The Oligocene to the Quaternary: climate and biology - Climate Change: Biological and Human Aspects - page 152

Altitude (m)

Present-day climate

5000

Glacial (LGM) climate
0.76

4500

° C 100 m -1

C 100 m -1

0.6 °

4000

3500

Páramo

3000

Andean forest

2500

Páramo

2000

Andean forest

Sub-Andean forest

1500

Sub-Andean forest

1000

Lowland forest

500

Lowland forest

Fig. 4.10 AltitudinaldistributionofmainvegetationbeltsacrossaColombianAndeanmountain.AfterHooghiemstra

andVanderHammen(2004).SeealsoFigure6.2a.

change (see Figure 4.10). Having said this, do not assume that the vegetation zones all
change uniformly. Often there are fundamental differences in altitudinal ecological
zonation between glacial and interglacial times. For example, a study of a Colombian
Andean mountain (Hooghiemstra and Van der Hammen, 2004) has shown that at the
LGM the rate of temperature decrease with altitude was 0.76 ◦ C 100 m − 1 compared
with 0.6 ◦ C 100 m − 1 today. This is due to the drier conditions at the LGM (cool
air holds less water than warm air, which is a different, but related, phenomenon to
cooler seas evaporating less; the moisture content of the air affects its heat-carrying
properties). Furthermore, the sub-Andean forest occupied a narrower band that may
be due to the lower altitudinal limit of glacial night frost, again due to the drier
conditions. The message here is that proportional and linear relationships of climate
and ecological parameters between different climate modes cannot be assumed.
Nonetheless, some tropical mountains, according to DNA divergence, have
provided a home for populations for over 6 million years. This is a similar duration to
that associated with some regions of African and Amazonian forest that were refugia
for many species. These tropical mountain and lowland refugia are so stable that they
also exhibit great genetic diversity that in some instances facilitates speciation itself
(Hewitt, 2000). Because of the short migration distances (i.e. short vertical rather than
long horizontal) and because mountain ranges sport so many environmental niches,
tropical mountains may partially explain greater species richness in the tropics.
Finally, some species in some areas could not cope with Quaternary glacial-
interglacial transitions. As Martina Pacher and Anthony Stuart (2008) point out, the
cave bear ( Ursus spelaeus ) was one of several spectacular megafaunal (large mam-
mal) species that became extinct in northern Eurasia during the late Quaternary. Vast
numbers of their remains have been recovered from many cave sites, almost certainly
representing animals that died during winter hibernation. U. spelaeus probably dis-
appeared from the Alps and adjacent areas - currently the only region for which there
is fairly good evidence - around 27 800 years ago, at the time of the LGM. Climatic