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In order to grow up successfully, a plant or animal must live in the right sort of place. An earthworm, for instance, is the right shape to live in the soil. Its body is constructed in such a way that it can move easily through the soil and feed on the plentiful supply of decaying vegetable matter which occurs there as humus. But if we dig up an earthworm and put it on a sheet of glass, it can neither move freely nor escape from its enemies. If we were to place food in front of it on the glass, the worm would probably be unable to reach it. The soil, therefore, is the earthworm’s natural environment, or what is often called its Habitat.All animals and plants have their particular habitats where they can live successfully and multiply. Some voles, for instance, live in holes in a bank. There they make their nests and rear their young close to their supply of food – insect larvae and wild fruits. Similarly, plants can live only in certain habitats – ferns and mosses require damp places, while species such as ivy prefer a wall or a tree trunk to climb up as they grow.
We must not forget that living things themselves form part of a habitat. One animal or plant may be dependent upon another for its food and even to assist in its reproduction. This is the case in many flowers which, as we have seen, depend upon insects of different kinds to transfer pollen from one flower to fertilize another.
The great naturalist Charles Darwin, who lived over one hundred years ago, discovered that clover could only be pollinated by bees. Because they have longer tongues than some insects, bees can reach the nectar at the bottom of the flowers upon which they feed. In a field of clover, voles often destroy the grass nests and larvae of the bee, and then use the nests in which to rear their own young. The voles are, in turn, eaten by birds of prey such as the owl, which fly over the field. Thus in a single field habitat, there is a community of plants and animals each depending upon the other for its supply of food.
We can summarize the situation as:Clover → bees → voles → owls →
Each separate source of food is like a link in a chain – often known as a Food Chain. What sort of organism would we expect to find at the right hand end of the chain ?
So long as the numbers of plants or animals at each link of the chain do not increase or decrease too much, the population of a habitat can go on living continuously as a Balanced Community.
But what happens if this balance should be upset by altering one or more of the links in the chain ? Suppose a gamekeeper kills off the owls and other birds of prey in the area. The enemies of the vole will then be reduced and the voles can multiply unhindered. With so many to feed, their food will become scarce and the voles will attack and destroy more nests of bumble bees, eating their larvae. This in turn will mean that fewer clover flowers will be pollinated and fewer seeds produced. Soon there will be no clover in the field, and the community will cease to exist.
Thus, by destroying owls, man can upset the balance in a field habitat. But he can do this in other ways as well. By spraying plants with insecticides such as DDT, for instance, he may kill not only insect pests, but also the bees and other useful insects visiting for nectar the flowers of the plants which have been sprayed .
Besides using harmful sprays, man can upset the balance of a community by other means. Many of our rivers are now heavily polluted with chemical waste from factories and even with sewage from town drains. This means that the fish in the rivers may be killed and that, in turn, the water fowl and other birds which feed on the fish may die either of starvation or poisoning.
Growing up means not only getting larger, but also using our senses and our brains to become more aware of the things around us.In this, man differs from all other animals. Not only does he have a memory but he is able to think and reason. That is to say, he is able to plan what he is going to do in the light of his experience, before he actually does it. Before we spray our roadside plants, or turn sewage into our rivers, or take bird’s eggs, we should pause to think what the results of our actions are likely to be.
In other words, we must develop and use
our ability to reason because, in the long run, we are the people who will bear
responsibility for the destruction or the preservation of the places in which
we live. The countryside, as well as being a source of food, is also there for
our enjoyment, and as we grow up we should become aware of how we can all be an
influence for good ( or bad ) in its preservation.
