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DIDAVISION


SIZE, SHAPE AND LIFE, Part II


SIZE, SHAPE AND LIFE, Part II
SIZE, SHAPE AND LIFE, Part II

Human beings tend to attribute their success exclusively to their intelligence. They usually forget another determining factor: their size. The world of small animals, however, is brimming with fascinating surprises, some of which are precisely related to their small size and the extraordinary variety of their different shapes.


The insects, the real champions of evolution
- Insects surpass the number of 800.000 species. In fact, the true number of insects is estimated as being more than 2 million.
- Despite their tiny size, insects have been able to colonise practically all the regions of the planet except for seas.
- What would happen if one of these small animals grew until it reached the size of an average mammal?

Advantages and drawbacks of being small
- Insects: the first thing that catches our eye is their small size.
- Though there is a stick insect in the tropical forests of Borneo that grows to more than half a meter long.
- The African Goliath beetle can reach a weight of 100 grams, which is a sort of record for this type of insect.
- Insects have rigid exoskeletons to protect them from danger, but which limits their growth
- Insects donít have lungs
- In addition to their size, insects surprise us with their tremendous variety of shapes. Firstly, they undergo a metamorphosis that radically changes their bodies when they go from being young to adult.
- A simple ant is capable of lifting 50 times its own weight.
- An antís nest can be 8 meters high.
- The protozoa living in fresh water, the plankton of seaweed and the bacteria that colonise our environment belong to a world of
which gravity has disappeared. In its place, electromagnetic forces impose their laws.

Armour and hollow tubes
- All arthropods, including insects, lack bones. They have exoskeletons which provides them with a protective shield, it also prevents them from perspiring something which, given their size could lead to excessive dehydration.
- Though the hollow shells of arthropods are very efficient, they can only grow to a certain size. As the shell increases in size, so internal tension increases proportionally. The explanation is connected with physics which tells us that all hollow structures such as cylinders become weaker the bigger they are.

The kingdom of transformers
- The diversity of shapes of terrestrial invertebrates seems to have no limits.
- In this particular aspect, insects play a leading role in the book of life.
- Most of them change their appearance at least once in their lives.
- In addition to the gift of metamorphosis, evolution has granted apparently capricious shapes to many insects that hide the secret of their survival.
- Their ability to merge and the fact they can stay motionless for hours, allows them pass totally Ė and happily Ė unnoticed.

When appearances deceive
- Some flies have changed their appearance to make themselves look like certain kinds of dangerous wasps.
- Surprising examples of this carnival aptitude can also be found in fish.
- The sea dragon found on the Australian Coast, has flattened its shape and lengthened its skin until it looks like a ribbon of seaweed.
- The Plant Kingdom also shows us examples of this.
- Some plants adopt weird shapes to reproduce.
- Some plants in the South African desert have developed shapes and colours similar to the stones which surround them, preventing animals detecting and eating them.
- Perhaps because small animals have shorter lives, evolution has equipped them with simpler repair systems.
- Lifeís history has demonstrated to us that small-sized species are extraordinary survivors.

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