What determines species diversity

In some parts of the world, such as the tropics, a diverse range of species exist, whereas in other areas of higher latitude very few have evolved. Biologists are striving to understand why. The interplay between environment and living organisms and between the organisms themselves play key roles in encouragingor discouraging diversity, as do human disturbances, predator-prey relationships, and other food web connections. But exactly how these and other forces work together to shape diversity is largely a mystery.