When you start thinking about why the tropics are such a diversity hotspot, the first thing that probably pops to mind is the climate. Sunshine. Rainfall. Temperature. After all, the climate that makes tropical destinations great for vacation might also attract other species. But before getting lost in these details, let’s look at the question in a different way.

At the most basic level, three processes affect diversity in any region: new species being generated, existing species going extinct, and species moving in and out — in other words, speciation, extinction, and migration:

• In the process of speciation, one lineage splits to produce two daughter species. This usually happens when groups from the same species stop breeding with one another. Eventually the two groups evolve into separate species.

• In the process of extinction, all the individuals of a species die. Once a species has gone extinct, it can’t “come back.”

• In the process of migration, a species moves into or out of an area or changes its range in some way.

How have these processes affected diversity in the tropics?