Browsing by Autor "Milton Zapata"

Now showing 1 - 2 of 2

Clasificación de Cuencas de Bolivia según la metodología de Pfafstetter / Classification of river basins of Bolivia using the method of Pfafstetter
(2013) Álvaro Martínez Crespo; Paul Van Damme; Milton Zapata
Hasta el momento, las cuencas en Bolivia no han sido clasificadas con un sistema estandar. Las clasificaciones existentes son subjetivas y generalmente no aplican sistemas de jerarquizacion. En este trabajo se aplico el metodo de Pfafstetter, reconocido a nivel mundial, el cual es de caracter numerico, topologico y natural porque sigue la direccion del drenaje del agua. Se ha podido clasificar las cuencas hasta el octavo nivel en algunos sistemas y para todo el territorio hasta el cuarto nivel. Se presenta un mapa de cuencas combinando diferentes niveles, y se discuten las posibles aplicaciones. Palabras clave: Cuencas, Pfafstetter, Bolivia, Clasificacion. ABSTRACT There does not exist a standard classification system for river basins in Bolivia. Most of the existing classification systems are subjective and do not consider hierarchical ranking of river basins. We present a classification system based on the Pfafstetter method, recognized internationally as a standard. This methodology is numerical, topological and natural because it follows the direction of the drainage water. Watersheds were classified until the eighth level in some regions and until the fourth level in the whole territory. We present a map combining different levels, and discuss possible applications. Key words: River basins, Pfafstetter, Bolivia, Classification
Evidence of history in explaining diversity patterns in tropical riverine fish
(Wiley, 2005) Pablo A. Tedesco; Thierry Oberdorff; Carlos A. Lasso; Milton Zapata; Bernard Hugueny
Abstract Aim Documentation of the ongoing effect of rain forest refuges at the last glacial maximum (LGM) on patterns of tropical freshwater fish diversity. Location Tropical South and Central America, and West Africa. Methods LGM rain forest regions and species richness by drainage were compiled from published data. GIS mapping was applied to compile drainage area and contemporary primary productivity. We used multiple regression analyses, applied separately for Tropical South America, Central America and West Africa, to assess differences in species richness between drainages that were connected and disconnected to rain forest refuge zones during the LGM. Spatial autocorrelation of the residuals was tested using Moran's I statistic. We added an intercontinental comparison to our analyses to see if a historical signal would persist even when a regional historical effect (climate at the LGM) had already been accounted for. Results Both area and history (contact with LGM rain forest refuge) explained the greatest proportions of variance in the geographical pattern of riverine species richness. In the three examined regions, we found highest richness in drainages that were connected to the rain forest refuges. No significant residual spatial autocorrelation was detected after considering area, primary productivity and LGM rain forest refuges. These results show that past climatic events still affect West African and Latin American regional and continental freshwater fish richness. At the continental scale, we found South American rivers more species‐rich than expected on the basis of their area, productivity and connectedness to rain forest refuge. Conversely, Central American rivers were less species‐diverse than expected by the grouped model. African rivers were intermediate. Therefore, a historical signal persists even when a regional historical effect (climate at the LGM) had already been accounted for. Main conclusions It has been hypothesized that past climatic events have limited impact on species richness because species have tracked environmental changes through range shifts. However, when considering organisms with physically constrained dispersal (such as freshwater fish), past events leave a perceptible imprint on present species diversity. Furthermore, we considered regions that have comparable contemporary climatic and environmental characteristics, explaining the absence of a productivity effect. From the LGM to the present day (a time scale of 18,000 years), extinction processes should have played a predominant role in shaping the current diversity pattern. By contrast, the continental effects could reflect historical contingencies explained by differences in speciation and extinction rates between continents at higher time scales (millions of years).