Evolution, 4th Edition

464 CHAPTER 17

These events profoundly affected the distributions of organisms (see Chapter

18). When sea level was lower, many terrestrial species moved freely between land

masses that are now isolated; for example, the ice-free Bering Land Bridge was a

conduit from Asia to North America for species such as woolly mammoths, bison,

and humans. The distributions of many species shifted toward lower latitudes dur-

ing glacial episodes and toward higher latitudes during interglacial episodes, when

tropical species extended far beyond their present limits. These repeated shifts in

Futuyma Kirkpatrick Evolution, 4e

Sinauer Associates

Troutt Visual Services

Evolution4e_17.33.ai Date 01-06-2017

Note: I kept the key as labeling across the two maps didn’t add clarity.

(A)

(B)

Thailand

Sumatra Sunda ShelfBorneo

Java

New Guinea

Arafura Basin

Australia

Philippines

Bering

Siberia Land Bridge

North

America

Alaska

Current land surface

Frozen sea (frozen most of the year)

Glaciers

Continental shelf exposed

Deep water

(≥ 200 m below current sea level)

Asia and North America

were broadly connected when

glaciation lowered sea level.

Wallace's Line separates two

distinct modern terrestrial faunas.

It corresponds to a deepwater

separation between continental plates.

FIGURE 17.33 Pleistocene glaciers

lowered sea level by 100 m or more,

so that many terrestrial regions that

are now separated by oceanic bar-

riers were connected. These maps

show the configuration of land in

two parts of the world about 15,000

years ago. (A) Eastern Asia and North

America were joined by the Bering

Land Bridge. Note the extent of the

glacier in North America. (B) Indone-

sia and other islands were con-

nected to either southeastern Asia or

Australia. (After [13].)

17_EVOL4E_CH17.indd 464 3/22/17 1:37 PM