Biology Reference
In-Depth Information
In northern Latin America, the páramo community probably developed
in the Pliocene in the highest elevations of the Transvolcanic Belt, and to-
gether with desert, it is among the latest of ecosystems to appear in modern
form in northern Latin America. This is consistent with its record in South
America, and with systematic studies that indicate modern páramo species
are often recently derived from lower altitude progenitors, rather than a
product of ancient in situ evolution.
SOUTH AMERICA
Changes in the biota of South America during the middle Miocene through
the Pliocene are anchored in three major events that altered the landscape
and supplemented trends in global climates. The fi rst involved closure of the
marine barrier between South America and North America (Coates 1997;
Jackson et al. 1996). The event can be dated to around 3.5 Ma, recognizing
that the few and discontinuous upland temperate habitats developed later
than the more extensive and continuous tropical lowland habitats. Also,
the Darién region at the border between eastern Panama and northwestern
Colombia closed last, and even today it is still virtually at sea level. Con-
sequently, continuity through the Darién was likely disrupted or reduced
through tectonic/orogenic activity, and from sea level fl uctuations in the
Quaternary. The biological consequences of reuniting two continents, and
the intermingling of biotas that had been separated from the Late Creta-
ceous through the late Pliocene, will be discussed in chapter 9, but suffi ce
it to say they were considerable as plants and animals moved in both direc-
tions across the new land bridge.
The second event was uplift of the Andes Mountains to modern eleva-
tions. Among the many results were that drying along the west coast of the
Central Andes intensifi ed and arid habitats expanded to form the Atacama
Desert of Peru and northern Chile. Other coastal areas to the north, beyond
the cold Humboldt Current, became wetter, as warmer moisture-laden
westerly winds rose off the Pacifi c Ocean in the region of the Colombian
Chocó (fi g. 2.45). An increasingly formidable barrier was established to the
east-west migration of low- to midelevation organisms (a gradually develop-
ing vicariant event), and to the north-south movement of high-altitude and
páramo organisms (a geographically isolating event), while the Andean val-
leys provided, and continue to provide, migrational Cis- and trans-Andean
pathways for organisms adapted to dry habitats.
One of the most dramatic physical changes wrought by the uplift of the
Northern Andes was a reversal in the fl ow of the Orinoco and the Amazon
