Patterns of richness, diversity and abundance of an odonate assemblage from a tropical dry forest in the Santiago Dominguillo Region, Oaxaca, México (Insecta: Odonata).

A study on the patterns of richness, diversity and abundance of the Odonata from Santiago Dominguillo, Oaxaca is presented here. A total of 1601 specimens from six families, 26 genera and 50 species were obtained through monthly samplings of five days each. Libellulidae was the most diverse family (21 species), followed by Coenagrionidae (19), Gomphidae (4) and Calopterygidae (3). The Lestidae, Platystictidae and Aeshnidae families were the less diverse, with only one species each. Argia was the most speciose genus with 11 species, followed by Enallagma, Hetaerina, Erythrodiplax and Macrothemis with three species each and Phyllogomphoides, Brechmorhoga, Dythemis, Erythemis and Orthemis with two species each. The remaining 17 genera had one species each. Argia pipila Calvert, 1907 and Leptobasis vacillans Hagen in Selys, 1877 were recorded for the first time for the state of Oaxaca. We also analysed the temporal patterns of taxonomic and phylogenetic divergence for the Santiago Dominguillo Odonata assemblage: the Shannon diversity value throughout the year was 21.07 effective species, while the Simpson diversity was 13.17. In general, the monthly phylogenetic divergence was higher than expected for taxonomic distinctness, and lesser for average taxonomic distinctness. Monthly diversity, evenness and taxonomic divergence showed significant positive correlations (from moderate to strong) with monthly precipitation values. The analysis of our results, however, indicates that an increase in rainfall not only influences the temporal diversity of species, but also the identity of supraspecific taxa that constitute those temporal assemblages, i.e. there is an increase in temporal phylogenetic divergence.

The longest fragment drives fish beta diversity in fragmented river networks: Implications for river management and conservation.

Connectivity plays a crucial role in maintaining the structural and functional attributes of river networks. Therefore, the loss of connectivity (fragmentation) alters the functioning and diversity patterns of the biota at local and regional scales. The global hydropower boom is one of the main drivers of river network fragmentation, with significant effects on the diversity of riverine biota. Analyses of beta diversity of fish assemblages in rivers with different degrees of fragmentation can give new insights into mechanisms that contribute to the responses of these assemblages to fragmentation. Here, fish beta diversity within six river networks of central Chile with different levels of fragmentation was studied to assess the responses of fish assemblages to fragmentation. A hypothesis of a significant effect of fragmentation on the beta diversity of native and non-native fish in riffles and pools was tested. This effect is expected to be modulated by both changes in environmental heterogeneity and direct obstruction of natural dispersal routes. Beta diversity based on variation of assemblage structure and environmental heterogeneity showed significant differences among river networks. Fish beta diversity showed a clear response to fragmentation in recently fragmented rivers. Specifically, the beta diversity of native fishes in pools and non-native fishes in riffles decreased with increase of the ratio between the longest non-fragmented sections of the river network to the total length of the network. These effects of fragmentation on fish assemblages were modulated by the biological features of each species, and open-water species were most severely affected. These results have significant implications for planning of the placement of new barriers in river networks subjected to hydropower boom. Planning of the placement of new barriers should consider the maintenance of long, connected sections within river networks in order to minimise the effects of fragmentation on fish biodiversity.

The influence of agricultural occupation and climate on the spatial distribution of Plusiinae (Lepidoptera: Noctuidae) on a latitudinal gradient in Brazil

Abstract Studies have reported the presence of certain Plusiinae species in both natural and agricultural landscapes, but their turnover in association with agricultural activities remains unexplored. Aiming to understand how the assemblages of Plusiinae are structured by agricultural occupation and climate, this study used automated light traps sampled moths in 18 sites in Brazil, across a broad latitudinal gradient. Our data has demonstrated that climate variables prevails as the most important variables influencing both the composition of Plusiinae and the abundance of its dominant species Chrysodeixis includens. On the other hand, the lack of significance found for the effect of variables representing agricultural occupation evidences that pest species are present both in agricultural and natural ecosystems, also sharing similar abundances at those locations. In other words, instead of following a gradient of agricultural occupation (e.g. crop sizes around sample sites) the composition of these extremely polyphagous insects is more clearly shaped by the latitudinal gradient, in which temperature and precipitation are better predictors. Thus, in contrary to our expectations, pest species inhabits both natural and agricultural landscapes at similar latitudinal sites, probably due to their wide polyphagy spectrum. These results can be used in management and monitoring programs of pest species in South America, since the local abundance variation and species composition can be more reliable predicted by changes in climate conditions.

Environmental structure affects taxonomic diversity but not functional structure of understory birds in the southwestern Brazilian Amazon / Estrutura ambiental afeta a diversidade taxonômica, mas não a estrutura funcional de aves de sub-bosque no sudoeste da Amazônia brasileira

Changes in environmental characteristics can affect habitat use by birds, impacting the number of individuals, number of species, and changing species composition and functional structure of assemblages. Metrics that evaluate the functional structure of biological assemblages constitute a complementary tool to the traditional taxonomic approach, because they quantify the differences between species by means of functional traits. We assessed the effect of environmental characteristics on the taxonomic diversity (species richness, species composition and number of individuals) and functional structure (functional richness, functional evenness, Raos functional diversity, and community-weighted mean traits) of bird assemblages in northern Mato Grosso state, in the southwestern Brazilian Amazon. We sampled birds in 32 plots. At each plot birds were captured using mist nets, and eight environmental variables were measured: canopy openness, leaf litter, elevation, number of trees in three classes of DBH, soil clay content, and distance to nearest stream. To evaluate functional structure, we measured seven morphological traits from individuals of each bird species. Habitat variables had a significant effect on taxonomic diversity. However, the general functional structure was not affected. Elevation and distance to nearest stream were the main variables driving changes in taxonomic diversity and had a minor effect on functional richness. The other metrics of functional structure were not significantly affected by the set of environmental variables. Our results suggest that the sampled bird assemblages exhibit some functional tolerance (redundancy) to small-scale environmental variation, implying certain resilience to ecosystem modification.(AU)

Mudanças nas características ambientais podem influenciar o uso do habitat por aves, afetando o número de indivíduos, a riqueza de espécies e alterando a composição de espécies e estrutura funcional das assembleias. Medidas que avaliam a estrutura funcional de assembléias biológicas constituem uma ferramenta complementar à abordagem taxonômica, pois quantificam as diferenças entre as espécies através de seus atributos funcionais. Nós acessamos o efeito de variáveis ambientais sobre a diversidade taxonômica (riqueza, composição de espécies e número de indivíduos) e estrutura funcional (riqueza funcional, equabilidade funcional, diversidade funcional e média dos atributos ponderada pelas abundâncias) de assembleias de aves no norte do estado de Mato Grosso. Amostramos aves em 32 parcelas. Em cada parcela as aves foram capturadas usando redes de neblina e oito variáveis ambientais foram mensuradas: abertura de dossel, volume de serapilheira, elevação, número de árvores em três classe de DAP, teor de argila no solo e distância ao riacho mais próximo. Para avaliar a estrutura funcional nós tomamos sete medidas morfológicas de cada espécie de aves. Encontramos um efeito significativo das variáveis do habitat sobre a diversidade taxonômica, porém, a estrutura funcional, de maneira geral, não foi afetada. Elevação e distância ao riacho mais próximo foram as variáveis que direcionaram as mudanças na diversidade taxonômica e tiveram um pequeno efeito na riqueza funcional. As demais métricas de estrutura funcional não foram afetadas significativamente pelo conjunto de variáveis ambientais. Nossos resultados sugerem que a assembleia estudada exibe certa tolerância funcional (redundância) à variação ambiental em pequena escala, implicando em alguma resiliência à modificação do ecossistema.(AU)

Environmental structure affects taxonomic diversity but not functional structure of understory birds in the southwestern Brazilian Amazon

Changes in environmental characteristics can affect habitat use by birds, impacting the number of individuals, number of species, and changing species composition and functional structure of assemblages. Metrics that evaluate the functional structure of biological assemblages constitute a complementary tool to the traditional taxonomic approach, because they quantify the differences between species by means of functional traits. We assessed the effect of environmental characteristics on the taxonomic diversity (species richness, species composition and number of individuals) and functional structure (functional richness, functional evenness, Rao's functional diversity, and community-weighted mean traits) of bird assemblages in northern Mato Grosso state, in the southwestern Brazilian Amazon. We sampled birds in 32 plots. At each plot birds were captured using mist nets, and eight environmental variables were measured: canopy openness, leaf litter, elevation, number of trees in three classes of DBH, soil clay content, and distance to nearest stream. To evaluate functional structure, we measured seven morphological traits from individuals of each bird species. Habitat variables had a significant effect on taxonomic diversity. However, the general functional structure was not affected. Elevation and distance to nearest stream were the main variables driving changes in taxonomic diversity and had a minor effect on functional richness. The other metrics of functional structure were not significantly affected by the set of environmental variables. Our results suggest that the sampled bird assemblages exhibit some functional tolerance (redundancy) to small-scale environmental variation, implying certain resilience to ecosystem modification. (AU)

Adult feeding moths (Sphingidae) differ from non-adult feeding ones (Saturniidae) in activity-timing overlap and temporal niche width.

According to classic ecology, resource partitioning by segregation along at least one of the three main niche axes (time, food, and space) must take place for the coexistence of species with similar ecological requirements. We used nocturnal light traps to investigate the assemblage structuration of two moth families: Sphingidae (23 species) and Saturniidae (13 species). Because competition for food among adults potentially occurs only among sphingids, only for this family did we expect less overlap of diel activity patterns than expected by chance and also a greater temporal niche width compared to saturniids. Moreover, we expected a greater number of sphingid species pairs to differ in activity timing compared to saturniid pairs. We also hypothesized that in the case of a lack of temporal structuration, sphingids would be morphologically structured in relation to proboscis length. Contrary to what we expected, both families overlapped their activity patterns more than expected by chance alone and sphingid moths were not morphologically structured. Nevertheless, there were 173 significant pairwise differences in temporal activity between sphingids, contrasting with no interspecific differences between saturniids. Sphingid species also showed a wider temporal niche width than saturniids, as expected. Predation risk and abiotic factors may have caused the overall similarities in activity patterns for both families. The temporal niche seemed not to be determinant for the assemblage structuration of moths as a whole for either of the studied families, but segregation along the temporal niche axis of some potentially competing species pairs can be a relevant factor for the coexistence of nectar-feeding species.

Aquatic bacterial assemblage structure in Pozas Azules, Cuatro Cienegas Basin, Mexico: Deterministic vs. stochastic processes.

The aim of this study was to determine the contributions of stochastic vs. deterministic processes in the distribution of microbial diversity in four ponds (Pozas Azules) within a temporally stable aquatic system in the Cuatro Cienegas Basin, State of Coahuila, Mexico. A sampling strategy for sites that were geographically delimited and had low environmental variation was applied to avoid obscuring distance effects. Aquatic bacterial diversity was characterized following a culture-independent approach (16S sequencing of clone libraries). The results showed a correlation between bacterial beta diversity (1-Sorensen) and geographic distance (distance decay of similarity), which indicated the influence of stochastic processes related to dispersion in the assembly of the ponds' bacterial communities. Our findings are the first to show the influence of dispersal limitation in the prokaryotic diversity distribution of Cuatro Cienegas Basin.

Climatic Variables Do Not Directly Predict Spider Richness and Abundance in Semiarid Caatinga Vegetation, Brazil.

Spiders are abundant in tropical ecosystems and exert predatory pressure on a wide variety of invertebrate populations and also serve as prey for many others organisms, being part of complex interrelationships influenced directly and indirectly by a myriad of factors. We examined the influence of biotic (i.e., prey availability) and abiotic (i.e., temperature, precipitation, relative humidity, real evapotranspiration) factors on species richness and abundance during a two-year period in the semiarid Caatinga vegetation in northeastern Brazil. Data were analyzed through partial autocorrelation functions, cross correlations, and a path analysis. A total of 2522 spiders were collected with beating tray, pit-fall traps, and malaise traps, comprising 91 species and 34 families. Spider abundance peaked in the rainy season. Our results suggest that total invertebrate abundance has a direct influence on spider richness and abundance, whereas the effects of precipitation were mainly indirectly related to most spider assemblage parameters. The increase in vegetation cover with the rainy season in the Caatinga provides more breeding and foraging sites for spiders and stimulates their activities. Additionally, rainfall in arid and semiarid ecosystems stimulated the activity and reproduction of many herbivore and detritivore invertebrates dependent on plant biomass and necromass consumption, leading to an increase in spider prey availability.

Variability of coastal suprabenthic assemblages from sandy beaches of the Caribbean coast of Venezuela / Variabilidad de agregaciones suprabentónicas costeras de playas arenosas de la costa Caribe de Venezuela

The suprabenthos or hyperbenthos is the macrofaunal assemblage of small-sized organisms that interact for some time in the benthic boundary layer. Information about the taxonomic composition and role of suprabenthic species, especially in littoral zones, is scarce and scattered. This work attempts to contribute alleviate this problem. We analyze the temporal and spatial variations of suprabenthic assemblages in the swash-zone from four beaches of the littoral coast of Venezuela. For each beach, two sites were chosen, and special attention was given to water and sediment characteristics. 12 environmental variables were measured: Dissolved oxygen, oxygen saturation percentage, pH, salinity, surface temperature, total, organic and inorganic suspended solids, total organic carbon, organic matter in sediment, grain size of sediment, and amount of dragged material of sample. All faunal samples were taken on a monthly basis during 2011; these were extracted using a manual suprabenthic sledge towed parallel to the shoreline. Samples were sorted and identified to their lowest possible taxonomic level. A total of 24 141 specimens (mean abundance: 26.16±55.35ind./m²) belonging to 21 taxonomic groups were identified. Analysis suggests that seasonality does not explain observed changes either in fauna or environmental variables. It was found that suprabenthic assemblages, total suprabenthos density, richness and environmental variables changed in a dissimilar fashion between months and beaches. The most frequent groups were amphipods and decapods; and at the species/categories level post-larval shrimp (Penaeidae), Grapsidae crab megalopae and Arenaeus cribarius megalopae were common. Dissimilarity between months in each beach was primarily explained by the abundance of amphipods, ctenophores, decapods and mysids. For particular months and selected beaches very high abundances of ctenophores were found. This group dominated the sample even though it is not usually a representative group in suprabenthos. Samples showed low correlations between suprabenthos and environmental variables. A somewhat stronger correlation could be established between water characteristics and dragged material abundance. The studied suprabenthos assemblage was found to have high taxa richness and very dynamic behaviour at spatial and temporal scale. Further analysis suggested that there is no evident pattern of distribution and that causality can not be directly attributed to temporal variation only. Possibly there is an influence of a synergy of environmentals or biological factors, rather than a single variable. The species Americamysis bahia and Americamysis taironana are reported for the first time in Venezuela. This study represents the first ecological research of the suprabenthos in the Caribbean region.

El suprabentos o hiperbentos es la agregación de organismos de pequeño tamaño que interactúan por cierto tiempo en la capa de límite bentónico. La información de la composición taxonómica y el papel de las especies suprabentónicas, especialmente en la zona litoral, es escasa. Este trabajo trata de contribuir a solventar este problema. Se analizó la variación espacial y temporal de la agregación suprabentónica en la zona de rompiente de cuatro playas en la costa litoral de Venezuela. Se dio especial atención al sedimento y características del agua. Todas las muestras fueron tomadas mensualmente durante el 2011. Las muestras fueron extraídas utilizando un trineo suprabentónico manual paralelo a la línea de costa. En cada playa se escogieron dos sitios. Las muestras fueron separadas e identificadas hasta el nivel taxonómico más bajo posible. Se midieron doce variables ambientales: oxígeno disuelto, porcentaje de saturación de oxígeno, pH, salinidad, temperatura superficial, sólidos suspendidos totales, inorgánicos y orgánicos, carbono orgánico total, materia orgánica en sedimento, tamaño del grano de sedimento y cantidad de material arrastrado en cada muestra. Se identificaron un total de 24 141 individuos (densidad promedio: 26.16±55.35ind./m2), pertenecientes a 21 grupos taxonómicos. Los análisis sugieren que la estacionalidad no explica los cambios observados en la fauna ni en las variables ambientales. La agregación del suprabentos, la densidad total, riqueza y variables ambientales cambiaron de manera diferente entre meses y playas. Los grupos más frecuentes fueron anfípodos y decápodos. A nivel de especies/categorías fueron las post-larvas de camarón (Penaeidae), las megalopas de cangrejos Grapsidae y de Arenaeus cribarius (Lamarck, 1818). La disimilitud entre meses en cada playa se debe principalmente a la abundancia de anfípodos, ctenóforos, decápodos y misidáceos. En meses particulares y algunas playas, se encontraron altas abundancias de ctenóforos. Este grupo dominó esas muestras, aún cuando no son frecuentemente un grupo representativo del suprabentos. Se encontraron bajas correlaciones entre el suprabentos y las variables ambientales. Una relación un poco más fuerte fue establecida con las características del agua y la abundancia de material arrastrado. La agregación de suprabentos estudiada tuvo una alta riqueza taxonómica y fue muy dinámica tanto espacial como temporalmente. Los análisis sugieren que no hay un patrón evidente de distribución y el azar no puede ser atribuido sólo a la variación temporal. Posiblemente hay influencia de una sinergia de factores ambientales o biológicos, más que de una variable en particular. Las especies Americamysis bahia (Molenock, 1969) y Americamysis taironana (Brattegard, 1973) se reportan por primera vez para Venezuela. Este es el primer estudio ecológico del suprabentos en el Mar Caribe.

Spatiotemporal variations of the ichthyofaunal structure accompanying the seabob shrimp, Xiphopenaeus kroyeri (Crustacea: Penaeidae), fishery in important fishery areas of the Santa Catarina shore, Brazil

The present study analyzed qualitatively and quantitatively the temporal and spatial changes in the fish assemblages present in seabob shrimp distribution sites in two important fishing areas of the Santa Catarina coast. Monthly bottom trawls, conducted between March 2007 and February 2008 in Balneário Barra do Sul and Penha, yielded a total of 38,608 specimens belonging to 54 species, of which 35 occurred in both regions. The Sciaenidae was the most represented family in both number of species and abundance of individuals. The dominant species were Stellifer rastrifer (Jordan, 1889), S. brasiliensis (Schultz, 1945), Paralonchurus brasiliensis (Steindachner, 1875), Isopisthus parvipinnis (Cuvier, 1830), Trichiurus lepturus (Linnaeus, 1758), and Pellona harroweri (Fowler, 1917). The ichthyofaunal structure showed a spatiotemporal dependence with significant differences in March 2007 and January and February 2008 between Balneário Barra do Sul and Penha. The main differences were attributed to dominant species, which were responsible for significantly altering the abundance of the assemblages. The species richness was similar in both sites, whereas the diversity and equitability indices showed monthly fluctuation patterns that differed between Balneário Barra do Sul and Penha. The Shannon index differed in August, September and November 2007 and January and February 2008, with an H' ranging from 0.74 to 1.98 influenced by dominant species, whereas significant variations were observed for the Pielou index in November 2007 and February 2008. The Berger-Parker index demonstrated a clear dominance pattern where the monthly numeric contribution of a single species ranged from approximately 30 to 80%. Although the results showed differences between fishing grounds 25% of the time, we conclude that fish assemblies captured as accompanying fauna in artisanal seabob shrimp fisheries showed statistically similar characteristics for most of the year, although Balneário Barra do Sul and Penha are 35 km away from each other.

Spatiotemporal variations of the ichthyofaunal structure accompanying the seabob shrimp, Xiphopenaeus kroyeri (Crustacea: Penaeidae), fishery in important fishery areas of the Santa Catarina shore, Brazil

The present study analyzed qualitatively and quantitatively the temporal and spatial changes in the fish assemblages present in seabob shrimp distribution sites in two important fishing areas of the Santa Catarina coast. Monthly bottom trawls, conducted between March 2007 and February 2008 in Balneário Barra do Sul and Penha, yielded a total of 38,608 specimens belonging to 54 species, of which 35 occurred in both regions. The Sciaenidae was the most represented family in both number of species and abundance of individuals. The dominant species were Stellifer rastrifer (Jordan, 1889), S. brasiliensis (Schultz, 1945), Paralonchurus brasiliensis (Steindachner, 1875), Isopisthus parvipinnis (Cuvier, 1830), Trichiurus lepturus (Linnaeus, 1758), and Pellona harroweri (Fowler, 1917). The ichthyofaunal structure showed a spatiotemporal dependence with significant differences in March 2007 and January and February 2008 between Balneário Barra do Sul and Penha. The main differences were attributed to dominant species, which were responsible for significantly altering the abundance of the assemblages. The species richness was similar in both sites, whereas the diversity and equitability indices showed monthly fluctuation patterns that differed between Balneário Barra do Sul and Penha. The Shannon index differed in August, September and November 2007 and January and February 2008, with an H' ranging from 0.74 to 1.98 influenced by dominant species, whereas significant variations were observed for the Pielou index in November 2007 and February 2008. The Berger-Parker index demonstrated a clear dominance pattern where the monthly numeric contribution of a single species ranged from approximately 30 to 80%. Although the results showed differences between fishing grounds 25% of the time, we conclude that fish assemblies captured as accompanying fauna in artisanal seabob shrimp fisheries showed statistically similar characteristics for most of the year, although Balneário Barra do Sul and Penha are 35 km away from each other.

Spatiotemporal variations of the ichthyofaunal structure accompanying the seabob shrimp, Xiphopenaeus kroyeri (Crustacea: Penaeidae), fishery in important fishery areas of the Santa Catarina shore, Brazil

The present study analyzed qualitatively and quantitatively the temporal and spatial changes in the fish assemblages present in seabob shrimp distribution sites in two important fishing areas of the Santa Catarina coast. Monthly bottom trawls, conducted between March 2007 and February 2008 in Balneário Barra do Sul and Penha, yielded a total of 38,608 specimens belonging to 54 species, of which 35 occurred in both regions. The Sciaenidae was the most represented family in both number of species and abundance of individuals. The dominant species were Stellifer rastrifer (Jordan, 1889), S. brasiliensis (Schultz, 1945), Paralonchurus brasiliensis (Steindachner, 1875), Isopisthus parvipinnis (Cuvier, 1830), Trichiurus lepturus (Linnaeus, 1758), and Pellona harroweri (Fowler, 1917). The ichthyofaunal structure showed a spatiotemporal dependence with significant differences in March 2007 and January and February 2008 between Balneário Barra do Sul and Penha. The main differences were attributed to dominant species, which were responsible for significantly altering the abundance of the assemblages. The species richness was similar in both sites, whereas the diversity and equitability indices showed monthly fluctuation patterns that differed between Balneário Barra do Sul and Penha. The Shannon index differed in August, September and November 2007 and January and February 2008, with an H' ranging from 0.74 to 1.98 influenced by dominant species, whereas significant variations were observed for the Pielou index in November 2007 and February 2008. The Berger-Parker index demonstrated a clear dominance pattern where the monthly numeric contribution of a single species ranged from approximately 30 to 80%. Although the results showed differences between fishing grounds 25% of the time, we conclude that fish assemblies captured as accompanying fauna in artisanal seabob shrimp fisheries showed statistically similar characteristics for most of the year, although Balneário Barra do Sul and Penha are 35 km away from each other.

Spatial pattern of a fish assemblage in a seasonal tropical wetland: effects of habitat, herbaceous plant biomass, water depth, and distance from species sources

The influence of habitat, biomass of herbaceous vegetation, depth and distance from permanent water bodies on the structure of fish assemblages of a seasonal floodplain was evaluated using data collected along 22 transects in an area of 25 km² in the floodplain of Cuiabá River, Pantanal, Brazil. Each transect was sampled for fish using throw traps and gillnets during the flood period of 2006. Multivariate multiple regression analysis and multivariate analysis of covariance indicated that depth was the only variable that affected the structure of the fish assemblage, both for quantitative data (abundance) and qualitative data (presence-absence). Species such as Neofundulus parvipinnis and Laetacara dorsigera were more abundant in shallower sites (below 25 cm), while Serrasalmus maculatus and Metynnis mola were found mostly in the deepest areas (over 55 cm). However, species such as Hoplias malabaricus and Hoplerythrinus unitaeniatus occurred at all sampled depths. Although the distribution of most species was restricted to a few sites, there was a positive relationship between species richness and depth of the water body. Surprisingly, the replacement of native vegetation by exotic pasture did not affect the fish assemblage in the area, at the probability level considered.(AU)

A influência do habitat, biomassa de vegetação herbácea, da profundidade e da distância de corpos d'água permanentes sobre a estrutura da assembleia de peixes da planície sazonalmente inundada foi avaliada com dados coletados em 22 transectos em uma área de 25 km²; na planície de inundação do rio Cuiabá, Pantanal. Cada transecto foi amostrado para peixes usando "throw trap" e rede de espera no período de cheia de 2006. Análises de regressão múltipla multivariada e análises de covariância multivariada indicaram que a profundidade foi a única das variáveis consideradas no estudo que afetou a estrutura da assembleia de peixes, tanto para os dados quantitativos (abundância) quanto para os dados qualitativos (presença-ausência). Espécies como Neofundulus parvipinnis e Laetacara dorsigera foram mais abundantes em locais mais rasos (abaixo de 25 cm), enquanto as espécies Serrasalmus maculatus e Metynnis mola foram encontradas principalmente nos locais mais profundos (acima de 55 cm). Entretanto espécies como Hoplias malabaricus e Hoplerythrinus unitaeniatus ocorreram em todas as profundidades amostradas. Apesar de grande parte das espécies apresentarem distribuição restrita a poucos locais, houve uma relação positiva entre a riqueza de espécies e a profundidade do corpo d'água. Surpreendentemente, no nível de probabilidade considerado, a substituição da vegetação nativa por pastagens exóticas não afetou a assembleia de peixes na área estudada.(AU)

Spatial pattern of a fish assemblage in a seasonal tropical wetland: effects of habitat, herbaceous plant biomass, water depth, and distance from species sources

The influence of habitat, biomass of herbaceous vegetation, depth and distance from permanent water bodies on the structure of fish assemblages of a seasonal floodplain was evaluated using data collected along 22 transects in an area of 25 km² in the floodplain of Cuiabá River, Pantanal, Brazil. Each transect was sampled for fish using throw traps and gillnets during the flood period of 2006. Multivariate multiple regression analysis and multivariate analysis of covariance indicated that depth was the only variable that affected the structure of the fish assemblage, both for quantitative data (abundance) and qualitative data (presence-absence). Species such as Neofundulus parvipinnis and Laetacara dorsigera were more abundant in shallower sites (below 25 cm), while Serrasalmus maculatus and Metynnis mola were found mostly in the deepest areas (over 55 cm). However, species such as Hoplias malabaricus and Hoplerythrinus unitaeniatus occurred at all sampled depths. Although the distribution of most species was restricted to a few sites, there was a positive relationship between species richness and depth of the water body. Surprisingly, the replacement of native vegetation by exotic pasture did not affect the fish assemblage in the area, at the probability level considered.

A influência do habitat, biomassa de vegetação herbácea, da profundidade e da distância de corpos d'água permanentes sobre a estrutura da assembleia de peixes da planície sazonalmente inundada foi avaliada com dados coletados em 22 transectos em uma área de 25 km²; na planície de inundação do rio Cuiabá, Pantanal. Cada transecto foi amostrado para peixes usando "throw trap" e rede de espera no período de cheia de 2006. Análises de regressão múltipla multivariada e análises de covariância multivariada indicaram que a profundidade foi a única das variáveis consideradas no estudo que afetou a estrutura da assembleia de peixes, tanto para os dados quantitativos (abundância) quanto para os dados qualitativos (presença-ausência). Espécies como Neofundulus parvipinnis e Laetacara dorsigera foram mais abundantes em locais mais rasos (abaixo de 25 cm), enquanto as espécies Serrasalmus maculatus e Metynnis mola foram encontradas principalmente nos locais mais profundos (acima de 55 cm). Entretanto espécies como Hoplias malabaricus e Hoplerythrinus unitaeniatus ocorreram em todas as profundidades amostradas. Apesar de grande parte das espécies apresentarem distribuição restrita a poucos locais, houve uma relação positiva entre a riqueza de espécies e a profundidade do corpo d'água. Surpreendentemente, no nível de probabilidade considerado, a substituição da vegetação nativa por pastagens exóticas não afetou a assembleia de peixes na área estudada.

Patterns of habitat segregation among large fishes in a Venezuelan floodplain river

Distribution and abundance of large fishes (SL>100 mm) in the río Cinaruco, a floodplain river in the Venezuelan llanos, were examined by gill net sampling in four habitat types: sand banks, backwater creeks, floodplain lagoons, and river channel. Sampling was standardized using nets (25 m x 2 m) of three mesh sizes set for 24-h periods. Based on data from >10,000 hours of gill netting over three years, there were significant differences in assemblage composition among the four habitats. Pair-wise comparisons suggested differences in assemblage composition between all pairs of habitats except creeks and lagoons. Differences in assemblage composition likely arose from species-specific habitat affinities. For example, 21 taxa were collected from both creeks and lagoons, but not from sand banks or the main river channel; each of these 21 taxa were associated with particular features characteristic of creeks and lagoons (e.g. abundant detritus). Assemblage structure also could be influenced by predation or other biological interactions, but mechanistic experiments are needed to evaluate this hypothesis. Assemblage composition was highly variable within all habitat types, likely the result of spatial and temporal heterogeneity associated with seasonal hydrology. Long distance migrations by prochilodontids and other taxa contributed to higher CPUE during the rising-water period of May 2002. Data from this study will provide a baseline to assess changes in the abundance and distribution of large-bodied fishes in response to increasing impacts from illegal commercial fishing in this region.

A distribuição e abundância de grandes peixes (SL>100 mm) no rio Cinaruco, um rio com uma planície inundação nos llanos da Venezuela, foram examinadas através de amostragens por redes de espera em quatro habitats: bancos de areia, riachos, lagoas da planície de inundação e o canal do rio. As amostragens foram padronizadas usando-se redes de espera (25 m x 2 m) de três tamanhos de malha expostas por períodos de 24 horas. Baseando-se em dados de mais de 10.000 horas de exposição de redes, coletados por três anos, foram verificadas diferenças significativas na composição da assembléia entre os quatro habitats. Comparações pareadas sugeriram que diferenças na composição da assembléia provavelmente se devem às afinidades espécie-habitat. Por exemplo, 21 taxa foram coletados em riachos e lagoas, mas não em bancos de areia ou no canal principal do rio, sendo que cada um destes 21 taxa foi associado a características particulares dos riachos e das lagoas (ex. detrito abundante). A estrutura da assembléia também poderia ser influenciada por predação ou outras interações biológicas, mas são necessários experimentos para avaliar esta hipótese. A composição da assembléia foi altamente variável dentro de todos os tipos de habitats, provavelmente devido à heterogeneidade espacial e temporal associada com a sazonalidade na hidrologia. As grandes migrações realizadas por prochilodontídeos e outros taxa contribuíram para uma maior captura por unidade de esforço (CPUE) durante o período de subida das águas, em maio de 2002. Os dados deste estudo fornecerão a base para a verificação de mudanças na abundância e distribuição dos peixes de grande porte em resposta aos crescentes impactos causados pela pesca comercial ilegal nesta região.

Patterns of habitat segregation among large fishes in a Venezuelan floodplain river

Distribution and abundance of large fishes (SL>100 mm) in the río Cinaruco, a floodplain river in the Venezuelan llanos, were examined by gill net sampling in four habitat types: sand banks, backwater creeks, floodplain lagoons, and river channel. Sampling was standardized using nets (25 m x 2 m) of three mesh sizes set for 24-h periods. Based on data from >10,000 hours of gill netting over three years, there were significant differences in assemblage composition among the four habitats. Pair-wise comparisons suggested differences in assemblage composition between all pairs of habitats except creeks and lagoons. Differences in assemblage composition likely arose from species-specific habitat affinities. For example, 21 taxa were collected from both creeks and lagoons, but not from sand banks or the main river channel; each of these 21 taxa were associated with particular features characteristic of creeks and lagoons (e.g. abundant detritus). Assemblage structure also could be influenced by predation or other biological interactions, but mechanistic experiments are needed to evaluate this hypothesis. Assemblage composition was highly variable within all habitat types, likely the result of spatial and temporal heterogeneity associated with seasonal hydrology. Long distance migrations by prochilodontids and other taxa contributed to higher CPUE during the rising-water period of May 2002. Data from this study will provide a baseline to assess changes in the abundance and distribution of large-bodied fishes in response to increasing impacts from illegal commercial fishing in this region.

A distribuição e abundância de grandes peixes (SL>100 mm) no rio Cinaruco, um rio com uma planície inundação nos llanos da Venezuela, foram examinadas através de amostragens por redes de espera em quatro habitats: bancos de areia, riachos, lagoas da planície de inundação e o canal do rio. As amostragens foram padronizadas usando-se redes de espera (25 m x 2 m) de três tamanhos de malha expostas por períodos de 24 horas. Baseando-se em dados de mais de 10.000 horas de exposição de redes, coletados por três anos, foram verificadas diferenças significativas na composição da assembléia entre os quatro habitats. Comparações pareadas sugeriram que diferenças na composição da assembléia provavelmente se devem às afinidades espécie-habitat. Por exemplo, 21 taxa foram coletados em riachos e lagoas, mas não em bancos de areia ou no canal principal do rio, sendo que cada um destes 21 taxa foi associado a características particulares dos riachos e das lagoas (ex. detrito abundante). A estrutura da assembléia também poderia ser influenciada por predação ou outras interações biológicas, mas são necessários experimentos para avaliar esta hipótese. A composição da assembléia foi altamente variável dentro de todos os tipos de habitats, provavelmente devido à heterogeneidade espacial e temporal associada com a sazonalidade na hidrologia. As grandes migrações realizadas por prochilodontídeos e outros taxa contribuíram para uma maior captura por unidade de esforço (CPUE) durante o período de subida das águas, em maio de 2002. Os dados deste estudo fornecerão a base para a verificação de mudanças na abundância e distribuição dos peixes de grande porte em resposta aos crescentes impactos causados pela pesca comercial ilegal nesta região.

Fish assemblages of tropical floodplain lagoons: exploring the role of connectivity in a dry year

Irregular rainfall and pronounced reductions of the hydrometric level in the year 2000 resulted in drastically altered hydrological connectivity of lentic environments in the upper Paraná River floodplain. The objective of the present work was to examine spatial and temporal patterns of fish assemblage attributes and structure in relation to limnological variables associated with hydrological connectivity. Fish were collected quarterly by seining in the marginal areas of 15 lagoons belonging to two biotopic categories (connected and disconnected). Variation in assemblage composition reflected the degree of hydrological connectivity. Values of assemblage attributes (species richness, density and biomass) were significantly lower in connected lagoons than in disconnected lagoons. Significantly higher values of species richness and biomass were recorded in November than in August. Rare species had the greatest effect on observed patterns in fish assemblage ordination (DCA). Observed patterns of variation in assemblage attributes were directly correlated with factors related to hydrological connectivity, such as depth, resources (zooplankton and chlorophyll a) and nutrients (total phosphorus).

A irregularidade das chuvas e as reduções pronunciadas no nível hidrométrico alteraram drasticamente a conectividade hidrológica dos ambientes lênticos da planície de inundação do alto rio Paraná em 2000. O presente trabalho teve como objetivo examinar os padrões espaciais e temporais dos atributos e da estrutura das assembléias de peixes em relação a variáveis limnológicas associadas à conectividade hidrológica. Os peixes foram coletados em arrastos trimestrais, na área marginal de 15 lagoas, pertencentes a duas categorias de biótopos (lagoas conectadas e desconectadas). Variações na composição das assembléias refletiram o grau de conectividade hidrológica. Os valores dos atributos das assembléias (riqueza de espécies, densidade e biomassa capturada) foram significativamente menores em lagoas conectadas em relação a lagoas desconectadas. Valores significativamente elevados de riqueza de espécies e biomassa capturada foram registrados em novembro em relação a agosto. Espécies raras tiveram os maiores efeitos nos padrões observados na ordenação das assembléias de peixes (DCA). Padrões observados na variação dos atributos das assembléias foram diretamente correlacionados a fatores relacionados à conectividade hidrológica, como a profundidade, os recursos (zooplâncton e clorofila a) e os nutrientes (fósforo total).

Fish assemblages of tropical floodplain lagoons: exploring the role of connectivity in a dry year

Irregular rainfall and pronounced reductions of the hydrometric level in the year 2000 resulted in drastically altered hydrological connectivity of lentic environments in the upper Paraná River floodplain. The objective of the present work was to examine spatial and temporal patterns of fish assemblage attributes and structure in relation to limnological variables associated with hydrological connectivity. Fish were collected quarterly by seining in the marginal areas of 15 lagoons belonging to two biotopic categories (connected and disconnected). Variation in assemblage composition reflected the degree of hydrological connectivity. Values of assemblage attributes (species richness, density and biomass) were significantly lower in connected lagoons than in disconnected lagoons. Significantly higher values of species richness and biomass were recorded in November than in August. Rare species had the greatest effect on observed patterns in fish assemblage ordination (DCA). Observed patterns of variation in assemblage attributes were directly correlated with factors related to hydrological connectivity, such as depth, resources (zooplankton and chlorophyll a) and nutrients (total phosphorus).

A irregularidade das chuvas e as reduções pronunciadas no nível hidrométrico alteraram drasticamente a conectividade hidrológica dos ambientes lênticos da planície de inundação do alto rio Paraná em 2000. O presente trabalho teve como objetivo examinar os padrões espaciais e temporais dos atributos e da estrutura das assembléias de peixes em relação a variáveis limnológicas associadas à conectividade hidrológica. Os peixes foram coletados em arrastos trimestrais, na área marginal de 15 lagoas, pertencentes a duas categorias de biótopos (lagoas conectadas e desconectadas). Variações na composição das assembléias refletiram o grau de conectividade hidrológica. Os valores dos atributos das assembléias (riqueza de espécies, densidade e biomassa capturada) foram significativamente menores em lagoas conectadas em relação a lagoas desconectadas. Valores significativamente elevados de riqueza de espécies e biomassa capturada foram registrados em novembro em relação a agosto. Espécies raras tiveram os maiores efeitos nos padrões observados na ordenação das assembléias de peixes (DCA). Padrões observados na variação dos atributos das assembléias foram diretamente correlacionados a fatores relacionados à conectividade hidrológica, como a profundidade, os recursos (zooplâncton e clorofila a) e os nutrientes (fósforo total).