227 research outputs found
Des rĂ©seaux trophiques au fonctionnement des Ă©cosystĂšmes lacustres : vers une intĂ©gration de lâhĂ©tĂ©rogĂ©nĂ©itĂ© et de la complexitĂ©
Les milieux aquatiques constituent des modĂšles essentiels pour comprendre le rĂŽle de la biodiversitĂ© et des interactions biotiques et abiotiques sur la structure des communautĂ©s et sur le fonctionnement des Ă©cosystĂšmes. La derniĂšre dĂ©cennie a Ă©tĂ© marquĂ©e par dâimportantes avancĂ©es :Aquatic ecosystems constitute essential models to understand the role of biodiversity and that of biotic and abiotic interactions on both community structure and ecosystem functioning. The last decade was marked by important breakthroughs:The objective is now to integrate this multidimensional complexity in order to reach a better prediction capacity of limnology as a discipline for human societies
Trophic groups and modules: two levels of group detection in food webs
Within food webs, species can be partitioned into groups according to various
criteria. Two notions have received particular attention: trophic groups, which
have been used for decades in the ecological literature, and more recently,
modules. The relationship between these two group definitions remains unknown
in empirical food webs because they have so far been studied separately. While
recent developments in network theory have led to efficient methods for
detecting modules in food webs, the determination of trophic groups (sets of
species that are functionally similar) is based on subjective expert knowledge.
Here, we develop a novel algorithm for trophic group detection. We apply this
method to several well-resolved empirical food webs, and show that aggregation
into trophic groups allows the simplification of food webs while preserving
their information content. Furthermore, we reveal a 2-level hierarchical
structure where modules partition food webs into large bottom-top trophic
pathways whereas trophic groups further partition these pathways into sets of
species with similar trophic connections. Bringing together trophic groups and
modules provides new perspectives to the study of dynamical and functional
consequences of food-web structure, bridging topological analysis and dynamical
systems. Trophic groups have a clear ecological meaning in terms of trophic
similarity, and are found to provide a trade-off between network complexity and
information loss
Skin Microvascular Thrombosis in Fusarium Infection in Two Early Biopsied Cases
Fusarium species cause rare and severe infections. Their incidence is increasing in immunocompromised patients but they are also observed in healthy hosts. Because of the rapid dissemination of infection and the frequent resistance of Fusarium species to antifungal drugs, histopathologic evidence of hyphae is very helpful to obtain the diagnosis rapidly. We report the clinical and pathological features of two patients with initial cutaneous lesions. Cutaneous early biopsies showed microvessel involvement with hyphae and thrombosis. Fusarium infection was confirmed by skin culture. Hyphae within a microvessel thrombus in the skin were highly suggestive of disseminated fungal infection. These pathological features enabled to establish an early diagnosis and to start efficient antifungal treatment. In early cutaneous biopsies of immunocompromised patients, the presence of cutaneous vessel thrombosis can suggest a fungal infection and may help to start specific therapy without delay for these life-threatening infections
Agent-based simulation of pedestrians' earthquake evacuation; application to Beirut, Lebanon
Most seismic risk assessment methods focus on estimating the damages to the
built environment and the consequent socioeconomic losses without fully taking
into account the social aspect of risk. Yet, human behaviour is a key element
in predicting the human impact of an earthquake, therefore, it is important to
include it in quantitative risk assessment studies. In this study, an
interdisciplinary approach simulating pedestrians' evacuation during
earthquakes at the city scale is developed using an agent-based model. The
model integrates the seismic hazard, the physical vulnerability as well as
individuals' behaviours and mobility. The simulator is applied to the case of
Beirut, Lebanon. Lebanon is at the heart of the Levant fault system that has
generated several Mw>7 earthquakes, the latest being in 1759. It is one of the
countries with the highest seismic risk in the Mediterranean region. This is
due to the high seismic vulnerability of the buildings due to the absence of
mandatory seismic regulation until 2012, the high level of urbanization, and
the lack of adequate spatial planning and risk prevention policies. Beirut as
the main residential, economic and institutional hub of Lebanon is densely
populated. To accommodate the growing need for urban development, constructions
have almost taken over all of the green areas of the city; squares and gardens
are disappearing to give place to skyscrapers. However, open spaces are safe
places to shelter, away from debris, and therefore play an essential role in
earthquake evacuation. Despite the massive urbanization, there are a few open
spaces but locked gates and other types of anthropogenic barriers often limit
their access. To simulate this complex context, pedestrians' evacuation
simulations are run in a highly realistic spatial environment implemented in
GAMA [1]. Previous data concerning soil and buildings in Beirut [2, 3] are
complemented by new geographic data extracted from high-resolution Pleiades
satellite images. The seismic loading is defined as a peak ground acceleration
of 0.3g, as stated in Lebanese seismic regulations. Building damages are
estimated using an artificial neural network trained to predict the mean damage
[4] based on the seismic loading as well as the soil and building vibrational
properties [5]. Moreover, the quantity and the footprint of the generated
debris around each building are also estimated and included in the model. We
simulate how topography, buildings, debris, and access to open spaces, affect
individuals' mobility. Two city configurations are implemented: 1. Open spaces
are accessible without any barriers; 2. Access to some open spaces is blocked.
The first simulation results show that while 52% of the population is able to
arrive to an open space within 5 minutes after an earthquake, this number is
reduced to 39% when one of the open spaces is locked. These results show that
the presence of accessible open spaces in a city and their proximity to the
residential buildings is a crucial factor for ensuring people's safety when an
earthquake occurs
When worlds collide: Invader-driven benthic habitat complexity alters predatory impacts of invasive and native predatory fishes
Interactions between multiple invasive alien species (IAS) might increase their ecological impacts, yet relatively few studies have attempted to quantify the effects of facilitative interactions on the success and impact of aquatic IAS. Further, the effect of abiotic factors, such as habitat structure, have lacked consideration in ecological impact prediction for many high-profile IAS, with most data acquired through simplified assessments that do not account for real environmental complexities. In the present study, we assessed a potential facilitative interaction between a predatory invasive fish, the Ponto-Caspian round goby (Neogobius melanostomus), and an invasive bivalve, the Asian clam (Corbicula fluminea). We compared N. melanostomus functional responses (feeding-rates under different prey densities) to a co-occurring endangered European native analogue fish, the bullhead (Cottus gobio), in the presence of increased levels of habitat complexity driven by the accumulation of dead C. fluminea biomass that persists within the environment (i.e. 0, 10, 20 empty bivalve shells). Habitat complexity significantly influenced predation, with consumption in the absence of shells being greater than where 10 or 20 shells were present. However, at the highest shell density, invasive N. melanostomus maximum feeding-rates and functional response ratios were substantially higher than those of native C. gobio. Further, the Relative Impact Potential metric, by combining per capita effects and population abundances, indicated that higher shell densities exacerbate the relative impact of the invader. It therefore appears that N. melanostomus can better tolerate higher IAS shell abundances when foraging at high prey densities, suggesting the occurrence of an important facilitative interaction. Our data are thus fully congruent with field data that link establishment success of N. melanostomus with the presence of C. fluminea. Overall, we show that invader-driven benthic habitat complexity can alter the feeding-rates and thus impacts of predatory fishes, and highlight the importance of inclusion of abiotic factors in impact prediction assessments for IAS
Le FORUM, Vol. 40 No. 1
https://digitalcommons.library.umaine.edu/francoamericain_forum/1048/thumbnail.jp
Le Forum, Vol. 41 No. 2
https://digitalcommons.library.umaine.edu/francoamericain_forum/1091/thumbnail.jp
A New Integrative and Mobilizable Element Is a Major Contributor to Tetracycline Resistance in Streptococcus dysgalactiae subsp. equisimilis
Tetracycline resistance in streptococci is mainly due to ribosomal protection mediated by the tet(M) gene that is usually located in the integrative and conjugative elements (ICEs) of the Tn916-family. In this study, we analyzed the genes involved in tetracycline resistance and the associated mobile genetic elements (MGEs) in Streptococcus dysgalactiae subsp. equisimilis (SDSE) causing invasive disease. SDSE resistant to tetracycline collected from 2012 to 2019 in a single hospital and from 2018 in three other hospitals were analyzed by whole genome sequencing. Out of a total of 84 SDSE isolates, 24 (28.5%) were resistant to tetracycline due to the presence of tet(M) (n = 22), tet(W) (n = 1), or tet(L) plus tet(W) (n = 1). The tet(M) genes were found in the ICEs of the Tn916-family (n = 10) and in a new integrative and mobilizable element (IME; n = 12). Phylogenetic analysis showed a higher genetic diversity among the strains carrying Tn916 than those having the new IME, which were closely related, and all belonged to CC15. In conclusion, tetracycline resistance in SDSE is mostly due to the tet(M) gene associated with ICEs belonging to the Tn916-family and a new IME. This new IME is a major cause of tetracycline resistance in invasive Streptococcus dysgalactiae subsp. equisimilis in our settings
Le Forum, Vol. 42 No. 3
https://digitalcommons.library.umaine.edu/francoamericain_forum/1096/thumbnail.jp
Le Forum, Vol. 43 No. 2
https://digitalcommons.library.umaine.edu/francoamericain_forum/1100/thumbnail.jp
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