Along with food, water, and shelter, a good habitat must also provide space. You can think of space as the "territory" needed to find food, water and shelter. Different animals require different amounts of space. For instance, a squirrel may find all its needs to survive in just a few acres, where a mountain lion’s territory might be over one hundred square miles. Food, water, shelter and space are the four basic components of a habitat; but some people also consider suitable arrangement to be one of the basics. Suitable arrangement means that each component - food, water, shelter and space - must exist in the correct amounts for an animal to survive. For example an animal can have the right amount of food, shelter and space, but not enough water. This situation could happen during a drought. Can you think of other examples where there would not be a suitable arrangement and what might cause it?

Most plants and animal are very specialized and able to survive in only a very specific habitat, where conditions are suited to them. For example, earthworms - which live in the moist soil - often have delicate, moist skin. Organisms found in drier habitats have thick, hard, outer shells (e.g. beetles) to prevent them from drying out. No two species in a habitat can occupy the same ecological niche for long. For example, if two types of birds in the same area feed on the same kind of berries, one or the other will be squeezed out or will have to adapt itself to a new source of food.

Science Is p 212