5. Environment Notes 01

Elaborate Notes

Basic Concepts of Ecology and Environment

Environment: The term ‘environment’ refers to the sum total of all conditions and influences that surround and affect an organism. While the philosopher Thomas Carlyle provided a generalist view of the environment as “everything that surrounds a life form,” a more scientific definition is crucial. In the Indian context, the Environment (Protection) Act, 1986, defines environment as including water, air, and land and the inter-relationship which exists among and between water, air and land, and human beings, other living creatures, plants, micro-organism and property. It is a composite of both biotic (living) and abiotic (non-living) components.
Ecology: Coined by the German biologist Ernst Haeckel in 1869, the term ‘ecology’ (from the Greek words Oikos meaning ‘house’ or ‘dwelling place’ and Logos meaning ‘study of’) is the scientific study of the interactions between organisms and their environment. It explores the distribution, abundance, and relationships of organisms and their interactions with the environment.
- Autoecology: This branch of ecology focuses on the study of an individual species in relation to its environment. It investigates its life history, population dynamics, behaviour, and adaptations to specific environmental conditions. For example, a study on the specific temperature and soil requirements of the Sal tree (Shorea robusta) would be an autoecological study.
- Synecology: This branch studies the relationship between a group of different species (a community) and their environment. It deals with the composition, structure, and development of communities. For instance, studying the interactions between various plants, animals, and microbes in a tropical rainforest ecosystem constitutes synecology.
Biotic Potential: This term refers to the maximum reproductive capacity of a population of organisms under optimum environmental conditions. It is the unrestrained growth of a population, often represented by an exponential growth curve. In reality, this potential is limited by environmental resistance (e.g., resource scarcity, predation, disease). For instance, a single bacterium, under ideal conditions, could produce a colony outweighing the Earth in a few days, demonstrating its high biotic potential.
Genetic Variation and Environmental Influence:
- Genotype & Ecotype: The genotype is the specific genetic makeup of an individual organism. An ecotype is a distinct population within a species that is genetically adapted to specific local environmental conditions. These variations are heritable. For example, the plant Achillea millefolium (Yarrow) shows different heights when grown at different altitudes in the Sierra Nevada mountains, a classic case study by Clausen, Keck, and Hiesey (1948) demonstrating genetic adaptation to local climates, thus forming different ecotypes.
- Phenotype & Ecad (or Ecophene): The phenotype is the observable physical and biochemical characteristic of an organism, determined by both its genotype and environmental influences. An ecad or ecophene refers to the phenotypic variations within a species that are induced by the environment and are not genetically inherited. For example, two plants with the same genotype may have different leaf sizes or heights depending on the amount of sunlight and nutrients they receive. This non-heritable, environmentally induced variation represents an ecad.
Species’ Response to Environment:
- Species Plasticity: This is the ability of an organism (or a species) to alter its physiology or morphology in response to changing environmental conditions. This capacity is biologically determined but allows for a range of phenotypic expressions from a single genotype. For instance, many plants exhibit plasticity by growing larger leaves in shady conditions to maximize light capture.
- Adaptation: This is an evolutionary process where a species becomes better suited to its habitat. It involves heritable changes in an organism’s traits (structural, physiological, or behavioural) that enhance its survival and reproduction. For example, the thick fur of a polar bear is a structural adaptation to the cold Arctic environment, while the nocturnal behaviour of desert animals is a behavioural adaptation to avoid extreme daytime heat.
Limiting Factors and Species Distribution:
- Tolerance Factors: Based on Shelford’s Law of Tolerance (1913), the success of an organism is dependent on a complex set of conditions, and each organism has a certain minimum, maximum, and optimal environmental factor or set of factors that determine its survival. These are limiting factors. For example, the salinity of water is a tolerance factor for fish; both excessively high and low salinity levels can be lethal.
- Habitat and Range: A habitat is the specific physical place or environment in which an organism lives. A range is the broader geographical area where a species can be found. A species’ range may encompass multiple habitats. For instance, the range of the Bengal Tiger spans across India, Nepal, and Bangladesh, including habitats like grasslands, mangrove swamps, and tropical forests.
- Bioclimatic Frontier: This is the geographical boundary that marks the limit of a species’ range, primarily determined by climatic factors that act as tolerance factors. For example, the treeline on mountains is a bioclimatic frontier for many tree species, determined by factors like low temperature and short growing seasons. Climate change is observed to be shifting these frontiers globally.

Taxonomical Classification

Taxonomy is the science of naming, defining, and classifying groups of biological organisms based on shared characteristics. The modern system was pioneered by Carl Linnaeus in the 18th century.

Domains: This is the highest taxonomic rank. Based on the work of Carl Woese (1977), who studied ribosomal RNA sequences, all life is divided into three domains:
1. Archaea: Single-celled microorganisms that are prokaryotic (lacking a cell nucleus). Many are extremophiles, living in harsh environments like hot springs and salt lakes.
2. Bacteria: A large domain of prokaryotic microorganisms. They are ubiquitous and have diverse metabolic types.
3. Eukarya: Organisms whose cells contain a nucleus and other membrane-bound organelles. This domain includes all animals, plants, fungi, and protists.
Kingdoms: The traditional five-kingdom classification was proposed by R.H. Whittaker in 1969. It is based on cell structure, mode of nutrition, and body organization.
1. Monera: Includes all prokaryotes (Bacteria and Archaea). They are unicellular and have a simple cellular structure.
2. Protista: Eukaryotic, mostly unicellular organisms. Examples include amoeba, paramecium, and algae.
3. Fungi: Eukaryotic, heterotrophic organisms with cell walls made of chitin. They are typically decomposers. Examples include mushrooms and molds.
4. Plantae: Eukaryotic, multicellular autotrophs that perform photosynthesis. They have cell walls made of cellulose.
5. Animalia: Eukaryotic, multicellular heterotrophs that are typically motile. They lack cell walls. This is the largest kingdom.
Hierarchy of Classification (from broad to specific):
- Phylum (in Animalia) / Division (in Plantae): A group of related classes. Organisms in a phylum share a common body plan. For example, Phylum Chordata includes all animals with a notochord (like vertebrates).
- Class: A group of related orders. For instance, within Phylum Chordata, the Class Mammalia includes all animals that have hair/fur and produce milk. Class Reptilia includes chordates with scales that lay eggs on land.
- Order: A group of related families. Within Class Mammalia, the Order Carnivora includes flesh-eating mammals like cats, dogs, and bears.
- Family: A group of related genera. The similarities are more pronounced. Within Order Carnivora, the Family Felidae includes all cat-like animals (e.g., lions, tigers, domestic cats).
- Genus: A group of closely related species. Members of a genus share a recent common ancestor but cannot typically interbreed. For example, the genus Panthera includes lions, tigers, jaguars, and leopards.
- Species: This is the fundamental unit of taxonomic classification. The biological species concept, most famously articulated by Ernst Mayr (1942), defines a species as a group of individuals that can actually or potentially interbreed in nature to produce fertile offspring. They share a common gene pool and have high morphological similarity. For example, Panthera leo (lion) and Panthera tigris (tiger) are different species within the same genus.

Ecosystem

The term ecosystem was coined by Arthur Tansley in 1935. It is a fundamental concept in ecology.

Biosphere: This is the global ecological system integrating all living beings and their relationships, including their interaction with the elements of the lithosphere, geosphere, hydrosphere, and atmosphere. It is the zone of life on Earth, a functional reality rather than a distinct physical layer.
Ecosystem Definition: An ecosystem is a structural and functional unit of the biosphere, where living organisms (biotic community) interact with each other and with their surrounding physical environment (abiotic components). It is a system defined by the flow of energy and the cycling of nutrients. Examples range from a small pond to a vast desert or ocean.
Components of an Ecosystem:
1. Abiotic Components: The non-living chemical and physical parts of the environment, such as sunlight, temperature, water, soil, and atmospheric gases.
2. Biotic Components: All living organisms within the ecosystem, structured into trophic levels.
3. Energy Component: The primary source of energy for most ecosystems on Earth is solar radiation.
Trophic Structure: This refers to the feeding relationships between organisms in an ecosystem. The concept was pioneered by Raymond Lindeman in 1942 with his paper “The Trophic-Dynamic Aspect of Ecology”. Organisms are categorized into trophic levels based on how many steps they are from the original source of energy.
- First Trophic Level: Producers (Autotrophs): Organisms that produce their own food.
  - Photoautotrophs: Use sunlight as an energy source through photosynthesis (e.g., green plants, algae, cyanobacteria).
  - Chemoautotrophs: Use chemical energy to produce food, typically in environments without sunlight, through chemosynthesis (e.g., sulfur-oxidizing bacteria in deep-sea hydrothermal vents).
- Second Trophic Level: Primary Consumers (Herbivores): Organisms that feed on producers (e.g., deer, grasshoppers, zooplankton).
- Third Trophic Level: Secondary Consumers (Carnivores/Omnivores): Organisms that feed on primary consumers (e.g., frogs, foxes, small fish).
- Fourth Trophic Level: Tertiary Consumers (Top Carnivores/Omnivores): Organisms that feed on secondary consumers (e.g., lions, eagles, sharks).
- An ecosystem typically has a maximum of four to five trophic levels because a significant amount of energy is lost (as heat) at each transfer, as described by the 10% rule of energy transfer.
Decomposers and Detritivores: These organisms are crucial for nutrient cycling. They break down dead organic matter and waste products.
- Decomposers: Primarily bacteria and fungi. They digest food externally by secreting enzymes onto the dead organic matter and then absorbing the pre-digested nutrients.
- Saprophytes: A type of decomposer (often used synonymously with fungi) that specifically feeds on dead and decaying organic matter.
- Detritivores: Organisms that ingest dead organic matter (detritus) internally (e.g., earthworms, millipedes). They help in breaking down material for decomposers.

Prelims Pointers

The term ‘ecology’ was coined by Ernst Haeckel in 1869.
The term ‘ecosystem’ was coined by Arthur G. Tansley in 1935.
Autoecology: Study of a single species and its environment.
Synecology: Study of a community of species and their environment.
Biotic Potential: Maximum reproductive rate of a species under ideal conditions.
Genotype: The genetic constitution of an individual organism.
Phenotype: The observable characteristics of an organism, resulting from genotype and environment interaction.
Ecotype: A genetically distinct population within a species adapted to specific local conditions.
Ecad (Ecophene): Phenotypic variation in a species due to environmental factors, which is not heritable.
Shelford’s Law of Tolerance: An organism’s success is determined by a range of environmental factors; too much or too little can be limiting.
Bioclimatic Frontier: The geographical limit of a species’ range determined by climatic factors.
Three Domains of Life (Carl Woese):
1. Archaea
2. Bacteria
3. Eukarya
Five Kingdom Classification (R.H. Whittaker, 1969):
1. Monera (Prokaryotes)
2. Protista (Unicellular Eukaryotes)
3. Fungi (Chitin cell wall, decomposers)
4. Plantae (Cellulose cell wall, autotrophs)
5. Animalia (No cell wall, heterotrophs)
Taxonomic Hierarchy (Descending): Domain → Kingdom → Phylum/Division → Class → Order → Family → Genus → Species.
Species: A group of organisms that can interbreed to produce fertile offspring.
Trophic Levels Concept: Proposed by Raymond Lindeman (1942).
Producers (Autotrophs): First trophic level (e.g., plants).
Primary Consumers (Herbivores): Second trophic level (e.g., deer).
Secondary Consumers (Carnivores): Third trophic level (e.g., fox).
Tertiary Consumers (Top Carnivores): Fourth trophic level (e.g., lion).
Chemoautotrophs: Organisms that derive energy from chemical reactions (e.g., bacteria in deep-sea vents).
Decomposers: Organisms like bacteria and fungi that break down dead organic matter.

Mains Insights

Inter-relationship between Genotype, Phenotype, and Environment:
- Cause-Effect: Environmental pressures (cause) drive natural selection, which acts on the phenotypic variations arising from an organism’s genotype. Over time, this leads to adaptation and the formation of ecotypes.
- Significance for Conservation: Understanding this relationship is vital for conservation biology. Climate change is altering environments faster than many species can adapt genetically. Species with high phenotypic plasticity might cope better in the short term, but long-term survival depends on genetic adaptation. This forms the basis for strategies like assisted migration and identifying climate-resilient populations.
- Historiographical View: The “nature vs. nurture” debate is mirrored here. While classical Darwinism emphasized genetic inheritance (nature), modern ecology recognizes the immense role of environmental factors (nurture) in shaping an organism’s observable traits (phenotype) through plasticity.
The Concept of Limiting Factors and Human Impact:
- Analysis: Human activities are altering the ‘tolerance factors’ for countless species on a global scale. Pollution introduces toxins that exceed tolerance limits, climate change alters temperature and precipitation patterns shifting bioclimatic frontiers, and habitat fragmentation creates physical barriers preventing migration.
- Consequences: When tolerance factors are exceeded, a species faces three choices: adapt, migrate, or perish (extinction). The current rate of environmental change is outpacing the evolutionary capacity for adaptation for many species, leading to range shifts (e.g., species moving towards poles or higher altitudes) and contributing to the sixth mass extinction.
Taxonomy as the Foundation of Biodiversity Conservation:
- Relevance: Effective biodiversity conservation is impossible without accurate taxonomy. We cannot protect what we cannot identify and name. Classification helps in:
  - Assessment: The IUCN Red List of Threatened Species relies on clear species definitions to assess the conservation status of organisms.
  - Legislation: Laws like the Wildlife (Protection) Act, 1972 in India, and international conventions like CITES list species that need protection. Ambiguity in taxonomy can create legal loopholes.
  - Identifying Endemic and Keystone Species: Taxonomy is the first step to identifying species that are unique to a region (endemic) or have a disproportionately large effect on their ecosystem (keystone), which often become conservation priorities.
Ecosystem as a Functional Unit: Implications for Governance:
- Perspective: Viewing the environment not as a collection of separate resources but as an integrated ecosystem (as defined by Tansley) has profound policy implications. It highlights interdependence – damage to one component (e.g., polluting a river) can have cascading effects on the entire system (e.g., harming fish populations, affecting livelihoods of fishers, impacting bird populations).
- Application in GS-II/III: This holistic view supports policies like Integrated Water Resource Management (IWRM), the Ecosystem Approach to fisheries management, and the rationale behind Environmental Impact Assessments (EIA), which aim to predict and mitigate the effects of projects on the entire ecosystem, not just isolated components.

Previous Year Questions

Prelims

Which one of the following is the best description of the term ‘ecosystem’? (UPSC CSE 2015) (a) A community of organisms interacting with one another. (b) That part of the Earth which is inhabited by living organisms. (c) A community of organisms together with the environment in which they live. (d) The flora and fauna of a geographical area.

Answer: (c) Explanation: An ecosystem is defined by the interaction of biotic components (the community of organisms) with their abiotic environment. Option (c) captures this relationship completely.
In the context of an ecosystem, which of the following is/are a correct description of a detritivore? (UPSC CSE 2021 - Modified based on concept)
1. They are organisms that ingest dead organic matter.
2. They include bacteria and fungi.
3. They are primary consumers. Choose the correct answer using the code given below. (a) 1 only (b) 2 and 3 only (c) 1 and 3 only (d) 1, 2 and 3
Answer: (a) Explanation: Detritivores, like earthworms, ingest dead organic matter. Bacteria and fungi are decomposers; they break down organic matter externally. Detritivores are not primary consumers; they feed on dead matter (detritus), not living producers.
Which of the following are decomposer organisms? (UPSC CSE 2021)
1. Virus
2. Fungi
3. Bacteria Select the correct answer using the code given below: (a) 1 and 2 only (b) 2 and 3 only (c) 1 and 3 only (d) 1, 2 and 3
Answer: (b) Explanation: Fungi and Bacteria are the principal decomposers in most ecosystems. Viruses are obligate parasites and are not considered decomposers as they require a living host cell to replicate.
Consider the following: (UPSC CSE 2023)
1. Bacteria
2. Fungi
3. Virus Which of the above can be cultured in an artificial/synthetic medium? (a) 1 and 2 only (b) 2 and 3 only (c) 1 and 3 only (d) 1, 2 and 3
Answer: (a) Explanation: Bacteria and Fungi can be grown on nutrient-rich artificial media (like agar plates) in a laboratory. Viruses lack their own cellular machinery and can only replicate inside living host cells, so they cannot be cultured in a synthetic medium alone.
With reference to the food chains in ecosystems, which of the following kinds of organism is/are known as decomposer organism/organisms? (UPSC CSE 2013)
1. Virus
2. Fungi
3. Bacteria Select the correct answer using the codes given below. (a) 1 only (b) 2 and 3 only (c) 1 and 3 only (d) 1, 2 and 3
Answer: (b) Explanation: This is a recurring theme. Fungi and Bacteria are the primary decomposers. Viruses do not perform this ecological role.

Mains

Define the concept of carrying capacity of an ecosystem as relevant to an environment. Explain how understanding this concept is vital for sustainable development. (UPSC CSE 2019)

Answer: Introduction: The carrying capacity of an ecosystem refers to the maximum population size of a biological species that can be sustained by that specific environment, given the food, habitat, water, and other resources available. The concept, rooted in population ecology, acts as a crucial indicator of ecological balance and limits to growth.

Body: Vitality for Sustainable Development: Understanding carrying capacity is fundamental to achieving sustainable development, which seeks to meet the needs of the present without compromising the ability of future generations to meet their own needs.
1. Resource Management: It provides a scientific basis for managing natural resources. For instance, knowing the carrying capacity of a forest for a herbivore population helps in wildlife management, while understanding the carrying capacity of a watershed guides water allocation for agriculture, industry, and domestic use without causing depletion.
2. Preventing Environmental Degradation: Exceeding the carrying capacity leads to resource depletion, pollution, and ecosystem degradation. For example, overgrazing in the Sahel region exceeded the land’s carrying capacity, leading to desertification. Sustainable practices aim to keep human activities within the regenerative capacity of the ecosystem.
3. Urban Planning: The concept is applicable to urban environments. Cities have a carrying capacity concerning air quality, water supply, waste management, and infrastructure. Unplanned urbanization that ignores these limits leads to slums, pollution, and a decline in the quality of life, which is antithetical to sustainable urban development (SDG 11).
4. Informing Policy and Legislation: The concept underpins environmental regulations. Environmental Impact Assessments (EIA), for instance, implicitly assess whether a proposed project will push the local environment beyond its carrying capacity. Policies on pollution control (e.g., BS-VI norms) are designed to reduce the load on the atmosphere’s carrying capacity for pollutants.
5. Guiding Economic Activity: It challenges the notion of infinite economic growth on a finite planet. It encourages a shift towards a circular economy, resource efficiency, and renewable energy, which reduce the per capita ecological footprint and allow for development within the Earth’s carrying capacity.
Conclusion: The concept of carrying capacity serves as a critical bridge between ecology and economics, reminding us that human well-being is intrinsically linked to the health of our ecosystems. For development to be truly sustainable, it must respect the ecological limits defined by the carrying capacity of our local and global environments.
What is biodiversity? Explain the major threats to biodiversity. How can it be conserved? (UPSC CSE 2019 - Modified to fit basics)

Answer: Introduction: Biodiversity, a portmanteau of “biological diversity,” refers to the variety and variability of life on Earth. It encompasses diversity at three levels: genetic diversity (variety of genes within a species), species diversity (variety of species within a habitat), and ecosystem diversity (variety of ecosystems in a region).

Body: Major Threats to Biodiversity (HIPPO): The primary threats to biodiversity can be summarized by the acronym HIPPO:
1. H - Habitat Loss and Fragmentation: This is the most significant threat. It occurs due to deforestation for agriculture, urbanization, and infrastructure development. When a habitat is fragmented, it creates smaller, isolated populations that are more vulnerable to extinction. The destruction of Amazon rainforests for cattle ranching is a prime example.
2. I - Invasive Alien Species: Species introduced, accidentally or intentionally, into a non-native ecosystem can outcompete native species for resources, introduce diseases, or alter the habitat, leading to the decline of native fauna and flora. The introduction of Nile Perch in Lake Victoria led to the extinction of hundreds of native cichlid fish species.
3. P - Pollution: Pollution of air, water, and soil degrades habitats and harms organisms directly. Acid rain harms forests, plastic pollution affects marine life, and pesticide runoff from farms causes eutrophication in water bodies, creating ‘dead zones’.
4. P - Population Growth (Human): The increasing human population drives higher consumption of natural resources, leading to an expansion of all other threats like habitat loss, pollution, and over-exploitation.
5. O - Over-exploitation: Harvesting species from the wild at rates faster than natural populations can recover. This includes overfishing, overhunting (poaching), and excessive logging. The near-extinction of the Bluefin Tuna due to overfishing is a stark example.
- Climate Change: A cross-cutting threat that exacerbates all others by altering temperature and weather patterns, forcing species to migrate (if possible) and leading to phenomena like coral bleaching.
Conservation Methods: Biodiversity conservation strategies are broadly categorized into two types:
1. In-situ Conservation (On-site): Protecting species in their natural habitats.
  - Method: Establishing protected areas like National Parks, Wildlife Sanctuaries, Biosphere Reserves, and Sacred Groves.
  - Example: Kaziranga National Park in India for the one-horned rhinoceros.
  - Advantage: It conserves the entire ecosystem and allows evolutionary processes to continue.
2. Ex-situ Conservation (Off-site): Conserving species outside their natural habitats.
  - Method: Using institutions like Zoological Parks, Botanical Gardens, Gene Banks, Seed Banks, and captive breeding programs.
  - Example: Cryopreservation of seeds in the Svalbard Global Seed Vault.
  - Advantage: It can save critically endangered species from imminent extinction and provides opportunities for research.
Conclusion: Protecting biodiversity is a moral, ethical, and economic imperative. A comprehensive strategy that combines in-situ and ex-situ methods, backed by strong political will, international cooperation (like CBD, CITES), and active community participation, is essential to halt the current extinction crisis and preserve Earth’s rich biological heritage for future generations.
Discuss the concept of an ecosystem and its functional aspects. (UPSC CSE 2021 - Generalised)

Answer: Introduction: An ecosystem, a term coined by A.G. Tansley, is a fundamental ecological unit comprising a community of living organisms (biotic components) interacting with their physical environment (abiotic components) as a system. These interactions are linked through nutrient cycles and energy flows, creating a stable, self-regulating system.

Body: Concept of an Ecosystem: An ecosystem is defined by its structure and function.
- Structure: Refers to its components, including:
  - Abiotic Components: Non-living factors like sunlight, temperature, water, soil composition, and topography.
  - Biotic Components: Living organisms classified by their feeding relationships into trophic levels: producers (plants), consumers (herbivores, carnivores), and decomposers (bacteria, fungi).
- Function: Refers to the processes that occur within the ecosystem. The key functional aspects are:
Functional Aspects of an Ecosystem:
1. Energy Flow: This is a unidirectional process, typically starting from the sun.
  - Producers capture solar energy via photosynthesis.
  - This energy is transferred through different trophic levels when one organism consumes another.
  - At each transfer, a significant portion of energy (around 90%) is lost as heat, in accordance with the second law of thermodynamics. This limits the number of trophic levels in a food chain, as explained by Lindeman’s 10% rule.
2. Nutrient Cycling (Biogeochemical Cycles): Unlike the one-way flow of energy, nutrients like carbon, nitrogen, and phosphorus are cycled continuously between the biotic and abiotic components of the ecosystem.
  - Decomposers play a critical role by breaking down dead organic matter and returning essential nutrients to the soil and water, making them available for producers again.
  - This cyclical process ensures the sustained availability of essential elements for life.
3. Productivity: This is the rate of biomass generation in an ecosystem.
  - Primary Productivity: The rate at which energy is converted by producers into biomass.
  - Secondary Productivity: The rate of biomass formation by consumers.
  - Ecosystem productivity varies greatly, with tropical rainforests and estuaries being highly productive, while deserts are not.
4. Ecological Succession: This is the process of change in the species structure of an ecological community over time. It is an orderly process that leads from a pioneer community (e.g., lichens on a bare rock) to a stable, mature climax community (e.g., a forest).
5. Homeostasis (Self-regulation): Ecosystems have a capacity to resist change and maintain a state of equilibrium through feedback mechanisms. For example, a rise in a predator population can reduce the prey population, which in turn leads to a decline in the predator population, thus maintaining a balance.
Conclusion: The functional aspects of an ecosystem highlight its dynamic and interconnected nature. Understanding these processes is vital for managing natural resources sustainably and for predicting the consequences of human activities, such as pollution and climate change, which disrupt these delicate functional balances.

GS Notes