River conservation in tropical versus
The conservation of tropical rivers presents special challenges given their evolutionary history, hydrological and ecological characteristics, and our limited understanding of how these systems function. Moreover, differences in socio-economic conditions, rates of human population growth, and related effects of globalization in tropical versus temperate countries often play an overriding role in determining the status of conservation efforts. Global disparities in river conservation resulting from such socio-economic differences are discussed in detail in Wishart et al. (this volume, Part II) and have great relevance to the issues discussed here. The approach of this chapter, however, is to focus on those aspects of tropical riverine systems which make them particularly vulnerable to human disturbance (i.e. hydrological and ecological characteristics) and ultimately to stress priority research and management needs for conservation. At the same time it is recognized that many tropical developing countries lack the financial resources for research and conservation. Moreover, research itself is inadequate if not backed by political will, and administrative and managerial infrastructure; this is an acute problem in developed and developing countries alike.
The evolutionary history of tropical riverine ecosystems is extremely complex and has contributed to high levels of biodiversity and endemism. Tropical regions have been characterized by long periods of climatic stability relative to temperate zones. The term ‘tropical’ is used here to refer to the broad and irregular equatorial area (approximately 30° north and south of the Equator) between the northern and southern subtropical zones of the drylands (i.e. as used here tropical areas are not confined to the latitude limits of Capricorn and Cancer; Pereira 1989). While the ice ages extirpated fish populations from many temperate freshwater environments during glacial periods, climatic fluctuations and associated changes in sea level throughout the Quaternary may actually have contributed to speciation in the tropics by aiding freshwater fish dispersal, particularly in South America (Weitzman and Weitzman, 1982; Lowe-McConnell, 1987). More than 2000 species of fish occur in the Amazon alone, with approximately 90% endemic. Of the 700 species in the Congo River of Africa about 70% are endemic. In contrast, there are about 250 species in the Mississippi River of North America (30% endemic) and fewer than 70 species (10% endemic) in the Danube River of Europe (World Conservation Monitoring Centre – WCMC, 1992). Lowe-McConnell (1987) summarizes general differences between ‘classical’ temperate rivers and their complex counterparts in tropical regions.
Given the differences between tropical and temperate riverine systems, theories and conservation strategies that have been developed based on studies of temperate streams may not be applicable or effective for tropical streams. For example, an understanding of the fate and transport of environmental contaminants in northern latitudes has little applicability to the tropics (Bordeau et al., 1989). Likewise, the applicability of hydropower technology (developed for rivers in the temperate zone) to tropical regions must be evaluated with respect to differing hydrological and biological