General introduction. Ecology deals with the structure and functioning of ecosystems. For understanding ecosystems, Environmental Science uses certain basic ideas such as ecological pyramids, biodiversity hotspots and levels of organisation. These concepts help us visualise how energy flows, how life is distributed, and how different units of nature are arranged from smallest to largest. Together, they form a strong conceptual foundation for the entire EVS syllabus.
(a) Ecological pyramid and energy flow
Meaning and definition of ecological pyramid
In any ecosystem, organisms are arranged in trophic levels – producers, primary consumers, secondary consumers, and so on. When these trophic levels are represented graphically as a series of steps or bars stacked one above the other, forming a shape similar to a pyramid, the diagram is called an ecological pyramid.
Definition:
“An ecological pyramid is a graphic representation of the relationship among different trophic levels in an ecosystem, showing their relative number, biomass or energy content in the form of a pyramid.”
The base of the pyramid always represents producers, and higher trophic levels are shown successively above, usually with decreasing size as we go up.
Types of ecological pyramids
In your EVS syllabus, three main types are mentioned:
- Pyramid of numbers: Shows the number of individuals at each trophic level.
- Pyramid of biomass: Shows the total biomass (dry weight) at each trophic level.
- Pyramid of energy: Shows the flow of energy at each trophic level per unit area per unit time.
For understanding energy flow, the pyramid of energy is the most important and always upright.
Concept of energy flow in an ecological pyramid
The basic law of energy flow in ecosystems is described by the unidirectional flow of energy and the 10% law (Lindeman’s law of trophic efficiency):
- Energy enters the ecosystem through producers (green plants), which convert solar energy into chemical energy by photosynthesis.
- This energy is then transferred from one trophic level to the next through feeding (herbivores, carnivores, top carnivores, etc.).
- At each transfer, a large portion of energy is lost as heat through respiration and other processes. On an average, only about 10% of the energy is passed on from one trophic level to the next.
Features of energy flow as shown by the ecological pyramid
- Always upright: The pyramid of energy is always upright because the amount of energy available decreases at each higher trophic level. Higher levels can never have more energy than lower ones.
- Unidirectional: Energy flows in one direction – from sun → producers → consumers → decomposers and finally lost as heat. It cannot be recycled like nutrients.
- Explains limited food chain length: As energy decreases sharply at each level, there are usually only 3–5 trophic levels in any food chain. This is also visible in the pyramid shape.
- Basis for ecological efficiency: The pyramid helps visualise that plant-based diets use energy more efficiently than meat-based diets, which is relevant for human food policy and sustainability.
Exam-point for (a)
- Define ecological pyramid clearly.
- Mention three types (numbers, biomass, energy).
- Emphasise that the pyramid of energy is always upright and shows decreasing energy upwards.
- Explain unidirectional flow and the 10% law in 3–4 lines.
(b) Importance of biodiversity hotspots (three reasons)
Meaning of biodiversity hotspot
The term biodiversity hotspot was introduced by Norman Myers to describe regions that are exceptionally rich in species diversity but are also highly threatened.
Definition (exam-friendly):
“A biodiversity hotspot is a region with a very high level of species richness and endemism (many species found nowhere else), which has already lost a large portion of its original natural vegetation and is under severe threat.”
For example, in India, the Western Ghats–Sri Lanka and the Indo-Burma regions are recognised as global biodiversity hotspots.
Why biodiversity hotspots are important for conservation – three main reasons
1. High species richness and endemism (biological importance)
- Hotspots contain an extraordinary concentration of species, including plants, animals and microorganisms.
- Many of these are endemic species (found only in that region and nowhere else in the world).
- Protecting hotspots therefore means protecting a very large fraction of global biodiversity in relatively small areas.
2. Severe threat and high rate of habitat loss (urgency of conservation)
- Hotspots are characterised not only by richness but also by having lost a major part (often more than 70%) of their original natural habitat due to deforestation, agriculture, urbanisation, etc.
- This means that species living there face a high risk of extinction in the near future.
- Conservation of hotspots is therefore an urgent priority to prevent irreversible loss of unique species and genetic diversity.
3. Efficient use of limited conservation resources (strategic importance)
- Resources for conservation (money, manpower, time) are always limited. It is not possible to protect every place with equal intensity.
- Focusing on biodiversity hotspots allows us to achieve maximum conservation “benefit” per unit effort, because protecting a small hotspot area can save thousands of species.
- Thus, hotspots provide a scientifically justified strategy for prioritising regions in national and global conservation planning.
Additional points (if you have time)
- Many hotspots are also centres of origin of cultivated plants and traditional knowledge, so they have high economic and cultural value.
- They supply important ecosystem services such as regulation of climate, water, and soil fertility, benefiting large human populations.
Exam-point for (b)
- Start with a one-line definition of biodiversity hotspot.
- Then give three clearly labelled reasons – (1) species richness & endemism, (2) severe threat, (3) efficient conservation priority.
- If space allows, add one line each on economic and ecosystem-service value.
(c) Levels of organization in an ecosystem
Concept of levels of organisation
Nature is organised in a hierarchical manner. We can study ecology at various levels – from individual organisms to the entire biosphere. These levels of organisation help us understand ecological relationships step by step and are frequently asked in examinations.
Main levels of organisation relevant to EVS
Commonly accepted ecological levels are:
- Individual (organism)
- Population
- Community
- Ecosystem
- Landscape/biome (sometimes discussed)
- Biosphere
1. Individual (organism)
- The smallest unit of ecological study is a single organism – e.g., one tree, one cow, one fish, one bacterium.
- At this level, ecology deals with how the individual adapts to its environment – tolerance limits, behaviour, physiology, etc.
2. Population
- A population is a group of individuals of the same species living in a particular area at a given time and capable of interbreeding.
- Example: all the deer in a forest, all the mango trees in an orchard, all the humans in a city.
- At this level, ecologists study population size, density, birth and death rates, age structure, growth and regulation.
3. Community
- A community consists of all the populations of different species living and interacting in a particular area.
- Example: the plant community of a grassland, the animal and plant community in a pond.
- This level focuses on species interactions (predation, competition, symbiosis), diversity and community structure (dominant and rare species, stratification).
4. Ecosystem
- An ecosystem is a functional system consisting of a community of living organisms (biotic components) and the non-living environment (abiotic components like air, water, soil, light, temperature) interacting as a unit.
- Examples: a pond ecosystem, forest ecosystem, grassland ecosystem, desert ecosystem.
- At this level, we study energy flow, food chains and food webs, nutrient cycles and ecosystem productivity.
5. Biome / Landscape (optional but good for 15 marks)
- A biome is a large regional unit characterised by a particular climate, soil type and dominant vegetation, such as tropical rain forest, desert, tundra, etc.
- A landscape refers to a cluster of interacting ecosystems within a geographical area.
6. Biosphere
- The biosphere is the highest level of organisation – it includes all living organisms on earth and their interactions with the atmosphere, hydrosphere and lithosphere.
- It is essentially the sum of all ecosystems and biomes on the planet.
Significance of understanding levels of organisation
- Helps in systematic study – from small units (organism) to global systems (biosphere).
- Clarifies that environmental problems (e.g., pollution, climate change, species extinction) can affect different levels and must be analysed appropriately.
- Provides a framework for conservation planning – protecting species, populations, habitats, habitats within ecosystems and the global biosphere.
Exam-point for (c)
- Write the levels in correct order: organism → population → community → ecosystem → biome/landscape → biosphere.
- Give 2–3 lines of explanation and one example for each level.
- End with a one-line significance: “These levels help in systematic ecological study and conservation.”
Overall conclusion (for Q8): Ecological pyramids, biodiversity hotspots and levels of organisation are three central concepts used to understand and manage the natural world. The ecological pyramid explains how energy flows and diminishes through trophic levels, reminding us of the limits of food chains. Biodiversity hotspots highlight priority regions where rich but threatened life-forms must be conserved urgently. Levels of organisation, from individuals to the biosphere, provide a structured way of studying and protecting nature at different scales. Together, these ideas strengthen our ecological understanding and support effective environmental conservation and sustainable development.