Biology Reference
In-Depth Information
there are cypress swamps with
Taxodium
and Spanish moss (
Tillandsia usne-
oides
). Coastal grasslands mix with oaks and
Sabal
palms in interior Florida
to form savannas. Deserts in the west, present as preadapted elements since
the late Eocene, are increasingly evident in the Basin and Range after the
middle Miocene, and the details of their distribution and composition back
50,000 years are revealed in packrat middens and back 10,000 years by
dendrochronology. Desert elements, like the grasslands, modernized in the
Pliocene and continued to do so in the dry intervals of the Quaternary.
The vegetation changes around 2 Ma in South America are well known
from a few areas, but we must use the ecological features of the modern
communities, along with context and ancillary information from indepen-
dent lines of inquiry, to infer early ice age vegetation and environments.
Clapperton (1993) and others provide insight into Quaternary environ-
ments at 2 Ma and younger times, and these presumably apply to all the
glacial/interglacial intervals. This evidence, summarized below, is relevant
to the once-debated topic of stability versus change in the tropical latitudes,
and currently to the concept of refugia (for references to the primary lit-
erature for the summary, see II, chap. 7, on the Quaternary; II, chap. 8, for
synthesis).
1. Frequent ponding from Quaternary tectonic movements in the Pastaza-
Marañon Basin in Amazonian Peru and Brazil.
2. Long-term fl uctuations in fl ooding cycles of the terra fi rme, that is, the
land along rivers at present beyond the annual fl oods.
3. Sedimentary evidence for repeated wet and dry periods within the Mesa
Formation of the Llanos along the Orinoco River basin, formed during the
Yarmouth Interglacial of North America, circa 475-300 kyr.
4. A complex of factors (summarized in Clapperton 1993, 148-51) indicat-
ing reduction and greater seasonality in MAP, a eustatic lowering of sea
level of between 25 and 130 m—applicable to each glacial maximum and
with implications for water-table levels—and a reduction in vegetation
cover.
5. Uplift of the Sierra Nevada de Santa Marta and the Cordillera de Mérida
of northern Venezuela at an annual rate of about 4 mm, or 2000 m during
the past 500,000 years. The present lower limit of glaciers in the moun-
tains is 5000 m (4000 m at the LGM), meaning that few glaciers were
present prior to the Quaternary and implying signifi cantly altered and
fl uctuating environments since that time.
6. Uplift of the Sierra de Perija on the Colombia-Venezuela border by 11-
16 mm a year during the Quaternary.
