Based on our three fundamental processes (speciation, extinction, and migration), we can come up with many different explanations, or hypotheses, for why the tropics are so diverse. For example, one possibility has to do with speciation rates. We could hypothesize that the tropics are diverse because they have higher speciation rates than other regions — in other words, that more species are produced in the tropics.
Above, we've given one hypothesis having to do with speciation to help explain tropical diversity. Think about the other two processes we are examining — extinction and migration. Can these processes help explain why the tropics are more diverse than other regions? Write down two or more other hypotheses that might help explain the LDG — at least one having to do with extinction, and at least one having to do with migration.