Glacial forest refuges

North - South movements are one response to climatic change. Another is for ranges to expand and coalesce or contract and fragment, and these events are crucial in the hypothesis of glacial forest refuges.

The ranges of tropical forests may change through the glacial cycle. Tropical forests, like those of Latin America (opposite), are now continuous over large (though decreasing) areas; but they may have shrunk and fragmented into smaller areas in the drier conditions of the Ice Age.

This (possible) glacial cycle of range fragmentation has been used to explain a number of biogeographic facts, including:

• the high diversity of living species in tropical forests;

• disjunct distributions such as the toucan R. ariel.

The fragmentation of ranges is exactly the kind of process that could cause allopatric speciation, and as each locality evolved its own species, different from that of other localities, the total diversity of species would increase.

The hypothesis of glacial refugia has been applied broadly, to explain such phenomena as the Müllerian mimicry rings of Heliconius and the language groups of Native Americans.

The following animation illustrates the process.