RESUMO
Studies on elevation diversity gradients have covered a large number of taxa and regions throughout the world; however, studies of freshwater fish are scarce and restricted to examining their changes along a specific gradient. These studies have reported a monotonic decrease in species richness with increasing elevation, but ignore the high taxonomic differentiation of each headwater assemblage that may generate high ß-diversity among them. Here, we analyzed how fish assemblages vary with elevation among regional elevation bands, and how these changes are related to four environmental clines and to changes in the distribution, habitat use, and the morphology of fish species. Using a standardized field sampling technique, we assessed three different diversity and two structural assemblage measures across six regional elevation bands located in the northern Andes (Colombia). Each species was assigned to a functional group based on its body shape, habitat use, morphological, and/or behavioral adaptations. Additionally, at each sampling site, we measured four environmental variables. Our analyses showed: (1) After a monotonic decrease in species richness, we detected an increase in richness in the upper part of the gradient; (2) diversity patterns vary depending on the diversity measure used; (3) diversity patterns can be attributed to changes in species distribution and in the richness and proportions of functional groups along the regional elevation gradient; and (4) diversity patterns and changes in functional groups are highly correlated with variations in environmental variables, which also vary with elevation. These results suggest a novel pattern of variation in species richness with elevation: Species richness increases at the headwaters of the northern Andes owing to the cumulative number of endemic species there. This highlights the need for large-scale studies and has important implications for the aquatic conservation of the region.
RESUMO
This paper summarizes the available information on the geology, hydrology, and biota of coastal streams located in the Gorgona National Natural Park (GNNP), and the Baudó and Darién ecoregions within the Biogeographic Chocó (Colombia). Despite of the scant number of studies, we hypothesized that these streams are consistent with the typology observed in volcanic oceanic islands in the Caribbean and the Pacific that do not conform to the tenets of the River Continuum Concept. Coastal streams in the Biogeographic Chocó are short (10(0)-10¹km) and steep and waterfalls and cascades are frequent due to tectonic origin. Step-and-pool sequences are common in montane reaches, while cobble-bed glides and riffles dominate in coastal plain reaches. Flow regimes are flashy in Pacific drainages (annual rainfall: <7000mm), but seasonally dry in the Caribbean drainages (<3500mm). Therefore, floods and droughts are important drivers of communities and ecosystem processes. Canopies are closed in low-order streams discharging directly to the ocean, thus contributing large amounts of litter. Diadromous fish and shrimp dominate consumer assemblages and various species are shared with streams in the Central America and the Antilles. These species play ecological roles probably equivalent to those found in other regions. These coastal streams are unique in terms of the number of primary freshwater fishes found (some endemics), and the functionally absence of diadromous gastropods. Rev. Biol. Trop. 62 (Suppl. 1): 43-64. Epub 2014 February 01.
A pesar de la escasez de estudios sobre la geología, hidrología y biota de las quebradas costeras ubicadas en el Chocó Biogeográfico, se hipotetiza que éstas se ajustan a la tipología observada en las islas oceánicas volcánicas del Caribe y el Pacífico, las cuales no cumplen con las predicciones del Concepto del Río Continuo. Estas quebradas son cortas (<10¹km) y muy pendientes debido a su origen tectónico, y presentan lechos dominados por bloques y cantos rodados. El régimen de caudal es torrencial en la vertiente Pacífico, pero estacionalmente seco en la vertiente Caribe. Los doseles cerrados aportan grandes cantidades de hojarasca a las quebradas que desembocan al mar con bajo orden. Las especies diádromas, con afinidades centroamericanas y antillanas, dominan los ensamblajes y posiblemente cumplen papeles ecológicos equivalentes a los establecidos en otras regiones. Particularmente, las quebradas costeras de esta provincia presentan varias especies de peces dulceacuícolas primarios, algunas endémicas, y carecen de gasterópodos. Los procesos geomorfológicos e hidrológicos de las cabeceras influyen sobre la dinámica ecosistémica de estas quebradas. Se proponen cinco hipótesis sobre la estructura y composición comunitaria. Se advierte que el PNNG es un modelo útil para la ecología lótica costera, pero que tiene particularidades.