Biodiversity of the Rewa Head B Zoological Society of London ...

in t r o d u C t i o n
Background to the expedition
The expedition was initially conceived as a sampling trip to collect faecal samples from
the giant otter (Pteronura brasiliensis) to obtain DNA for use in a phylogeographical
study being carried out by Rob Pickles at the Zoological Society of London and the
University of Kent. The Rewa Head was purported to have evaded the depredations of
hunters during the trade in giant otter fur and due to its isolated nature has witnessed
little human impact over the centuries. It was recommended by Nicole Duplaix who
conducted the first study on giant otters in the 1970s in Suriname. Due to the unexplored
and unprotected status of the Rewa Head, it was decided to maximize the time spent
above Corona Falls by conducting coincidental biodiversity studies, namely camera
trapping, mist-netting and spot-count transects.
The Guianan Shield
Figure 4. The Guianan Shield straddles five countries in northern South America and its streams feed
three drainage basins. High degrees of endemism and species diversity coupled with the largest tract
of unbroken tropical forest anywhere in the world makes this an extremely important eco-region.
Guyana is located in the northern part of the Guianan Shield, a vast Precambrian craton
uplifted during the formation of the Andes in the Oligocene, 3.5 million years ago. The
craton formation has determined the hydrology of the region, resulting in a watershed
across its back which splits the flow of streams north-south. Across this 250 million
hectares of northern South America lies the largest tract of pristine forest anywhere in
the tropics. The Guianan Shield contains some of the most carbon-rich forests in South
America and represents an important carbon dioxide sink in the fight against climate
change (Saatchi et al 2007). Added to this, the Shield possesses extremely high levels
of biodiversity and endemism as a result of Pleistocene refugia. Over 20,000 species of
vascular plants are found in the Guiana Shield, 35% of which are endemic. Similarly 975
bird species are found in this eco region, of which 15% are endemic (Ellenbroek 1996).
Lying between 1 and 9 degrees north of the Equator with a coast in the Carribean,
Guyana receives most of its weather patterns from the Caribbean Intertropical
Convergence Zone (ICZ) with a seasonality driven by a rainy season arriving in early
May lasting until mid-August, followed by another short rainy season in December. Its
forests are hot and humid with between 2000-4000mm of rain annually.
6 Biodiversity of the Rewa Head