Are tropical streams really different?

TitleAre tropical streams really different?
Publication TypeJournal Article
Year of Publication2009
AuthorsBoyero, L, Ramírez, A, Dudgeon, D, Pearson, RG
JournalJournal of the North American Benthological Society
Accession NumberLUQ.1033

In the preface of a recent collection of review articles on tropical stream ecology, Dudgeon (2008) stated that there is no such thing as a “typical” tropical stream. The tropics make up the area of the globe between lat 23°N and 23°S, and include a great variety of climatic, geologic, and geomorphologic conditions (Boulton et al. 2008). Thus, tropical streams can flow through landscapes as varied as evergreen rain forests, deciduous seasonal forests, high-altitude grasslands, or even deserts. This diversity suggests that generalizations about tropical streams might be difficult to come by, but it also indicates that much is to be learned about stream ecology in tropical regions. Several major obstacles hinder the study of tropical streams. An obvious gap is our limited knowledge of their benthic faunas. European, North American, and, to a lesser extent, Australian and New Zealand stream invertebrates have been studied extensively and are well known, but this is not the case for most tropical stream invertebrates. Many insect larval stages have not been related to adults, and identification to species is not possible. Their life histories are unknown, but are often assumed (without good reason) to be similar to those of related temperate taxa. For example, certain traits, such as feeding habits, can differ among close relatives at different latitudes. Baetids and leptophlebiids (Ephemeroptera) are generally scrapers or collector-gatherers in temperate streams, but the baetids, Acanthiops from Kenya and Andesiops from Bolivia, and the leptophlebiids, Atalophlebia from the Australian Wet Tropics and Barba from Papua New Guinea, are shredders (Yule 1996, Dobson et al. 2002, Molina 2004, Cheshire et al. 2005). Studies of tropical streams have been restricted to intense activity by a small number of research groups in a few geographic regions, particularly in Costa Rica, Hong Kong, Kenya, Puerto Rico, Queensland, and Venezuela, although some important work has been done elsewhere. This geographic limitation constrains our ability to understand tropical regions in general. Moreover, it highlights the need for effective communication among dispersed groups of tropical researchers and between workers in tropical and temperate latitudes. Publication of compendia on tropical stream ecology, an activity that the Journal of the North American Benthological Society (J-NABS) has pioneered, is a powerful tool for enhancing communication and stimulating research in the tropics. The 1stJ-NABS special issue on tropical streams was published 20 y ago. It focused on unifying approaches to the study of streams in different biomes (Stanford and Covich 1988) and included topics such as spatial and temporal scales of patchiness and disturbance. The papers in the series mainly reviewed available data from the tropics and emphasized the need for a global perspective when constructing theories for the organization of stream ecosystems (Minshall 1988). The 2ndJ-NABS special issue on tropical streams was published in 1995 (Jackson and Sweeney 1995). It focused on descriptive research and included papers on invertebrate taxonomy and life histories, nutrient dynamics, pesticides, and gene flow in invertebrate populations. Only 2 papers, one on leaf-litter processing rates (Campbell and Fuchshuber 1995) and one on disturbance and recolonization of stony substrata (Rosser and Pearson 1995), focused on ecological processes. The range of topics reflected efforts to arrive at a broader understanding of tropical streams, but highlighted the limited amount of information that was applicable at the ecosystem level. The 3rdJ-NABS special issue on tropical streams was “New vistas in Neotropical stream ecology” and was published in 2006 (Wantzen et al. 2006). It included studies undertaken at sites in Central and South America and the Caribbean, and embraced an array of topics, including caddisfly biology, organic-matter processing, algal biomass, invertebrate distribution, fish biogeography, and ecological assessment. This issue was concerned solely with the Neotropics, but it demonstrated that understanding of tropical stream ecology had progressed substantially. This 4th compendium of tropical stream studies arose from a special session, “Are tropical streams ecologically different?,” during the 54th annual meeting of the North American Benthological Society (2006; Anchorage, Alaska, USA). The goals of the session were to present novel patterns and notions on the functioning of tropical streams with a special emphasis on energy sources and pathways fueling the ecosystem and the consumers they support and to provide a broad geographical context that would allow comparisons among different tropical areas. This strategy, it was hoped, would yield some generalizations about tropical stream ecosystem processes. This special issue includes most of the research presented at that session and some additions. Studies represent a wide array of tropical streams, including those in Central America (Costa Rica), South America (Venezuela), Asia (Hong Kong and Peninsular Malaysia), Africa (Madagascar), and the Pacific islands (Micronesia), and some subtropical streams (northern New South Wales, Australia). It includes an analysis of global-scale latitudinal patterns in freshwater biodiversity. Given the small number of studies making up this issue, the extent to which they reveal novel and unexpected patterns is surprising. They confirm the variability of conditions and environments in streams within the tropics and underscore the need for further studies of streams from all tropical regions. Such investigations should include basic taxonomic work, autecological studies, and elucidation of ecological processes and interactions, including foodweb structure and dynamics.