We get knowledge of animals from reports or features of animals on TV or radio. But how much do we know about animals? Possibly you could speak out a lot of words about that subject, but all you could tell is very little to this colorful world.
Just considering the quantity of animals, there are almost two million species of animals on this planet today and their continued survival after one billion years is testament to their endurance and brilliance.
At one extreme they are the big cats and elephants that most of us are familiar with, to the unknown animals somewhere beneath the sea bed. At another extrem, the worlds largest living animals, baleen whales can live up to 25 metres long and weigh 120 tons. At the other end of the scale are microscopic organisms and sub microscopic flies and beetles. These animals are so tiny that their weight is negligible but they still possess the body systems that are needed for survival.
Animals are highly complex compared to other forms of life, in regards of skeleton, cycling systerm, nerve, etc.. Particularly in terms of the nerve of animals, they are extremely responsive. Even the most simplest of animals react quickly to changes around them, shrinking away from potential danger or reaching out for food. The animals that are able to learn from experience and are unique to the animal world, are those animals with well developed nervous systems.
The different charactoristics of animals allow them to live and reproduce in different ways. Whales have few natural predators and the same is true of elephants, which is the largest land animal. They are able to process food on a very large scale because of the massive size of their bodies. However they take a long time to reach maturity, which means that they are slow to reproduce. Insects on the other hand are easy prey for many animals and their small size means that their bodies are not as energy efficient as large animals. But because they can breed very quickly when the conditions are in their favour, their numbers can rise at a very fast rate.
In the animal world, vertebrates are the most familiar and flourishing branch. These animals which have backbones include the fastest animals on land, sea and air and also the world’s most intelligent species (homo sapiens). Vertebrates are all related to each other, sharing a common ancestry that goes back millions of years. However despite the fact that vertebrates lead the animal kingdom in many fields, they only make up a small minority of the animal species known today. The vast majority of species are invertebrates - animals without backbones. Invertebrates often have very little in common with each other (unlike vertebrates), apart from their lack of a backbone. The giant squid which is the largest invertebrate, can measure over 16 metres long but it is very much an exception. Most of the invertebrates are very small and live in inaccessible habitats.
Most animals are cold blooded (ectothermic), which means that their body temperature is determined by that of their surroundings. The ability to generate their own heat and to maintain a constant internal temperature, regardles of the conditions outside, is particular to warm blooded (endothermic) birds and mammals. This difference in body temperature has some far reaching effects on the ways that animals lead their lives; this is because animal bodies work best when they are warm.
Reptiles, amphibians and insects are cold blooded animals. They can exist very easily when the conditions are warm but if the temperature drops, their work rate and energy slows down. They are able to absorb some heat by being out in the sunshine but if the temperature falls below about 50 degrees fahrenheit, their muscles work so slowly that they find it difficult to move. Mammals and birds are hardly affected by this kind of temperature change. When the temperature falls below freezing, their internal heat and good insulation helps them to remain active.
In a physical way vertebrates function as separate units even though they may live together in families or in larger groups. In the invertebrate world it is not unusual for animals to be permanently linked to together, forming clusters that are known as colonies. These colonies often look and behave like single animals. Most are static but some, particularly those that live in the sea, are able to move around. Colonial species include some of the world’s most amazing invertebrates.
Animals are able to break food up by digesting it and then absorb the substances that are released. These substances go into the animals cells where they are combined with oxygen to release energy. This process is called cellular respiration and is a controlled form of burning, with food acting as the fuel.
All animals, regardless of their lifestyle ultimately provide food for other animals. All are connected by food chains which pass food and energy to one another. 90 per cent of an animal’s energy is used to make its own body work and therefore food chains are rarely more than six links long.