Management
    1. Ecosystems are dynamic and subject to change due to natural processes and human activities.
    1. Management strategies should be flexible, continuously monitored, and adjusted based on new knowledge and changing conditions.
  6. Equity and Stakeholder Participation
    1. The benefits derived from ecosystems should be shared fairly.
    1. Active participation of all stakeholders (government, local communities, private sector, NGOs) is essential for legitimacy and effectiveness.
  7. Ecosystem Services Focus
    1. Management should safeguard ecosystem services such as climate regulation, water purification, soil fertility, pollination, and cultural values.
    1. Recognizing the economic and intrinsic value of these services strengthens conservation efforts.
  8. Long-Term Perspective
    1. Conservation decisions must account for long-term impacts rather than short-term gains.
    1. This ensures ecological resilience and intergenerational equity.

2. Explain the human impact on ecosystem functioning, global energy flow, food security and public health.

Ans Humans are a major driving force in shaping ecosystems and their processes. While development and technology have improved living standards, they have also caused significant disruptions to the natural balance of ecological systems.

1. Impact on Ecosystem Functioning

2. Impact on Global Energy Flow

3. Impact on Food Security

4. Impact on Public Health

3. Explain the causes, types and processes of succession.

Ans Causes, Types, and Processes of Succession

Ecological succession is a fundamental natural process that describes the gradual and predictable changes in species composition, community structure, and ecosystem functioning over time. It explains how simple communities are replaced by more complex ones until a relatively stable ecosystem is established. The causes of succession are varied and can be broadly divided into biotic, climatic, edaphic, and anthropogenic factors. Climatic causes include variations in temperature, rainfall, humidity, light intensity, and wind, which alter the growth and survival of species and drive changes in vegetation patterns. For example, a shift in rainfall may cause grasslands to transform gradually into shrublands or forests. Edaphic causes relate to soil conditions such as pH, texture, fertility, moisture, and erosion. Over time, the weathering of rocks or deposition of sediments can create conditions favorable for new species to colonize, thereby initiating succession. Biotic causes are linked to living organisms—competition for resources, predation, parasitism, grazing, and human activities all influence which species thrive or decline, leading to succession. For instance, overgrazing by herbivores may degrade a grassland and open up opportunities for shrubs or invasive plants to dominate. In addition, disturbances like floods, landslides, volcanic eruptions, forest fires, storms, and human activities such as deforestation, agriculture, or mining often destroy existing communities and set the stage for new successional processes. Thus, succession is driven by both natural and anthropogenic factors that continuously reshape ecosystems.

Succession is broadly classified into different types based on origin, nature, and the environment where it occurs. The two primary categories are primary succession and secondary succession. Primary succession occurs in lifeless areas where there is no pre-existing soil or organic matter, such as newly formed volcanic lava, sand dunes, bare rock surfaces, or glacial retreats. Here, organisms colonize for the first time, beginning with hardy pioneer species like lichens, algae, and mosses that can tolerate extreme conditions and contribute to soil formation. Over centuries, these areas develop into stable ecosystems like forests. In contrast, secondary succession takes place in areas where a biological community previously existed but was disturbed or destroyed, leaving behind soil and seeds. Examples include abandoned agricultural fields, burned forests, or flood-affected lands. Since the soil is already present, secondary succession progresses more quickly than primary succession, often restoring ecosystems within decades. Apart from these, succession is also classified as autogenic succession, driven by changes caused by the organisms themselves, and allogenic succession, driven by external factors such as climate change or soil erosion. Furthermore, based on the environment, succession may be hydrosere (in water bodies like lakes and ponds), xerosere (in dry habitats like deserts or rocks), or lithosere (on bare rocks).

The process of succession unfolds in an orderly sequence of stages. It begins with nudation, where a bare area without any life is exposed due to disturbances or natural processes. This is followed by migration, when seeds, spores, and propagules of pioneer species disperse to the new habitat. Next comes colonization, where these pioneer species establish themselves, often being hardy organisms such as lichens, mosses, and algae that can tolerate harsh conditions. Their growth contributes to soil development by breaking down rocks and accumulating organic matter. This leads to the establishment stage, where new plants like grasses and herbs invade, enriching the soil and providing food for small animals. Gradually, the process advances to the competition and reaction stage, where different species compete for light, water, and nutrients, and their interactions modify the environment. For example, shrubs may outcompete grasses, and later, trees may overshadow shrubs. Over time, more complex communities develop, and biodiversity increases. Finally, succession culminates in the stabilization or climax stage, where a mature, self-sustaining community forms, characterized by a stable balance between producers, consumers, and decomposers. The climax community depends on the region’s climate—tropical rainforests in humid zones, grasslands in dry areas, or tundra in polar regions. Importantly, succession is not always linear; disturbances may set it back or redirect it, but the general tendency is toward greater complexity and stability.

4. Explain the structure and function of ecosystem.

Ans Structure of an Ecosystem

The structure of an ecosystem refers to the living (biotic) and non-living (abiotic) components and their interactions that make up the system.

  1. Abiotic Components – These are the non-living physical and chemical factors that influence life, such as sunlight, temperature, soil, air, water, and nutrients. They provide the basic environment and raw materials for living organisms.
  2. Biotic Components – These are the living organisms in the ecosystem, further classified into:
    1. Producers (Autotrophs): Green plants, algae, and some bacteria that capture solar energy and convert it into chemical energy through photosynthesis.
    1. Consumers (Heterotrophs): Organisms that depend on others for food. They are further divided into:
      1. Primary consumers (herbivores like deer, cows, insects),
      1. Secondary consumers (carnivores like snakes, frogs),
      1. Tertiary consumers (top carnivores like lions, eagles).
    1. Decomposers (Saprotrophs): Microorganisms such as fungi and bacteria that break down dead organic matter into simpler substances, recycling nutrients back into the environment.

Thus, an ecosystem’s structure can be visualized as trophic levels (producers → consumers → decomposers) linked by food chains and food webs, supported by abiotic conditions.

Functions of an Ecosystem

Ecosystems perform vital functions that maintain ecological balance and support life on Earth:

  1. Energy Flow – The primary function of an ecosystem is the flow of energy. Solar energy captured by producers flows through consumers and decomposers in a unidirectional manner, forming food chains and food webs.
  2. Nutrient Cycling (Biogeochemical Cycles) – Ecosystems recycle essential nutrients like carbon, nitrogen, phosphorus, and water, ensuring their continuous availability. For example, decomposers release nutrients back into the soil for reuse by plants.
  3. Ecological Regulation – Ecosystems regulate climate, air quality, and hydrological cycles. Forests maintain rainfall patterns, wetlands filter water, and oceans regulate temperature and carbon storage.
  4. Biological Support – Ecosystems provide habitats for countless species, ensuring biodiversity, genetic resources, and species interactions such as pollination and seed dispersal.
  5. Productivity – Ecosystems contribute to primary productivity (energy captured by producers) and secondary productivity (energy transferred to consumers), forming the basis of the food supply.
  6. Provision of Services – Ecosystems provide food, fuel, fiber, medicine, and cultural benefits to humans, while also regulating processes like flood control, soil fertility, and disease regulation.

5. Explain the biogeochemical cycling of nitrogen and phosphorus.

Ans Biogeochemical Cycling of Nitrogen and Phosphorus

Biogeochemical cycles are natural pathways by which essential elements like nitrogen and phosphorus circulate through the atmosphere, lithosphere, hydrosphere, and biosphere, maintaining ecosystem balance. Both nitrogen and phosphorus are vital nutrients required for growth and survival of living organisms, and their cycles illustrate how these elements move between the environment and organisms.

1. Nitrogen Cycle

Nitrogen is a key component of proteins, nucleic acids (DNA, RNA), and chlorophyll. Although nitrogen gas (N₂) makes up about 78% of the atmosphere, most organisms cannot use it in this form. The nitrogen cycle converts atmospheric nitrogen into biologically usable forms and back again.

Main Processes:

  1. Nitrogen Fixation – Conversion of atmospheric nitrogen (N₂) into ammonia (NH₃) or related compounds.
    1. Biological fixation by nitrogen-fixing bacteria (e.g., Rhizobium, Azotobacter, cyanobacteria) in soil or root nodules.
    1. Abiotic fixation through lightning and industrial processes (Haber-Bosch).
  2. Nitrification – Conversion of ammonia into nitrites (NO₂⁻) and then into nitrates (NO₃⁻) by nitrifying bacteria (Nitrosomonas, Nitrobacter). Nitrates are readily absorbed by plants.
  3. Assimilation – Plants take up nitrates and ammonium to form amino acids, proteins, and nucleic acids. Animals then obtain nitrogen by consuming plants or other animals.
  4. Ammonification – Decomposition of dead organisms and organic waste by bacteria and fungi releases ammonia (NH₃) back into the soil.
  5. Denitrification – Conversion of nitrates back into nitrogen gas (N₂) or nitrous oxide (N₂O) by anaerobic bacteria (Pseudomonas, Clostridium), returning nitrogen to the atmosphere.

Ecological Importance: The nitrogen cycle maintains soil fertility, supports plant growth, and regulates atmospheric nitrogen balance. Human activities such as overuse of fertilizers, industrial emissions, and burning fossil fuels disturb this cycle, leading to eutrophication, acid rain, and greenhouse gas emissions.

2. Phosphorus Cycle

Phosphorus is an essential element for ATP (energy transfer), nucleic acids, phospholipids (cell membranes), and bones and teeth. Unlike nitrogen, carbon, or oxygen, phosphorus does not have a gaseous phase, so its cycle is relatively slow and localized.

Main Processes:

  1. Weathering of Rocks – Phosphate ions (PO₄³⁻) are released into soil and water bodies through the weathering of phosphate-rich rocks.
  2. Absorption by Plants – Plants absorb inorganic phosphates from the soil and incorporate them into organic molecules such as DNA, RNA, and ATP.
  3. Transfer through Food Chain – Herbivores obtain phosphorus from plants, and carnivores from herbivores. Phosphorus is essential for energy metabolism and skeletal development.
  4. Return via Decomposition – Decomposers like bacteria and fungi break down organic matter from dead organisms and excreta, releasing phosphates back into the soil or water.
  5. Sedimentation and Geological Uplift – In aquatic ecosystems, phosphates may be carried to oceans and deposited as sediments, eventually forming phosphate rocks. Over geological time, uplift and weathering reintroduce phosphorus into the cycle.

Ecological Importance: Phosphorus is a limiting nutrient in many ecosystems, meaning its availability often controls plant growth. Excess phosphorus from fertilizers and detergents can cause eutrophication in water bodies, leading to algal blooms and oxygen depletion.