B7.4 What can we learn from natural ecosystems?

B7.4 What can we learn from natural ecosystems?

In a perfect closed loop system no material enter or leave the system – waste products from one organism or process are used by another organism or process – the output from one part of the system becomes the input to another part.

In reality, it is impossible to have a perfect closed loop system in an ecosystem – this is because organisms migrate out of the area and some nutrients are transported away by the wind, rain or rivers.

In stable ecosystems including rainforests, the output (loses) is balanced by gains.

An ecosystem is a type of closed loop system since most waste materials are not lost but are used as food or reactants.

Within a natural ecosystem, most waste materials are not lost – they can be used as food or reactants for animals, plants and microorganisms:

  • Oxygen is waste product from photosynthesis – it is used in respiration
  • Carbon dioxide is a waste product from respiration – it is used in photosynthesis
  • Dead organic matter (e.g. fallen leaves, fruits, flowers, faeces, remains of bodies) is used directly as food or processed into useful nutrients by microorganisms – these microorganisms use digestive enzymes to break down complex molecules into simpler nutrients.

Different organisms have very different approaches to achieving successful reproduction

To reproduce successfully, organisms need to maximise the chances of the offspring reaching adulthood and reproducing themselves.

Females usually produce a large number of eggs, while males produce large quantities of sperm – this ensures a high chance that at least one successful fertilisation will occur.

When organisms produce large numbers of reproductive cells (such as pollen, sperm and eggs) or reproductive structures (such as flowers and fruit), these ensure that reproduction is likely to be successful.

The unsuccessful cells and structures are recycled into the ecosystem – they are usually used as nutrients for animals or microorganisms.

In stable ecosystems the production of large quantities of these reproductive structures is not wasteful, since the surplus (the number of animals in a given population that are “above” the carrying capacity.




Vegetation is an essential part of many ecosystems:

  • Roots help to stabilise the soil – preventing it from being eroded by heavy rain (especially in rainforests). Vegetation also reduces soil erosion since foliage protects the soil from direct rainfall
  • Trees provide shade from the sun and help to insulate the forest floor at night – therefore stabilising the temperature
  • Transpiration from trees helps to promote cloud formation

Humans benefit from and depend on ecosystems to provide a huge range of resources and processes – these are known as “ecosystem services” – for example:

  • Providing clean water and air
  • Pollination of crops
  • Fertile soil
  • Mineral nutrients
  • Fish
  • Game – wild animals that are hunted for their meat, such as grouse, wild salmon and deer

However, human activities often affect ecosystems in negative ways because human systems are not closed loop systems because some waste leaves the system.

Human waste from households, agriculture and industry leaves the system as non-recycled waste, as well as through pollution from burning fossil fuels – this means the system is losing resources.

Sometimes the waste can build up to harmful, which then affect other organisms – bioaccumulation is when toxins build up in a food chain – the animals at the top of the food chain are affected most severely:

Human activities can unbalance an ecosystem, changing the inputs and outputs so much that the ecosystem can no longer adapt – this means that the system is no longer a closed loop.

Eutrophication is where an excess of nutrients is put into a system, causing the productivity of the system to increase while causing the balance of organisms to change, often drastically and irreversibly.

When humans take away too many resources as biomass, then this reduces the amount available to be recycled within the ecosystems.

For example cutting down a rainforest for wood removes a large number of trees – the tree canopies would have protected the soil from rainfall and the roots would have bound the soil together – the tress would have also provided habitats for other organism.

Removing too many trees causes the closed ecosystem to become open – the soil dries out and is blown away and the organisms that relied on the trees for survival die

Another example is overfishing

In some parts of the world, natural vegetation has been removed and replaced with crops for food or the production of fuels (called biofuels) or by grazing animals

As well as destroying the natural habitat and reducing biodiversity, soil erosion can cause rivers to become clogged up with silt, plus the lack of shade and moisture in the soil can cause desertification.

The use of natural resources by humans can only be sustainable if used at a rate at which they can be replaced

Crude oil is formed from the remains of plants and animals that died millions of years ago – the biomass is covered by silt and rock and subjected to immense pressure and heat – over millions of years this causes the biomass to be converted into oil.

The use of crude oil does not fulfil the requirements of a closed loop system because:

  • Crude oil takes millions of years to form from the decay of dead organisms
  • Energy released from burning crude oil originated from the Sun when these organisms were alive (“fossil sunlight energy”).

Sunlight is a sustainable source of energy – it will not run out for another five billion years – and it allows sustainable agriculture and the growth of natural ecosystems.

Fish populations can be preserved if quotas (a limited amount of something, often specified by law – e.g. there are quotas on fishing that cannot be exceeded) are observed which means that each country has an entitlement to catch only a certain number of each type of fish. Some animal population can be restocked

Forests can be preserved if the trees are replanted – sustainable cropping of forests – involves cutting down selected trees in an area – can also be adopted to maintain the forest ecosystem.

Sometimes, there are tensions between conservation efforts and the needs of local communities. For example, even though the process of mining for gold in the Brazilian rainforest damages the natural ecosystem, the people employed as miners still need to earn money to support their families.