Does invasion by armored catfish shift trophic ecology of native fishes? Evidence from stable isotope analysis.

Popular as aquarium fish, armored catfishes from South America (Pterygoplichthys spp.) have been introduced and become invasive in tropical and subtropical regions worldwide. These ecosystem engineers can deplete basal resources (e.g., periphyton and detritus), with potential negative effects for native fauna. We studied the trophic ecology of fishes in the Usumacinta River Basin, Guatemala, where Pterygoplichthys is now widespread and locally abundant. We analyzed stable isotopes (δ13 C, δ15 N) in fish tissues and basal resources to assess the potential impact of Pterygoplichthys on the trophic ecology of six co-occurring native fishes that feed at a similar trophic level (Astyanax aeneus, Dorosoma petenense, Thorichthys pasionis, Oscura heterospila, Poecilia mexicana, and Gambusia sexradiata). The study was conducted during the dry season in the La Pasion (LPR; high invasion) and San Pedro (SPR; low invasion) rivers. We compared isotopic spaces occupied by native fish and Pterygoplichthys, estimated isotopic overlap, and evaluated the trophic displacement of native species. We also evaluated the relationships of environmental factors, including the relative biomass of the invasive catfish, with δ13 C and δ15 N signatures. Except for P. mexicana, native species had lower isotopic overlap with the catfish in LPR. Native fish isotopic spaces were compressed and shifted toward higher trophic positions in LPR relative to SPR. Benthic food resources were important for Pterygoplichthys in both rivers, and water-column resources had greater relative importance (RI) for native species in LPR. Native fish δ13 C was significantly associated with Pterygoplichthys biomass, conductivity, and water flow velocity; and water depth and sedimentation had a significant association with native fish δ15 N. Findings provide evidence that invasive Pterygoplichthys, along with environmental factors, impact the trophic ecology of native fish in the Usumacinta Basin. Additional field research conducted over longer time periods and mesocosm experiments that account for fish assemblage and environmental variation could elucidate Pterygoplichthys impacts via food resource depletion or habitat alteration.

Populares como peces de acuario, los plecóstomos de América del Sur (Pterygoplichthys spp.) han sido introducidos y se han vuelto invasivos en regiones tropicales y subtropicales de todo el mundo. Estos ingenieros ecosistémicos pueden agotar los recursos basales (p. ej., perifiton y detritos), con posibles efectos negativos para la fauna nativa. En esta investigación estudiamos la ecología trófica de los peces en la cuenca del río Usumacinta, Guatemala, donde Pterygoplichthys se ha dispersado y es localmente abundante. Analizamos isótopos estables (δ13 C, δ15 N) en tejidos de peces y recursos basales para evaluar el impacto potencial de Pterygoplichthys en la ecología trófica de seis peces nativos que se alimentan a un nivel trófico similar (Astyanax aeneus, Dorosoma petenense, Thorichthys pasionis, Oscura heterospila, Poecilia mexicana y Gambusia sexradiata). El estudio se realizó en la temporada seca en los ríos La Pasión (LPR; alta invasión) y San Pedro (SPR; baja invasión). Comparamos el espacio isotópico ocupado por peces nativos y Pterygoplichthys, estimamos la superposición isotópica y evaluamos el desplazamiento trófico de las especies nativas. También evaluamos las relaciones de los factores ambientales, incluida la biomasa relativa del plecóstomo, con las señales isotópicas δ13 C y δ15 N. Con excepción de P. mexicana, las especies nativas tuvieron una menor superposición isotópica con el plecóstomo en LPR. En peces nativos se observó compresión y desplazamiento de espacios isotópicos hacia posiciones tróficas más altas en LPR en relación con SPR. Los recursos alimenticios bentónicos fueron importantes para Pterygoplichthys en ambos ríos, y los recursos de la columna de agua tuvieron mayor importancia relativa para las especies nativas en LPR. Los valores de δ13 C en peces nativos están significativamente asociados con la biomasa de Pterygoplichthys, la conductividad y la velocidad del flujo de agua; la profundidad del río y la sedimentación tuvieron una asociación significativa con los valores de δ15 N de peces nativos. Los hallazgos proporcionan evidencia de que Pterygoplichthys, junto con factores ambientales, impactan la ecología trófica de los peces nativos en la cuenca del Usumacinta. Investigación de campo adicional durante períodos de tiempo prolongados y experimentos de mesocosmos que integren dinámicas de ensamblaje de peces y variación ambiental podrían dilucidar los impactos de Pterygoplichthys a través del agotamiento de los recursos alimentarios o la alteración del hábitat.

Early impacts of the largest Amazonian hydropower project on fish communities.

Hydropower is a threat to freshwater fishes. Despite a recent boom in dam construction, few studies have assessed their impact on mega-diverse tropical rivers. Using a before-after study design, we investigated the early impacts of the Belo Monte hydroelectric complex, the third-largest hydropower project in the world, on fishes of the Xingu River, a major clear-water tributary of the lower Amazon. We explored impacts across different river sectors (upstream, reservoir, reduced flow sector, and downstream) and spatial scales (individual sectors vs. all sectors combined) using joint species distribution models and different facets of diversity (taxonomic, functional, and phylogenetic). After 5 years of the Belo Monte operation, species richness declined ~12% in lentic and ~16% in lotic environments. Changes in abundance were of less magnitude (<4%). Effects were particularly negative for species of the families Serrasalmidae (mainly pacus), Anostomidae (headstanders), Auchenipteridae, and Pimelodidae (catfishes), whereas no taxonomic group consistently increased in richness or abundance. The reservoir and downstream sectors were the most impacted, with declines of ~24-29% in fish species richness, overall reductions in fish body size and trophic level, and a change in average body shape. Richness and abundance also declined in the reduced river flow, and changes in size, shape, and position of fins were observed. Relatively minor changes were found in the upstream sector. Variation in functional and phylogenetic diversity following river impoundment was subtle; however, across sectors, we found a reduction in functional divergence, indicating a decline in the abundance of species located near the extremities of community functional space. This may be the first sign of an environmental filtering process reducing functional diversity in the region. Greater changes in flow and habitats are expected as hydropower operations ramp up, and continued monitoring is warranted to understand the full scope and magnitude of ecological impacts.

Genetic identification and diversity of stocks of the African bonytongue, Heterotis niloticus (Osteoglossiformes: Arapaiminae), in Nigeria, West Africa.

Inland fisheries are an important source of protein and income for people in Africa. Their sustainable management can greatly benefit from identification of regional genetic stocks and characterization of their genetic diversity, but such information is lacking for most African freshwater fisheries. The African bonytongue, Heterotis niloticus, is an important component of inland fisheries in West Africa. Nigeria has the largest fishery for African bonytongues, representing ~ 86% of the global total. Recent declines in yields at some Nigerian locations, however, suggest current levels of exploitation may be unsustainable. Habitat degradation also may be impacting some stocks. Despite its commercial and nutritional importance, the African bonytongue has been the subject of scant genetic research to support management. We examined patterns of genetic diversity in natural populations of H. niloticus at four locations in Nigeria, including Kainji Lake, a reservoir on the Niger River in north-central Nigeria, and three southern localities (Ethiope River, Igbokoda River, and Epe Lagoon), as well fish from the Ouémé River delta near Porto Novo, Benin. Eighty-five specimens were genotyped for nine microsatellite-loci. Genetic diversity estimates were highest at Kainji Lake, and substantially lower at southern localities. High levels of genetic differentiation were detected between samples from Kainji Lake and those from southern localities. Low, yet significant FST values were observed among samples from southern Nigerian localities that were more differentiated from the sample from nearby coastal Benin. We thus recommend that African bonytongues from the five locations be considered distinct genetic stocks and managed accordingly.

How do lizard niches conserve, diverge or converge? Further exploration of saurian evolutionary ecology.

BACKGROUND: Environmental conditions on Earth are repeated in non-random patterns that often coincide with species from different regions and time periods having consistent combinations of morphological, physiological and behavioral traits. Observation of repeated trait combinations among species confronting similar environmental conditions suggest that adaptive trait combinations are constrained by functional tradeoffs within or across niche dimensions. In an earlier study, we assembled a high-resolution database of functional traits for 134 lizard species to explore ecological diversification in relation to five fundamental niche dimensions. Here we expand and further examine multivariate relationships in that dataset to assess the relative influence of niche dimensions on the distribution of species in 6-dimensional niche space and how these may deviate from distributions generated from null models. We then analyzed a dataset with lower functional-trait resolution for 1023 lizard species that was compiled from our dataset and a published database, representing most of the extant families and environmental conditions occupied by lizards globally. Ordinations from multivariate analysis were compared with null models to assess how ecological and historical factors have resulted in the conservation, divergence or convergence of lizard niches. RESULTS: Lizard species clustered within a functional niche volume influenced mostly by functional traits associated with diet, activity, and habitat/substrate. Consistent patterns of trait combinations within and among niche dimensions yielded 24 functional groups that occupied a total niche space significantly smaller than plausible spaces projected by null models. Null model tests indicated that several functional groups are strongly constrained by phylogeny, such as nocturnality in the Gekkota and the secondarily acquired sit-and-wait foraging strategy in Iguania. Most of the widely distributed and species-rich families contained multiple functional groups thereby contributing to high incidence of niche convergence. CONCLUSIONS: Comparison of empirical patterns with those generated by null models suggests that ecological filters promote limited sets of trait combinations, especially where similar conditions occur, reflecting both niche convergence and conservatism. Widespread patterns of niche convergence following ancestral niche diversification support the idea that lizard niches are defined by trait-function relationships and interactions with environment that are, to some degree, predictable and independent of phylogeny.

Derived loss of signal complexity and plasticity in a genus of weakly electric fish.

Signal plasticity can maximize the usefulness of costly animal signals such as the electric organ discharges (EODs) of weakly electric fishes. Some species of the order Gymnotiformes rapidly alter their EOD amplitude and duration in response to circadian cues and social stimuli. How this plasticity is maintained across related species with different degrees of signal complexity is poorly understood. In one genus of weakly electric gymnotiform fish (Brachyhypopomus), only one species, B. bennetti, produces a monophasic signal while all other species emit complex biphasic or multiphasic EOD waveforms produced by two overlapping but asynchronous action potentials in each electric organ cell (electrocyte). One consequence of this signal complexity is the suppression of low-frequency signal content that is detectable by electroreceptive predators. In complex EODs, reduction of the EOD amplitude and duration during daytime inactivity can decrease both predation risk and the metabolic cost of EOD generation. We compared EOD plasticity and its underlying physiology in Brachyhypopomus focusing on B. bennetti. We found that B. bennetti exhibits minimal EOD plasticity, but that its electrocytes retained vestigial mechanisms of biphasic signaling and vestigial mechanisms for modulating the EOD amplitude. These results suggest that this species represents a transitional phenotypic state within a clade where signal complexity and plasticity were initially gained and then lost. Signal mimicry, mate recognition and sexual selection are potential factors maintaining the monophasic EOD phenotype in the face of detection by electroreceptive predators.

Scientists' warning to humanity on the freshwater biodiversity crisis.

Freshwater ecosystems provide irreplaceable services for both nature and society. The quality and quantity of freshwater affect biogeochemical processes and ecological dynamics that determine biodiversity, ecosystem productivity, and human health and welfare at local, regional and global scales. Freshwater ecosystems and their associated riparian habitats are amongst the most biologically diverse on Earth, and have inestimable economic, health, cultural, scientific and educational values. Yet human impacts to lakes, rivers, streams, wetlands and groundwater are dramatically reducing biodiversity and robbing critical natural resources and services from current and future generations. Freshwater biodiversity is declining rapidly on every continent and in every major river basin on Earth, and this degradation is occurring more rapidly than in terrestrial ecosystems. Currently, about one third of all global freshwater discharges pass through human agricultural, industrial or urban infrastructure. About one fifth of the Earth's arable land is now already equipped for irrigation, including all the most productive lands, and this proportion is projected to surpass one third by midcentury to feed the rapidly expanding populations of humans and commensal species, especially poultry and ruminant livestock. Less than one fifth of the world's preindustrial freshwater wetlands remain, and this proportion is projected to decline to under one tenth by midcentury, with imminent threats from water transfer megaprojects in Brazil and India, and coastal wetland drainage megaprojects in China. The Living Planet Index for freshwater vertebrate populations has declined to just one third that of 1970, and is projected to sink below one fifth by midcentury. A linear model of global economic expansion yields the chilling prediction that human utilization of critical freshwater resources will approach one half of the Earth's total capacity by midcentury. Although the magnitude and growth of the human freshwater footprint are greater than is generally understood by policy makers, the news media, or the general public, slowing and reversing dramatic losses of freshwater species and ecosystems is still possible. We recommend a set of urgent policy actions that promote clean water, conserve watershed services, and restore freshwater ecosystems and their vital services. Effective management of freshwater resources and ecosystems must be ranked amongst humanity's highest priorities.

A cascade of dams affects fish spatial distributions and functional groups of local assemblages in a subtropical river

Dams reduce the longitudinal connectivity of rivers and thereby disrupt fish migration and the spatial distribution of species, impacts that remain poorly studied for some Neotropical rivers from mega-diverse basins. We investigated the spatial distribution of fish species with different trophic and movement/reproductive/size characteristics to assess how functional groups have responded to a cascade of dams on the Uruguai River in southern Brazil. Fish abundance, biomass, and species composition were evaluated at eight locations along the longitudinal gradient. The fish assemblage in the upper stretch was mainly characterized by small and medium-sized species at higher trophic levels, whereas the sites located furthest downstream displayed more medium and large-sized species, including many carnivorous species. Species with high fecundity, seasonal migrants, and catfishes with internal fertilization were common in the river´s middle and lower reaches. Detritivorous species dominated areas distant from the dams. Overall, functional diversity of local fish assemblages was greater in lower reaches. The cascade of dams has impacted the distribution of functional groups of local fish assemblages of Uruguai River. The alteration of functional groups in upper reaches of the river has potential consequences for ecosystem processes and services, such as nutrient cycling and fisheries.(AU)

As barragens reduzem a conectividade longitudinal dos rios e interrompem a migração e a distribuição espacial das espécies, configurando impactos pouco estudados para alguns rios Neotropicais megadiversos. Investigamos a distribuição espacial de espécies de peixes com diferentes características tróficas e reprodutivas para avaliar como grupos funcionais responderam a uma cascata de reservatórios no rio Uruguai, sul do Brasil. Abundância de peixes, biomassa e composição de espécies foram avaliadas em oito locais ao longo do gradiente longitudinal. A assembleia de peixes no trecho superior foi caracterizada principalmente por espécies de pequeno e médio porte em níveis tróficos mais elevados, enquanto que os ambientes localizados mais a jusante apresentaram mais espécies de médio e grande porte, incluindo muitas espécies carnívoras. Espécies com alta fecundidade, migradores sazonais e bagres com fertilização interna foram comuns no curso médio e inferior. Espécies detritívoras dominaram áreas distantes das barragens. A diversidade funcional das assembleias de peixes locais foi maior nas partes inferiores. A cascata de barragens impactou a distribuição dos grupos funcionais das assembleias de peixes locais no rio Uruguai. A alteração da diversidade funcional no curso superior do rio tem consequências potenciais para a dinâmica e serviços do ecossistema, como ciclagem de nutrientes e pesca.(AU)

Incorporating indirect pathways in body size-trophic position relationships.

Body size, trophic position (TP), and trophic niche width are important elements of food webs; however, there is still debate regarding their interrelationships. Most studies have tested these correlations using datasets restricted to carnivores and bivariate models that disregard potential indirect effects of other factors, their interactions, and phylogeny. We analyzed relationships among TP, consumer size, maximum food item size, food item size variation (a proxy for trophic niche width), and two other traits (gut length and mouth width) using confirmatory path analysis of an extensive dataset for freshwater fishes that encompass both carnivorous and non-carnivorous species. Consumer size was associated with maximum food size, food size variation, mouth width, and gut length, all of which mediated indirect relationships between body size and TP. Mouth gape was associated with maximum food size, and consumers that fed on larger food items had higher TP. Consumers with relatively long guts generally fed on small and homogeneous food items near the base of the food web. Models were consistent whether or not accounting for phylogeny, but varied according to trophic guilds. However, the body size of both carnivorous and non-carnivorous was not directly associated with TP. Therefore, the incorporation of functional traits and their intermediate pathways is critical for understanding size-based trophic relationships of animals that encompass diverse feeding strategies. Our results caution approaches that rely on body size as a surrogate for TP, especially in systems where plants and detritus are consumed directly by a significant number of animals, such as in most freshwater ecosystems.

What do stable isotopes tell us about the trophic ecology of Thamnodynastes hypoconia (Serpentes: Dipsadidae) in southern Brazil?

Snakes are a useful model for ecological studies because they are gape-limited predators that may undergo ontogenetic changes in diet. We analyzed carbon and nitrogen stable isotope ratios to estimate percent contributions of different prey to snake biomass, trophic positions and isotopic niche width of juveniles and adults of the snake Thamnodynastes hypoconia. We also estimated the isotopic niche overlap between the two age categories. During eight intervals over a two-year period, we collected samples of whole blood and scales at a site in southern Brazil. Isotopic ratios of carbon and nitrogen did not differ between juveniles and adults for either tissue type, nor did mean trophic positions of juveniles and adults differ. The percent contribution of prey categories to snake biomass differed to a limited extent between the two years, with Hylidae being the most important anuran group assimilated during the first year and Leptodactylidae during the second year, for both ages. The isotopic niche occupied by adult snakes was slightly larger than that of juveniles when the analysis was based on data from whole blood samples, as expected because snakes are gape-limited. We found a reverse pattern when the analysis was based on scales, which may indicate that adult snakes have a smaller niche over the long term as they become selective foragers in certain prey. Isotopic overlap between juveniles and adults occurred during the two years, but it was bigger during the second year. We infer that, despite differences in gape size, juvenile and adult snakes in the study area exploit similar prey, with the degree of trophic similarity varying interannually.

Can ancestry and morphology be used as surrogates for species niche relationships?

Species interactions are difficult to quantify, and, consequently, many studies have used species traits and phylogeny as proxies under an assumption of niche conservatism (i.e., closely related and morphologically similar species should have similar niches). However, few studies have investigated whether niches actually are conserved within and across diverse communities. Here, we tested the degree to which phylogenetic relatedness and morphological similarity predict diets and stable isotopic ratios (δ 15N and δ 13C), two common descriptors of the trophic niche, in fish assemblages of two small streams in the Neotropics. We also tested the strength of the association between isotopic ratios and diet composition and found significant correlations implying that isotopic signals reveal trophic structure despite error associated with estimates of trophic enrichment and variation associated with tissue preservation, metabolism, and other factors affecting isotopic ratios. Morphological traits yielded a significant phylogenetic signal, and both morphological traits and phylogeny were correlated with diet composition, with morphological traits being a stronger predictor. We infer that functionally relevant morphological traits of fish can be used to infer trophic niches for certain kinds of questions and analyses when trophic data are lacking. However, we highlight that using phylogenetic and morphological data in combination with dietary and/or isotopic data can improve resolution of assemblage trophic structure and niche diversification.

Local environmental factors influence beta-diversity patterns of tropical fish assemblages more than spatial factors.

A major goal in ecology is to understand mechanisms that influence patterns of biodiversity and community assembly at various spatial and temporal scales. Understanding how community composition is created and maintained also is critical for natural resource management and biological conservation. In this study, we investigated environmental and spatial factors influencing beta diversity of local fish assemblages along the longitudinal gradient of a nearly pristine Neotropical river in the Colombian Llanos. Standardized surveys were conducted during the low-water season at 34 sites within the Bita River Basin. Physical, chemical, and landscape parameters were recorded at each site, and asymmetric eigenvector maps were used as spatial variables. To examine the relative influence of dispersal and environmental variables on beta diversity and its components, distance-based redundancy analysis (db-RDA) and variation partitioning analysis were conducted. We proposed that spatial scale of analysis and position within the river network would constrain patterns of beta diversity in different ways. However, results indicated that in this system, high beta diversity was consistent among species assemblages no matter the scale of analysis or position within the river network. Species replacement (turnover) dominated beta diversity, an indication of the importance of species sorting. These findings suggested that conservation of fish diversity in tropical rivers requires maintenance of both habitat heterogeneity (spatial variation in habitat conditions) and connectivity at the scale of entire river basins.

Floodplain land cover affects biomass distribution of fish functional diversity in the Amazon River.

Land-cover change often shifts the distribution of biomass in animal communities. However, the effects of land-cover changes on functional diversity remain poorly understood for many organisms and ecosystems, particularly, for floodplains. We hypothesize that the biomass distribution of fish functional diversity in floodplains is associated with land cover, which would imply that fish traits affect behavioral and/or demographic responses to gradients of land cover. Using data from surveys of 462 habitats covering a range of land-cover conditions in the Amazon River floodplain, we fitted statistical models to explain landscape-scale variation in functional diversity and biomass of all fish species as well as subsets of species possessing different functional traits. Forest cover was positively associated with fish biomass and the strength of this relationship varied according to functional groups defined by life history, trophic, migration, and swimming-performance/microhabitat-use traits. Forty-two percent of the functional groups, including those inferred to have enhanced feeding opportunities, growth, and/or reproductive success within forested habitats, had greater biomass where forest cover was greater. Conversely, the biomass of other functional groups, including habitat generalists and those that directly exploit autochthonous food resources, did not vary significantly in relation to forest cover. The niche space occupied by local assemblages (functional richness) and dispersion in trait abundances (functional dispersion) tended to increase with forest cover. Our study supports the expectation that deforestation in the Amazon River floodplain affects not only fish biomass but also functional diversity, with some functional groups being particularly vulnerable.

Unexpected fish diversity gradients in the Amazon basin.

Using the most comprehensive fish occurrence database, we evaluated the importance of ecological and historical drivers in diversity patterns of subdrainage basins across the Amazon system. Linear models reveal the influence of climatic conditions, habitat size and sub-basin isolation on species diversity. Unexpectedly, the species richness model also highlighted a negative upriver-downriver gradient, contrary to predictions of increasing richness at more downriver locations along fluvial gradients. This reverse gradient may be linked to the history of the Amazon drainage network, which, after isolation as western and eastern basins throughout the Miocene, only began flowing eastward 1-9 million years (Ma) ago. Our results suggest that the main center of fish diversity was located westward, with fish dispersal progressing eastward after the basins were united and the Amazon River assumed its modern course toward the Atlantic. This dispersal process seems not yet achieved, suggesting a recent formation of the current Amazon system.

Regime shift in fish assemblage structure in the Yangtze River following construction of the Three Gorges Dam.

Dams have well-documented ecological impacts on downstream river segments; however, long-term impacts of river impoundment have rarely been investigated in upstream reaches. Using data from long-term standardized surveys, we analyzed temporal changes in fish assemblages in the Yangtze River upstream of the Three Gorges Dam (TGD) before, during and after its construction. Our analysis indicated fish assemblage regime shifts in the two closer reaches in 2008, in accordance with the filling to 172.5 m in 2008; and in the other reach, farthest from the TGD, in 2011, indicating timing of the effects being related to distance. These shifts were evident in relative abundance of native fish species rather than non-native species and have altered community structures and functional groups. Relative abundance of the lotic guilds declined in the two closer reaches, but increased in the farthest. Invertivores declined, but piscivores and opportunistic life-history strategists increased in all reaches. We conclude that construction of TGD had led to significant changes in species distributions influenced by species functional traits. Our findings emphasize the need for long-term monitoring of fish assemblages before and after dam construction in order to understand ecological responses to hydrological changes for effective resource management in regulated rivers.

Intercontinental trends in functional and phylogenetic structure of stream fish assemblages.

Understanding of community assembly has been improved by phylogenetic and trait-based approaches, yet there is little consensus regarding the relative importance of alternative mechanisms and few studies have been done at large geographic and phylogenetic scales. Here, we use phylogenetic and trait dispersion approaches to determine the relative contribution of limiting similarity and environmental filtering to community assembly of stream fishes at an intercontinental scale. We sampled stream fishes from five zoogeographic regions. Analysis of traits associated with habitat use, feeding, or both resulted in more occurrences of trait underdispersion than overdispersion regardless of spatial scale or species pool. Our results suggest that environmental filtering and, to a lesser extent, species interactions were important mechanisms of community assembly for fishes inhabiting small, low-gradient streams in all five regions. However, a large proportion of the trait dispersion values were no different from random. This suggests that stochastic factors or opposing assembly mechanisms also influenced stream fish assemblages and their trait dispersion patterns. Local assemblages tended to have lower functional diversity in microhabitats with high water velocity, shallow water depth, and homogeneous substrates lacking structural complexity, lending support for the stress-dominance hypothesis. A high prevalence of functional underdispersion coupled with phylogenetic underdispersion could reflect phylogenetic niche conservatism and/or stabilizing selection. These findings imply that environmental filtering of stream fish assemblages is not only deterministic, but also influences assemblage structure in a fairly consistent manner worldwide.

First account of plastic pollution impacting freshwater fishes in the Amazon: Ingestion of plastic debris by piranhas and other serrasalmids with diverse feeding habits.

Reported here is the first evidence of plastic ingestion by freshwater fishes in the Amazon. Plastic bags, bottles, fishing gear, and other products are entering Amazonian water bodies and degrade into meso- and micro-plastic particles that may be ingested, either directly or indirectly via food chains, by fishes. Examination of stomach contents from 172 specimens of 16 serrasalmid species from lower Xingu River Basin revealed consumption of plastic particles by fishes in each of three trophic guilds (herbivores, omnivores, carnivores). Overall, about one quarter of specimens and 80% of species analyzed had ingested plastic particles ranging from 1 to 15 mm in length. Fourier transform infrared spectroscopy indicated 12 polymer types, including 27% identified as polyethylene, 13% polyvinyl chloride, 13% polyamide, 13% polypropylene, 7% poly(methyl methacrylate), 7% rayon, 7% polyethylene terephtalate, and 13% a blend of polyamide and polyethylene terephtalate. Dimensions of ingested plastic particles varied among trophic guilds, even though the frequency and mass of ingested particles were not significantly different among fishes with different feeding habits.

First evidence of microplastic ingestion by fishes from the Amazon River estuary.

This study investigated occurrence of microplastic particles in digestive tracts of fishes from the Amazon River estuary. A total of 189 fish specimens representing 46 species from 22 families was sampled from bycatch of the shrimp fishery. Microplastic particles removed from fish gastrointestinal tracts were identified using Attenuated Total Reflectance - Fourier Transform Infrared (ATR-FTIR). In total, 228 microplastic particles were removed from gastrointestinal tracts of 26 specimens representing 14 species (30% of those examined). Microplastic particles were categorized as pellets (97.4%), sheets (1.3%), fragments (0.4%) and threads (0.9%), with size ranging from 0.38 to 4.16 mm. There was a positive correlation between fish standard length and number of particles found in gastrointestinal tracts. The main polymers identified by ATR-FTIR were polyamide, rayon and polyethylene. These findings provide the first evidence of microplastic contamination of biota from the Amazon estuary and northern coast of Brazil.

Fish metacommunity structure in Caño Maraca, an important nursery habitat in the Western Llanos of Venezuela

We investigated spatial and seasonal variation of fish assemblages of Caño Maraca, a creek in Venezuela's Western Llanos, a region with strong wet-dry seasonality. Fishes were surveyed over a 19-year period at three sites along the longitudinal gradient: a headwater site with a narrow channel, a middle site with shallow channels traversing a seasonal wetland, and a lower site where the channel has higher banks. Assemblage composition and presence of species with juveniles and various life history strategies were compared during wet and dry seasons. Overall, fish species richness was lowest at the headwater site and highest at the downstream site. During the wet season, however, species richness is greatest at the middle site, a pattern associated with migration into the site for reproduction and use of the wetland as a nursery. During the dry season, species richness is greater at the downstream site where habitat quality is sufficient to provide suitable habitat for many species. Fish movements and population dynamics in Caño Maraca respond to seasonal environmental changes, and the fish metacommunity appears influenced by species sorting (habitat selection), mass effects (source-sink dynamics), patch dynamics (interspecific differences in colonization and species interaction) as well as random factors (dry-season strandings).(AU)

Investigamos la variación espacial y temporal de los ensambles de peces en el Caño Maraca, un arroyo localizado en los Llanos Occidentales de Venezuela, región caracterizada por una fuerte estacionalidad húmedo-seco. La ictiofauna fue evaluada en intervalos durante un período de 19 años, en tres sitios a lo largo del gradiente fluvial longitudinal: El primer sitio en la cabecera con un canal estrecho e hidrología estable, el segundo, intermedio con canales poco profundos atravesando un humedal estacional y el ultimo en la zona baja donde el canal tiene bancos más altos. La composición del ensamblaje y la presencia de especies con juveniles y diversas estrategias de historia de vida fueron comparadas durante las estaciones húmedas y secas. En general, la riqueza de especies de peces fue menor en el sitio de la cabecera y más alta en el sitio aguas abajo. Sin embargo, durante la época húmeda, la riqueza de especies fue mayor en el sitio central, patrón asociado con la reproducción de peces y el uso del humedal como criadero. Durante la época seca, la riqueza de especies fue mayor en la zona baja donde la calidad del hábitat es suficiente para proporcionar un hábitat adecuado para muchas especies. El movimiento de los peces y la dinámica poblacional en Caño Maraca están relacionadas a cambios ambientales estacionales. Adicionalmente la metacomunidad de peces parece estar influenciada por el ordenamiento de especies (selección de hábitat), efectos de masas (dinámica fuente-sumidero), dinámica de parches (involucrando diferencias interespecíficas en la tasa de colonización y capacidad competitiva) y factores aleatorios (relacionados con la duración de la estación seca).(AU)

Toward a Periodic Table of Niches, or Exploring the Lizard Niche Hypervolume.

Widespread niche convergence suggests that species can be organized according to functional trait combinations to create a framework analogous to a periodic table. We compiled ecological data for lizards to examine patterns of global and regional niche diversification, and we used multivariate statistical approaches to develop the beginnings for a periodic table of niches. Data (50+ variables) for five major niche dimensions (habitat, diet, life history, metabolism, defense) were compiled for 134 species of lizards representing 24 of the 38 extant families. Principal coordinates analyses were performed on niche dimensional data sets, and species scores for the first three axes were used as input for a principal components analysis to ordinate species in continuous niche space and for a regression tree analysis to separate species into discrete niche categories. Three-dimensional models facilitate exploration of species positions in relation to major gradients within the niche hypervolume. The first gradient loads on body size, foraging mode, and clutch size. The second was influenced by metabolism and terrestrial versus arboreal microhabitat. The third was influenced by activity time, life history, and diet. Natural dichotomies are activity time, foraging mode, parity mode, and habitat. Regression tree analysis identified 103 cases of extreme niche conservatism within clades and 100 convergences between clades. Extending this approach to other taxa should lead to a wider understanding of niche evolution.

Body size-trophic position relationships among fishes of the lower Mekong basin.

Body size is frequently claimed to be a major determinant of animal trophic interactions, yet few studies have explored relationships between body size and trophic interactions in rivers, especially within the tropics. We examined relationships between body size and trophic position (TP) within fish assemblages in four lowland rivers of the Lower Mekong Basin in Cambodia. Stable isotope analysis (based on δ15N) was used to estimate TP of common fish species in each river, and species were classified according to occupation of benthic versus pelagic habitats and major feeding guilds. Regression analysis yielded strong correlations between body size and TP among fishes from the Sesan and Sreprok rivers, but not those from the Mekong and Sekong rivers. The Mekong fish assemblage had higher average TP compared with those of other rivers. The relationship between body size and TP was positive and significantly correlated for piscivores and omnivores, but not for detritivores and insectivores. The body size-TP relationship did not differ between pelagic and benthic fishes. Body size significantly predicted TP within the orders Siluriformes and Perciformes, but not for Cypriniformes, the most species-rich and ecologically diverse order in the Lower Mekong River. We conclude that for species-rich, tropical fish assemblages with many detritivores and invertivores, body size would not be an appropriate surrogate for TP in food web models and other ecological applications.