Why do tropical communities tend to have greater species diversity than temperate or polar communities?

Tropical climates are better suited for a multitude of species of plants and animals.

Explanation:

The reason for this is tropical climates are easier to handle then harsh winters because almost all tropical climates are near the equator so it tends to stay warmer year round creating a year round growing period. Polar climates are harsher on the plants than the animals. Also consider this the fact that there would be no herbivore animals for predators to eat so that limits what can grow in the polar climates.