Life and climate in an ice age - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 6

of dry grassland that resembled extant subarctic steppe communities. Evidence
was provided that this region might have contained an arid but productive, grass-
dominated ecosystem. This mammoth steppe system might have sustained
mammalian herds all year round.
According to Barton et al. (2002), rainfall in North America was about 50%
higher than at present, but most of that rainfall was concentrated in the winters
while summers were very dry. They cite the example of the ponderosa pine that
requires summer rainfall. It is virtually absent from the fossil record during ice
ages. They also cite the absence of the pinyon pine in the fossil record for ice
ages. The combination of low temperatures and summer drought is thought to be
the cause. Thus, Barton et al. (2002) disputed the commonly held belief that the
Ice Age was cooler and wetter and that plants simply shifted their distribution by
moving south or downwards in elevation. The examples of ponderosa and pinyon
pines were cited to support their contention that the differences were far more
complex.
Burroughs (2005) shows a map of Australia and New Guinea conjoined as a
single continent when the oceans were at their lowest.
Colinvaux (2007) wrote an extraordinary book detailing 50 years of research
in an attempt to define the climate of the Amazon region during the past Ice Age.
This topic begins with an emphasis on the vast difference in the number of species
of flora and fauna in the Amazon vs. mid-latitude zones.
The great diversity of species in the tropics:

.In
warmer climates there are more kinds of living things than in the colder north;
many, many more kinds. But why should this be? The temptation is to say,
'Obvious! It is nicer in the tropics; more productive; wet and warm; no winter;
living is good and lots of species take advantage of it. Next question please.' But
that answer is no answer. [There are] lots of living things in Europe and North
America, thousands of kinds of animals and plants. The problem is that the wet
tropics have more kinds still, many more.''

'' ... has long been one of the knottiest problems of ecological theory ...

Colinvaux (2007) asserted that the great diversity of flora and fauna in the
tropics is not simply explained by its current favorable climate. The impact of ice
ages is likely to be related. Mountain ranges in Europe tend to run east-west.
As the great ice sheets moved down on Europe during the Ice Age, expanding
mountain glaciers moved northward catching the flora and fauna in a ''pincer
movement''. The flora and fauna were prevented from moving southward by the
blockade of east-west mountain ranges. Europe never fully expanded its flora and
fauna during intervening interglacial periods. By contrast, in North America,
mountain ranges tend to run north-south, providing passes for flora and fauna to
move southward during ice ages. Nevertheless, North America is endowed with far
less diversity than the tropics.
A theory was proposed to account for the huge diversity in the tropics.
According to this theory, the climate in the tropics during the Ice Age was arid