Physical habitat as predictor of fish trophic structure in Brazilian Atlantic rainforest streams

Trophic structure of fish assemblages is one of the most sensitive indicators of changes in streams environments. Since it is crucial to understand the response of trophic groups to habitat alteration, our study aimed to address this research gap by assessing the influence of substrate composition, meso-habitat variability, and bank stability, on the richness, biomass, and number of individuals of carnivores, invertivores, omnivores, and herbivorous-detritivores. Using an electrofishing device, we sampled 13 Atlantic rainforest streams reaches in a degradation gradient, located in the upper Paranapanema river basin. Sample points were ranked using a physical habitat index. More pristine streams had high availability of twigs, trunks, rocks and boulders in the substrate, great meso-habitat variability, and the presence of roots, trunks, and rocks in the margins. Canonical correlations between habitat characteristics and trophic groups explained more than 90% of data variability. Richness and number of individuals of invertivores increased in more preserved stream reaches, while richness of carnivores and number of individuals of omnivores decreased. These results demonstrate that trophic structure varies according to level of degradation, and that invertivore richness represents the best indicator of fish trophic structure responses to physical habitat alterations in streams.(AU)

A estrutura trófica da assembleia de peixes é um dos indicadores mais sensíveis a alterações ambientais em riachos. Considerando a relevância de entender a resposta de grupos tróficos à alteração ambiental, este estudo buscou preencher esta lacuna científica avaliando a influência da composição do substrato, variabilidade de meso-hábitats e estabilidade das margens sobre riqueza, biomassa e número de indivíduos de peixes carnívoros, invertívoros, onívoros e herbívoros-detritívoros. Amostramos com pesca elétrica 13 trechos de riachos de Mata Atlântica com estado de conservação variável, localizados na parte superior da bacia do alto rio Paranapanema. Os pontos amostrais foram ranqueados pelo índice de hábitat fisico. Riachos mais presevados apresentaram mais galhos, troncos, matacões e blocos no substrato, maior variabilidade de meso-hábitats e maior quantidade de raízes, troncos e rochas nas margens. As correlações canônicas explicaram mais de 90% da variabilidade dos dados. A riqueza e o número de indivíduos de invertívoros aumentaram em riachos mais preservados, enquanto que a riqueza de carnívoros e o número de indivíduos onívoros diminuíram. Estes resultados demonstram que a estrutura trófica varia em resposta ao nível de preservação, e que a riqueza de invertívoros é o melhor indicador de respostas da estrutura trófica às alterações do hábitat em riachos.(AU)

Variación espacial y temporal en la composición de la dieta de peces invertívoros en un río neotropical, Venezuela

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.