4.1 Ecosystems and energy flow

Energy flows in food chains from:

  • producers – the plants – to
  • 1st consumers – plant-eaters to
  • 2nd and 3rd etc consumers – the meat-eaters and parasites- to
  • Decomposers: worms, snails, bacteria, fungi

Pollution and accumulation of persistent chemicals

When certain chemicals enters the food chains, they may accumulate in the fatty tissues or bones and increase in amount for every step in the food chain. Persistent Organic Pollutants (POPs) are regarded as particularly dangerous accumulating chemicals.

Ecosystems can be disrupted

Eosystems may change suddenly or over time. If the change happens over a long period of time, most species can adapt to the new conditions.


Puffin (Alca arctica), Noss, Shetland Islands. Vulnerable species due to changes in the environment and overfishing. Photo: P. Prokosch

Ecosystems may be disrupted through natural causes, such as a natural change in climate, or natural disasters like earthquakes, volcanic eruptions and tsunamies. Human activities may also disrupt ecosystems, locally as well as globally. Human activities may enhance existing natural processes or cycles, such as the greenhouse effect, or create completely new conditions, such as depleting the ozone layer with ozone depleting chemicals, or add POPs to the energy flow in the food chains.

Pollution through high concentrations of waste and secreta may affect water bodies and cause eutrophication.

Ecosystem services
Ecosystem services are the benefits people obtain from ecosystems. These include provisioning services such as food, water, timber, and fiber; regulating services that affect climate, floods, disease, wastes, and water quality; cultural services that provide recreational, aesthetic, and spiritual benefits; and supporting services such as soil formation, photosynthesis, and nutrient cycling
Millennium Ecosystem Assessment – Synthesis

More comprehensive information


Chapter 3 3. Impacts
Chapter 4 4. Ecosystems
4.1 Ecosystems and energy flow
4.2 Forests
4.3 Agricultural land
 4.4 Oceans
Chapter 5 5. Green economy