Understand the basic principles of ecology, including the levels of organization in ecology, the importance of studying ecology, and key ecological concepts.
Introduction to Ecology – Study Notes
1. What Is Ecology?
- Definition: The scientific study of how organisms interact with each other and with their physical environment.
- Scope: Ranges from microscopic interactions (e.g., bacteria and nutrients) to global patterns (e.g., climate change).
2. Levels of Ecological Organization
| Level |
Description |
Typical Scale |
Key Questions |
| Organism |
Individual living entity |
1 m or less |
How does a single organism obtain energy? |
| Population |
Group of conspecific individuals in a given area |
10²–10⁶ individuals |
What controls population size? |
| Community |
All populations of different species that interact in a locale |
Hundreds of species |
How do species coexist? |
| Ecosystem |
Community + abiotic (non‑living) environment |
Watersheds, forests, coral reefs |
How do energy and nutrients flow? |
| Biome |
Large geographic region with characteristic climate & dominant life forms |
Continental scale |
What patterns of vegetation dominate? |
| Biosphere |
All ecosystems on Earth |
Planetary |
How do global processes (e.g., carbon cycle) operate? |
3. Fundamental Ecological Concepts
| Concept |
Core Idea |
Example |
| Habitat |
The physical environment where a species lives |
A pond for amphibians |
| Niche |
The role a species plays (resources used, behavior, interactions) |
The niche of a honeybee: pollinator, nectar feeder |
| Limiting Factors |
Anything that restricts population growth (biotic or abiotic) |
Food scarcity, temperature extremes |
| Carrying Capacity (K) |
Maximum sustainable population size in a given environment |
K of deer in a forest depends on available forage |
| Succession |
Directional change in community composition over time |
Primary succession on volcanic lava → lichens → mosses → forest |
| Energy Flow |
One‑way transfer of energy through trophic levels (producer → consumer → decomposer) |
Sun → phytoplankton → zooplankton → fish → shark |
| Nutrient Cycling |
Recycling of elements (C, N, P, etc.) through biotic and abiotic reservoirs |
Decomposition returns nitrogen to soil |
4. Energy in Ecosystems
- Source: Solar radiation (photosynthesis) → primary production.
- Trophic Levels:
- Producers (autotrophs) – capture solar energy.
- Primary consumers (herbivores) – eat producers.
- Secondary & tertiary consumers (carnivores/omnivores) – eat other consumers.
- Decomposers (fungi, bacteria) – break down dead organic matter.
- Energy Loss: ~10 % of energy transferred to the next level (10 % rule).
- Ecological Pyramids: Visual tools showing decreasing energy, biomass, or number of organisms upward through trophic levels.
5. Matter (Nutrient) Cycles
| Cycle |
Main Processes |
Key Organisms |
| Carbon |
Photosynthesis, respiration, decomposition, combustion |
Plants, microbes, animals |
| Nitrogen |
Nitrogen fixation, nitrification, assimilation, denitrification |
Rhizobia bacteria, nitrifying bacteria |
| Phosphorus |
Weathering → dissolution, uptake, sedimentation |
Plants, fungi, aquatic microbes |
| Water |
Evaporation, transpiration, |
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