Questions: Invasiveness depends in part on the ability of exotic species to either exclude native dominants or to fill an empty niche. Comparisons of niches and effects of closely related native and invasive species enable the investigation of this topic. Does Spartina anglica invade European salt marshes through competitive exclusion of the native Spartina maritima or due to the occurrence of an empty ecological niche in highly anoxic conditions? Study Site: The Arcachon Bay (France).Methods: At three intertidal levels, we quantified competitive response and effect abilities of the two species through a cross-transplantation removal experiment. We also compared the biomass, root/shoot ratio, productivity and environmental conditions (elevation, salinity, redox potential and soil moisture) of salt marsh communities dominated by the exotic Spartina anglica or the native Spartina maritima at three intertidal levels.Results: Both established species showed similar biotic resistance to the invasion of the other species, but the exotic showed important intraspecific facilitation for growth. Species had similar niches and total biomass along a gradient of anoxic conditions, but the exotic had a much higher root/shoot ratio and productivity than the native. Owing to its rhizome density, the exotic showed high ability to increase sediment oxygenation, likely to explain its important intraspecific facilitation. Conclusions:Our results showed that the invasion success of S. anglica cannot be explained by the competitive exclusion of the native or by its ability to fill an empty niche along a gradient of anoxia. Its behaviour as a self-facilitator invasive engineer very likely explains its rapid spread in the Bay and biotic resistance to the colonization of other congeneric species when established in dense patches. Additionally, we suggest that physical disturbance in marsh communities dominated by the native S. maritima may disrupt its biotic resistance against the invasion of S. anglica. K E Y W O R D S biological invasion, biotic interactions, competitive effect, removal experiment, Spartina anglica, Spartina maritima | 213 Journal of Vegetation Science PROENÇA Et Al.
An early assessment of biological invasions is important for initiating conservation strategies. Instrumental progress in high spatial resolution (HSR) multispectral satellite sensors greatly facilitates ecosystems’ monitoring capability at an increasingly smaller scale. However, species detection is still challenging in environments characterized by a high variability of vegetation mixing along with other elements, such as water, sediment, and biofilm. In this study, we explore the potential of Pléiades HSR multispectral images to detect and monitor changes in the salt marshes of the Bay of Arcachon (SW France), after the invasion of Spartina anglica. Due to the small size of Spartina patches, the spatial and temporal monitoring of Spartina species focuses on the analysis of five multispectral images at a spatial resolution of 2 m, acquired at the study site between 2013 and 2017. To distinguish between the different types of vegetation, various techniques for land use classification were evaluated. A description and interpretation of the results are based on a set of ground truth data, including field reflectance, a drone flight, historical aerial photographs, GNSS and photographic surveys. A preliminary qualitative analysis of NDVI maps showed that a multi-temporal approach, taking into account a delayed development of species, could be successfully used to discriminate Spartina species (sp.). Then, supervised and unsupervised classifications, used for the identification of Spartina sp., were evaluated. The performance of the species identification was highly dependent on the degree of environmental noise present in the image, which is season-dependent. The accurate identification of the native Spartina was higher than 75%, a result strongly affected by intra-patch variability and, specifically, by the presence of areas with a low vegetation density. Further, for the invasive Spartina anglica, when using a supervised classifier, rather than an unsupervised one, the accuracy of the classification increases from 10% to 90%. However, both algorithms highly overestimate the areas assigned to this species. Finally, the results highlight that the identification of the invasive species is highly dependent both on the seasonal presence of itinerant biological features and the size of vegetation patches. Further, we believe that the results could be strongly improved by a coupled approach, which combines spectral and spatial information, i.e., pattern-recognition techniques.
Field measurements of bed elevation and related wave events were performed within a tidal marsh, on two cordgrass species, Spartina anglica (exotic) and Spartina maritima (native), in the Bay of Arcachon (SW France). Bed- and water-level time series were used to infer on the sediment behavior patterns from short to long term. A consistent response was found between the bed-level variation and the wave forcing, with erosion occurring during storms and accretion during low energy periods. Such behavior was observed within the two species, but the magnitude of bed-level variation was higher within the native than the exotic Spartina. These differences, in the order of millimeters, were explained by the opposite allocation of biomass of the two species. On the long term, the sedimentation/erosion patterns were dominated by episodic storm events. A general sediment deficit was observed on the site, suggested by an overall bed-level decrease registered within both species. However, further verification of within species variation needs to be considered when drawing conclusions. Despite possible qualitative limitations of the experimental design, due to single point survey, this work provides original and considerable field data to the understanding the different species ability to influence bed sediment stabilization and their potential to build marsh from the mudflat pioneer stage. Such information is valuable for coastal management in the context of global change.
In this work, we have investigated the interactions of polypeptides composed of the sequence of six alanines and one arginine (A6R) grouped in three nanosheet structures with maximum, intermediate, and minimal spatial overlap of polyalanine–arginine peptide molecules, allowing an evaluation of their porosity in water solution. Our results obtained through molecular dynamics show a well-equilibrated structure for the final configuration of A6R nanosheets with maximum spatial overlap indicating a low porosity, whereas the model with intermediate nanosheet separation presents greater infiltration, despite maintaining the membrane structure. The electrically charged A6R model with minimal spatial overlap did not maintain the membrane structure. With only one agglomerate having large water infiltration, the alanines still remained in the inner part of this agglomerate, whereas the arginines are located outside, characterizing amorphous blocks. By extracting a peptide from the membrane through pulling methodology, we have observed how membrane stiffness is established with the self-organization of the peptides in the membrane, associating such results with the infiltration of water molecules in the structure.
Ecosystem engineering effects of dominant species on habitats and consequently on other species are likely to propagate through time at longer distance than the close neighbourhood. Such effects are important to disentangle from short-term biotic effects, especially in biological invasions, as engineering can explain changes in invasion rates over the course of the invasion. We assessed the contribution and spatial dynamics of ecosystem engineering effects of a strong invader, the cordgrass Spartina anglica, on Zostera noltei, a foundation seagrass species of muddy intertidal systems in Europe. Z. noltei transplants were grown at different positions along transects crossing intact S. anglica patches, cut patches and nearby bare sediment on tidal flats in the Bay of Arcachon (France), in order to separate ecosystem engineering effects from short-term biotic effects and evaluate their likely spatial propagation. Bed altimetry, sediment redox potential and granulometry were measured in all treatments. Within Spartina patches, we found strong negative ecosystem engineering effects of the cordgrass on the seagrass associated with increased sediment elevation and relative fine sediment content. Up to 2 m outside the patch, we found significant negative ecosystem engineering effects and positive short-term biotic effects, but they were weak and counterbalanced each other. We conclude that S. anglica can transform a marine muddy intertidal habitat into a drier and more oxidized terrestrial habitat, no longer suitable for the seagrass. Although these effects may propagate at several metres from a patch, they appeared to be too weak to likely affect the seagrass at the scale of a whole bay.
A Biossegurança Laboratorial (BL) é uma temática necessária a ser discutida durante a formação de biólogos, principalmente para aqueles que desejam atuar na área da saúde, e que também querem realizar atividades profissionais em laboratórios. Graças à importância que esta temática apresenta para a saúde do biólogo, esta pesquisa teve como objetivo analisar o conhecimento dos estudantes de Ciências Biológicas do Consórcio CEDERJ em relação ao tema BL. Aplicou-se um questionário por meio do Google formulário (Google Forms), onde foi possível coletar dados de 63 estudantes que desejaram participar da pesquisa. Observou-se que a maioria possui o correto conhecimento sobre a aplicabilidade laboratorial de itens como: jaleco, luva, óculos de proteção, equipamentos, materiais e objetos perfurocortantes. Por outro lado, a maioria não conhece o uso adequado de cabine de segurança e tampouco sobre o nível de risco laboratorial para a saúde do profissional. Logo, conclui-se que a participação em disciplinas curriculares, que abordam os conceitos de biossegurança, apresentam determinada eficácia na formação profissional de biólogos, porém, sugere-se que esses profissionais continuem a buscar por uma capacitação adicional a sua formação, a fim de realizar seu trabalho com eficiência.
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