Highest Species Richness Values Research Articles

Biodiversity of zooplankton communities in the Upper Paraná River floodplain: interannual variation from long-term studies

We investigated the effect of interannual variation of hydrosedimentological regime and connectivity on the zooplankton biodiversity in the Upper Paraná River floodplain. Zooplankton samplings were undertaken between 2000 and 2007, in different environments of the floodplain, including connected and isolated floodplain lakes, backwaters, rivers and channels. The zooplankton included 541 species. Rotifers showed the highest species richness and abundance. Among the zooplankton species, 71 represent new occurrence records for the floodplain. The species accumulation curve showed a continuous increase in gamma diversity, demonstrating the importance of long-term research for accurate knowledge of biodiversity in heterogeneous and dynamic ecosystems, such as the floodplains. Interannual beta diversity among studied years indicated a lesser alteration in community composition in 2001, when a long limnophase period was observed. In most of the environments, the highest species richness values were related to the greatest flooding amplitudes. Flooding amplitude, which is associated with connectivity, favors faunal exchange amongst the environments and between the pelagic and littoral zones. This explains the occurrence of both planktonic and non-planktonic species within the community. On the other hand, mean zooplankton abundance values were higher when a long isolation period occurred. Differences between the potamophase and limnophase amplitude associated with connectivity among the environments were the most important factors for the structure and dynamics of the zooplankton community in the Upper Paraná River floodplain.

Estacionalidad y estructura de la vegetación en la comunidad de anfibios y reptiles de Chamela, Jalisco, México

Se evaluó el efecto de la estacionalidad ambiental y la estructura de la vegetación en los patrones espacio-temporales de la comunidad (composición, diversidad, riqueza y abundancia relativa) de losanfibios y reptiles de la región de Chamela, Jalisco. Tres sitios fueron muestreados, mediante un diseño de bloque dentro de una matriz de vegetación de arroyo (VA) y bosque tropical caducifolio (BTC) utilizando tres técnicas complementarias de muestreo (trampeo; parcelas de búsqueda intensiva y transectos visuales) durante la época de secas y de lluvias. Se registraron 34 especies (25 de reptiles y nueve de anfibios). Las curvas de acumulación de especies y los índices predictores de riqueza, sugieren que el esfuerzo de muestreo fue el adecuado. Los valores más altos de riqueza, diversidad y abundancia se registraron en la VA. Se registraron mayores fluctuaciones estacionales en anfibios que en reptiles, y en el BTC que en la VA. Se documenta un recambio de especies, tanto espacial (matriz de vegetación VA-BTC) como temporal (estacional), más marcado en anfibios cuyo registro de individuos fue mínimo durante la época de secas y solo dentro de la VA. La VA es importante para el mantenimiento de la diversidad herpetofaunística, no sólo por su menor estacionalidad y mayor productividad, sino por su mayor complejidad estructural. Se encontró una mayor respuesta de los anfibios hacia los cambios en la estructura de la vegetación que los reptiles, los cuales estuvieron más ampliamente distribuidos espacial y temporalmente.

Habitat relationships of diurnal raptors at local and landscape scales in southern temperate grasslands of Argentina

We evaluated the relationship between an assemblage of diurnal raptors and local-and landscape-scale habitat variables in the eastern portion of South America's temperate grasslands in Argentina (37°32'-37°45'S, 57°19'-57°26'W). The landscape is a mosaic of agroecosystems and natural grasslands. Raptor species were sampled using fixed-distance point-counts, from October 2004 to February 2005. We used generalised additive models to analyse the relationship between raptor occurrence or abundance and environmental predictors at two spatial scales: local (at plot level) and landscape (areas of 25 and 100 km2 around the survey points). At local scales we measured vegetation height and percentage cover. Landscape-scale variables included percentage of each habitat type, landscape diversity, and fractal dimension. Higher values of species richness were recorded in landscapes with a complex matrix of disturbed and undisturbed plots. The abundance of Chimango Caracara (Milvago chimango) was positively associated with roads, sites with a complex matrix of disturbed and undisturbed plots, and high levels of forest cover. The presence of Long-winged Harrier (Circus buffoni) increased in landscapes dominated by natural habitats, mainly natural grasslands. The presence of Southern Crested Caracara (Caracara plancus) increased mostly in plots with high amounts of short grass cover and away from roads. Based on our results, we suggest that maintenance patches of natural grassland is essential for the preservation of ground-nesting species, and preservation of habitat diversity would ensure that most of the raptor species in the assemblage had their ecological requirements met.

Environmental factors, regional body size distributions and spatial variation in body size of local avian assemblages

ABSTRACTAim To determine how well variation in median body size of avian assemblages is predicted by (1) the environmental models usually employed in analyses of Bergmann's rule and (2) random sampling from the regional body size frequency distribution. If body size frequency distributions of local assemblages represent a random sample of a regional frequency distribution, then geographical variation in body sizes of assemblages might be a consequence of the determinants of spatial variation in species richness rather than direct influences on body size per se.Location Southern Africa.Methods Median body masses (as a measure of body size) of avian assemblages were calculated for quarter‐degree grid cells across South Africa and Lesotho. The relationship between median body mass and four environmental variables (minimum and maximum monthly temperatures, precipitation and seasonality in the normalized difference vegetation index, as a measure of seasonality in productivity) was examined using general linear models first without taking spatial autocorrelation into account, and then accounting for it by fitting an exponential spatial covariance structure. Model fit was assessed using the Akaike information criterion and Akaike weights. At each species richness value, random assemblages were sampled by either drawing species randomly from the regional body mass frequency distribution, or drawing species from the regional body mass frequency distribution with a probability proportional to their geographical distribution in the area. The ability of randomizations to predict actual body masses was examined using two‐tailed Fisher exact tests.Results Seasonality in productivity was the only environmental variable that remained a significant predictor of body mass variation in spatially explicit models, though the positive relationship was weak. When species richness was included in the models it remained the only significant predictor of size variation. Randomizations predicted median body mass poorly at low species richness, but well at high richness.Main conclusions Environmental models that have previously been proposed explain little of the variation in body mass across avian assemblages in South Africa. However, much of the variation in the median mass of assemblages could be predicted by randomly drawing species from the regional body mass frequency distribution, particularly using randomizations in which all species were drawn from the regional body mass frequency distribution with equal probability and at high species richness values. This outcome emphasizes the need to consider null expectations in investigations of the geographical variation in body size together with the probable environmental mechanisms underlying spatial variation in average size. Moreover, it suggests that in the South African avifauna, spatial variation in the body sizes of assemblages may be determined indirectly by the factors that influence geographical variation in species richness.

Community ecology of the metazoan parasites of namorado sandperches, Pseudopercis numida Miranda-Ribeiro, 1903 and P. semifasciata Cuvier, 1829 (Perciformes: Pinguipedidae), from the coastal zone of the State of Rio de Janeiro, Brazil

One hundred and twenty-eight specimens of namorado sandperches, 62 P. numida and 66 P. semifasciata, collected between October 2002 and June 2003 off the Cabo Frio, Rio de Janeiro, Brazil (Lat 23 degrees S and Long 42 degrees W), were examined to study their metazoan parasites. Parasite communities of these fish were composed basically of endoparasites, mainly digenean and cestodes species, with low prevalence and abundance but having high parasite species richness values (at the component community level). Among these values, that found for P. numida is the highest so far recorded for marine fishes from the Neotropical Region. Thirty-nine species of metazoan parasites were collected: 36 from P. numida and 28 from P. semifasciata. Twenty-five parasite species were common to both species of namorado sandperches. Pseudopercis numida and P. semifasciata are new host records for all parasite species collected, with the exception of Microcotyle pseudopercis. Choanodera sp., Leurodera decora, Neolebouria georgenascimentoi, and Proctoeces sp. which were recorded for the first time in the South American Atlantic Ocean. Gnathia sp. from P. numida and Scolex pleuronectis from P. semifasciata were the species having the greatest dominance frequency. Parasite abundance in P. numida and P. semifasciata were positively correlated with the host total length. Only in P. numida was parasite species richness correlated positively with the host total length. No significant differences between endoparasite infracommunities of P. numida and P. semifasciata were detected. The ectoparasites of P. numida had higher values for parasite abundance, parasite richness, Brillouin index, evenness index, and Berger-Parker index than those of the ectoparasites of P. semifasciata. Comparisons among all ecto- and endoparasites showed the ectoparasites of P. numida as the most heterogeneous group. Low similarity values were observed among the three types of parasite infracommunities of the two hosts.

Phytoplankton taxonomic composition and temporal changes in a tropical reservoir

Phytoplankton assemblages of the Barra Bonita Reservoir (Sao Paulo State, Brazil) were studied monthly between April 2002 and January 2004. Samples were taken at six depths (0 m, 1 m, 3 m, 5 m, 10 m and bottom) at a single station located 3 km upstream of the reservoir dam. The vertical distribution of environmental and biological variables was homogeneous (p > 0.05) during most of the period, possibly due to wind action and the rainfall regimes. Significant variability was found only on the temporal scale (p < 0.05). Generally, the highest values of species richness and diversity were recorded during the dry period. Taxonomic analysis of the phytoplankton assemblages revealed 139 distributed over nine groups: Chlorophyceae (44), Bacillariophyceae (40), Cyanophyceae (28), Conjugatophyceae (10), Euglenophyceae (8), Xanthophyceae (5), Chrysophyceae (2), Dinophyceae (1) and Cryptophyceae (1). The relative abundance of Cyanophyceae (colonies of Microcystis aeruginosa and free cells of Microcystis sp.) and Bacillariophyceae (Aulacoseira granulata filaments) was notably greater than that of other groups during dry and rainy seasons. The dynamics of phytoplankton assemblages in Barra Bonita Reservoir was mainly driven by physical factors, particularly vertical mixing and residence time. The coexistence of R strategists (diatoms) and S strategists (cyanobacteria) recorded in the first year, and the continuous dominance of cyanobacteria in the second year revealed a pattern of inter-annual variability mainly driven by changes in z mix /z eu ratios and continued eutrophication.

Modelling species richness and life form composition in Sahelian Burkina Faso with remote sensing data

Species distribution modelling is an important tool in planning conservation strategies, in predicting effects of environmental change and in delineating patterns of species diversity. Until now, the majority of studies dealing with predicted species distributions were conducted at regional scales by using climatic and biomass parameters with low spatial resolution as environmental variables. On the contrary, informed decision-making regarding conservation priorities mainly takes place on a local scale. We used the genetic algorithm for rule-set production (GARP), environmental layers (derivates of high-resolution LANDSAT ETM+ satellite images) and 13,380 geo-referenced records from collection and relevé data to model distributions of vascular plant species in the Sahelian zone of Burkina Faso. For each species, records were divided randomly in a training dataset for model generation and a test dataset to evaluate the modelled distribution maps. Single distributions of 138 highly accurately modelled species were summed up for life forms and total species richness. Highest values of species richness are found in the NW of the study area. The pattern of vascular plant diversity appears to be closely linked to sandy soils and to water availability: watercourses, tiger bush vegetation and dune ridges are more diverse than pediplain. Chamaephytes show a more pronounced preference of dunes over pediplain than other life forms, while geophyte diversity is highest near watercourses. Hemicryptophyte diversity is most evenly distributed. Therophyte diversity is closest to all vascular plant diversity. Phanerophyte diversity is highest in tiger bush vegetation and close to watercourses. Our approach holds a wide application potential to model species distributions and diversity where environmental data are scarce.

Database records as a surrogate for sampling effort provide higher species richness estimations

The compilation of all the available taxonomic and distributional information on the species present in a territory frequently generates a biased picture of the distribution of biodiversity due to the uneven distribution of the sampling effort performed. Thus, quality protocol assessments such as those proposed by Hortal et al. (Conservation Biology 21:853–863, 2007) must be done before using this kind of information for basic and applied purposes. The discrimination of localities that can be considered relatively well-surveyed from those not surveyed enough is a key first step in this protocol and can be attained by the previous definition of a sampling effort surrogate and the calculation of survey completeness using different estimators. Recently it has been suggested that records from exhaustive databases can be used as a sampling-effort surrogate to recognize probable well-surveyed localities. In this paper, we use an Iberian dung beetle database to identify the 50 × 50 km UTM cells that appear to be reliably inventoried, using both data derived from standardized sampling protocols and database records as a surrogate for sampling effort. Observed and predicted species richness values in the shared cells defined as well-surveyed by both methods suggest that the use of database records provides higher species richness values, which are proportionally greater in the richest localities by the inclusion of rare species.

Three main stressors acting on the Ria Formosa lagoonal system (Southern Portugal): Physical stress, organic matter pollution and the land–ocean gradient

During the last 15 years of the 20th century, several researchers carried out extensive sampling of benthic macrofauna communities in the Ria Formosa lagoon. The main objective of this paper is to discern the main communities of benthic fauna of the Ria Formosa and the leading stressors that limit them based on this large data set. The high species richness and high diversity values observed at most of the stations or groups of stations indicate a good ecological status, with the exception of the sewage-impacted areas and the physically stressed areas. It was possible to define three main stressors acting on the Ria Formosa. The most important is the physical stress imposed by the limited water renewal in some areas of the Ria Formosa. The second is the nutrient and organic matter pollution that is limited to the vicinity of the sewage outfall stations and to some locations of the Ria Formosa. This is due to the dual effects of the low residence time of water, but also due to a degradation of water quality in places of relatively restricted water circulation but with high primary production, symptoms of eutrophication. The third stressor is the natural land–ocean gradient, denoting the influence of seawater exchanges and emersion time, attenuated by the high water exchange rates of Ria Formosa. It was possible to differentiate the anthropogenic stress from the natural physical stress through the application of multivariate analysis. However, both structural (species richness and diversity indices) and functional indicators (trophic composition) indicate the same trend – low species richness, low diversity indices, and a community dominated by detritivores species at the locations characterized by high anthropogenic impact or by physical stress. The physically stressed areas were dominated by chironomid larvae and hydrobiid gastropods and the most polluted areas were dominated by oligochaetes, mainly tubificids.

Community structure of benthic foraminifera in the Gulf of Mexico

The classic papers of Phleger [Phleger, F.B, 1951. Foraminifera Distribution, Part I. Geological Society of America Memoir 46, 1–88.] and Parker [Parker, F.L., 1954. Distribtuion of the foraminifera in the Northeastern Gulf of Mexico. Bulletin of the Museum of Comparative Zoology 111, 453–588, 13 plates.] form the benchmark foraminiferal data sets for the northwestern and northeastern Gulf of Mexico, respectively. These pioneer researchers occupied stations from shelf to abyssal depths. SHE analysis, a method examining the distribution of cumulative sample values of species richness ( S), the information function ( H) and evenness ( E) with increasing number of individuals ( N), was used to establish 18 foraminiferal communities and evaluate their community structure. Regression analyses, as well as plots of ln S, H and ln E versus ln N (Biodiversitygrams, BDGs), indicate that the majority of the communities exhibit a log series pattern. Theoretical log series values of S, H and E are similar to the regression estimates from observed values in the northeastern Gulf. In the northwestern Gulf, however, observed values of species richness are lower and evenness higher than those expected for a log series, indicating a dramatic difference in community structure between east and west. Since the sampling time of Phleger, subsequent workers have found higher values of species richness and lower values of evenness in the northwestern Gulf. Either biodiversity values have changed since Phleger's 1947 (1951) sampling suggesting a fundamental change in the environmental regime of the northwestern Gulf of Mexico or, as has been suggested, Phleger's data are incorrect due to some sampling methodology. A comprehensive study with suitable experimental design including downcore samples will be required to resolve this dichotomy.

Composição e riqueza florística do componente arbóreo da Floresta Atlântica submontana na região de Imbaú, Município de Silva Jardim, RJ

O presente trabalho teve por objetivo avaliar a composição florística arbórea de um trecho de Floresta Atlântica submontana na região de Imbaú, Silva Jardim, RJ. Esta região formava um contínuo florestal que foi fragmentado há mais de 50 anos por práticas agropecuárias. Cinco fragmentos foram selecionados e em cada um deles foram alocadas quatro parcelas de 100×5 m. Todas as árvores vivas com DAP &gt; 5 cm foram amostradas e identificadas. No hectare amostrado foram encontradas 161 espécies distribuídas por 39 famílias. A similaridade florística entre os fragmentos foi alta, com índice de Morisita variando de 0,36 a 0,79. As famílias Leguminosae, Lauraceae e Rubiaceae apresentaram a maior riqueza de espécies. A comparação florística com uma floresta madura da região indicou forte decréscimo na riqueza de espécies que, juntamente com a elevada densidade de espécies secundárias iniciais, indicam que estas matas se encontram em estádio sucessional secundário. Analisando a similaridade florística entre a região de Imbaú e outras 17 florestas do Rio de Janeiro, observou-se maior similaridade com as florestas submontanas mais próximas geograficamente. Devido ao avançado processo de fragmentação e à importância ecológica destes fragmentos para a manutenção da flora e fauna, sugere-se que a região de Imbaú deva ser prioritária em programas de conservação e manejo de áreas de Mata Atlântica.

Differences in the diversity of oribatid mite communities in forests and agrosystems lands

A field study was conducted in the province of Burgos (Castile, NW of Spain) to assess the role and influence of the different anthropic use of soil on the oribatid mite communities (Acari, Oribatida). Soil samples from 20 representative soil sites of the Castilian upland steppes, with cultured, pastureland or forest soil uses, were taken in spring and autumn 2000. Thereafter, soil samples were analysed in terms of their mesofaunal biodiversity, measured using the real and relative diversity of the oribatid mite communities. Collected individuals were identified to species level, being altogether 111 Oribatid species. Results from communities' ordination analysis showed clear gradients based on community variables. One of these was defined by plots with high values of diversity and species richness which correspond to the less anthropic natural soils, mainly oak forest. In contrast, the most anthropic agrosystems soils, including extensive cereal crops, most of them receiving only mineral fertilisation or having human management, were placed in opposite gradients. Differences in biodiversity between crop lands and natural soils were also confirmed by ANOVA. The seasonality, measured in terms of difference between spring and autumn plots, played a minimum role in explaining differences of diversity. Nevertheless autumn diversity values were slightly higher than those of spring, except for crops.

Analysis of the blennioid assemblages associated with different rocky shore habitats in the Ligurian Sea

The differences among blennioid assemblages (families Blenniidae and Tripterygiidae) on different habitats were assessed at two localities of the Ligurian Sea, namely Arenzano and Riva Trigoso. The assemblage composition and species relative density were evaluated visually on four different habitats of diverse wave exposure and substratum orientation (macro‐habitat characteristics): two vertical intertidal and subtidal habitats (exposed and sheltered rockwalls) and two horizontal subtidal habitats (semi‐exposed flat rock and boulders and pebbles). Each habitat was also characterized in relation to micro‐habitat features, such as substratum complexity, heterogeneity and amount of algae cover. Patterns of differences among habitats in assemblage variables and fish density, and the influences of macro‐ and micro‐habitat features on these patterns were studied at small (within localities) and large (across localities) spatial scales. Higher values of species richness (S), diversity and evenness (J) were generally associated with vertical habitats, as a result of a positive correlation with substratum orientation. The presence of an intertidal zone in the rockwall habitats may partially explain the observed differences in assemblage variables between vertical and horizontal habitats. The strength of relationships between S, and J and the other investigated habitat variables (exposure, complexity, heterogeneity and algae cover) varied greatly depending on spatial scale. All these relationships were positive, except for complexity. Significant variation in the assemblage total density among habitats was recorded only at Arenzano, where a larger number of fishes were counted on rockwalls rather than on the horizontal habitats. The positive effect of orientation on fish total density was strictly dependent on spatial scale. Fish total density showed a negative correlation with complexity and a positive correlation with heterogeneity, both relationships being unaffected by spatial scale. The unexpected relationship with complexity was probably due to the fact that, in the most complex habitat (i.e. boulder and pebbles), the potential positive effect of high complexity on fish density might be overcome by the negative influence of other environmental features, such as horizontal orientation and low wave exposure. Complexity and heterogeneity thus seemed good predictors of fish total density, but their role needs to be carefully interpreted. The most marked differences in species composition and relative density were found between rockwalls and the other habitats, mostly due to an unbalanced distribution of some stenoecious species. Variations in species relative density were related to different combinations of both macro‐ and micro‐habitat features, and these relationships usually changed depending on spatial scale.

Littoral invertebrates associated with aquatic plants and bioassessment of ecological status in Lake Bracciano (Central Italy)

Lake Bracciano is a large and deep volcanic lake which plays an unquestionable role for drawing water source and for fishing and recreational activities. The existence of a project aimed at increasing the amount of water drawn from the lake suggested the advisability of undertaking an ecological analysis of the invertebrate community associated with aquatic plants in order to obtain a detailed knowledge of its composition, biodiversity and quantitative structure, and to provide a set of basic and essential information for defining the ecological status in the littoral zone and for future bioassessments in the lake ecosystem. A good water quality, approaching oligotrophy, was evidenced both from data on aquatic vegetation, which showed the extensive colonization of Charales (down to a depth of about 20 m), and from faunal parameters such as high species richness and diversity values, presence and abundance of bioindicator taxa (mainly cladocerans and gastropods), abundances of total fauna. Nevertheless, a considerable disappearance of the reed thicket due to the intense shore management for recreational purposes have negatively influenced the colonization of the more shallow and productive waters, so evidencing a negative trend of the littoral quality.

Patrones de distribución espacial de la riqueza de especies de vertebrados en un área de transición biogeografica: de la Navarra pirenaica a la mediterránea

Uneven distribution of biodiversity over the Earth's surface is a consequence of historic, environmental and functional factors. In this paper, spatial patterns of amphibians, reptiles, mammals and birds have been studied in a biogeographical gradient between Pyrenean and Mediterranean environments in Navarra. Also, the relationships between biodiversity, species richness, and biogeographical gradient have been measured with directional semivariograms and GIS. Results show correlations between biogeographical change and spatial patterns of vertebrates: reptiles have the higher values of species richness in the ecotone, while amphibians have an uneven distribution. Mammals and birds show lineal correlations with biogeographical change but in opposite directions.

Polychaetes associated to a Cymodocea nodosa meadow in the Canary Islands: assemblage structure, temporal variability and vertical distribution compared to other Mediterranean seagrass meadows

The structure, diversity and temporal distribution of the infaunal polychaetes associated with Cymodocea nodosa meadows were studied in Tenerife (Canary Islands). The samples were collected monthly throughout a year, to depths of 13–16 m. The sediment was extracted by means of PVC cores, in which four layers were separated (i.e. 0–5 cm, 5–10 cm, 10–20 cm and 20–30 cm). A total of 1,167 polychaete specimens, belonging to 69 taxa were collected, representing one of the most dominant groups in the benthic assemblage throughout the entire year. The most common families were Syllidae, Paraonidae and Spionidae, both in terms of abundance and species richness. The dominant species were Streptosyllis bidentata, Aricidea assimilis and Exogone parahomoseta mediterranea, representing also the only constant species throughout the year. The highest values of species richness, diversity, equitability and abundance of polychaetes occurred in September. The multifactorial analysis of abundances (i.e. cluster analysis and non-metric, multi-dimensional scaling) indicated temporal segregation of the samples from July, August and September (i.e. the warmest months) with respect to those from the rest of the year, due to structural differences in the assemblage. Polychaete species have been found to a depth of up to 30 cm in the sediment. Nevertheless, most of them (89%) occurred in the upper 5 cm of the sediment, with an increase of specimens in deeper layers in February (i.e. due to sporadic episodes of higher hydrodynamics). To compare the vertical distribution of polychaetes, additional core samples were collected in two seagrass meadows (i.e. C. nodosa and Ruppia cirrhosa) at Ebro’s Delta (NW Mediterranean); these were separated into five layers (i.e. 0–5 cm, 5–10 cm, 10–15 cm, 15–20 cm, 20–25 cm). The results obtained for the R. cirrhosa meadow (98% of the polychaetes within the upper 5 cm) agree with those for the Canarian C. nodosa meadow, while the polychaetes reached up to 15 cm depth in the Mediterranean C. nodosa meadow (i.e. ~39% between 0 and 5 cm, ~41% between 5 and 10 cm, ~20% between 10 and 15 cm). Our results indicated that the structural characteristics of the assemblages appeared to be more strongly controlled by the combined characteristics of the sediment (i.e. lack of oxygen, granulometry and degree of compaction) than by the seagrass species building the meadow.

Biodiversity and structure of the polychaete fauna from soft bottoms of Bahia Todos Santos, Baja California, Mexico

Abstract This paper describes diversity patterns of the polychaete fauna in Bahia Todos Santos (Pacific Ocean, Baja California, Mexico). Thirty-nine stations were sampled in October 1994. Measurements of depth, temperature, salinity, dissolved oxygen, organic content and sediment particle size were made. Polychaetes constituted 64% of all invertebrate macrofauna, with 13,757 specimens in 44 families representing 203 species. The best represented families were Spionidae, Capitellidae, Paraonidae, Cirratulidae, Maldanidae, Ampharetidae and Nephtyidae. Bahia Todos Santos presented high species richness (species/station); values varied between 6 (near the harbor) and 67 species (next to Estero Punta Banda). Higher species richness values (48 species to 67/station) were located in the southern section of the bay. Abundances (individuals/station) were generally high (120–1434) except for some coastal stations. Nearly one-third of the stations presented H′ values higher than 4.00. Diversity (H′) values ranged from 2.06 to 4.80; higher diversity values were found in the southern section of the bay. The stress-predictability modeling characterized approximately 70% of stations as presenting favorable and stable conditions. Pearson and Bray–Curtis coefficients separated stations in relation to their sediment particle size, depth and location in the bay. Principal component analysis determined that organic matter content, percentage of silt-clay, and water depth accounted for 95% of the total variance for all environmental factors measured. Correspondence analysis distinguished three groups of species: Group A species with an extensive distribution throughout the bay and relatively high abundances, Group B species abundant in the shallow areas, especially near the harbor, and Group C species present in the area of the submarine canyon. Non-metric multidimensional scaling analysis separated five groups of stations, depending on depth, grain size and location in the bay. Our results show that Bahia Todos Santos is a favorable environment for polychaete development, their distribution being strongly related to sediment characteristics. The dominant trophic group corresponds to deposit-feeders (91 species).

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).

Arthropod and filarioid parasites associated with wild rodents in the northeast marshes of Buenos Aires, Argentina.

During 1995, 16 species of arthropods and 2 species of filarioids, totaling 1 287 specimens were collected from 64 wild rodents captured in the Hudson Natural Reserve, Buenos Aires, Argentina. Infestation parameters and indexes were analyzed. Host specific richness was S = 6, diversity H = 1.48, and relative density RDI = 40%. High values of parasite species richness and diversity were found on Oligoryzomys delticola (S = 9; H = 1.40), Oxymycterus rufus (S = 9; H = 1.37), and Oligoryzomys flavescens (S = 9; H = 1.28), followed by Scapteromys aquaticus (S = 6; H = 0.17), and Akodon azarae (S = 4; H = 1.20). Deltamys kempi was infested only by Androlaelaps rotundus. O. delticola and O. flavescens showed the highest similarity index (O = 74.19%), followed by O. flavescens with S. aquaticus, as a result of historical processes and shared microhabitats. Considering arthropods-filarioids associations, significant affinity was observed in Litomosoides bonaerensis with Hoplopleura travassosi, Laelaps paulistanensis, and Gigantolaelaps wolffsohni.

Diversity of biting midges of the genus Culicoides Latreille (Diptera: Ceratopogonidae) in the area of the Yacyretá Dam Lake between Argentina and Paraguay.

The Culicoides communities have been analyzed between 1993/1998 in the area influenced by the Yacyret Dam Lake (Paran River, Argentina-Paraguay). Adults of Culicoides were collected monthly by using CDC light traps exposed for 24 h in 9 sampling sites located at both margins of the river; 21 species were recorded. Highest values of species richness were recorded during 1993/1994, being Quiteria and Corpus the sites with the higest number of species (10 and 11, respectively). The species diversity was elevated in Quiteria, Zaim n, Candelaria, Santa Tecla, Capit n Meza and Corpus (Shannon's diversity index 1.0-1.9) while Corate , Ituzaing and Aguapey showed less richness and diversity. The more abundant species were C. insignis, C. venezuelensis, C. leopoldoi, C. limai, C. flinti, C. debilipalpis, C. paraensis and C. guttatus. C. insignis, potential vector of bluetongue virus (BTV) to domestic and wild rumiants in the Neotropical region, is the predominant species in the area and was the only species widely distributed. C. paraensis, a proven vector of Oropouche virus to humans, is a common and abundant species. C. pusillus and C. lahillei, potential vectors of BTV and a filarial parasite, respectively, were occasionally collected. The taxonomic structure of communities was constant during the study period. The occasional species were not characteristic to one particular site and their presence could be related to non-intrinsic conditions.