Concept preview

What you will be able to do

1. 01Model population growth as exponential or logistic and explain carrying capacity K.
2. 02Distinguish density-dependent from density-independent limiting factors.
3. 03Describe the five main species interactions and their effect on each partner.
4. 04Explain ecological succession, the value of biodiversity, its threats and conservation.

An ecosystem is easier to understand if we zoom in on one level at a time. A population is all the individuals of a single species living in the same area at the same time — all the rabbits in a meadow, say, or all the oak trees in a wood. A community is all the different populations living and interacting together in that area, and the community plus its non-living surroundings make up the ecosystem. Ecologists study populations closely because their size is never fixed: it rises when births and immigration exceed deaths and emigration, and falls when the reverse is true. Understanding what makes a population grow, level off or crash is central to everything from saving an endangered species to controlling a pest or a disease.