The Biotic enviroment involves all the living organisms that come regularly into contact with each other, how they interact and their mutual influences. An ecosystem consists basically of the following:

Producers | Consumers | Decomposers| Biological Rhytms |

• Producers
  

  Producers are organisms which are able to manufacture organic compounds from inorganic substances from their enviroment. Green plants are able to do this by means of photosynthesis, where the sun provides the necessary energy. Therefore these green plants are the autotrophic organisms or primary producers in most ecosystems.

• Consumers
  

  This component is made up of organisms which cannot make organic compounds from inorganic substances. They are dependant upon autotrophic oraganisms and are the consumers or heterotrophic organisms in an ecosystem. The consumers are further subdivided according to their diet, into:

  • herbivores or plant eaters which are the primary consumers eg. cows, giraffes, elephants, etc;
  • carnivores or meat eaters which are the secondary consumers; some carnivores are called predators (eg. lions, leopard, fish eagle, etc) which catch their prey, kill it and then eat it; others are called scavengers ( eg. vultures) which usually eat what is left by the predators;
  • omnivores eat plant and animal material and can be primary, secondary and tertiary consumers simutaneously; a human beings is a good example of an omnivore.

  The main consumers of an Ecosystem.

• Decomposers
  

  These are usually saprophytic organisms such as bacteria and fungi and that obtain their energy by decomposing the corpses and other dead parts of organisms. They break down all the organic material of the bodies of producers and consumers into inorganic materials that are restored to the soil or water to be reused by producers.

Biological Rhythms (Biorhythms)

Regular rhythmic changes occur in the activities of plants and animals. These are caused by factors such as light and heat from the sun, the tides, seasons, phases of the moon and the rotation of the earth. These regular, rhythmic changes are called biorhythms and they can be divided into:

Daily rhythms Lunar and Tidal rhythms Seasonal rhythms
	Biological Rhythms

• Daily rhythms
  The daily rhythm of light and darkness which repeats every 24 hours as a result of the rotation of the earth, has influences on many organisms.

   

  Examples:
  

  • some animals are more active during the day because of the light and temperature eg. springbok, some birds, etc, while others are active during the night eg. lions, owls and bats;
  • green plants photosynthesize only in daylight;
  • the leaves and flowers of some plants react to light and darkness, eg. the drooping of thorn tree leaves as it gets dark and the flowers of vygies which open as the intensity of the light and temperature inceases;
  • zooplanton in the sea and lakes show daily rhythmic movements; during day they move vertically deeper into the water, away from the light; during the night they come to the surface where they feed on the drifting phytoplankton.

   

• Lunar and Tidal rhythms
  The phases of the moon have an influence on the tides in the sea which, in their turn, influence the behaviour of the marine animals which live in the intertidal zone.

   

  Examples:
  

  • many littoral crabs rhythmically change colour from dark at high tide to pale at low tide;
  • intertidal crustaceans and the eel-like grunion have activities which match the activities of the sea. During the spring tides from March to August, these fish swim in pairs (male and female) onto the beaches a couple of days after each high spring tide. While the female lays her eggs, the male curls around her and immediately releases his sperm cells which then fertilize the eggs. The fish then return to the sea on the next wave. Because the eggs are laid while the tides are gradually lessening, the waves will not reach them until the next high spring tide two weeks later. During this time the eggs develop and hatch and the baby fish are then carried back to the sea on the high spring tide.

   

• Seasonal rhythms
  The behaviour of plants and animals is usually suited to withstand the seasons.

   

  Examples:
  

  • deciduous trees lose their leaves during winter and become dormant;
  • annual plants form seeds which survive the winter or the dry season and germinates after the first spring rains;
  • certain animals hibernate i.e. their heart beat slowly and respiration decreases so that the winter can passed in a type of unconsciousness, eg. bats;
  • adult insects die when the frosts arrive; many spent the winter in the form of eggs and pupae;
  • many animals migrate during the winter to where the weather is warmer eg. swallows; various marine mammals also migrate, mainly between feeding and breeding grounds, eg. wilde beest migrate in response to seasonal rainfall and food availability.

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