This topic covers the basic principles of ecology, including the levels of organization in ecology, key ecological concepts such as ecosystems, populations, and communities, and the interactions between biotic and abiotic factors in the environment.
Introduction to Ecology – Study Notes
1. What Is Ecology?
- Definition: Ecology is the scientific study of interactions among organisms and between organisms and their environment.
- Scope: Ranges from microscopic bacteria in soil to the dynamics of entire biomes and the planet as a whole.
- Goal: Understand patterns and processes that shape the distribution, abundance, and diversity of life.
2. Levels of Ecological Organization
| Level |
Description |
Example |
| Organism |
Individual living being |
A single oak tree |
| Population |
Group of individuals of the same species in a given area |
A herd of white‑tailed deer |
| Community |
All populations that interact in a location |
Forest understory plants, insects, birds, and mammals |
| Ecosystem |
Community + physical (abiotic) environment |
A lake with its fish, algae, water chemistry, and shoreline |
| Biome |
Large geographic area with characteristic climate & life forms |
Temperate deciduous forest, tropical rainforest |
| Biosphere |
All ecosystems on Earth; the global sum of life |
The planet’s combined terrestrial and marine ecosystems |
3. Core Ecological Concepts
-
Habitat vs. Niche
- Habitat: Physical place where an organism lives.
- Niche: The organism’s functional role (resources used, activities, interactions).
-
Energy Flow
- Sun → Producers (photosynthesis) → Primary consumers → Secondary/tertiary consumers → Decomposers
- Energy is lost as heat at each trophic transfer (~10 % efficiency).
-
Matter Cycling
- Elements (C, N, P, S, etc.) cycle through biotic and abiotic components.
- Key cycles: Carbon, Nitrogen, Phosphorus, Water.
-
Population Dynamics
- Growth models:
- Exponential: ( N_{t+1}=rN_t ) (ideal, unlimited resources)
- Logistic: ( N_{t+1}=rN_t\left(1-\frac{N}{K}\right) ) (carrying capacity (K))
- Regulating factors: birth/death rates, immigration/emigration, resource availability, predation, disease.
-
Community Interactions
- Competition (interspecific & intraspecific)
- Predation & herbivory
- Mutualism, commensalism, parasitism
- Facilitation (one species improves conditions for another)
-
Succession
- Primary succession: starts on bare substrate (e.g., volcanic lava).
- Secondary succession: follows disturbance where soil remains (e.g., after fire).
- Climax community: historically viewed as a stable end‑point; now seen as a dynamic mosaic.
-
Biodiversity
- Alpha diversity – species richness within a site.
- Beta diversity – turnover of species between sites.
- Gamma diversity – total diversity across a landscape or region.
4. Major Ecosystem Types
| Ecosystem |
Dominant Climate |
Characteristic Producers |
Typical Consumers |
| Terrestrial Forest |
Varies (tropical, temperate, |
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