Biology Reference
In-Depth Information
Figure 4.4
Cleared leaf of
Epilobium suffruticosum.
Illustration provided by
Richard Keating. Photograph
by Shirley A. Graham.
example, in the Atacama Desert (chap. 2)—the assumption appears gen-
erally valid, and overall ecological stasis at the generic level since at least
45 Ma emerges as a rather common characteristic of plants and animals.
A potential limitation to the method is that the present distribution of
an organism may not necessarily refl ect its potential distribution; that is,
where an organism does occur is not always the same as where it can occur.
After each reshuffl ing following major environmental changes, for exam-
ple, the eighteen to twenty glacial cycles of the past 2.6 million years, and
the fi ner-scale Holocene events of the past 11,000 years, some organisms
simply may not have had time or opportunity to regain their full range. It is
known that the armadillo, alligator, possum, and recent introductions like
fi re ants and African bees, are spreading northward partly in response to
global warming but also owing to a lag time in migration. Barriers such as
highways, cities, farms, ranch lands, and cut-over forests have progressively
restricted the movement of many organisms over the past two centuries.
The reconstruction of paleoenvironments based on the 1900 occurrence of
