Compositional change in fish assemblages along the Andean piedmont - Llanos floodplain gradient of the río Portuguesa, Venezuela

Abstract

The Llanos is an extensive area of savannas and floodplains in central and western Venezuela that encompasses a gradual elevation gradient from the río Orinoco to the foothills of the Andean piedmont. The río Portuguesa is one of the major rivers in this region that until recently had escaped major anthropogenic impacts and still maintains substantial seasonal fish migrations. However, little work has been conducted on fish ecology in this river. The present study analyzes museum collections sampled at 28 locations along the longitudinal gradient of the río Portuguesa to assess similarity of species composition from the foothills of the Andean piedmont to the lowland llanos floodplain. The standardized samples used in this analysis contained greater than 133 species representing 6 orders and 27 families, dominated by characiforms (61 species) and siluriforms (52 species). Detrended correspondence analysis (DCA) ordination of samples revealed a continual pattern of compositional change, and species are added at a faster rate than they are lost as one moves from the foothills of the piedmont to the low llanos. Based on DCA, samples from three elevational segments were found to significantly differ in fish species composition. Assemblages in the upper reaches contained unique species of loricariid catfishes, small pimelodid and trichomycterid catfishes, and small characiforms not observed at lower elevations. The lowland reach contained species of cichlids, large catfishes and characids not collected from the other two regions. Samples from the middle region revealed transitional species composition. Longitudinal species turnover probably reflects differences in environmental characteristics such as a water velocity, substrate composition and disturbance regime. Findings from this broad-scale analysis contribute to a baseline for future studies of fish ecology in this region.<br>Llanos corresponde a uma área extensa de savanas e planícies de inundação situadas no centro e no oeste da Venezuela, abrangendo um gradiente de elevação desde o rio Orinoco até a região montanhosa na base da cordilheira dos Andes. O rio Portuguesa é um dos principais rios desta região, até recentemente livre de maiores impactos antropogênicos, mantendo relevantes migrações sazonais de peixes. Apesar disto, poucos estudos sobre ecologia de peixes têm sido conduzidos neste ambiente. O presente estudo analisa coleções de museus amostradas em 28 locais ao longo do gradiente longitudinal do rio Portuguesa, avaliando a similaridade na composição das espécies desde a região montanhosa na base da cordilheira dos Andes até as terras baixas da planície de inundação do Llanos. As amostras padronizadas utilizadas nesta análise continham mais de 133 espécies, representando 6 ordens e 27 famílias, dominadas por caraciformes (61 espécies) e siluriformes (52 espécies). A ordenação das amostras através da análise de correspondência com remoção do efeito do arco (DCA) revelou um padrão contínuo de mudança na composição, com taxa de adição de espécies superio...

Patterns in fish species composition and assemblage structure in the upper Salado River lakes, Pampa Plain, Argentina

“…This was early highlighted for steeped temperate rivers in North America (Burton & Odum, 1945), Europe (Huet, 1949) and South America (Petry & Schulz, 2006). This pattern was also revealed in tropical fluvial ecosystems where altitudinal gradient seems to be one of the most important factors determining fish species distribution (Hoeinghaus et al, 2004;Súarez & Petrere Júnior, 2007). Under such conditions, in spite of the higher number of species at lower reaches, some fish species occur exclusively at headwaters whereas others occur exclusively at downstream.…”

Environmental factors predicting fish community structure in two neotropical rivers in Brazil

“…Among the fewer, comparable studies in tropical regions, especially the Neotropics, are the studies of Garutti (1988), Uieda & Barreto (1999), Mazzoni & Lobón-Cerviá (2000), Abes & Agostinho (2001), Pavanelli & Caramaschi (2003), Chernoff et al (2004), Hoeinghaus et al (2004), Layman & Winemiller (2005), and Arrington & Winemiller (2006).…”

Evolución De La Integridad Estructural De Ecosistemas Lóticos Del Piedemonte Llanero Frente a La Intervención Antrópica

“…Algunos autores, por ejemplo, sostienen que la riqueza y diversidad de la comunidad íctica en los ríos no está relacionada directamente con la cobertura de bosques riparios sino con la anchura del canal, la profundidad y el caudal (Angermeier y Karr, 1983;Bojsen y Barriga, 2002;Hoeinghaus et al, 2004) mientras que otros investigadores afirman que la heterogeneidad espacial y la cobertura de bosques de galería, en corrientes como las del piedemonte llanero colombiano, produce un incremento de la riqueza y diversidad ícticas ya que obedece a un ordenamiento discontinuo de hábitats en mosaico y no a un continuo longitudinal como acontece con otros ríos que descienden desde un gradiente altitudinal. (Briceño et al, 1996;Flecker, 1997;Winemiller y Jepsen, 1998).…”

“…Los tipos de impacto antrópico en las áreas de piedemonte y su efecto sobre la biodiversidad han sido investigados en corrientes de Venezuela (Winemiller et al, 1996;Hoeinghaus et al, 2004;Allan et al, 2006, Allan et al 2012, Colombia (Briceño et al, 1998;Ricaurte et al, 2012), Panamá (Angermeier y Karr, 1983), Argentina (Bistoni et al 1999), Trinidad (Fraser et al 1999), Brasil (Abes y Agostinho, 2001), Ecuador (Bogsen y Barriga, 2002), Estados Unidos (Freeman y Marcinek, 2006;Utz et al, 2010) y en una amplia gama de corrientes tropicales (Wohl 2006;Xin et al, en prensa, 2014). Las causas de estos impactos son muy variadas: urbanización de las cuencas, deforestación, desbalance por mal manejo del recurso hídrico, sedimentación, contaminación del agua por actividades domésticas y agropecuarias y fragmentación de los bosques (Winemiller et al, 1996;Allan et al, 2006;Freeman y Macinek, 2006;Utz et al, 2010).…”