Habitat, environment or ecosystem?
Natural ecosystems
Agricultural ecosystems
Food webs
Succession
Succession: A case study |
"No man is an island". This saying is true for all living things. The activities of all organisms affect, and are affected by, their living and non-living surroundings.
Habitat, environment or ecosystem?
An organism's habitat is where it lives (e.g. a freshwater pond or a forest).
Its environment is all the living and non-living features in its habitat which affect its survival.
Its ecosystem is the self-sustaining system in which it and other organisms interact with each other and with the non-living parts of the environment.
A study of an ecosystem therefore includes the energy pathways between organisms (food chains and food webs) as well as the cycling of matter such as water, carbon, oxygen and nitrogen.
Natural ecosystems
In natural ecosystems, matter is cycled with nutrients being returned
to the environment by the action of decomposers, ready for re-use by other
organisms. Water, too, is cycled.
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Agricultural ecosystems
In agricultural ecosystems, however, Man removes the crop of plants or
animal stock, so the nutrients are not cycled. Continual replacement of
nutrients by composting or fertilisers is essential to maintain high productivity.
Food webs
A food web of an ecosystem shows how different food chains link together,
since most animals eat more than one food type and are in turn food for
more than one consumer.
Succession
An ecosystem is not a static situation, but one in which components change
through time.
A pioneer ecosystem is one which is newly-developed after a major environmental upheaval. Fire, flood, drought or volcanic eruption can all leave an area totally devoid of life. Relatively soon, however, seeds will be carried in by wind, water or passing animals. Many will be unable to grow, but some simple plants may be able to germinate, and as they grow they will perhaps change the nature of the soil and trap moisture so that other species can now also develop. Predictable changes will occur as the ecosystem evolves with a greater diversity of organisms and more stability in the food web, as it is not totally dependent on just a few species. Over time the organisms and environment change until finally the mature (climax) ecosystem is produced . This slow evolution of an ecosystem in a predictable direction is called succession because earlier species alter the environment making it more suitable for others coming after.
In Asia and South America, archaeologists are uncovering whole cities
of ancient civilisations which have been totally covered with vegetation
similar to the surrounding jungle. After the humans left, dirt would have
accumulated in crevasses and corners, creating micro-habitats for the
germination of seeds. As they grow, their roots force between cracks in
the stone, weathering it away and creating more soil which in turn holds
more water and can sustain larger plants. Decaying of vegetation and animal
faeces will further enrich and develop the soil, so new organisms can
survive. Eventually the climax ecosystem is reached which is the same
as the surroundings!
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