Ecology: The scientific study of the interactions and relationships between organisms and their environment. The term "ecology" was coined by Ernst Haeckel in 1866 (from Greek Oikos 'house' + Logos 'study').
The environment includes:
Biotic factors: All the living components (e.g., plants, animals, bacteria).
Abiotic factors: All the non-living physical and chemical components (e.g., sunlight, temperature, water, soil).
2. Levels of Organization
Ecology studies life at various levels of complexity. These levels are hierarchical:
Organism (Individual): Studies adaptations of a single organism.
Population: A group of individuals of the same species in the same area.
Community: A group of populations of different species interacting in the same area.
Ecosystem: The community (biotic) plus its non-living (abiotic) environment. Focuses on energy flow and nutrient cycling.
Landscape: A mosaic of interconnected ecosystems. For example, a landscape might include patches of forest, grassland, and a lake.
Biome: A large regional community of plants and animals, primarily determined by climate (e.g., desert, tundra, rainforest).
Biosphere: The sum of all parts of the Earth where life exists.
Diagram: A pyramid or flowchart showing the levels: Organism → Population → Community → Ecosystem → Landscape → Biome → Biosphere.
3. Habitat and Ecological Niche
Common Question: Differentiate between habitat and niche.
Habitat = Address (Where it lives)
Niche = Profession (What it does, its role, and its resource requirements)
Habitat
The habitat is the physical place or environment where an organism lives. It's the organism's "address."
Example: The habitat of a pitcher plant is a nutrient-poor bog.
Ecological Niche
The niche is the functional role of a species in an ecosystem. It includes its tolerance to abiotic factors and its resource needs.
G.E. Hutchinson's Niche: An "n-dimensional hypervolume," where each dimension is a resource or environmental factor.
Types of Niches:
Fundamental Niche: The full range of conditions and resources an organism *could potentially* use, with no competition.
Realized Niche: The part of the fundamental niche an organism *actually* occupies due to limiting factors, especially competition.
4. Ecosystem Stability: Resistance & Resilience
Ecosystem stability is the ability to withstand disturbances.
Resistance: The ability to avoid change when a disturbance occurs.
Example: A mature forest is resistant to a mild windstorm.
Resilience: The ability to recover quickly *after* a disturbance.
Example: A grassland is not resistant to fire, but is highly resilient and grows back fast.
5. Branches of Ecology: Autecology & Synecology
Feature
Autecology (Species Ecology)
Synecology (Community Ecology)
Unit of Study
Individual or Population (single species)
Community or Ecosystem (multiple species)
Focus
Adaptation, life history, population dynamics
Species interactions, community structure, energy flow
Example
A study of the water needs of a saguaro cactus.
A study of all plant and animal interactions in the Sonoran Desert.
6. Major Terrestrial Biomes
Biomes are large-scale ecosystems defined by climate (temperature and precipitation) and dominant vegetation.
Biome
Climate
Dominant Vegetation
Key Characteristics
Tropical Rainforest
Hot and wet all year.
Broadleaf evergreen trees.
Highest biodiversity. Nutrient-poor soil.
Savanna
Hot, with distinct wet and dry seasons.
Grasses with scattered trees.
Supports large grazing mammals. Fire-adapted.
Desert
Very dry (low precipitation). Hot or cold.
Succulents, drought-tolerant shrubs.
Water-saving adaptations (e.g., nocturnal).
Temperate Grassland
Moderate precipitation, four seasons.
Grasses.
Very fertile soil. Adapted to fire/grazing.
Temperate Deciduous Forest
Moderate precipitation, four seasons.
Broadleaf deciduous trees (oak, maple).
Trees lose leaves in winter. Rich soil.
Taiga (Boreal Forest)
Cold, with short summers and long winters.
Coniferous evergreen trees (spruce, fir).
Largest biome. Acidic, nutrient-poor soil.
Tundra
Extremely cold and dry.
Mosses, lichens, dwarf shrubs.
Permafrost (permanently frozen subsoil).
7. Ecological Amplitude, Ecotypes & Ecoclines
Ecological Amplitude (Tolerance Range)
The range of an environmental factor (e.g., temperature) within which a species can survive and reproduce.
Stenotopic:Narrow tolerance range (specialists). Example: Coral.
Eurytopic:Wide tolerance range (generalists). Example: Cockroach.
Ecotypes
A genetically distinct population of a species that is adapted to specific local environmental conditions. They can still interbreed with other ecotypes.
Example:Yarrow (Achillea millefolium) plants at high altitudes are genetically dwarf, while those at low altitudes are tall.
Ecoclines (or Clines)
A gradual, continuous change in the traits of a species or community composition over a geographical gradient.
Example: The progressive decrease in tree height as you move up a mountain.
8. Limiting Factors: Liebig's & Shelford's Laws
Liebig’s Law of the Minimum (1840)
This law states that growth is controlled not by the total amount of resources available, but by the scarcest resource (the "limiting factor").
Analogy: The Leaky Barrel. A barrel's capacity to hold water is limited by its shortest stave (plank). It doesn't matter how high the other staves are; water will leak out at the level of the shortest one.
Example: Plant growth in a lake may be limited by the amount of phosphorus, even if nitrogen, sunlight, and water are abundant. Adding more nitrogen will not increase growth; only adding phosphorus will.
Shelford’s Law of Tolerance (1913)
This law expands on Liebig's. It states that an organism's success is determined by a range of environmental factors, and that for each factor, there is a minimum, maximum, and optimum level.
Optimum Range: The level at which the organism functions best and has the largest population.
Zone of Physiological Stress: The levels above and below the optimum, where the organism can survive but is stressed and reproduces poorly.
Zone of Intolerance: The levels below the minimum or above the maximum, where the organism cannot survive.
In short: Too much of a good thing can be just as bad as too little. (e.g., too much water can be as bad as too little).
Diagram: A bell-shaped curve. X-axis = "Environmental Factor" (e.g., Temperature). Y-axis = "Population Size." Label the "Zone of Intolerance" (low ends), "Zone of Stress," and "Optimum Range" (peak of the curve).
9. Ecological Factors
These are the components of the environment that affect organisms. They are broadly classified as abiotic (non-living) and biotic (living).
Climatic Factors (Abiotic)
Temperature: Affects metabolic rates.
Light: Essential for photosynthesis; affects photoperiodism.