What happens to the number of species as you go toward the equator?

In general, as you move from the poles to the equator the number of different species increases. There are a few different ideas about why this occurs, but many of them have to do with energy.

There are different amounts of energy available in different parts of the globe. Sunlight reaches the equator at more direct angles and more consistently throughout the year, providing more energy for photosynthesis. With more photosynthesis comes more plant growth and more net primary productivity. This forms the basis for food chains, and with more energy available from the primary producers, such as plants, there is more energy available to support more food chains, and thus more species. At the poles there is less energy from sunlight, so there is less energy to support food chains resulting in fewer overall species.