Innumerable small and large plants and animals live in harmony in the diverse geographical, environment and climatic conditions of the world. Organisms of the same species living successfully under different environments become modified or adopted differently. As a result, from a common ancestor with diverse characters animals and plants evolve. This diversification of organisms is called bio-diversity. So, the diversification found among the animals is known as Animal diversity and the diversification among the .plants is known as Plant diversity.
To survive and disseminate successfully under various geographical regiotns the diversities that have arisen among the animals through adaptations and essential modifications of their external and internal morphology, size, shape, behavior etC. is called animal diversity. Due to this diversification various species of animals have arisen in the world.