Habitat structural complexity and morphological diversity of fish assemblages in a Neotropical floodplain river

High species richness and evenness in structurally complex habitats has been hypothesized to be associated with niche partitioning. To test this idea, relationships between habitat structural complexity in river littoral-zone habitats and morphological diversity of tropical fishes were examined in the Cinaruco River, Venezuela. Six habitat attributes were quantified in 45 sites spanning a range of structural complexity. Fishes were collected during day and night to estimate species density and relative abundances at each site. Twenty-two morphological variables were measured for each species. Principal components analysis (PCA) of physical habitat data yielded two axes that modeled >80% of variation across sites. The first two axes from PCA of fish morphological variables modeled >70% of variation. Species density during both day and night was negatively associated with flow velocity and positively associated with habitat complexity. Similarity of day and night samples from the same site was significantly greater for sites with high habitat complexity and low flow. In general, mean local assemblage morphological PC scores were not significantly associated with habitat PC scores. Average, maximum, and standard deviation of morphological Euclidean distances of local assemblages revealed positive associations with structural complexity and negative associations with flow. These relationships held even when the positive relationship of species density was statistically removed from assemblage morphological patterns. Findings suggest that both species niche compression and assemblage niche space increase when habitat complexity is greater and flow velocity is lower in this tropical lowland river.Electronic Supplementary Material Supplementary material is available for this article at     

Sporotrichosis in the Orinoco river basin of Venezuela and Colombia

Six cases of sporotrichosis from the Orinoco river basin of Venezuela and Colombia are described; two are of the localized cutaneous type and four are lymphocutaneous. Diagnosis was based on the patient's clinical history and mycological culture. Epidemiology and distinctive cultural habits of the patients are discussed in connection with disease etiology.Abbreviations CAICET Amazonas Center for Investigation and Control of Tropical Diseases - TFA Amazonas Federal Territory     

Periodic shedding and replacement of venomous caudal spines,with special reference to South American freshwater stingrays,Potamotrygon spp.

Synopsis The number of venomous caudal spines and their length and position relative to one another were determined in seven species of South American freshwater rays (Potamotrygonidae) and eight marine or euryhaline species of four families from the Caribbean Coast of South and Central America. Most species have two visible spines at certain stages in the shedding-replacement cycle and only one visible spine at other stages (following shedding). If we include the embryological beginnings of the spines before they erupt and become visible, the spine counts of most rays are actually 2 rather than 1 or 2. Since most species apparently follow this pattern, spine counts are of little use in distinguishing between species except in the relatively few that may have only one, or no spines. Eight captive Potamotrygon specimens maintained in simulated tropical temperature conditions over 12 months showed periodic shedding and replacement of spines. The molts were biannual for a given ray but annual for a given spine. They alternated between two spine loci and their cycles were approximately six months out of phase with each other. Recent studies on Dasyatis sabina by others report only one molt per year, with replacement spines forming always posterior to the primary spine rather than alternating between posterior and anterior. Supernumerary spines (counts of more than two, up to five) are also discussed, as are counts of one and zero.     

Some notes about the Intermediate Disturbance Hypothesis and its effects on the phytoplankton of the middle Orinoco river

Phytoplankton behaviour in the middle reaches of the Orinoco river (middle basin) is discussed in relation to the Intermediate Disturbance Hypothesis. Seven sets of samples were taken from two channels formed below the confluence of Meta and Orinoco rivers between September 1990 and August 1991. The Orinoco river channel (ORISMA-1) had many more species than the Meta river channel (ORISMA-2). Chlorophyceae dominated both, except during the rising water period when Bacillariophyceae were dominant. The quantitative dominancy alternates among Chlorophyceae, Bacillariophyceae and Cryptophyceae in both river channels, with minima averaging 14 329 and maxima of 1038 392 cells per liter. The phytoplankton concentration of both river channels is negatively correlated with variability in suspended sediments load. The Shannon-Weaver diversity for ORISMA-1 gives higher values than those from ORISMA-2 and oscillates between 1.37 to 3.52. Disturbances due to increases of water level and high concentration of suspended sediment can be the driving force governing phytoplankton behaviour in large rivers.     

Ammoglanis natgeorum,a new miniature pencil catfish (Siluriformes: Trichomycteridae) from the lower Atabapo River,Amazonas, Venezuela

A new species of the sand-dwelling catfish genus Ammoglanis is described from a marginal habitat of the lower Atabapo River, a left-bank blackwater tributary of the upper Orinoco River in Amazonas, Venezuela, adjacent to the border with Colombia. Ammoglanis natgeorum is distinguished from all congeners by trunk pigmentation pattern consisting of scattered ventral chromatophores concentrated around the anal-fin base and numerous additional meristic and anatomical characteristics. A. natgeorum is the second species of Ammoglanis described from the Orinoco River basin after Ammoglanis pulex, and several shared character states (e.g., eight total dorsal-fin rays, overall coloration pattern and presence of two finger-like papillae posterior to chin) suggest that it is more closely related to Ammoglanis obliquus (from the central Amazon basin) and A. pulex than to other congeners.     

Methane emissions from the Orinoco River floodplain, Venezuela

Methane emissions were measured over a 17-monthinterval at 21 locations on the Orinoco fringingfloodplain and upper delta (total area,14,000 km²). Emissions totaled 0.17 Tgyr^–1, or 7.1 mmol d^–1 (114 mg d^–1;standard deviation, ±18%) per m² of watersurface. Ebullition accounted for 65% of emissions. Emission rates were about five times as high forfloodplain forest as for open water or macrophytemats. Emission rates were positively correlated withcarbon content of sediment and amount of methane inthe water column, and negatively correlated withdissolved oxygen, but the correlations were weak. Emission from floodplain soils occurred only when thewater content of soil exceeded 25%, which occurredwithin 20 m of standing water during floodplaindrainage (3 months/yr). Bare soils emitted 60mmol/day per m of shoreline length; soils covered bystranded macrophyte beds emitted five times thisamount. Total emissions were accounted for primarilyby flooded forest (94%); macrophyte mats, open water,and exposed soils made only small contributions. Theflux-weighted mean ¹³C for the floodplainwas –62 ± 8; for D the mean was –271 ± 27. The ¹³C and D were negativelycorrelated. Overall emission rates were notably lowerthan for the Amazon. The depth and duration offlooding are considerably less for the Orinoco thanfor the Amazon floodplain; oxygen over sediments isthe rule for the Orinoco but not for the Amazon. TheOrinoco data illustrate the difficulty of generalizingemission rates. Current information for tropicalAmerica, including revised estimates for inundatedarea along the Amazon, indicate that methane emissionsfrom tropical floodplains have been overestimated.     

Aquatic vegetation of the Orinoco River Delta (Venezuela). An overview

The Orinoco River Delta is a complex of relatively unknown ecosystems made up of aquatic and semiaquatic habitats. The region includes a Mariusa National Park and the Orinoco Delta River Biosphere Reserve. The 23 sites studied included lentic habitats (lagoons and creeks) and lotic habitats (streams of variable breadth and current) which varied range from black to white waters. A collection of aquatic vascular plants was made and the physical and chemical variables were measured. A total of 100 species were identified, 48% of which are new records for the Delta territory. A Canonical Correspondence Analysis divided the species and communities into two groups: The lentic habitats of lakes and lagoons, which show a greater species richness and the lotic habitats of the main river courses. This study forms part of an ongoing research project on the floristic and abiotic characteristics of the aquatic communities in the Orinoco River Delta.     

Microgeographic diversity in the neotropical knife-fish Eigenmannia macrops (Gymnotiformes,Sternopygidae)

Synopsis Examination of 681 individuals of electric knife-fishes, Eigenmannia macrops, from the Orinoco River, Venezuela, revealed a pattern of morphological diversity which covaried with habitat. Fishes from the caños (small stream tributaries) are on average smaller than those from offshore habitats and lagoons. Even at the same body size the tails of caño fishes are relatively shorter, their bodies are deeper, and their heads are relatively wider than those from other habitats. Caño fishes are more different from fishes of the deep channels than from those of the shallow channels, beaches, or lagoons. Several factors are examined for their possible relationship to the origin of the observed diversity including electrophysiology, locomotory adaptation, growth rate and ecology. The problems of genetic versus physiological bases of morphological variation are addressed.     

Vegetation changes induced by dam construction in a tropical estuary: the case of the Mánamo river,Orinoco Delta (Venezuela)

This study documents the increased distribution of mangrove communities into the oligohaline regions of the Mánamo river as a consequence of a dam constructed in 1965. The dam caused a major change in the discharge regime of the water, stopping the annual floodings and allowing an extensive upriver intrusion of saline waters. Penetration of salt water from the sea due to the daily tides, that would be observed only during the dry season, occurs now throughout the year.Three sites were chosen along the upper, middle and lower river course. The evolution of site geomorphology and vegetation was evaluated over 3 periods, from 1932 to 1996, using aerial photographs and recent field surveys. Soil and plant samples were taken in the mangrove communities of two sites nearer to the river mouth along 100 m transects inland from the river fringe. The influence of sea water in soils was measured by the concentration of Na, Mg, Cl and SO4 in the interstitial soil water. In plants, the impact of soil salinity was determined by the concentration of Na, K, and Mg in mature leaves.The geomorphological processes created new habitats (sand bars) for aquatic and terrestrial vegetation. In the middle and lower river course tidal penetration of sea water due to lower river discharge salinized the soil, allowing mangrove establishment. This occurred mainly in the open sand bars or in areas with sparse herbaceous vegetation. The ion content was higher in the down river site and also higher in the subsoils compared with the topsoils. The apparent expansion rate of a plant community dominated by a mangrove species (Rhizophora mangle) increased from 1 ha yr–1 prior to the regulation of water flow, to 6–7 ha yr–1 after the river closure. The dam influences the entire Mánamo river basin, affecting the distribution of halophytic species along the river fringes.     

Plant use knowledge of the Winikina Warao: The case for questionnaires in Ethnobotany

A questionnaire was used to measure plant use knowledge for 18 plants from 40 randomly selected Winikina Warao respondents of two villages in the Orinoco River Delta, Venezuela. Five use values are presented: reported use (RU) value for each plant and plant part; plant part value (PPV); specific use (SU) value; intraspecific use value (IUV); and overall use value (OUV). The overall use value can be used to target plants of potential interest to researchers. Although certain precautions must be taken when undertaking this type of study, questionnaires are important tools that can be used to assess the dynamic interplay between people and the plants they use.

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Conocimiento del uso de plantas de los winikina warao: el caso de cuestionarios en etnobotánica

Resumen  Un cuestionario fue utilizado para medir el conocimiento de 18 plantas usadas por los Winikina Waroa del delta del rio Orinoco, Venezuela. Cinco valores de uso son presentados: valor de uso reportado (RU) para cada planta y parte de planta; valor de la parte de planta (PPV); valor de uso especifico (SU); y valor de uso total (OUV). El valor de uso total se puede utilizar para escoger plants de interés a investigadores. Aunque es necesario tomar ciertas precauciones para emprender un estudo de este tipo, cuestionarios son herramientas que se pueden utilizar para asesar la interacción dinmica que existe entre la gente y su uso de plantas.