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Part XX: How Organisms Communicate
The Effect of Chemical Stimuli
An organism cannot live in isolation -
A rabbit eating grass in a field needs to be constantly alert
Some male birds develop colourful plumage so that
HOW ANIMALS COMMUNICATE
The Effect of Stimuli on the Behaviour of an organism
An organism cannot live in isolation - it needs to be able to communicate with other organisms, either of the same species or of different species.
Communication is more evident in animals, although plants also need to communicate with each other at certain stages of their development. For an animal, communication can mean the difference between life or death. Animals have well developed nervous systems which allow them to react quickly to signals given out by other animals.
Animals and plants react to stimuli (sing. stimulus) which may come from other living things or from the environment. A stimulus usually causes the organism which receives it to respond to it. Therefore the stimulus changes the behaviour of the organism in some way.
A rabbit eating grass in a field needs to be constantly alert and must be able to react quickly to stimuli such as movement, a sound or a strange smell in the air. The rabbit responds to these stimuli by quickly moving out of danger. This movement is the response to the stimulus and the rabbit's behaviour has changed from being still and eating to moving out of danger.
Some stimuli are only given out by animals and plants at certain times of the year.
Many animals mate in the Spring. The males of certain species change their behaviour in a way which will attract females, or vice versa. The behaviour of many species of birds can be used as a good example to illustrate this point. Many male birds start to sing in Springtime. Each species of bird has its own particular song to attract females of the same species.
Some male birds develop colourful plumage so that the females will be attracted by a visual stimulus as well as by sound. This is interesting because it shows us that a stimulus not only changes the behaviour of an organism but it can also change the way it grows and develops.
Most stimuli are precise and the behaviour of an organism in response to a stimulus is often immediate. We call this a reflex reaction. A bird will respond to the open mouth of its chick by dropping food into it. This reaction is so automatic that the bird will place the food into an open mouth of a fish at the surface of the water!
Humans also show automatic reactions. New born babies will hold onto something which is put into their hand, such as a finger. This is called the grip reflex. This reflex can also be seen in monkeys and apes - the young use it to hang on to their mothers.
The signals which an organism uses can be visual (sight), sensual (touch), auditory (sound) or chemical. A few animals are able to use an electrical stimulus. Most organisms use more than one type of stimulus. For example, a flower uses colour and scent to attract an insect.
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