Structural variability and invasions of pioneer plant communities in riparian habitats of the middle Adour River (SW France)

1995 ◽  
Vol 73 (1) ◽  
pp. 33-44 ◽  
Author(s):  
Eric Tabacchi
Keyword(s):  
Exotic Species ◽  
Life Forms ◽  
River Channels ◽  
Main River ◽  
Main River Channel ◽  
Pioneer Plant ◽  
Littoral Zones ◽  
History Of ◽  
Number Of Individuals ◽  
Sw France

The pioneer vegetation of five distinct littoral zones along the middle Adour River (SW France) was investigated during three successive low water periods. There was a high year to year variability in the hydrology of the river during the period of study with a normal (1987), a wet (1988), and a dry year (1989). Changes in population and life forms density of both native and exotic species were analyzed. Communities were species rich when 45% of the 428 species present in the study area (2-km-long stretch) were found in the 10 × 10 m plots. Most of the species were annuals, but perennials were also abundant. The exotic component represented nearly 20% of the species and of the total number of individuals. There was high spatial variability in pioneer communities; sites of the main river channel differed from those along abandoned arms in species composition and population densities. The communities responded to changes in the hydrology of the preceding growing season. Sharp year to year differences were found in population and species density. The nature of the hydrological change drove those changes. Plots located in the oldest arms of the river showed a greater sensitivity to flooding conditions than those located in young littoral zones, with an increase in hygrophilous species. Alternatively, plots adjacent to active river channels showed greater sensitivity to drought conditions, as the density of short-lived and exotic species increased. Comparatively, exotics appeared to be more sensitive to the type of hydrological changes than natives. Warmer years also affected native plants, which reacted like invasive species. Relationships between the observed changes, the level of hydrological disturbance, and the recent history of each site are discussed in this paper with the possibility of using introduced species as descriptors of climatic and hydrologic changes. Key words: riparian vegetation, pioneer community, community structure, biological invasions, hydrological perturbation, variability.

scholarly journals Restoring dissolved organic carbon subsidies from floodplains to lowland river food webs: a role for environmental flows?

2016 ◽  
Vol 67 (9) ◽  
pp. 1387 ◽  
Author(s):  
Darren S. Baldwin ◽  
Matthew J. Colloff ◽  
Simon M. Mitrovic ◽  
Nick R. Bond ◽  
Ben Wolfenden
Keyword(s):  
Food Webs ◽  
Environmental Flows ◽  
Ecological Condition ◽  
Lowland River ◽  
River Channels ◽  
Apparent Lack ◽  
River Floodplain ◽  
Main River ◽  
Main River Channel ◽  
Terrestrial Subsidies

Environmental flows are managed events in river systems designed to enhance the ecological condition of aquatic ecosystems. Although not traditionally seen as important in lowland rivers, there is mounting evidence that terrestrial subsidies can be an important energy source in aquatic metazoan food webs. We argue that the apparent lack of importance of terrestrial subsidies to many lowland river food webs may reflect an artefact resulting from historical anthropogenic changes to lowland river–floodplain ecosystems, including the loss of lateral connectivity between rivers and their floodplains, changes in floodplain land use and carbon stores, and loss of sites of transformation within the main channel. The loss of floodplain subsidies to the main river channel can be partially redressed using environmental flows; however, this will require mimicking important aspects of natural high-flow events that have hitherto been overlooked when targeting environmental flows to a limited suite of biota. We suggest that key biotic targets for environmental flow releases may not be achievable unless river–floodplain subsidies are sufficiently restored. Environmental flows can go some way to addressing this shortfall, but only if floodplain subsidies to river channels are explicitly included in the design and management of environmental flows.

scholarly journals The ichthyofauna of drifting macrophyte mats in the Ivinhema River, upper Paraná River basin, Brazil

2011 ◽  
Vol 9 (2) ◽  
pp. 403-409 ◽  
Author(s):  
Cíntia Karen Bulla ◽  
Luiz Carlos Gomes ◽  
Leandro Esteban Miranda ◽  
Angelo Antonio Agostinho
Keyword(s):  
Fish Assemblages ◽  
Mesh Size ◽  
Paraná River ◽  
Parana River ◽  
Main River ◽  
Main River Channel ◽  
Dispersal Vectors ◽  
Upper Paraná River ◽  
Number Of Individuals

We describe the fish assemblages associated with drifting macrophyte mats and consider their possible role as dispersal vectors in the Ivinhema River, a major tributary of the upper Paraná River, Brazil. Fish associated with drifting mats were sampled in the main river channel during January and March 2005, when the wind and/or the increased water level were sufficient to transport macrophyte stands. Fish in the drifting mats were sampled with a floating sieve (4 m long x 2 m wide x 0.6 m high, and 2 mm mesh size). In the laboratory, larvae, juvenile, and adult fish were counted and identified to the lowest possible taxonomic level. In four drifting macrophyte mats we captured 218 individuals belonging to at least 28 species, 17 families, and 6 orders. Aphyocharax dentatus, Serrasalmus spp., and Trachelyopterus galeatus were the most abundant taxa associated with the mats, but species richness ranged from 6 to 24 species per mat. In addition, 85% of the total number of individuals caught was larvae and juveniles. Although preliminary and based on limited samples, this study of drifting macrophyte mats was the first one in the last unregulated stretch of the Paraná River remaining inside Brazilian territory, and alerts us to the potential role of macrophytes mats as dispersers of fish species in the region.

scholarly journals Alien Species vs. Native Species: From Community Ecology to Eco-Evolutionary Dynamics

2019 ◽  
Author(s):  
Andersonn Silveira Prestes
Keyword(s):  
Alien Species ◽  
Exotic Species ◽  
Native Species ◽  
Evolutionary Dynamics ◽  
Evolutionary Processes ◽  
Native Communities ◽  
Individualized Approach ◽  
History Of ◽  
Relationship Of ◽  
The Relationship

The establishment and spread of exotic species is a contemporary major concern. Alien species may become invasive in their new habitat, leading to both/either environmental and/or economic impacts. I briefly reviewed the literature in the last decade about the relationship of exotic species and native communities. I identified that professionals usually approach the subject in two main points of view: (1) researchers tend to point out the impacts of alien species on entire communities, evaluating if the relationship is positive, negative or neutral; (2) they focus on the eco-evolutionary processes involved in the introductions, the dynamics of invasion, and individual study cases. When evaluating the response of introductions to entire communities, evidence seems to be ambiguous and may support positive, negative or neutral relationship, especially depending on the scale approached. The unique eco-evolutionary pathways of each introduction may be a great shortcoming in the searching for generalities. On the other hand, advances have been made in understanding the dynamics of invasion on different lineages through a more selective/individualized approach. I suggest that the dynamics of invasion might be studied through a perspective in which different eco-evolutionary processes, levels of organization (from gene to entire communities), the history of the organism(s) and time are taken into account. Individual cases might be compared in attempt to understand how the relationship exotic and native works and in the search for generalities.

scholarly journals The divergence history of European blue mussel species reconstructed from Approximate Bayesian Computation: the effects of sequencing techniques and sampling strategies

2018 ◽  
Author(s):  
Christelle Fraïsse ◽  
Camille Roux ◽  
Pierre-Alexandre Gagnaire ◽  
Jonathan Romiguier ◽  
Nicolas Faivre ◽  
...  
Keyword(s):  
Frequency Spectrum ◽  
Approximate Bayesian Computation ◽  
Exome Capture ◽  
Bayesian Computation ◽  
Sampling Strategies ◽  
Migration Rates ◽  
History Of ◽  
Site Frequency Spectrum ◽  
Approximate Bayesian ◽  
Number Of Individuals

AbstractGenome-scale diversity data are increasingly available in a variety of biological systems, and can be used to reconstruct the past evolutionary history of species divergence. However, extracting the full demographic information from these data is not trivial, and requires inferential methods that account for the diversity of coalescent histories throughout the genome. Here, we evaluate the potential and limitations of one such approach. We reexamine a well-known system of mussel sister species, using the joint site frequency spectrum (jSFS) of synonymous mutations computed either from exome capture or RNA-seq, in an Approximate Bayesian Computation (ABC) framework. We first assess the best sampling strategy (number of: individuals, loci, and bins in the jSFS), and show that model selection is robust to variation in the number of individuals and loci. In contrast, different binning choices when summarizing the joint site frequency spectrum, strongly affect the results: including classes of low and high frequency shared polymorphisms can more effectively reveal recent migration events. We then take advantage of the flexibility of ABC to compare more realistic models of speciation, including variation in migration rates through time (i.e. periodic connectivity) and across genes (i.e. genome-wide heterogeneity in migration rates). We show that these models were consistently selected as the most probable, suggesting that mussels have experienced a complex history of gene flow during divergence and that the species boundary is semi-permeable. Our work provides a comprehensive evaluation of ABC demographic inference in mussels based on the coding site frequency spectrum, and supplies guidelines for employing different sequencing techniques and sampling strategies. We emphasize, perhaps surprisingly, that inferences are less limited by the volume of data, than by the way in which they are analyzed.

scholarly journals Crevasse splays within a lignite seam at the Tomisławice opencast mine near Konin, central Poland: architecture, sedimentology and depositional model

Geologos ◽  
2020 ◽  
Vol 26 (1) ◽  
pp. 25-37 ◽  
Author(s):  
Lilianna Chomiak
Keyword(s):  
Middle Miocene ◽  
Structural Features ◽  
Fine Grained ◽  
Opencast Mine ◽  
Main River ◽  
Main River Channel ◽  
Lignite Mine ◽  
Flooding Event ◽  
Crevasse Splay ◽  
Sandy Sediments

AbstractThe present article focuses predominantly on sandy deposits that occur within the Middle Miocene lignite seam at the Tomisławice opencast mine, owned by the Konin Lignite Mine. As a result of mining activity, these siliciclastics were available for direct observation in 2015–2016. They are situated between two lignite benches over a distance of ~500 m in the lower part and ~200 m in the higher part of the exploitation levels. The maximum thickness of these sandy sediments, of a lenticular structure in a S–N cross section, is up to 1.8 m. With the exception of a thin lignite intercalation, these siliciclastics comprise mainly by fine-grained and well-sorted sands, and only their basal and top layers are enriched with silt particles and organic matter. Based on a detailed analysis of the sediments studied (i.e., their architecture and textural-structural features), I present a discussion of their genesis and then propose a model of their formation. These siliciclastics most likely formed during at least two flood events in the overbank area of a Middle Miocene meandering or anastomosing river. Following breaching of the natural river levee, the sandy particles (derived mainly from the main river channel and levees) were deposited on the mire (backswamp) surface in the form of crevasse splays. After each flooding event, vegetation developed on the top of these siliciclastics; hence, two crevasse-splay bodies (here referred to as the older and younger) came into existence. As a result, the first Mid-Polish lignite seam at the Tomisławice opencast mine is currently divided in two by relatively thick siliciclastics, which prevents a significant portion of this seam from being used for industrial purposes.

scholarly journals The fluvial history of Mars

2012 ◽  
Vol 370 (1966) ◽  
pp. 2193-2215 ◽  
Author(s):  
Michael H. Carr
Keyword(s):  
Climatic Conditions ◽  
River Channels ◽  
Erosion And Deposition ◽  
Running Water ◽  
The Earth ◽  
Outflow Channels ◽  
History Of ◽  
Valley Networks ◽  
River Valleys ◽  
Steep Slopes

River channels and valleys have been observed on several planetary bodies in addition to the Earth. Long sinuous valleys on Venus, our Moon and Jupiter's moon Io are clearly formed by lava, and branching valleys on Saturn's moon Titan may be forming today by rivers of methane. But by far the most dissected body in our Solar System apart from the Earth is Mars. Branching valleys that in plan resemble terrestrial river valleys are common throughout the most ancient landscapes preserved on the planet. Accompanying the valleys are the remains of other indicators of erosion and deposition, such as deltas, alluvial fans and lake beds. There is little reason to doubt that water was the erosive agent and that early in Mars' history, climatic conditions were very different from the present cold conditions and such that, at least episodically, water could flow across the surface. In addition to the branching valley networks, there are large flood features, termed outflow channels. These are similar to, but dwarf, the largest terrestrial flood channels. The consensus is that these channels were also cut by water although there are other possibilities. The outflow channels mostly postdate the valley networks, although most are still very ancient. They appear to have formed at a time when surface conditions were similar to those that prevail today. There is evidence that glacial activity has modified some of the water-worn valleys, particularly in the 30–50° latitude belts, and ice may also be implicated in the formation of geologically recent, seemingly water-worn gullies on steep slopes. Mars also has had a long volcanic history, and long, sinuous lava channels similar to those on the Moon and Venus are common on and around the large volcanoes. These will not, however, be discussed further; the emphasis here is on the effects of running water on the evolution of the surface.

scholarly journals “Equal Rights for all Civilized Men”:

1992 ◽  
Vol 37 (3) ◽  
pp. 376-397 ◽  
Author(s):  
Michael O. West
Keyword(s):  
Equal Rights ◽  
Political Struggle ◽  
Political Skills ◽  
Political Tactics ◽  
History Of ◽  
Southern Rhodesia ◽  
The Right ◽  
Number Of Individuals

SummaryBetween 1924 and 1961 elite Africans in Southern Rhodesia (colonial Zimbabwe) waged a protracted political struggle for the right legally to drink “European” liquor, which had been banned to colonized Africans under the Brussels Treaty of 1890. Refusing to be lumped with the black masses and basing their claim on the notion that there should be “equal rights for all civilized men”, elite Africans argued that they had attained a cultural level comparable to that of the dominant European settlers and should therefore be exempt from the liquor ban. This struggle, which ended successfully in 1961, also highlights other important themes in the history of the emergent African elite in Southern Rhodesia, most notably its political tactics and consciousness. The quest for European liquor helped to hone political skills as well, as a number of individuals who participated in it later became important African nationalist leaders.

scholarly journals From cosmos to intelligent life: the four ages of astrobiology

2012 ◽  
Vol 11 (4) ◽  
pp. 345-350 ◽  
Author(s):  
Marcelo Gleiser
Keyword(s):  
Chemical Elements ◽  
Life Forms ◽  
Big Bang ◽  
Self Awareness ◽  
First Stars ◽  
History Of ◽  
Life On Earth ◽  
The Big Bang ◽  
The Universe ◽  
Intelligent Life

AbstractThe history of life on Earth and in other potential life-bearing planetary platforms is deeply linked to the history of the Universe. Since life, as we know, relies on chemical elements forged in dying heavy stars, the Universe needs to be old enough for stars to form and evolve. The current cosmological theory indicates that the Universe is 13.7 ± 0.13 billion years old and that the first stars formed hundreds of millions of years after the Big Bang. At least some stars formed with stable planetary systems wherein a set of biochemical reactions leading to life could have taken place. In this paper, I argue that we can divide cosmological history into four ages, from the Big Bang to intelligent life. The physical age describes the origin of the Universe, of matter, of cosmic nucleosynthesis, as well as the formation of the first stars and Galaxies. The chemical age began when heavy stars provided the raw ingredients for life through stellar nucleosynthesis and describes how heavier chemical elements collected in nascent planets and Moons gave rise to prebiotic biomolecules. The biological age describes the origin of early life, its evolution through Darwinian natural selection and the emergence of complex multicellular life forms. Finally, the cognitive age describes how complex life evolved into intelligent life capable of self-awareness and of developing technology through the directed manipulation of energy and materials. I conclude discussing whether we are the rule or the exception.

scholarly journals Habitat factors differentiating the occurrence of Ostracoda (Crustacea) in the floodplain of a small lowland River Krąpiel (N-W Poland)

2020 ◽  
pp. 23
Author(s):  
Agnieszka Szlauer-Łukaszewska ◽  
Vladimir Pešić
Keyword(s):  
Abiotic Factors ◽  
River Channel ◽  
Water Bodies ◽  
Oxbow Lakes ◽  
Factors Associated ◽  
Main River ◽  
Main River Channel ◽  
Habitat Factors ◽  
Sediment Sorting ◽  
Physical And Chemical

We analysed the occurrence of ostracods in a small river, taking into account all the types of water bodies in the floodplain − these included helocrenes, oxbow lakes, and ponds, as well as the main river channel. The objective of the study was to investigate the variation in ostracod communities and identify those factors determining species distribution. The environmental factors considered were the type of water body, responsible for 17% of the variance, the physical and chemical water properties (29%), and the biotic and abiotic factors associated with the substrate type (23%). Among the factors associated with the substrate, sediment sorting, plant coverage and insolation were the most important. The ostracod fauna of the helocrenes differed from that of the other water bodies in the floodplain. In the water bodies of the Krąpiel valley and in the main river channel, 33 ostracod species were recorded, of which 26 were found in the main river channel. Refugia in the floodplain were the main source of the diversity and abundance of ostracods in the main river channel. The mean density in the main river channel was very low, at 330 indiv. m−2, while in the water bodies of the floodplain it was the greatest, reaching up to 5568 indiv. m−2.

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