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Birth, death, and relocation

Looking at tropical diversity in terms of speciation, extinction, and migration is a bit like taking a long term view of how many people live in a particular region by keeping track of the number of births, the number of deaths, and the number of people moving in and out of the area. Regions where the birth rate is high (and the death rate is low) or where lots of people move into the area are likely to be crowded. Regions where the death rate is high (and the birth rate is low) or where lots of people move out of the area are likely to be relatively empty. The balance between these different processes is what determines the number of people living in any particular region.

The balance between birth rate, death rate, and migration determines the number of people living in any particular region

Similarly, in the tropics (or any other region), diversity is ultimately the result of new species being born (speciation), species dying (extinction), and species that move in and out of the region (migration).

Check your understanding of these processes with a quick question ...


Multiple choice
3. Three processes affect the diversity in a region — speciation, extinction, and migration (moving in or out). Which of the following sets of processes would lead to increasing diversity in a region?

 A.  High rate of speciation, low rate of extinction, no species moving in or out.
 B.  Low rate of speciation, high rate of extinction, no species moving in or out.
 C.  Equivalent rates of speciation and extinction, high rate of immigration (species arriving), low rate of emigration (species leaving).
 D.  Equivalent rates of speciation and extinction, no species moving in or out.
 E.  A and C
 F.  B and D



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Investigation Phase IV: Why the tropics?