Levels of organisation
Species → ecosystem.
Species. A group of organisms that can interbreed to produce fertile offspring.
The infertility of hybrids (e.g. mule = horse × donkey) shows the two parents are different species.
Population. All the individuals of ONE species living in a defined area at the same time.
Community. All the populations of all the species living together in an area, interacting.
Ecosystem. A community plus its abiotic (non-living) environment — soil, water, climate. Ecosystems are largely self-sustaining: nutrients cycle, but energy flows through and is lost.
Habitat vs niche.
- Habitat = the place an organism lives (where).
- Niche = its role / how it uses resources (what it does).
Two species cannot occupy exactly the same niche in the same habitat (competitive exclusion principle).
- Species ⊂ population ⊂ community ⊂ ecosystem.
- Habitat (where) vs niche (role).