Geoscience Reference
In-Depth Information
Low-latitude wetland
case studies
15
15.1 Introduction
tropics coupled with lower extinction rates,
greater amount of received solar radiation, higher
average temperatures, and other biotic and
abiotic factors. Reducing the rate of species loss
consequently requires equal if not greater atten-
tion to be paid to the tropics and lower latitudes
(Gaston 2007). However, in the tropics, biodiver-
sity protection is further complicated by human
demand and the socio-economic and develop-
mental realities that many countries face.
In this i rst set of case studies focusing on
the low latitudes, we i nd the selected wetlands
supporting a scale of species richness and
density seldom observed elsewhere. However,
human resource demands from these wetlands
also play critically inl uential roles in their sus-
tainability. This chapter considers some of the
large and globally renowned tropical wetland
sites including the Sundarbans of South Asia,
the Okavango of southern Africa, the Pantanal
of South America and the Gulf of Mexico coast
of the United States.
These examples cover a wide variety of tropi-
cal and subtropical wetland habitats. Coastal
mangrove ecosystems are found in the Sundar-
bans and the Everglades, while a mosaic of
fresh-water, intermediate, brackish, and saline
marsh environments are found across vast sec-
tions of the Pantanal, Okavango, Mississippi
Delta, Everglades, and Laguna Madre. Moreover,
three of the regions considered in this chapter:
the Sundarbans, Okavango and Pantanal, include
wetlands that span across country borders,
The low latitudes span between the Equator and
30° latitude across the northern and southern
hemispheres. This region receives intense solar
radiation throughout the year with variable pre-
cipitation patterns ranging from year-round rain-
fall closer to the equator to distinct wet and dry
seasons farther away in the tropics. The tropical
air masses that control climates within this geo-
graphic belt give rise to tropical moist, tropical
wet and dry, and tropical dry climates. For the
most part, these temperature and precipitation
regimes provide suitable growing conditions
year round for a wide diversity of l ora and fauna.
Scientists have long since established a cor-
relation between latitudinal gradient and species
diversity (Gaston 2007). Empirical evidence
suggests that species richness decreases with
increasing latitude from the tropics to the poles,
with recent analyses supporting the idea of the
tropics as both a cradle and museum of biodi-
versity ( Jablonski, Roy and Valentine 2006). This
gradient is observed in terrestrial, marine and
to a lesser extent in fresh-water realms, with
some variation by region and habitat type (Hil-
lebrand 2004).
Several reasons have been provided for this
observed species richness gradient. However, an
agreed upon explanation remains elusive. Some
have suggested that the higher speciation rates
in the lower latitudes may be due to a longer
and more stable period of diversii cation in the
