🌿 Chapter 01 · Topic 01 · Ecology Basics
Ecology Basics & Ecosystem Structure
Definition of ecology, levels of biological organisation, biotic & abiotic components, types of ecosystems, and key concepts like habitat, niche, and ecotone.
What is Ecology?
Ecology is the scientific study of the relationships and interactions between organisms and their environment — both living (biotic) and non-living (abiotic) components.
🔑 Coined by Ernst Haeckel (1866) — from Greek oikos (house) + logos (study). Haeckel defined it as “the study of the economy of nature.”
Branches of Ecology:
- Autecology — study of a single species/organism and its environment (also called population ecology)
- Synecology — study of groups of organisms (communities) and their environment (also called community ecology)
- Landscape Ecology — study of spatial patterns and ecological processes across landscapes
- Global Ecology — study of the biosphere as a whole
Exam Tip: Autecology = Auto (self/single) → one species. Synecology = Syn (together) → community/group.
Levels of Organisation
Ecology operates at multiple levels of biological organisation, from the individual organism to the entire biosphere:
| Level | Description | Example |
|---|---|---|
| Organism | Individual living being | A tiger, a mango tree |
| Population | Group of same species in an area | All tigers in Sundarbans |
| Community | All populations in an area | All organisms in a forest |
| Ecosystem | Community + abiotic environment | A pond, a forest |
| Biome | Large regional ecosystem with similar climate | Tropical rainforest, tundra |
| Biosphere | All ecosystems on Earth combined | The entire living world |
Memory Aid: O-P-C-E-B-B → Organism → Population → Community → Ecosystem → Biome → Biosphere
Ecosystem Structure
An ecosystem has two major structural components:
1. Biotic Components (Living)
- Producers (Autotrophs) — green plants, algae, phytoplankton; synthesise food via photosynthesis
- Consumers (Heterotrophs) — animals that feed on producers or other consumers
- Primary consumers — herbivores (deer, rabbit, grasshopper)
- Secondary consumers — carnivores feeding on herbivores (frog, fox)
- Tertiary consumers — top carnivores (eagle, lion)
- Decomposers (Saprotrophs) — bacteria and fungi; break down dead organic matter; release nutrients back into soil
2. Abiotic Components (Non-living)
- Climatic factors — temperature, light, rainfall, humidity, wind
- Edaphic factors — soil type, soil pH, mineral content, texture
- Aquatic factors — water, dissolved oxygen, salinity, turbidity
- Inorganic substances — CO₂, O₂, N₂, water, minerals
- Organic substances — proteins, carbohydrates, humus
Key Point: Decomposers are sometimes called reducers or microconsumers. They are essential for nutrient cycling and are the link between biotic and abiotic components.
Types of Ecosystems
| Category | Type | Examples |
|---|---|---|
| Natural | Forest | Tropical, temperate, boreal |
| Grassland | Savanna, prairie, steppe | |
| Desert | Hot (Sahara), cold (Ladakh) | |
| Aquatic | Freshwater (pond, river), marine (ocean, coral reef) | |
| Artificial | Cropland / Agro-ecosystem | Paddy fields, wheat farms |
| Enclosed systems | Aquarium, zoo, garden |
Terrestrial vs Aquatic Ecosystems:
- Terrestrial — land-based; influenced by soil, temperature, rainfall; e.g., forests, deserts, grasslands
- Aquatic — water-based; divided into freshwater (lentic: still water; lotic: flowing water) and marine ecosystems
- Wetlands — transitional zones between terrestrial and aquatic; highly productive; e.g., mangroves, marshes
Key Ecosystem Concepts
| Term | Definition | Example |
|---|---|---|
| Habitat | Physical place where an organism lives (the “address”) | A pond is the habitat of a frog |
| Niche | Functional role of an organism in its ecosystem (the “profession”) | A frog’s niche = insect controller |
| Ecotone | Transition zone between two ecosystems | Mangrove between land and sea |
| Edge Effect | Greater species diversity at ecotones than in either adjacent ecosystem | More birds at forest-grassland edge |
| Keystone Species | Species with disproportionately large effect on ecosystem; its removal causes collapse | Sea otter, tiger, elephant |
| Indicator Species | Species whose presence/absence indicates environmental health | Lichens (air quality), mayflies (water quality) |
Habitat vs Niche: Habitat = where an organism lives. Niche = what it does there. Two species can share a habitat but NOT the same niche (Gause’s Competitive Exclusion Principle).
Ecotone Examples for Exam: Mangrove (land-sea), estuary (river-sea), forest edge (forest-grassland), littoral zone (land-water). Ecotones have high biodiversity due to the edge effect.
Revision Checklist
✅ Ecology coined by Ernst Haeckel in 1866
✅ Autecology = single species; Synecology = community
✅ Levels: Organism → Population → Community → Ecosystem → Biome → Biosphere
✅ Biotic = producers, consumers, decomposers
✅ Abiotic = temperature, light, water, soil, minerals
✅ Decomposers = bacteria + fungi; essential for nutrient cycling
✅ Natural ecosystems: forest, grassland, desert, aquatic
✅ Artificial ecosystems: cropland, aquarium
✅ Habitat = address; Niche = profession
✅ Ecotone = transition zone between two ecosystems
✅ Edge effect = higher biodiversity at ecotones
✅ Keystone species — removal causes ecosystem collapse
✅ Two species cannot occupy the same niche (Gause’s Principle)
✅ Autecology = single species; Synecology = community
✅ Levels: Organism → Population → Community → Ecosystem → Biome → Biosphere
✅ Biotic = producers, consumers, decomposers
✅ Abiotic = temperature, light, water, soil, minerals
✅ Decomposers = bacteria + fungi; essential for nutrient cycling
✅ Natural ecosystems: forest, grassland, desert, aquatic
✅ Artificial ecosystems: cropland, aquarium
✅ Habitat = address; Niche = profession
✅ Ecotone = transition zone between two ecosystems
✅ Edge effect = higher biodiversity at ecotones
✅ Keystone species — removal causes ecosystem collapse
✅ Two species cannot occupy the same niche (Gause’s Principle)