Last reviewed 4 Nov 2026 · 2 min read
1. Ecosystem services
The Millennium Ecosystem Assessment (2005) grouped the benefits people get from ecosystems into four types:
| Service | Examples |
|---|---|
| Provisioning | Food, fresh water, timber, fibre, fuel, medicines, genetic resources |
| Regulating | Climate regulation, flood control, water purification, pollination, pest and disease control, erosion control |
| Cultural | Recreation, tourism, spiritual and aesthetic value, education |
| Supporting | Soil formation, nutrient cycling, primary production, habitat — needed for all other services |
2. Valuing ecosystems
- Values may be direct use (timber, fish), indirect use (flood protection), option (future use, e.g. medicines) and non-use / existence value.
- Costanza et al. (1997) estimated the global value of ecosystem services at more than the world's GDP at the time.
- TEEB — The Economics of Ecosystems and Biodiversity (2007 onwards) — makes nature's value visible in decision-making.
- Payment for ecosystem services (PES) — users pay those who protect the service (e.g. a city paying upstream farmers to protect a watershed).
3. Carrying capacity
DefinitionCarrying capacity (K)
The maximum population of a species that an environment can support indefinitely without degrading it, given the food, water, habitat and other resources available.
Population growth models
| Model | Form | Shape |
|---|---|---|
| Exponential | J-shaped curve — unlimited resources | |
| Logistic (Verhulst) | S-shaped (sigmoid) — growth slows as N approaches K |
- r = intrinsic rate of natural increase; N = population; K = carrying capacity.
- Growth is fastest at N = K/2.
- Limiting factors — food, water, space, predators, disease. Liebig's law of the minimum: growth is limited by the scarcest resource; Shelford's law of tolerance: too much or too little of a factor limits survival.
- Overshoot — population exceeds K temporarily, degrading the habitat and causing a crash.
Worked ExampleLogistic growth
A deer population has K = 1,000 and r = 0.2 per year. Growth rate at N = 500: deer per year — the maximum possible.