Ecology, Environment & Biodiversity – Lecture 1: Introduction to Ecology

Mizoram Civil Service Exam Notes | Environment Series

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If you’re preparing for UPSC, MPSC, or any state civil services exam, Environment & Ecology is one of the most scoring subjects. These are my personal notes from coaching class, converted into blog format so you can study anytime, anywhere.

Let’s start from the very beginning — What is Ecology?

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What is Ecology?

• The word Ecology comes from the Greek word oikology — derived from oikos (house/home/habitat) + logos (study).
• (Interesting fact: The word “economics” also comes from oikos — oikonomy means “house keeping”)
• The term Ecology was coined by Ernst Haeckel in 1866, a German zoologist.
• Ecology means the study of the house or the habitat of an organism — a living animal or plant.

Key Definitions of Ecology

Scholar	Year	Definition
Elton	1927	“The study of animals and plants in relation to their habits and habitats”
Odum	1971	“Scientific study of the structure and function of nature”
Krebs	1978	“The scientific study of interactions that determine the distribution and abundance of organisms”

MPSC 2012 Question: Who first used and defined “ecology” in 1866?
Answer: (b) Haeckel

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Branches of Ecology

1. Autecology (Ecology of Individuals)

• Also known as ecology of individuals
• Unit of study = individual organism
• Studies details of their geographic distribution, morphology, taxonomic position, and life cycles

2. Synecology (Ecology of Groups)

• Studies groups of organisms (communities)
• Focuses on natural groups affecting each other’s life
• Unit of study = community

Exam Tip: The branch of ecology which deals with individual organisms as a unit of study is known as (a) Autecology

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Factors Influencing Ecology

Ecological factors are broadly divided into two types:

Biotic Factors (Living)

• Autotrophs — producers
• Heterotrophs — consumers
• Decomposers — break down organic matter

Abiotic Factors (Non-living)

• Light
• Temperature
• Water
• Atmospheric gases
• Wind
• Soil
• Physiographic factors

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Biotic Factors in Detail

Autotrophs

• Produce organic compounds on their own
• Derive chemical energy from carbohydrate food molecules (C₆H₁₂O₆)
• Production needs:
• Carbon source → CO₂
• Energy → Light or reaction of inorganic compounds
• Light energy (free energy) → converted into chemical energy (potential energy), i.e., food like sugar

Types of Autotrophs:

• Photolithoautotrophs — organisms using light (plants, algae, etc.)
• Chemolithoautotrophs — organisms using oxidation of inorganic compounds (some bacteria)
• Autotrophs that transform sunlight to make food → Photosynthesis
• Using inorganic compounds → Chemosynthesis

MPSC 2012: Which organism does not require sunlight to live?
Answer: (a) Chemosynthetic bacteria

UPSC 2014: Which is the process involved in photosynthesis?
Answer: (b) Free energy is converted into potential energy and stored

UPSC Question: The synthesis of organic compounds from inorganic compounds utilizing energy stored in inorganic substance is called?
Answer: (b) Chemosynthesis

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Heterotrophs

• Organisms that obtain carbon for growth and development from other organic substrates
• Examples: Fungi, some bacteria, animals (Herbivores, Carnivores, Omnivores)
• Depend on autotrophs at various trophic levels (1° 2° 3° 4° 5° … upto)

Classic Food Chain Example:

Grass → Grasshopper → Frog → Snake → Eagle

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Decomposers

• Organisms that break down organic materials to gain nutrition and energy
• They release raw nutrients into the environment after breaking down
• Examples: Bacteria, Fungi (Note: NOT viruses — decomposers do not contain viruses)

UPSC 2013: With respect to food chain, which organisms are decomposers?

1. Virus 2. Fungi 3. Bacteria
   Answer: (b) 2 and 3 only

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Abiotic Factors in Detail

Light

• Light energy (sunlight) is the primary source of energy for all ecosystems
• Used by green plants during photosynthesis
• Key factors of light that play an important role:
• Quality of light — blue and red are the two bands of light that plants can absorb
• Intensity of light — depends on latitude and season
• Length of light period (Photoperiod) — categorized as:
  • (i) Long day
  • (ii) Short day
  • (iii) Day neutral

Plant Types Based on Light Period:

• Long Day Plants → related to the darkness to which the plant is exposed; does not require a lot of light; no flowering if exceeded
• Short Day Plants → require a minimum length of dark period/night
• Day Neutral Plants → light period does not matter for them

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Temperature

• Contributes to erosion and creation of soil
• Different organisms have different cellular tolerances for cold and heat

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Water

• Important component in erosion and generation of soils
• Terrestrial and freshwater environments require animals and plants to conserve water and evolve ways to maintain water/salt balance

Plants Categorized by Water Adaptation:

Type	Description	Example
Xerophyte	Evolutionary adaptations for dry/xeric environments; requires minimum water	Cactus
Hydrophyte	Evolutionary adaptations for wet/hydric environments; requires large amount of water	Lotus, Hyacinth
Mesophyte	Evolutionary adaptations for moderate conditions	All land plants

Exam Question: The plants which can survive with minimum quantity of water?
Answer: (d) Xerophytes

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Atmospheric Gases

• Most important gases used by plants and animals:
• Oxygen — Respiration
• Carbon Dioxide — Photosynthesis (plants)
• Nitrogen — Lightning & bacteria → plant nutrition

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Soil (Abiotic Factor — continued from Lecture 1)

• Has physical, chemical, and biological properties
• Properties include: colour, texture, structure, moisture, air, density, bulkiness
• Key soil characteristics: pH, cation exchange capacity, anion (AEC), base saturation

Soil particle sizes:

• Clay: < 0.002 mm
• Silt: 0.002 – 0.02 mm
• Fine sand: 0.02 – 0.2 mm
• Coarse sand: 0.2 mm – 2 mm
• Gravel: > 2 mm

Biological prep of soil: Roots of trees, microorganisms in soil (bacteria, actinomycetes), worms, rodents, etc.

Physiographic Factors

• Altitude, latitude, slope, aspect, etc.

Quick Revision Summary

Topic	Key Point
Ecology coined by	Ernst Haeckel, 1866
Autecology	Individual organisms
Synecology	Groups/communities
Autotrophs	Make their own food
Heterotrophs	Depend on others
Decomposers	Break down organic matter
Photosynthesis	Light energy → chemical energy
Chemosynthesis	Inorganic compounds → organic compounds
Xerophyte	Dry environment plants (e.g., cactus)
Hydrophyte	Wet environment plants (e.g., lotus)

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This wraps up our introduction to the core pillars of Ecology!
Did the notes clarify the foundational definition of ecology, the critical distinction between Autecology and Synecology, and exactly how previous MPSC/UPSC questions target biotic and abiotic factors? I’ll post the next chapter soon.