Variety Is the Spice of Life

Have you ever wondered why there are so many kinds of living things on Earth? Why are there more than 7,000 species of reptiles, 8,000 types of grass, and 350,000 different beetles? Scientists have found and named one and a half million species of plants and animals, and think that there are still at least 30 million more waiting to be discovered.

So many species exist today because the Earth has such a large variety of habitats. A habitat is the type of environment in which plants and animals live. If habitats were the same everywhere, fewer kinds of plants and animals would probably exist. Creatures may face ice and snow each day, or sun and sand. Fish swim in fresh or salt water. Plants live in shady, moist valleys or on windy, open clifftops. Each species has special structures or ways of behaving that help it survive. These special features are called adaptations.

Let’s chart the diversity of a few categories of life. Count the number of times each symbol appears (cross out the symbols as you count). Write the totals under “#.” Each symbol represents 1,000 different species. Figure out how many species each type of organism has and color in the correct number of blocks on the graph.

Today there are many different habitats on Earth, but it hasn’t always been so. Take, for example, the time when the first dinosaurs lived (about 225 million years ago). The climate throughout the world was hot and muggy, and the same kinds of plants and animals were found everywhere. Compared with today’s species count, there were many, many fewer kinds of plants and animals. Gradually, there were climate and geological changes as well as adaptations in the plants and animals themselves. These changes made it possible for the amazing number of species alive today.

Look carefully through this farmhouse window at the living things in the country scene. Decide which plants and animals are not in their correct habitats and circle them. Then color the picture.