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The number of wild animals which inhabit a habitat over a long period of time are termed the carrying capacity. This differs from habitat to habitat depending on the animals that live there and on what they eat.
The slightest disturbance in this delicate balance, will cause a chain reaction in the ecosystem, affecting all the plants and animals.
The establishment of a new living area and the cultivation of crops can cause a chain reaction and do a great deal of damage to an ecosystem.
Name 2 more disturbances which will cause an imbalance in an ecosystem
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2. INTERESTING
The number of mice in a particular area depends on the availability of seeds to be eaten. In turn, the number of mice determine how many kestrel can live in the area, as they feed on mice.
A certain plant which grows in forests from Natal to Mozambique grows very slowly for the first few years. After 6 years it becomes the dominant plant in the undergrowth. If conditions become favourable (after 7 years) all plants in the forest flower simultaneously. Enough seeds are dispersed and all the plants die. It remains an enigma why the flowering (which so seldom occurs) is followed by death.
After the plants have died there is so much dry material on the forest floor that there is danger of destructive fires. While the plants are in flower the bee-swarms in the forest increase. People visit the forests to rob the hives.
The increase in bees leads to an increase in the number of birds that feed on bees. As the seeds fall to the ground, the number of rats increase to eat it, which in turn results in an increase of small hawks and owls.
When the seeds germinate the rats leave the forest in large numbers and invade the sugar-cane fields. Here they do so much damage that people are obliged to send their cats into the affected areas.
We cannot say what happens to the birds, hawks, owls and cats but this proves that the behaviour of one organism can affect all kinds of other organisms. The relationships between organisms and environments are therefore very complex.
True or false:
(a) Certain plants take many years before flowering.
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(b) Birds eat bees.
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(c) The change in behaviour of one organism will not affect the others.
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Why do rats invade the sugar plantations?
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(d) Select and write down an incorrect statement from among those given below:
- · The number of animals living in a particular area depends on the amount of available food.
- · Dry seeds, leaves and twigs can cause fires, if ignited.
- · Simultaneously means ‘one-by-one’, not all at the same time.
- · Hawks and owls enjoy catching rats.
3. BIOSPHERE
Our environment provides something without which we cannot live, namely natural resources and non-living matter. We need natural resources such as sunlight, fresh air and soil.
From space, planet Earth is seen as a small blue sphere. A closer view, however, reveals that life on earth is only confined to a thin layer (approximately 80 km thick) of water, soil and air. This layer, stretching from the depths of the ocean to the atmosphere, is referred to as a biosphere (living space).
THE EARTH
Assessment
Learning Outcome 2: The learner will know and be able to interpret and apply scientific, technological and environmental knowledge.
Assessment Standard 2.3: We know this when the learner interprets information.