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Registro: 113 (1 / 113)

Título del Articulo: Disentangling population strategies of two cladocerans adapted to different ultraviolet regimes

Autores: Carla E. Fernández^bMelina Campero, Cintia Uvo, Lars-Anders Hansson

Fecha de Publicación: 2018

Descriptores: cladocera, Daphnia, life-history traits, stress, structural equation modeling, ultraviolet radiation

Abstract:

Zooplankton have evolved several mechanisms to deal with environmental threats, such as ultraviolet radiation (UVR), and in order to identify strategies inherent to organisms exposed to different UVR environments, we here examine life- history traits of two lineages of Daphnia pulex. The lineages differed in the UVR dose they had received at their place of origin from extremely high UVR stress at high- altitude Bolivian lakes to low UVR stress near the sea level in temperate Sweden. Nine life- history variables of each lineage were analyzed in laboratory experiments in the presence and the absence of sub- lethal doses of UVR (UV- A band), and we identified trade- offs among variables through structural equation modeling (SEM). The UVR treatment was detrimental to almost all life- history variables of both lineages; however, the Daphnia historically exposed to higher doses of UVR (HighUV) showed a higher overall fecundity than those historically exposed to lower doses of UVR (LowUV). The total offspring and ephippia production, as well as the number of clutches and number of offspring at first reproduction, was directly affected by UVR in both lineages.

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Registro: 112 (2 / 113)

Título del Articulo: DNA Metabarcoding of Amazonian Ichthyoplankton Swarms

Autores: M. E. Maggia; Y. Vigouroux; J. F. Renno; F. Duponchelle; E. Desmarais; J. Nunez; C. García-Dávila3; F. M. Carvajal-Vallejos; E. Paradis; J. F. Martin; C. Mariac

Fecha de Publicación: 2017

Abstract:

Tropical rainforests harbor extraordinary biodiversity. The Amazon basin is thought to hold 30% of all river fish species in the world. Information about the ecology, reproduction, and recruitment of most species is still lacking, thus hampering fisheries management and successful conservation strategies. One of the key understudied issues in the study of population dynamics is recruitment. Fish larval ecology in tropical biomes is still in its infancy owing to identification difficulties. Molecular techniques are very promising tools for the identification of larvae at the species level. However, one of their limits is obtaining individual sequences with large samples of larvae. To facilitate this task, we developed a new method based on the massive parallel sequencing capability of next generation sequencing (NGS) coupled with hybridization capture. We focused on the mitochondrial marker cytochrome oxidase I (COI). The results obtained using the new method were compared with individual larval sequencing. We validated the ability of the method to identify Amazonian catfish larvae at the species level and to estimate the relative abundance of species in batches of larvae. Finally, we applied the method and provided evidence for strong temporal variation in reproductive activity of catfish species in the Ucayalı ´River in the Peruvian Amazon. This new time and cost effective method enables the acquisition of large datasets, paving the way for a finer understanding of reproductive dynamics and recruitment patterns of tropical fish species, with major implications for fisheries management and conservation.

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Registro: 111 (3 / 113)

Título del Articulo: Effects of UVB radiation on grazing of two cladocerans from high-altitude Andean lakes

Autores: Carla Eloisa Fernandez^bDanny Rejas

Fecha de Publicación: 2017

Abstract:

Climate change and water extraction may result in increased exposition of the biota to ultraviolet-B radiation (UVB) in high-altitude Andean lakes. Although exposition to lethal doses in these lakes is unlikely, sub-lethal UVB doses may have strong impacts in key compartments such as zooplankton. Here, we aimed at determining the effect of sub-lethal UVB doses on filtration rates of two cladoceran species (Daphnia pulicaria and Ceriodaphnia dubia). We firstly estimated the Incipient Limiting Concentration (ILC) and the Gut Passage Time (GPT) for both species. Thereafter we exposed clones of each species to four increasing UVB doses (treatments): i) DUV-0 (Control), ii) DUV-1 (0.02 MJ m2), iii) DUV-2 (0.03 MJ m2) and iv) DUV-3 (0.15 MJ m2); and estimated their filtration rates using fluorescent micro-spheres. Our results suggest that increasing sub-lethal doses of UVB radiation may strongly disturb the structure and functioning of high-altitude Andean lakes. Filtration rates of D. pulicaria were not affected by the lowest dose applied (DUV-1), but decreased by 50% in treatments DUV-2 and DUV-3. Filtration rates for C. dubia were reduced by more than 80% in treatments DUV-1 and DUV-2 and 100% of mortality occurred at the highest UVB dose applied (DUV-3).

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Registro: 110 (4 / 113)

Título del Articulo: ¿Qué factores determinan la distribución altitudinal de los peces de ríos tropicales andinos?

Autores: Evans De La Barra1^bJosé Zubieta, Gastón Aguilera, Mabel Maldonado, Marc Pouilly, Thierry Oberdorff2

Fuente: REVISTA BIOLOGIA TROPICAL

Fecha de Publicación: 2016

Descriptores: species richness, Bolivian Amazon, mountain streams, maximum slopes in the main river

Abstract:

Altitudinal gradients represent an appropriate system to assess whether there is a relationship between richness patterns, environmental variables, and the ecological processes that determine the species type and number inhabiting a given area. In mountain streams freshwater fishes, the most prevalent relationship is a monotonic decrease in species richness with elevation. The objective of this study was to evaluate four hypotheses that can explain the negative relationship between local fish species richness and altitude, 1) the hypothesis of decreasing energy availability, 2) the hypothesis of increasing climate severity, 3) the hypothesis of habitat diversity, and 4) the hypothesis of isolation by physical severity of the environment. Fish and macro-invertebrates were collected following standard methods from 83 sites (between 200-4 000 meters) of two river basins in the Bolivian Amazon.

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Registro: 109 (5 / 113)

Título del Articulo: Metacommunity patterns across three Neotropical catchments with varying environmental harshness

Autores: THIBAULT DATRY†‡^bADRIANO S. MELO§, NABOR MOYA‡¶, JOSE ZUBIETA‡, EVANS DE LA BARRA‡ AND THIERRY OBERDORFF

Fecha de Publicación: 2016

Abstract:

Most metacommunity studies indicate that dispersal processes play a minor role compared with species sorting in explaining metacommunity organisation, in particular, in stream systems. However, the role of dispersal could vary with environmental harshness, as a result of frequent resetting of community succession by disturbances and the selection of generalist species from regional species pools. The importance of dispersal may also be mitigated by species dispersal ability.In this study, we explored how species sorting and dispersal shaped invertebrate and ﬁsh metacommunities across streams in three tropical headwater catchments in Bolivia with contrasting environmental harshness, including ﬂow regime, altitude and climate conditions. We addressed the hypothesis that the relative roles of dispersal and species sorting vary with environmental harshness: we predicted that the role of species sorting would predominate in benign conditions, whereas that of dispersal would predominate under moderate environmental harshness, and that neither dispersal nor species sorting would be relevant to explain metacommunities under high environmental harshness. We also hypothesised that the role of dispersal would decrease with increasing species dispersal ability.

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Registro: 108 (6 / 113)

Título del Articulo: The expansion of Arapaima cf. gigas (Osteoglossiformes: Arapaimidae) in the Bolivian Amazon as informed by citizen and formal science

Autores: Paul A. Van Damme^bClaudia Coca Méndez, Milton Zapata, Fernando M. Carvajal-Vallejos, Joachim Carolsfeld3 and Julian D. Olden

Fecha de Publicación: 2015

Descriptores: fish, bony tongue, introduced species, artisanal fisheries, Upper Madera River, Riberalta

Abstract:

The giant osteoglossomorph fish Arapaima cf. gigas was introduced to the northern Bolivian Amazon over a half century ago and now contributes significantly to commercial fisheries. Despite this, little is known regarding its current distribution and invasion potential. Here, we address this knowledge gap using two complementary methods: interviewing key informants and examining fisheries landing records in the principal landing site (Riberalta). Both interviews and landing data revealed that the species represents approximately 50% of the total commercial catches, and that it now occupies approximately 340 km2 of floodplain lakes in the Beni, Orthon and Madre de Dios River basins. The annual yield is estimated at 258 t, equivalent to 0.76 kg/ha/year. The current geographic distribution represents approximately one-quarter (24%) of floodplain lakes in the lower Bolivian Amazon, suggesting high fisheries potential of the species if it would also colonize the remaining Mamoré and Iténez River basins. The potential for negative ecosystem impacts of the A. cf. gigas invasion seems likely, considering the large body size, life history and feeding ecology of this species, but has not yet been clearly demonstrated. Factors that might limit further expansion are natural barriers (waterfalls) in the lower Mamoré, and periodic cold temperature conditions in the Mamoré and Iténez River basins.

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Registro: 107 (7 / 113)

Título del Articulo: Fish-AMAZBOL: a database on freshwater ﬁshes of the Bolivian Amazon

Autores: Fernando M. Carvajal-Vallejos • Re ´my Bigorne • Ame ´rica J. Zeballos Ferna ´ndez • Jaime Sarmiento • Soraya Barrera • Takayuki Yunoki • Marc Pouilly • Jose ´ Zubieta • Evans De La Barra • Michel Jegu ´ • Mabel Maldonado • Paul Van Damme • Ricardo Ce ´spedes • Thierry Oberdorff

Fecha de Publicación: 2014

Abstract:

The Bolivian part of the Amazon Basin contains a mega diverse and well-preserved ﬁsh fauna. Since the last decade, this ﬁsh fauna has received an increasing attention from scientists and the national authorities as ﬁshes represent one of the most important sources of proteins for local human communities. However, this ﬁsh fauna still remains poorly documented. Here, we present a database for

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Registro: 106 (8 / 113)

Título del Articulo: Tropical high-altitude Andean lakes located above the tree line attenuate UV-A radiation more strongly than typical temperate alpine lakes

Autores: Ximena Aguilera^ba Xavier Lazzaroa, and Jorge S. Coronel

Fecha de Publicación: 2013

Abstract:

Tropical high-altitude Andean lakes are physically harsh ecosystems. Located above the treeline (≥4000 m a.s.l.), they share common features with temperate alpine lakes, which impose extreme conditions on their aquatic organisms: e.g., strong winds, broad diel variations in water temperature, and intense solar ultraviolet radiation (UVR). However, because of their latitude, they diﬀer in two major ecological characteristics: they lack ice cover during the winter and they do not present summer water column stratiﬁcation. We sampled 26 tropical high-altitude Andean lakes from three regions of the Bolivian Eastern Andes Cordillera during the wet period (austral summer). We performed an ordination to better describe the typology of Andean lakes in relation to the environmental variables, and we assessed the relationships among them, focussing on the UV-A transparency (360 nm) throughout the water column. We found a positive correlation between UV-A transparency calculated as Z1% (the depth which reaches 1% of the surface UV-A), the lake maximum depth and Secchi transparency (r = 0.61). Z1% of UV-A was smaller in shallow lakes than in deep lakes, indicating

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Registro: 105 (9 / 113)

Título del Articulo: Limitación por nutrientes y pastoreo como factores de control de las densidades de bacterias y algas planctónicas en una laguna altoandina (Cochabamba, Bolivia)

Autores: Danny Rejas^bCarla Valverde y Carla E. Fernández

Fuente: Rev. Bol. Ecol. y Cons. Amb

Fecha de Publicación: 2012

Descriptores: Bacterioplancton, fitoplancton, dilución, depredación

Abstract:

En ecosistemas acuáticos, el flujo de materia y energía es canalizado a través de dos redes tróficas alternativas: el bucle microbiano, basado en bacterias y la cadena trófica clásica, basada en fitoplancton. Llevamos a cabo dos experimentos de adición selectiva de nutrientes/dilución para estudiar los mecanismos de control bottom-up (limitación por nutrientes) y top-down (pérdidas por pastoreo) de bacterias y algas planctónicas en Laguna Toro, una laguna altoandina en Bolivia. El crecimiento bacteriano no estaba limitado por el carbono (C), sino co-limitado por nitrógeno (N) y fósforo (P). El crecimiento fitoplanctónico fue limitado por P. El crecimiento bacteriano fue sostenido principalmente por nutrientes reciclados por el microzooplancton, mientras que el crecimiento algal fue sostenido por fuentes internas. Proponemos que las bacterias superan a las algas en la competencia por nutrientes inorgánicos, evitando que las algas usen los nutrientes reciclados. Las tasas de pastoreo microzooplanctónico fueron relativamente bajas, consumiendo 59% de la producción bacteriana y 48% de la producción algal. Sin embargo, debido a las densidades extremadamente bajas de mesozooplancton, probablemente el microzooplancton sea el mayor responsable de la transferencia de C a los niveles tróficos superiores.

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Registro: 104 (10 / 113)

Título del Articulo: Effect of water quality on growth of four fish species in the Iténez basin (Upper Madera, Amazon)

Autores: Esther López Siangas & Marc Pouilly & Adamit Vallejos & Tamara Pérez & Danny Rejas

Fecha de Publicación: 2012

Descriptores: Otoliths.Agereading.Mercury.White water.Clearwater

Abstract:

Fish growth is an indicator of populations’ life conditions that could be used to detect stress due to contamination. In this study, age of fishes of four species (Psectrogaster essequibensis, Schizodon fasciatus, Triportheus angulatus and Pygocentrus nattereri) from the Iténez basin (Upper Madera, Amazon) were estimated by otolith readings, and growth parameters were estimated by using the Von Bertalanffy Growth Function. Populations of four sites were compared in order to detect the effect of natural and anthropogenical water chemistry differences. One of these sites was directly impacted by gold mining activities whereas the three others were only influenced by mild human activities and presented white or clear waters. Species growth coefficient (K) varied from 0.28 (P. nattereri), to 0.39 (P. essequibensis), 0.69 (S. fasciatus) and 1.71 (T. angulatus).

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Registro: 103 (11 / 113)

Título del Articulo: A REDESCRIPTION OF BRANCHINECTA POLLICIFERA HARDING, 1940, AND ITS PLACEMENT IN A NEW GENUS (BRANCHIOPODA: ANOSTRACA: BRANCHINECTIDAE)

Autores: D. Christopher Rogers and Jorge S. Coronel

Fecha de Publicación: 2011

Descriptores: Archaebranchinecta, Branchinecta, fairy shrimp, melanisation

Abstract:

Branchinecta pollicifera is redescribed from type material and additional material collected from Bolivian bofedal wetlands. Specific unique gonopod and genital segment features demonstrate that B. pollicifera constitutes a new genus, Archaebranchinecta, morphologically distinct from Branchinecta sensu stricto. Additionally, in B. pollicifera, the gonopod proximal projection is bifurcated as opposed to a spiniform Branchinecta, and the first abdominal segment bears a pair of ventrolateral spinule covered plates. These plates are unique amongst Anostraca. The form of the male second antennae in this species and in the related fossil species B. barstowensis demonstrates a potential close relationship, and this species is also referred to Archaebranchinecta. We also report melanisation in Andean anostracans.

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Registro: 102 (12 / 113)

Título del Articulo: Desarrollo de un índice multimétrico basado en macroinvertebrados acuáticos para evaluar la integridad biológica en ríos de los valles interandinos de Bolivia

Autores: Nabor Moya; Eduardo Domínguez; Edgar Goitia; Thierry Oberdorff

Fuente: Asociación Argentina de Ecología

Fecha de Publicación: 2011

Descriptores: ríos neotropicales, perturbación antropogénica, bioindicadores, insectos acuáticos]

Abstract:

Se presenta un índice multimétrico que permite discriminar la variabilidad ambiental natural de la antropogénica en 91 sitios (63 sitios de referencia y 28 sitios perturbados) distribuidos de manera uniforme a lo largo de la cuenca alta del Río Grande (Bolivia). En este procedimiento se utilizaron inicialmente 12 métricas que reflejan distintos atributos de la estructura y el funcionamiento de la comunidad de macroinvertebrados acuáticos, por su potencial como indicadoras de alteración de ambientes acuáticos. En principio, usando los sitios de referencia, se desarrollaron modelos estadísticos que describen la respuesta de las distintas métricas a la variabilidad ambiental natural. Luego se utilizaron estos modelos para predecir la respuesta de las métricas en condiciones alteradas, para lo cual se usaron los sitios que presentaban distintos tipos de perturbación antropogénica (i.e., perturbación por actividad agrícola, urbana y minera). De las 12 métricas iniciales se conservaron sólo cinco para elaborar el índice final (riqueza total, abundancia total, riqueza de Ephemeroptera, Plecoptera y Trichoptera (EPT), porcentaje en abundancia de EPT y porcentaje en abundancia de raspadores). Estas métricas resultaron las más efectivas al responder de manera significativa al gradiente de perturbación. Este índice distinguió con claridad los sitios de referencia de los perturbados, y mostró una relación lineal negativa significativa frente a un gradiente de perturbaciones físicas y químicas. Esta aproximación puede servir como herramienta de biomonitoreo para evaluar la integridad biótica y la biodiversidad acuática en los ríos de la región de los valles interandinos de Bolivia.

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Registro: 101 (13 / 113)

Título del Articulo: Scale dependency of processes structuring metacommunities of cladocerans in temporary pools of High-Andes wetlands

Autores: Steven A. J. Declerck^bJorge S. Coronel, Pierre Legendre and Luc Brendonck

Fecha de Publicación: 2011

Abstract:

Metacommunity structure can be shaped by a variety of processes operating at different spatial scales. With increasing scale, the compositional variation among local communities (beta diversity) may reflect stronger environmental heterogeneity, but may also reflect reduced exchange of organisms between habitat patches. We analyzed the spatial architecture of a metacommunity of cladoceran zooplankton in temporary pools of High Andes wetlands, with the objective of explaining the spatial dependency of its structure. The spatial distribution of the pools is hierarchical and highly discontinuous: pools are clustered within small wetlands, which lay scattered over valleys that are separated from each other by mountain ridges.

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Registro: 100 (14 / 113)

Título del Articulo: Bottom-up and top-down control of phytoplankton growth in an Amazonian várzea lake

Autores: Danny Rejas^bKoenraad Muylaert

Fecha de Publicación: 2010

Descriptores: white-water, nutrient limitation, grazing, phytoplankton growth, Amazon, Bolivia.

Abstract:

Laguna Bufeos is a pristine várzea lake in the upper Madera basin, close to the Andes mountains. Two sets of experiments were carried out during the low-water and high-water season to determine bottom-up and top-down regulation of phytoplankton growth rates. Nutrient addition assays indicated that phytoplankton was primarily limited by N during both the high- and low-water season. Measurements of phytoplankton growth rates at different depths in the lakes indicated photoinhibition close to the water surface and slightly negative growth rates below 1 m depth. Incubations of phytoplankton in the presence and absence of mesozooplankton indicated no signiﬁ cant grazing pressure of mesozooplankton.

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Registro: 99 (15 / 113)

Título del Articulo: Description of the first South American species of Neocylloepus Brown (Coleoptera: Elmidae): N. chaparensis sp. nov. from Bolivia

Autores: Studies on Neotropical Fauna^bEnvironment Veronica Manzoa, N. Moya

Fuente: Studies on Neotropical Fauna and Environment

Fecha de Publicación: 2010

Descriptores: Bolivia; Elmidae; larvae; Neocylloepus; South America; water beetle

Abstract:

A new species of riffle beetle from Bolivia, Neocylloepus chaparensis sp. nov., is described and illustrated from adults of both sexes and the larva. This is the first species of Neocylloepus Brown described from South America. The new species is compared with other species described in the genus. Distributional records, diagnoses and a key to distinguish the species of genus are included.Se describe una nueva especie de élmido de Bolivia, Neocylloepus chaparensis sp. nov. Se describe e ilustra los adultos de ambos sexos y la larva. Esta es la primera especie del género descripta para América del Sur. La nueva especie es comparada con todas las otras especies conocidas de Neocylloepus. Se incluyen nuevos datos de distribución, diagnósis y claves para identificar adultos y larvas del género.

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Registro: 98 (16 / 113)

Título del Articulo: Macroinvertebrate community response to acid mine drainage in rivers of the High Andes (Bolivia)

Autores: Paul Andre^bVan Dammea, Caroli Hamelb, Alfredo Ayalab, Lieven Bervoets

Fecha de Publicación: 2008

Abstract:

Several High Andes Rivers are characterized by inorganic water pollution known as acid mine drainage (AMD). The aim of this study was to assess the relationship between metal concentrations in the sediments and the macroinvertebrate communities in two river basins affected by AMD. In general, the taxon diversity of the macroinvertebrate community at the family level was low. The concentrations of Cd, Cu, Zn, Pb and Ni at mining sites were higher than at unpolluted sites. The pH of the water was alkaline (7.0–8.5) in unpolluted sites, whereas it dropped to very low values (<3) at mining sites. Redundancy Analysis (RDA) showed that pH was the best predictor of macroinvertebrate community richness. The number of macroinvertebrate families decreased gradually with increasing acidity, both in pools and rifﬂes, though it is suggested that rifﬂe communities were more affected because they are in closer contact with the acid water

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Registro: 97 (17 / 113)

Título del Articulo: The genetic legacy of polyploid Bolivian Daphnia: the tropical Andes as a source for the North and South American D. pulicaria complex

Autores: JOACHIM MERGEAY^bXIMENA AGUILERA,† STEVEN DECLERCK, ADAM PETRUSEK,‡ TINE HUYSE§ and LUC DE MEESTER

Fuente: Molecular Ecology

Fecha de Publicación: 2008

Descriptores: Andes, Cladocera, Daphnia pulex, phylogeography, polyploidy, South America

Abstract:

We investigated genetic variation in asexual polyploid members of the water flea Daphnia pulex complex from a set of 12 Bolivian high-altitude lakes. We used nuclear microsatellite markers to study genetic relationships among all encountered multilocus genotypes, and combined this with a phylogenetic approach using DNA sequence data of three mitochondrial genes. Analyses of mitochondrial gene sequence divergence showed the presence of three very distinct clades that likely represent cryptic undescribed species. Our phylogenetic results suggest that the Daphnia pulicaria group, a complex of predominantly North American species that has diversified rapidly since the Pleistocene, has its origin in South America, as specific tests of topology indicated that all three South American lineages are ancestral to the North American members of this species group.

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Registro: 96 (18 / 113)

Título del Articulo: Developmental costs of rapid growth in a damselﬂ y

Autores: ARJAN DE BLOCK ^bMELINA C AMPERO,R OBBY S TOKS

Fuente: Ecological Entomology

Fecha de Publicación: 2008

Descriptores: Damselﬂ y larvae , developmental costs , ﬂ uctuating asymmetry , growth rate , trade-off .

Abstract:

D evelopmental costs of rapid growth in terms of increased fluctuating asymmetry are expected to contribute to the widespread occurrence of growth rates below the physiological maximum, but have rarely been demonstrated. Here, these costs are studied for the first time in an invertebrate, the damselfly Lestes viridis, using a rearing experiment where early- and late-hatched larvae of both sexes were reared at decreasing or permanent water levels.Late-hatched animals were more asymmetrical than early-hatched animals except for males in the drying treatment. Also, females were more asymmetrical than males except in early-hatched animals in the drying treatment.The data presented suggest that in females but not in males treatment groups with higher growth rates have more asymmetrical wings. However, at the individual level no relationship between growth rate and asymmetry was present.

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Registro: 95 (19 / 113)

Título del Articulo: ackwell Publishing Ltd Metamorphosis offsets the link between larval stress, adult asymmetry and individual quality

Autores: M. Campero^bM. De Block, F. Ollevier, and R. Stoks

Fecha de Publicación: 2008

Descriptores: complex life cycle, damselﬂies, ﬂuctuating asymmetry, immune function

Abstract:

Many animals have a complex life cycle (CLC) with a discrete larval and adult stage, often separated by metamorphosis (Moran 1994). One challenge for life-history theory is to understand whether and how stressors in the larval stage affect adult ﬁtness in such animals. Although it is typically assumed these effects are entirely mediated through age and size at metamorphosis (Roff 2002), recent studies suggest this may be only partly true (e.g. De Block & Stoks 2005; Stoks, De Block & McPeek 2006a). Therefore, we need studies identifying which other adult traits that may affect adult ﬁtness are shaped by larval stressors and which are not.

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Registro: 94 (20 / 113)

Título del Articulo: Distribution patterns, population status and conservation of Melanosuchus niger and Caiman yacare (Crocodylia, Alligatoridae) in oxbow lakes of the Ichilo river floodplain, Bolivia

Autores: Ximena Aguilera^bJorge S. Coronel, Thierry Oberdorff , Paul A. Van Damme3

Fuente: Unidad de Limnología y Recursos Acuáticos

Fecha de Publicación: 2008

Descriptores: Bolivian Amazon, Caiman yacare, floodplain lakes, Melanosuchus niger

Abstract:

Caiman yacare (lagarto) and Melanosuchus niger (black caiman), sympatric species in the Bolivian Amazon basin, have been severely overexploited in the past. We present the results of a standardized survey of C. yacare and M. niger populations in order to evaluate their actual population status in twelve oxbow lakes of the Ichilo River floodplain. Additionally we explored the effect of environmental and anthropogenic variables on caiman distribution patterns. The average density of C. yacare and M. niger in the shoreline of floodplain lakes was of 6 and 1 ind/km, respectively. For both species, the population was composed mainly of juvenile individuals.

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