Are tropical streams really different?

Abstract

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 238N and 238S, 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.