Evolution, 4th Edition

208 CHAPTER 8

centers [6, 26]. Thus, many species are tracking their niche by shifting where they

live, as the environment to which they are adapted moves northward and to higher

elevations. These are not evolutionary changes, just geographic changes, and in fact,

there is no evidence that most species have evolved broader or more extreme climate

tolerance. Many other species, however, are not able to keep up with climate change,

even by shifting where they live. A variety of environmental challenges prevents

them from maintaining a stable range size while moving with the envelope of suit-

able habitat. As with the weather, predicting how species will respond to the shift-

ing constellation of ecological factors triggered by climate change is very difficult

[36]. But the hope that evolutionary adaptation might rescue most species from the

challenges of rapid climate change appears to be dim [26].

Futuyma Kirkpatrick Evolution, 4e

Sinauer Associates

Troutt Visual Services

Evolution4e_08.17.ai Date 01-19-2017

Equator Pole

Latitude

Climatically suitable

Equator Pole

Latitude

Previously suitable Newly suitable

Mortality

Mortality Mortality

Mortality

Equator Pole

Latitude

Equator Pole

Mountain

Latitude

Equator Pole

Latitude

Equator Pole

Latitude

(A) Original population (B) Distribution shifts with climate change

(C) Declining habitat size (D) Dispersal barrier

(E) Limited dispersal ability (F) Range expansion by adaptation

Au: OK to label faded rabbits “mortality”? See above.

FIGURE 8.17 Species living along an environmental gradient

(for example, correlated with latitude) can respond to climate

change in several ways. These cartoons depict a species living in

the northern hemisphere. (A) Before change occurs, the range is

limited to the north and south by physiological factors. (B) With

global warming, some species are able to maintain a stable range

size by shifting to the north. (C) Other species run out of habitat

at their northern limit, causing the range to shrink as the southern

limit moves north. (D) Dispersal barriers prevent some species

from tracking the moving envelop of suitable habitat. (E) Species

with limited dispersal abilities may not be able to keep up with

rapidly changing conditions. (F) If species are able to adapt to

the new conditions at the south while tracking the envelope of

previously suitable conditions, the range will expand. Of the six

possibilities described in the figure, only this one includes evolu-

tionary change. This outcome is rarely observed. (After [18].)

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08_EVOL4E_CH08.indd 208 3/23/17 9:12 AM