ABSTRACT
RESUMEN En los trópicos, el cambio climático puede significar un incremento en la temperatura que puede afectar la diversidad biológica de los ecosistemas fluviales, favoreciendo la llegada de especies propias de aguas más cálidas. La variación de temperatura puede también afectar las relaciones tróficas y el metabolismo del sistema. En el presente estudio, se analizó el efecto de 2-4 °C de aumento de la temperatura del agua sobre el ensamble de diatomeas y el metabolismo del río Tota (alta montaña andina). Para este propósito, se utilizaron canales artificiales de recirculación, en los que diariamente se midieron variables fisicoquímicas (pH, conductividad, temperatura, oxígeno disuelto y velocidad del agua), se recolectaron e identificaron diatomeas, se midió la clorofila-a y el metabolismo mediante cámaras recirculantes. Se encontraron diferencias significativas entre las variables fisicoquímicas medidas. Aunque no se pudo detectar diferencias significativas en la variables respuesta atribuibles al aumento de la temperatura, si hubo respuestas cualitativas en la clorofila y en el metabolismo. El trabajo experimental representa un aporte para el estudio del impacto del aumento de temperatura sobre los sistemas lóticos de alta montaña en Colombia. Los resultados ilustran los posibles cambios que se pueden registrar en los sistemas de alta montaña andina como consecuencia del cambio climático.
ABSTRACT The variation in temperature associated with climate change in the tropics may affect biodiversity of river ecosystems, favoring the arrival of warmer water species. The variation in temperature can also affect the trophic relationships and metabolism of the river ecosystem. In the present study, we sought to determine the effect of 2-4 °C increase of water temperature in the river Tota (Andean high mountain) on the diatoms assemblage and river metabolism. For this purpose, artificial recirculation channels were used, and physicochemical variables (pH, conductivity, temperature, dissolved oxygen and water velocity) were daily measured, diatoms were collected and identified, chlorophyll-a was measured, and metabolism was estimated by means of recirculating chambers. We find significant differences in the physicochemical variables. Qualitative changes in chlorophyll and metabolism were observed, but significant differences in response variables attributable to the increase in temperature could not be detected. The experimental work represents an input to studies about temperature increase impact over high mountain lotic systems. The results illustrate the possible changes that can be recorded in the Andean high mountain systems as a result of climate change.
ABSTRACT
Spatial and temporal variation in diet composition of invertivore fishes in a tropical stream, Venezuela. Invertivores fishes are an important component of neotropical streams and they represent a link between aquatic invertebrates and piscivorous species. This study evaluated the breadth diet and interspecific food overlap of nine invertivores fish species during three consecutive hydrological phases: falling (December/07, January/08, February/08 and March/08), low (April/08) and rising waters (June/08), in two sections of a Venezuelan neotropical stream, which were located at different elevation, high watershed (HW) and low watershed (LW). The fishes were collected with a beach seine (5mm mesh) between 8:00 and 11:00 hours. The diet of each species was evaluated using an index of relative importance (IRI), which includes as variables the number, weight and occurrence frequency of food items consumed. The Levin’ index (Bi) and Morisita (IM) were used to estimate the breadth diet and interspecific food overlap, respectively. All estimations were made using the numeric proportion of preys. Nine fish species were captured, eight Characiformes, of which three were captured in HW (Knodus deuteronoides, Creagrutus bolivari and C. melasma) and five in LW (Thoracocharax stellatus, Moenkhausia lepidura, Cheirodon pulcher, Ctenobrycon spilurus and Aphyocharax alburnus), and one Cyprinodontiformes (Poecilia reticulata), which was also found in HW. In HW aquatic insects were the main resource consumed by fishes while plant material and terrestrial arthropods were secondary resources. In LW the fishes ingested all of these items in addition to zooplankton (Copepoda, Cladocera and larval stages of Decapoda). However, there was a temporal replacement with a predominance of zooplankton in falling and low water. In general, the breadth diet decreased during the falling water in both sections and increased in rising water. However, the average breadth diet was higher in HW. The interspecific food overlap was high in HW while low values were more frequent in LW and its temporal variation was opposed in both sections during almost all the sampling period. Rev. Biol. Trop. 59 (3): 1217-1231. Epub 2011 September 01.
La ictiofauna invertívora es un componente importante en los ríos neotropicales y representa un enlace entre los invertebrados acuáticos y los piscívoros. En el presente trabajo se evaluó la amplitud y sobreposición interespecífica de dieta de nueve especies de peces invertívoros durante tres fases hidrológicas consecutivas: descenso (diciembre/07, enero/08, febrero/08, marzo/08), aguas bajas (abril/08) y ascenso de aguas (junio/08) en dos secciones de un río venezolano ubicadas a distinta altitud (subcuenca alta, SA y subcuenca baja, SB). Los peces se recolectaron con una red de cerco (0.5cm entrenudos) entre las 8:00 y 11:00 horas. La dieta de cada especie se evaluó usando un índice de importancia relativa (IIR) que incluyó el número, peso y frecuencia de ocurrencia de los items consumidos. Para estimar la amplitud y sobreposición interespecífica de dieta se emplearon los índices de Levín (Bi) y Morisita (IM), respectivamente. Todas las estimaciones se realizaron con la frecuencia numérica de las presas consumidas. Se capturaron nueve especies, ocho Characiformes, tres en SA (Knodus deuteronoides, Creagrutus bolivari y C. melasma) y cinco en SB (Thoracocharax stellatus, Moenkhausia lepidura, Cheirodon pulcher, Ctenobrycon spilurus y Aphyocharax alburnus) y un Cyprinodontiformes (Poecilia reticulata), capturada en SA. En SA el principal recurso consumido fueron insectos acuáticos mientras que el material vegetal y los artrópodos terrestres fueron recursos secundarios. En SB, las especies consumieron estos items además de zooplancton (Copepoda, Cladocera y estadios larvales de crustáceos Decapoda), pero hubo una sustitución temporal con un predominio de zooplancton en descenso y aguas bajas. En general, la amplitud de la dieta disminuyó en descenso de aguas en ambas secciones e incrementó en ascenso de aguas. Sin embargo, la amplitud promedio fue mayor en SA. La sobreposición interespecífica de dieta fue alta en SA mientras que en SB fueron más frecuentes los valores bajos y en casi todo el registro su variación temporal fue opuesta en ambas secciones.
Subject(s)
Animals , Feeding Behavior/physiology , Fishes/physiology , Fishes/classification , Gastrointestinal Contents , Rivers , Seasons , VenezuelaABSTRACT
Taxonomically, blackflies (Simuliidae) are among the best-known aquatic insects in Brazil. However, information on their distribution is lacking for many regions. We sampled simuliids in 50 streams in the Chapada Diamantina region, State of Bahia, located in three distinct geographical areas, 20 at Lençóis, 18 at Mucugê, and 12 at Rio de Contas. We analyzed simuliid species richness and distribution in the Chapada Diamantina area as a whole, as well as in each of the three distinct geographical areas. We collected 20 species, three of which were not yet described and two were described after our sampling. The three areas are distinct in relation to environmental variables, mainly owing to differences in altitude and water pH. Four species were restricted to Rio de Contas, while four other species were restricted to Mucugê. Sixteen species were present in Mucugê and fifteen in Rio de Contas. Only twelve species were present in Lençóis, despite the higher sampling effort. Rio de Contas appears to be the area that harbors the highest species richness. Species richness was related to environmental factors only when evaluated on a small spatial scale (i.e. when each area was analyzed separately). Although we have not tested for causal relationships, our findings agree with other studies that showed that pH and altitude are important factors with which species richness and species distribution appear to be associated.
A família Simuliidae é taxonomicamente uma das mais conhecidas entre os insetos aquáticos no Brasil. No entanto, faltam informações relativas à sua distribuição em muitas regiões do Brasil. Foram coletadas larvas e pupas de borrachudos em 50 riachos na região da Chapada Diamantina, BA, localizados em três regiões geográficas distintas, 20 em Lençóis, 18 em Mucugê e 12 em Rio de Contas. Foram analisadas a riqueza e distribuição de espécies da área da Chapada Diamantina como um todo, bem como em cada uma das três áreas geográficas distintas. Coletamos 20 espécies, das quais três ainda não foram descritas e duas foram descritas após este estudo. As três áreas são distintas em relação às variáveis ambientais, principalmente devido às diferenças de altitude e pH da água. Quatro espécies foram coletadas apenas em Rio de Contas, enquanto outras quatro apenas em Mucugê. Dezesseis espécies foram encontradas em Mucugê e quinze em Rio de Contas, enquanto em Lençóis encontramos apenas doze espécies, mesmo com o maior esforço de amostragem exercido naquela região. Rio de Contas parece ser a região que abriga a maior riqueza de espécies. A riqueza de espécies foi relacionada a fatores ambientais apenas quando avaliada em pequena escala espacial (ou seja, quando cada área foi analisada separadamente). Apesar de não ter sido realizado um teste causal, os resultados aqui obtidos corroboram outros estudos que mostraram que o pH e altitude são fatores importantes com os quais a riqueza e a distribuição de borrachudos podem estar associadas.