Ecosystems

The Biosphere

The biosphere can be divided into ecosystems. Ecosystems are made of groups of organisms living in the same area, and their non-living environment. These groups of organisms are called communities. The area in which a community lives is called a habitat. The organisms which make up a community are constantly interacting with each other and with the non-living environment.

The biosphere can be divided into three different types of environment in which habitats are found. These are the sea water, fresh water and the land. The atmosphere does not contain any permanent habitats, but many animals and plants use it to move from place to place.

Fresh-water

Johnny's Fact File No.69 The largest surfaces of fresh water are those of Lake Superior in Canada (8100km2) and the Amazon river in Brazil (6400km2).

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Fresh-water provides different habitats for animals and plants. In a lake or a pond, the water is mostly still. In a river, however, the water is fast flowing near its source and moves much more slowly near its mouth. The plants in the ponds are fresh water phytoplankton and pondweeds. There may even be plants, such as duckweed and water lilies, floating on the surface of the water.

In rivers, where the water is constantly flowing, the plants are mostly algae which are attached to the river bed. The herbivores and carnivores found in river water need to be adapted to stop them being washed downstream by the flowing water. The animals living near the source of the river would need to be more adapted than those living near the mouth of the river. Pond animals have no need of such adaptations since the water around them does not flow.

One advantage of living in a watery habitat is that the surrounding temperature does not change very much during the day. Also, fast flowing river water mixes well with the oxygen in the air. This means that the water in this habitat has a lot of dissolved oxygen in it. Pond water , however, has less dissolved oxygen. These environmental factors will have an effect on the organisms living in the different habitats.

Seas and Oceans

Johnny's Fact File No.70 The total area of the Earth which is covered by the sea is 363 million km2. This is two thirds of the Earth's surface.

The sea can be divided into three main habitats. These are deep-sea waters, coastal waters and the intertidal areas. In the deep-sea waters there are tiny plants which make up the phytoplankton. The phytoplankton is never found more than 80 metres below the surface of the sea. This restriction exists because sunlight is not able to penetrate beyond a depth of 80 metres.

Johnny's Fact File No.71 80% of the sea water which covers the Earth's surface has a temperature of 5°C. The highest sea water temperature is 30°C in the Red Sea. The lowest sea water temperature is -1,5°C in the Antarctic Ocean.

In coastal waters the plants are phytoplankton and seaweeds. Seaweeds belong to a group of plants called the algae (singular: alga). Seaweeds are not found in deep-sea waters because the need to be attached to a solid surface, such as a rock.
The intertidal zone is covered with sea water when the tide is in and uncovered when the tide is out. The plants in this area are seaweeds. These seaweeds have to survive the violence of waves as the tide moves in and out. The herbivores and carnivores found in this habitat also need to develop ways to remain where they are as the waves crash over them.

Johnny's Fact File No.72 In most of the sea water, oxygen makes up to 34% of the dissolved gases. In cold seas and in deep water there are 8cm3 of dissolved oxygen per 1dm3 of sea water. There is less dissolved oxygen in warm, tropical waters where the figure can be as low as 2cm3 per 1dm3.

The organisms which live in the intertidal zone are adapted to live in a very hostile environment. They are constantly exposed to extremes of temperature and spend part of their lives in water and part of their lives out of it.

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© Paul Billiet and Shirley Burchill 2008