Geography Reference
In-Depth Information
FIGURE 7.3
Alpine and forest areas of the southern Rocky Mountains, USA. Dark areas represent
forest cover between upper treeline bounded by the snow-covered alpine zone, and lower treeline
bounded by grassland and steppe vegetation. Note the forest and alpine connectivity (corridors)
between mountain ranges and insular nature of others. (NASA Earth Observatory.)
The geographic isolation of mountain areas has several important evolutionary and
floristic consequences. First, isolation, in conjunction with limited area, decreases the
probability of genetic infusion from outside sources. Consequently, adaptations derived
through natural selection tend to reflect specific, highly localized environmental condi-
tions and the development of endemic species or subspecies (Körner 1995; DeChaine
and Martin 2005). This process can be further magnified on mountainous oceanic is-
lands where
genetic drift,
the random selection of genetic traits from a few colonizing
individuals (
founder effect)
) can accelerate the development of endemic taxa (Templeton
1980). In terrestrial environments, isolated, lower-latitude mountain floras tend to re-
semble adjacent, lower-elevation floras. The alpine flora of San Francisco Peaks in
northern Arizona, for example, is almost exclusively composed of subalpine species
(Schaack 1983) and has a low similarity to the rest of the Rocky Mountains in alpine
species (Hadley 1987).
Plant Community Characteristics
Search WWH ::
Custom Search