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origins of habitat variety This planet would surely impress every extraterrestrial creature - like a blue jewel the earth glimmers in the dark. And if inhabitants of other stars ever were attracted by this appealing sight, they would soon discover even more amazing things. On earth there are the most varied natural habitats - oceans and deserts, masses of ice and vast mountain ranges. However, the greatest miracle which they could record in their log file would be the seemingly immeasurable variety of forms of life on our planet. During the past three billion years, a variety of species has developed on Earth which cannot be found anywhere else in our solar system and possibly not even in the whole universe. Animal and plant species are so numerous that so far only 1.4 million of the estimated at least 20 to 30 million species have been identified and scientifically categorized. The variety of eco-systems is the reason for this enormous bio-diversity. The numerous habitats, e.g. mountain ranges with alternating vegetation zones, savannas and steppes, forests and wetlands in different forms, deserts, tundra, oceans, Arctic and Antarctic, all form different habitats which meet the needs of different groups of species. Every species has adapted to its specific habitat thus ensuring its survival. Everyone with tropical fish in a fish-tank at home knows that neon fish die in water cooler than 4°C. Trout, in turn, cannot spawn in water which is too warm or too acidic. The adaptability and consequently the occurrence of individual species can be wide-ranging. |
They depend on physical and chemical factors, such as temperature, light, degree of moisture, salt and gas concentrations. Mechanical factors may also be of utmost importance for survival, e.g. water movement, sound or soil conditions. And since nobody is alone in the world, the presence of other animals and plants may either encourage or discourage the emergence of certain species - be it as partners in a symbiosis or as enemies, parasites or competitors. Over millions of years all species have thus constantly and collectively adjusted their appearances, behaviour, spread and social hierarchies of their habitats to their surroundings. That was their only way to secure survival. Let's look at the example of mammals in deserts. Many of them have developed longer ears and legs than their relatives in more moderate climate zones because longer parts of the body are better suited to release body heat. Snow hares change their fur colour from brown in the summer to white in the winter in order to better be able to hide from predators. Many animals of the northern hemisphere, for instance, polar bears and brown bears, hibernate in the cold, meagre winter season, while tropical lip bears do not need to spend the winter in a state like a deep sleep because of plentiful food supplies that are available to them all year round.
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