Large woody debris input and its influence on channel structure in agricultural lands of Southeast Brazil.

Riparian forests are important for the structure and functioning of stream ecosystems, providing structural components such as large woody debris (LWD). Changes in these forests will cause modifications in the LWD input to streams, affecting their structure. In order to assess the influence of riparian forests changes in LWD supply, 15 catchments (third and fourth order) with riparian forests at different conservation levels were selected for sampling. In each catchment we quantified the abundance, volume and diameter of LWD in stream channels; the number, area and volume of pools formed by LWD and basal area and tree diameter of riparian forest. We found that riparian forests were at a secondary successional stage with predominantly young trees (diameter at breast height <10 cm) in all studied streams. Results showed that basal area and diameter of riparian forest differed between the stream groups (forested and non-forested), but tree density did not differ between groups. Differences were also observed in LWD abundance, volume, frequency of LWD pools with subunits and area and volume of LWD pools. LWD diameter, LWD that form pools diameter and frequency of LWD pools without subunits did not differ between stream groups. Regression analyses showed that LWD abundance and volume, and frequency of LWD pools (with and without subunits) were positively related with the proportion of riparian forest. LWD diameter was not correlated to riparian tree diameter. The frequency of LWD pools was correlated to the abundance and volume of LWD, but characteristics of these pools (area and volume) were not correlated to the diameter of LWD that formed the pools. These results show that alterations in riparian forest cause modifications in the LWD abundance and volume in the stream channel, affecting mainly the structural complexity of these ecosystems (reduction in the number and structural characteristics of LWD pools). Our results also demonstrate that riparian forest conservation actions must consider not only its extension, but also successional stage to guarantee the quantity and quality of LWD necessary to enable the structuring of stream channels.

A new remarkable and Critically Endangered species of Astyanax Baird & Girard (Characiformes: Characidae) from Chapada Diamantina, Bahia, Brazil, with a discussion on durophagy in the Characiformes.

Astyanax brucutu is described from the rio Pratinha, rio Paraguaçu basin, Bahia, Brazil. The new species is promptly distinguished from other characids by having four, rarely three, robust, rounded, and usualy tricuspid teeth on inner premaxillary series and similar teeth on dentary. The species is furthermore characterized by a series of unusual character states in the Characidae, including head blunt in lateral and dorsal views, longitudinal foreshortening of lower jaw, ventral margin of third infraorbital distinctly separated from horizontal limb of preopercle, leaving a broad area without superficial bones, mesethmoid anteroventrally expanded, and adductor mandibulae and primordial ligament remarkably developed. Analysis of gut contents of adults revealed the almost exclusive presence of crushed shells of tiny gastropods of the family Hydrobiidae. The robust anatomy of jaws, teeth, muscles and associated ligaments are likely adaptations to durophagy, a feeding strategy unusual among characids. Astyanax brucutu is known only from its type locality, an approximately 670 m long, transparent and isolated perennial epigean watercourse surrounded by subterranean or intermittent rivers. The distinctive combination of environmental features characterizing the area of occurrence of the new species is not observed elsewhere in the basin or adjacent basins. A series of severe anthropogenic impacts, associated with the restricted geographic range of the species, implies that A. brucutu should be regarded as Critically Endangered (CR) according to IUCN Red List Criteria.

When roads cross streams: fish assemblage responses to fluvial fragmentation in lowland Amazonian streams

Roads affect biodiversity by increasing mortality rates, habitat loss, and natural landscape fragmentation. Poorly installed culverts can impound streams, changing the environmental conditions, and affecting aquatic communities. We evaluated the effects of road crossings on the taxonomic composition and functional structure of fish assemblages in lowland eastern Amazonian streams, Brazil. We tested the hypothesis that the presence of road-derived impoundments affects assemblage taxonomic and functional composition and structure. Two predictions were addressed: (1) Species and functional group composition will differ in impounded reaches in relation to lotic reaches; (2) Assemblages in downstream lotic reaches will be richer in species and functional groups in relation to upstream lotic and impoundment reaches. We sampled five streams crossed by roads presenting impoundment formation, conducted by visual census (day, dusk, and night) in 200 m line transects. Assemblage composition from lentic reaches was different from lotic reaches, and Shannon diversity from downstream reaches was different from upstream and impoundment, however, beta diversity partitioning between lotic reaches showed higher nestedness contribution, reinforcing the role of impoundment in limiting fish dispersal between lotic reaches. These results suggest that impoundments impose environmental and dispersal constraints to fish, affecting their longitudinal distribution in streams fragmented by roads.(AU)

Estradas afetam a biodiversidade aumentando as taxas de mortalidade, perda de hábitat e fragmentação. Cruzamentos mal instalados represam riachos, alterando as condições ambientais e afetando as comunidades aquáticas. Avaliamos os efeitos deste impacto sobre a estrutura taxonômica e funcional das assembleias de peixes em riachos da Amazônia Oriental, Brasil. Testamos a hipótese de que a presença dos alagados derivados de estradas afeta a composição e estrutura taxonômica e funcional das assembleias. Nossas predições foram: (1) A composição de espécies e grupos funcionais é diferente entre trechos alagados e lóticos; (2) Assembleias nos trechos à jusante serão mais ricas em espécies e grupos funcionais que os trechos à montante e alagados. Amostramos cinco riachos cruzados por estradas com formação de alagamentos por censo visual (dia, crepúsculo e noite) em transectos lineares de 200 m. A composição das assembleias dos trechos lênticos diferiu dos lóticos, e a diversidade de Shannon à jusante diferiu dos trechos montante e alagados, entretanto, nos lóticos, houve maior contribuição do aninhamento na partição da diversidade beta, reforçando o papel do represamento na limitação da dispersão de peixes entre estes. Sugerimos que os represamentos impõem restrições ambientais e de dispersão aos peixes, afetando sua distribuição longitudinal em riachos fragmentados por estradas.(AU)

Functional trophic composition of the ichthyofauna of forest streams in eastern Brazilian Amazon

This study aimed to describe the functional organization of the ichthyofauna of forest streams from northeastern Pará State, Brazil, based on behavioral observation of species' feeding tactics. Seven streams were sampled between June and November, 2010, during snorkeling sessions, totaling 91h 51min of visual censuses at day, dusk, and night periods. Seventy three species distributed in six orders, 26 families and 63 genera were observed, with dominance of Characiformes, followed by Siluriformes. From information gathered by ad libitum observations, each species was included in one of 18 functional trophic groups (FTGs), according to two main characteristics: (1) its most frequently observed feeding tactic; and (2) its spatial distribution in the stream environment, considering their horizontal (margins or main channel) and vertical (water column) dimensions. The most frequent FTGs observed were Nocturnal invertebrate pickers (9 species), Diurnal channel drift feeders (8 spp.), Diurnal surface pickers (7 spp.), and Ambush and stalking predators (6 spp.). The FTGs herein defined enable a comparative analysis of the structure and composition of ichthyofauna in different basins and environmental conditions, which presents an alternative approach to the use of taxonomic structure in ecological studies. The ichthyofauna classification based in FTGs proposed in this study is compared to three other classifications, proposed by Sazima (1986), Sabino & Zuanon (1998) and Casatti et al. (2001). .

Este estudo teve como objetivo descrever a organização funcional da fauna de peixes de riachos do nordeste do estado do Pará, Brasil, com base em observações comportamentais das táticas alimentares das espécies. Sete igarapés foram amostrados entre junho e novembro de 2010 por técnicas de observações diretas durante sessões de mergulho livre, totalizando 91h 51min de observação, nos períodos diurno, crepuscular vespertino e noturno. Foram observadas 73 espécies distribuídas em seis ordens, 26 famílias e 63 gêneros, com predomínio de Characiformes, seguidos por Siluriformes. A partir de informações coligidas por observações ad libitum, as espécies foram organizadas em 18 grupos tróficos funcionais (GTFs), de acordo com duas características principais: (1) a tática alimentar observada com maior frequência; e (2) sua distribuição espacial no riacho, considerando suas dimensões lateral (margens e canal central) e vertical (coluna d'água). Os GTFs mais frequentes foram Catadores noturnos de invertebrados (9 espécies), Coletores diurnos de canal (8 spp.), Catadores diurnos de superfície (7 spp.), e Predadores de tocaia e emboscada (6 spp.). Os GTFs aqui definidos possibilitam uma análise comparativa da estrutura e composição da ictiofauna, que representa uma abordagem alternativa ao uso da estrutura taxonômica em estudos ecológicos. A classificação da ictiofauna baseada em GTFs proposta neste trabalho é comparada com outras três classificações, propostas por Sazima (1986), Sabino & Zuanon (1998) e Casatti et al. (2001).