Invasive potential of golden and zebra mussels in present and future climatic scenarios in the new world

Hydrobiologia - Biological invasions and climate change are important drivers of biodiversity loss. In freshwater ecosystems, golden and zebra mussels are two highly aggressive invasive species...     

Flying over water: how “On bird species diversity” influenced aquatic ecology

Habitat complexity has long been known to influence animal community structure by increasing the number of available habitats. Fifty years have passed since MacArthur brothers published the seminal paper “On bird species diversity”, which revolutionized studies of habitat structure. This paper first evidenced and quantified the relationship between species diversity (birds) and habitat structural complexity (the number of stratified layers of landscape vegetation). In this article, we aim to pay homage to R. H. MacArthur’s contribution and to briefly analyze the citation history and influence of “On bird species diversity”, focusing primarily on aquatic studies. We searched for all papers that cited “On bird species diversity” on Thomson Reuters (ISI—Web of Knowledge) and analyzed them for temporal citation trends. In addition, considering only aquatic papers, we explored whether and how habitat complexity was measured, as well as the ecological organization level, attributes of organisms, taxonomic groups and study design (observational or experimental). “On bird species diversity” citations increased over time, but this paper was less cited by limnologists compared to terrestrial and marine scientists. The majority of investigations in aquatic ecosystems quantified habitat complexity, but few used mathematical modeling. The high number of citations, which continues to increase, shows the great influence of “On bird species diversity” on ecological studies and typifies it as a classic in the ecological literature. However, the low citation frequency found in papers devoted to freshwater ecosystems indicates that limnologists in general neglect this original contribution in studies of habitat complexity.     

Catalysts of Cu(II) and Co(II) ions adsorbed in chitosan used in transesterification of soy bean and babassu oils - a new route for biodiesel syntheses

Catalysts of Cu(II) and Co(II) adsorbed in chitosan was used in transesterification of soy bean and babassu oils. The catalysts were characterized by infrared, atomic absorption and TG, and biodiesels was characterized by infrared, NMR, CG, TG, physic chemistry analysis. The maximum adsorption values found for copper and cobalt cations were 1.584 and 1.260mgg(-1), respectively, in 180min. However, conversion of oils in biodiesel was better when used Co(II) adsorbed in chitosan.     

Secondary productivity (3H-Leucine and 3H-Thymidine incorporation), abundance and biomass of the epiphytic bacteria attached to detritus of Typha domingensis pers. in a tropical coastal lagoon

Senescent, naturally dried leaves of Typha domingensis were incubated inthe littoral region of a coastal lagoon and epiphytic bacterial volume,abundance, biomass and secondary productivity were measured during 127 daysof decomposition. The peak of cell abundance was registered at t =127 days when expressed per leaf surface area (10.07×10⁷cells cm^-2; 7.26 µgC cm^-2), and at t= 26 days when expressed per biofilm dry mass (38.10 ×10⁷ cells (mgDM biofilm)^-1, 30.52 µgC(mgDM biofilm)^-1). The highest values of bacterial biovolumesand lower turnover time were usually obtained in the beginning of thecolonization. Leu:Tdr ratios were also higher in the beginning of thecolonization, when bacterial community presented unbalanced metabolism.Consequently, the highest discrepancies between the bacterial secondaryproduction estimated by leu and Tdr incorporation were observed in the first2 days of decomposition. On average, the bacterial secondary productivityestimated by leu incorporation was 2.1 times higher than the valuesestimated by Tdr incorporation when the empirical factor for Tdr wasobtained from the relationship between Tdr and biomass increment. Thisdifference increased to 4.2 when the empirical factor was obtained from therelationship between Tdr and cell numbers increment. An average of bothmethods (0.0037 to 0.1397 µgC cm^-2 h^-1)produced results that fall within the range reported in the literature forepiphytic bacteria of freshwater ecosystems.     

Species richness and beta diversity of aquatic macrophytes in a large subtropical reservoir (Itaipu Reservoir, Brazil): the influence of limnology and morphometry

Assessment of the environmental factors that control species richness (S) is a central issue in ecology. In this study, aquatic macrophyte S was estimated in 235 sampling sites distributed in 8 arms of a large (1350 km²) subtropical reservoir (Itaipu Reservoir, Brazil). Morphometric variables (area, shoreline development and length of shoreline, all measured for each arm; n= 8) and environmental variables measured at each sampling site (extinction coefficient of light (k), electrical conductivity, fetch, distance from the main reservoir body; n = 235) were used to predict aquatic macrophyte S at two spatial scales. At arm scale, linear regression analysis indicated that length of shoreline was a better predictor of S than area. At sampling site scale, multiple regression analysis indicated that S was significantly predicted by electrical conductivity, fetch and distance from the main body. However, other relationships with predictive interest was demonstrated by using non-traditional regression approaches. This analysis started by the visual inspection of scatter plots. The bivariate relationship between S and fetch, for example, showed an envelope or a `left triangle' pattern. The relationship between the number of submerged species and k showed an asymmetrical left triangle pattern. Using randomization procedures, it was demonstrated that these patterns were not generated by chance alone. Beta diversity (estimated within the arms) was significantly and positively correlated with spatial environmental variability. Overall, these results indicate that the prediction of aquatic macrophytes assemblage variables in large waterbodies, specially S, is more complex than previous studies have suggested.     

Bond length pattern associated with charge carriers in armchair graphene nanoribbons

The geometry configuration of charged armchair graphene nanoribbons (AGNRs) is theoretically investigated in the framework of a two-dimensional tight-binding model that includes lattice relaxation. Our findings show that the charge distribution and, consequently, the bond length pattern is dependent on the parity of the nanoribbon width. In this sense, the lattice distortions decrease smoothly for increasingly wider GNRs. As should be expected, AGNRs belonging to a particular family present similar patterns for the bond lengths. The interplay between the electron-phonon coupling and band gap is also investigated. The results show that the electron-phonon coupling strength is fundamental to promote the transition from metallic towards semiconducting-like behavior for the band gap. Most important, such strength is crucial on defining the degree of lattice distortions in AGNRs.     

Effects of structural heterogeneity provided by the floating macrophyte <Emphasis Type="Italic">Eichhornia azurea</Emphasis> on the predation efficiency and habitat use of the small Neotropical fish <Emphasis Type="Italic">Moenkhausia sanctaefilomenae</Emphasis>

Macrophytes have a fundamental structuring role in aquatic environments. Several authors have suggested that trophic interactions are particularly mediated by aquatic plants. In the current article, we evaluated the effects of the structural heterogeneity provided by Eichhornia azurea (Kunth) roots on predation and habitat use by the small fish Moenkhausia sanctaefilomenae (Steindachner). We tested the hypotheses that (i) high structural heterogeneity protects macroinvertebrates against predation by M. sanctaefilomenae; (ii) distinct prey types are differently protected by the refuge provided by roots; and (iii) the behavior of M. sanctaefilomenae is affected by the structural heterogeneity provided by macrophyte roots. To test these hypotheses, we performed an experiment in 20 l aquaria in which macroinvertebrates (Cypricercus sp. and Chironomus sp.) were exposed to M. sanctaefilomenae predation for 4 h under three structural heterogeneities, represented by different root densities. High structural heterogeneity protected macroinvertebrates against predation. Additionally, E. azurea roots similarly protected different prey species. The macrophyte spatial structure substantially changed the habitat use of M. sanctaefilomenae. In general, our results corroborated the hypothesis that the structural heterogeneity provided by E. azurea roots significantly affects predation and habitat use by M. sanctaefilomenae. Handling editor: S. Declerck     

Invasive alien species records are exponentially rising across the Earth

Humans are facilitating the introduction and range expansion of invasive alien species (IAS), which have negatively impacted ecological and socio-economic systems worldwide. Understanding the global diffusion of IAS is important for developing environmental policies and management strategies. We estimate the rate of increase and the doubling times of the number of new records of 178 IAS using a global dataset with c. 3.4 million records obtained over c. 100 years. Here, we show that the number of records of IAS have exponentially increased with a mean double time of c. 14 years across the Earth. For the most analysed species, the number of records increased faster in the non-native than native continents, suggesting that such IAS might be exponentially expanding their range size. We also found that each continent has a taxonomic group with a particular increase in IAS records. Governments and scientists should pay attention to these taxonomic groups to implement appropriate control or management actions. Our study provides an indication that the current local, regional and continental efforts to control invasions may be not sufficient at the global scale. This is a concerning situation given the great number of areas available for invasion worldwide.

     

Aquatic macrophytes in the large, sub-tropical Itaipu Reservoir, Brazil

In the last three decades, rapid assessment surveys have become an important approach for measuring aquatic ecosystem biodiversity. These methods can be used to detect anthropogenic impacts and recognize local or global species extinctions. We present a floristic survey of the aquatic macrophytes along the Brazilian margin of the Itaipu Reservoir conducted in 2008 and compare this with a floristic survey conducted ten years earlier. We used ordination analysis to determine whether assemblage composition differed among reservoir arms. Macrophyte species were sampled in each of the 235 sampling stations using a boat, which was positioned inside three places of each macrophyte stand to record species and search for small plants. We also collected submerged plants using a rake with the boat moving at constant velocity for ten minutes. We assigned individual macrophyte species to life form and identified representative species for each life form. A total of 87 macrophyte taxa were identified. The "emergent" life forms contained the highest number of species, followed by "rooted submerged" life forms. The extensive survey of macrophytes undertaken in September 2008 recorded more species than a survey conducted between 1995 and 1998. This could be due to changes in water physico-chemistry, disturbances due to water drawdown and the long period between surveys, which may have allowed natural colonization by other species. Additionally, differences in the classification systems and taxonomic resolution used in the surveys may account for differences in the number of species recorded. Assemblage composition varied among the arms and was affected by underwater radiation (as measured using a Secchi disk) and fetch. Five non-native species were found. Two of these non-native species (Urochloa subquadripara and Hydrilla verticillata) are of special concern because they have a high frequency of occurrence and occupy large marginal areas of the reservoir. Future surveys should be conducted to determine the habitat most frequently colonized by these species. This would allow management strategies to be developed to protect native aquatic biota and prevent interference with the recreational and commercial uses of the Itaipu Reservoir.