Ecology - Geography | Geography for UPSC CSE PDF Download

Fundamental Concepts and Principles of Ecology

Organisms and the Environment:

• Organisms have basic needs for energy and matter obtained from the environment.
• Environment includes abiotic (nonliving) factors like sunlight, soil, temperature, and biotic (living) factors including other organisms.

Niche:

• Niche refers to a species' role in its ecosystem, encompassing its interactions with biotic and abiotic factors.
• Key aspects involve the food it eats and how it acquires food.

Habitat:

• Habitat denotes the physical environment where a species resides and adapts.
• Determined mainly by abiotic factors like temperature and rainfall.

Competitive Exclusion Principle:

• Different species in a habitat must have distinct niches to avoid competition for resources.
• Two species occupying the same niche in the same location will lead to competition and displacement.

The Ecosystem:

• An ecosystem comprises all biotic and abiotic elements in an area, varying in size (e.g., a lake, a log).
• Constant energy inputs (usually sunlight) sustain ecosystems, while matter is recycled (e.g., water, carbon, nitrogen).

Ecosystem Classification:

• Coined by A.G. Tansley, an ecosystem is a self-sustaining unit involving complex interactions between biotic and abiotic components.
• Classified as terrestrial (forests, deserts) and aquatic (ponds, oceans), or manmade (crop lands, aquariums).

Types of Ecosystems:

• Natural Ecosystems:
  • Dependent on solar radiation, providing essentials like food, fuel, and medicines.
  • Some rely on energy subsidies like wind, rain, and tides, like tropical rainforests and coral reefs.
• Manmade Ecosystems:
  • Solar energy-dependent (agricultural fields, aquaculture ponds).
  • Fossil fuel-dependent (urban and industrial ecosystems).

Components of an Ecosystem

Abiotic Components (Nonliving)

Physical Factors:

• Sunlight, temperature, rainfall, humidity, and pressure.
• Sustain and limit organism growth in an ecosystem.

Inorganic Substances:

• Carbon dioxide, nitrogen, oxygen, phosphorus, Sulphur, water, rock, soil, and minerals.

Organic Compounds:

• Carbohydrates, proteins, lipids, and humic substances.
• Act as building blocks for living systems, bridging the gap between biotic and abiotic components.

Biotic Components (Living)

Classified into different groups:

Producers:

• Green plants perform photosynthesis, creating food for the ecosystem.
• Termed autotrophs, absorbing water, nutrients, carbon dioxide, and solar energy.

Consumers:

• Heterotrophs, relying on food synthesized by autotrophs.
• Divided into:
  • Herbivores (e.g., cow, deer, rabbit) feeding directly on plants.
  • Carnivores (e.g., lion, cat, dog) consuming other animals.
  • Omnivores (e.g., humans, pigs, sparrows) feeding on both plants and animals.

Decomposers:

• Also known as saprotrophs, mostly bacteria and fungi.
• Break down dead organic matter of plants and animals, secreting enzymes externally.
• Vital for nutrient recycling, also termed detrivores or detritus feeders.

Ecosystem – Structure and Function

Ecosystem Structure

• Interaction between biotic and abiotic components defines the physical structure of an ecosystem.
• Species composition and stratification are vital structural features:
  • Species Composition: Identifying and enumerating plant and animal species.
  • Stratification: Vertical and horizontal distribution of species across different levels.
• Structural components function collectively, contributing to ecosystem functionality.

Functional Aspects of Structural Components

• Species Composition:
  • A community comprises populations living together in a specific place and time.
  • Different ecosystems exhibit unique species compositions based on habitat and climate.
  • The variety and number of species in a community influence its stability and balance.
• Stratification:
  • Refers to the vertical and horizontal distribution of plants within an ecosystem.
  • In forests, the top canopy consists of tall trees, followed by shorter trees, shrubs, herbs, and grasses.
  • Different layers harbor distinct flora and fauna, forming vertical stratification.
  • Deserts display sparse, discontinuous layers with minimal vegetation and animals, showcasing horizontal stratification.

Functions of Ecosystems

• Ecosystems are complex dynamic systems performing several crucial functions:
  • Energy Flow: Transferring energy through food chains.
  • Nutrient Cycling: Biogeochemical cycles facilitating the movement of nutrients.
  • Ecological Succession: Continuous development or change within ecosystems.
  • Homeostasis: Mechanisms maintaining ecosystem stability through feedback control.
• Examples of ecosystems include natural environments like ponds, lakes, forests, grasslands, and manmade ones such as aquariums, gardens, or lawns.

Energy Flow through Ecosystem

Ecosystem Dynamics and Food Chains

• Food chains and energy flow are essential ecosystem properties that create dynamism.
• Charles Elton introduced the concepts of Food Chain, Food Web, and Ecological Pyramid.

Food Chain

• It's the transfer of food energy from producers to organisms through repeated consumption.
• Each step in the chain is a trophic level.
• Example: Grass → Grasshopper → Frog → Snake → Hawk/Eagle.
• Limited steps due to energy loss as heat, typically 4 or 5 trophic levels.

Trophic Levels in Food Chain

• Autotrophs: Producers converting inorganic material into chemical energy via photosynthesis.
• Gross Primary Production (GPP): Total energy stored in photosynthesis; Net Primary Production (NPP) is the available energy to consumers.
• Herbivores: Primary consumers eating plants directly.
• Carnivores: Secondary or tertiary consumers.
• Omnivores: Eating both plants and animals.
• Decomposers: Recycling nutrients from dead organisms.

Types of Food Chains

• Grazing food chains: From plants to herbivores to carnivores.
• Detritus food chains: From dead organic matter to detritivores and further up the chain.

Food Web

• Interconnected trophic levels form a network called a food web.
• Animals can belong to multiple food chains.
• Represents a more realistic model of energy flow in ecosystems.

Energy Flow and Ecological Pyramid

• Linear energy flow in ecosystems with decreasing energy quantity at successive trophic levels.
• Ecological pyramids: Graphic representations of trophic levels in an ecosystem.

Types of Ecological Pyramids

• Pyramid of number: Represents the number of organisms at each trophic level. May sometimes invert.
• Pyramid of biomass: Depicts the total standing crop biomass at each trophic level, sometimes inverted in aquatic ecosystems.
• Pyramid of energy: Illustrates the total energy at each trophic level, never inverted.

Biogeochemical Cycles

Nutrient Cycling (Biogeochemical Cycles)

• Movement of nutrient elements through an ecosystem is known as nutrient cycling or biogeochemical cycles, involving gaseous and sedimentary cycles.
• Energy flow in ecosystems is linear, while nutrient flow is cyclical within the closed system of the biosphere.

Types of Nutrient Cycles

• Gaseous cycles (e.g., nitrogen, carbon) have reservoirs in the atmosphere, while sedimentary cycles (e.g., sulfur, phosphorus) have reservoirs in Earth's crust.

The Carbon Cycle

• Most significant among biogeochemical cycles, influencing life's composition. Human activities have altered this cycle significantly since the Industrial Revolution.
• Carbon flows among storage pools in the atmosphere, oceans, and land. Increased CO2 concentrations result from human activity, impacting the atmosphere.

Processes in the Carbon Cycle

• Photosynthesis: Green plants utilize CO2 in sunlight, converting it into organic matter and releasing oxygen.
• Respiration: All organisms respire, releasing CO2 into the atmosphere.
• Decomposition: Dead organic matter decomposes, releasing CO2 by microorganisms.
• Combustion: Burning biomass releases carbon dioxide.

Human Impact on the Carbon Cycle

• Large-scale deforestation and fossil fuel consumption in industries, power plants, and automobiles contribute to increased CO2 emissions, a major cause of global warming.

The Nitrogen Cycle

• Nitrogen is crucial for protein and is cycled by various organisms.
• Processes include nitrogen fixation, nitrification, assimilation, ammonification, and denitrification.

Water Cycle (Hydrological Cycle)

• Water, essential for life, cycles through evaporation, condensation, and precipitation.
• Only a small percentage of Earth's water is fresh and available for use, driven by solar radiation and gravity.

Phosphorus Cycle

• Phosphorus, vital for biological structures, is obtained from rocks, absorbed by plants, and passed through the food chain.
• Unlike carbon, phosphorus does not have a significant gaseous exchange with the atmosphere.

Phosphorus in the Environment

• Rocks' weathering releases phosphates, absorbed by plants and further transferred through the food chain, with phosphate solubilizing bacteria aiding in decomposition.

Ecological Succession

Ecological Succession and Definitions

• Hult coined the term "Ecological Succession" referring to orderly community changes. Odum termed it as "Ecosystem Development."
• Ragnar Hult published the first comprehensive study on ecological succession in 1881, recognizing the shift from numerous pioneer communities to stable ones.

Dynamic Nature of Biotic Communities

• Ecological succession involves the replacement of plant and animal communities over time in an area, influenced by both biotic and abiotic factors.

Changes during Succession

• Both plant and animal communities undergo alterations during succession, leading to species colonization and decline.

Sere and Seral Stages

• The sequence of changing communities in an area is termed "sere," with transitional communities known as "seral stages."

Types of Successions

• Primary succession occurs in barren areas, while secondary succession follows disturbances in existing vegetation.

Primary Succession

• Pioneer species colonize bare land, forming a pioneer community. Successive replacement of communities leads to a stable climax community.

Climax Community

• The climax community is mature, complex, and stable, in equilibrium with climate and habitat factors.

Types of Successions based on Moisture

• Xerarch occurs on dry land like bare rock, while hydrarch occurs in water bodies like ponds or lakes.

Secondary Succession

• Results from the disturbance or removal of existing vegetation, often quicker due to the availability of soil nutrients and dormant organisms.

Causes of Ecological Succession

• Initial causes involve habitat destruction by climatic and biotic factors.
• Continuing causes relate to population shifts due to migration, industrialization, and competition.
• Stabilizing causes include land fertility and climatic conditions.

Homeostasis of Ecosystem

• Ecosystems self-regulate and resist changes, maintaining stability through negative feedback mechanisms.

Productivity of Ecosystem

• Ecosystem productivity measures organic matter accumulation over time.
• Types include primary productivity (gross and net), secondary productivity, and net productivity.

Primary Productivity

• Gross primary productivity measures total photosynthesis, while net primary productivity accounts for stored organic matter minus plant respiration.

Secondary Productivity

• Measures energy storage at consumer levels like herbivores, carnivores, and decomposers.

Net Productivity

• Refers to stored organic matter remaining after consumption by heterotrophs, indicating biomass increase in primary producers.

Principles of Ecology

• Ecosystem Overview:

  • Ecosystems are fundamental units that integrate the physical environment and living organisms, allowing the study of interactions between biotic and abiotic components.
  • Autotrophic and heterotrophic components play significant roles within ecosystems.

• Interconnected Components: Biotic and abiotic elements within the biosphere's ecosystem are closely related, facilitating energy, water, chemical, and sediment transfer via large-scale cyclic mechanisms.

• Sustained Life and Ecosystems: Sustained life is a characteristic of ecosystems rather than individual organisms or populations.

• Environmental Principles: Holliman's four environmental principles emphasize material cycles, interrelatedness of systems and problems, finite Earth resources, and nature's refinement of stable ecosystems.

• Uniformitarianism in Processes: Physical and biological processes follow the principle of uniformitarianism, operating similarly across time periods but with varying rates due to human-induced environmental changes.

• Natural Hazards and Biological Communities: Natural hazards affect biological communities, often creating severe risks to both wildlife and humans.

• Organism-Environment Interactions: All living organisms and the physical environment mutually react, with interactions at different levels - positive, negative, or neutral.

• Solar Radiation and Energy Flow: Solar radiation, harnessed via photosynthesis by green plants, drives ecosystem energy flow following thermodynamic laws.

• Trophic Levels and Energy Transfer: Energy moves from lower to higher trophic levels, but higher levels often receive energy from multiple sources.

• Trophic Level Relationships: Principles highlight the relationship between trophic levels, energy transfer, efficiency, and food chain length.

• Biogeochemical Cycles: Inorganic and organic substances circulate via closed biogeochemical cycles among biosphere components.

• Ecosystem Productivity: Ecosystem productivity relies on solar radiation availability and plant efficiency in converting it to chemical energy.

• Ecosystem Stability: Self-regulating mechanisms maintain ecological stability through diversity, complexity, and homeostatic mechanisms.

• Ecosystem Instability: Ecosystems become unstable when unable to adapt to environmental changes.

• Dynamic Nature of Ecosystems: Charles Darwin's evolutionary concepts exemplify the dynamic nature of ecosystems.

• Evolution and Mutation: Concepts of species evolution were challenged by mutation theory, proposing inheritable variations via spontaneous change.

• Sere and Climax Vegetation: Transitional stages of vegetation changes culminate in a stable climax community through succession.

• Successional Changes: Ecological succession and ecosystem development involve changes leading to increased complexity, structure, productivity, soil maturity, and stability.

• Human Impact on Ecosystems: Human activities reduce ecological diversity and complexity by exploiting natural resources.

• Preserving Ecosystem Diversity: Urges the application of ecological knowledge to preserve diversity in a world facing rapid resource depletion.