As defined in the dictionary, 'A place where a plant or an animal naturally occurs', an animals habitat is a vital part of an animals everyday life process.
Without habitat, life would not exist. Think of this. Humans, put here on earth with the surroundings of trees, water, mountains... and now, picture the earth without these things. Life as we know it, would not exist.
Animals rely on these three things and many more. For example, fish rely on their habitat, which is water. If it's habitat is polluted, then the fish will die. This goes the same on all animals, big or small.
Habitat not only relates to surroundings, but for the animals source for food. Habitats for birds, for example, the forest and trees, if gone, would kill the birds that relied on the forest for everyday use. Not only would they die, but the animals that relied on the birds would die and so on.
Habitat is taken for granted. As humans, for example, we have our own habitat, which we are destroying by pollution, toxic waste, etc.. By destroying the rain forest, Ozone layer, and many other things, we are messing up many habitats, not only ours, but ALL animals, for all animals rely on the earth as their habitat. This relates to evolution and an animals adaptation to a paticuliar climate and region. Because habitats constantly change, an animals abiltiy to change adaptations determine if the animal will live or die.