Arboreal ants use the "Velcro® principle" to capture very large prey

Plant-ants live in a mutualistic association with host plants known as "myrmecophytes" that provide them with a nesting place and sometimes with extra-floral nectar (EFN) and/or food bodies (FBs); the ants can also attend sap-sucking Hemiptera for their honeydew. In return, plant-ants, like most other arboreal ants, protect their host plants from defoliators. To satisfy their nitrogen requirements, however, some have optimized their ability to capture prey in the restricted environment represented by the crowns of trees by using elaborate hunting techniques. In this study, we investigated the predatory behavior of the ant Azteca andreae which is associated with the myrmecophyte Cecropia obtusa. We noted that up to 8350 ant workers per tree hide side-by-side beneath the leaf margins of their host plant with their mandibles open, waiting for insects to alight. The latter are immediately seized by their extremities, and then spread-eagled; nestmates are recruited to help stretch, carve up and transport prey. This group ambush hunting technique is particularly effective when the underside of the leaves is downy, as is the case for C. obtusa. In this case, the hook-shaped claws of the A. andreae workers and the velvet-like structure of the underside of the leaves combine to act like natural VelcroH that is reinforced by the group ambush strategy of the workers, allowing them to capture prey of up to 13,350 times the mean weight of a single worker

Ants mediate the structure of phytotelm communities in an ant-garden bromeliad

The main theories explaining the biological diversity of rain forests often confer a limited understanding of the contribution of interspecific interactions to the observed patterns. We show how two-species mutualisms can affect much larger segments of the invertebrate community in tropical rain forests. Aechmea mertensii (Bromeliaceae) is both a phytotelm (plant-held water) and an ant-garden epiphyte. We studied the influence of its associated ant species (Pachycondyla goeldii and Camponotus femoratus) on the physical characteristics of the plants, and, subsequently, on the diversity of the invertebrate communities that inhabit their tanks. As dispersal agents for the bromeliads, P. goeldii and C. femoratus influence the shape and size of the bromeliad by determining the location of the seedling, from exposed to partially shaded areas. By coexisting on a local scale, the two ant species generate a gradient of habitat conditions in terms of available resources (space and food) for aquatic invertebrates, the diversity of the invertebrate communities increasing with greater volumes of water and fine detritus. Two-species mutualisms are widespread in nature, but their influence on the diversity of entire communities remains largely unexplored. Because macroinvertebrates constitute an important part of animal production in all ecosystem types, further investigations should address the functional implications of such indirect effects

Proof of uniform convergence for a cell-centered AP discretization of the hyperbolic heat equation on general meshes

International audienceWe prove the uniform AP convergence on unstructured meshes in 2D of a generalization, of the Gosse-Toscani 1D scheme for the hyperbolic heat equation. This scheme is also a nodal extension in 2D of the Jin-Levermore scheme described in [18] for the 1D case. In 2D, the proof is performed using a new diffusion scheme

Numerical model applied to the reassessment of the serviceability and safety of AAR-affected power-plant

ICAAR 2016 - 15th International Conference on Alkali-Aggregate Reaction, Sao Paulo, BRESIL, 03-/07/2016 - 07/07/2016Veytaux power-plant is a hydraulic facility affected by AAR. The concrete deformations of the structure are transmitted to sensitive equipments connected to it with major consequences on the serviceability and safety. Predicting the amplitude and rate of future displacements is an essential condition to choose the manager's strategy: adaptation of the equipment, repair or strengthening of the structure... The main difficulty lies in the heterogeneous moisture distribution which induces complex expansion gradients and the complex interactions between chemically-induced swelling and mechanical resistance of less-affected parts of the structure. Hence, the prediction of the displacement transmitted to the equipments requires a complete chemo-mechanical model of the structure. A macroscopic model is used and takes into account various coupling with moisture, temperature and stress states in the concrete. Its fitting requires several data: material samples from the structure for laboratory tests, monitoring devices for measuring displacements, moisture and temperature.... The resulting heterogeneous displacements in the concrete structure allow to re-assess the stress-state generated in the anchored equipment, especially in the 130-m long main distributor pipe

A Static Analyzer for Large Safety-Critical Software

We show that abstract interpretation-based static program analysis can be made efficient and precise enough to formally verify a class of properties for a family of large programs with few or no false alarms. This is achieved by refinement of a general purpose static analyzer and later adaptation to particular programs of the family by the end-user through parametrization. This is applied to the proof of soundness of data manipulation operations at the machine level for periodic synchronous safety critical embedded software. The main novelties are the design principle of static analyzers by refinement and adaptation through parametrization, the symbolic manipulation of expressions to improve the precision of abstract transfer functions, the octagon, ellipsoid, and decision tree abstract domains, all with sound handling of rounding errors in floating point computations, widening strategies (with thresholds, delayed) and the automatic determination of the parameters (parametrized packing)

Des plantes tropicales qui forment des mares : les broméliacées-citerne : un écosystème aquatique miniature capital pour la biodiversité

Les plantes qui présentent des structures anatomiques permettant de retenir de l'eau en permanence sont assez répandues en milieu tropical. Si beaucoup sont maintenant cultivées pour être vendues en jardineries, faisant le bonheur des amateurs, elles forment en milieu naturel des écosystèmes aquatiques encore très peu étudiés et renferment une biodiversité que l'on est loin d'avoir recensée. En Amérique centrale et du Sud, les broméliacées-citerne, qui représentent les plus nombreuses et les plus diversifiées de ces "plantes-mares", permettent à des organismes très variés d'accomplir leur cycle de vie

A temporary social parasite of tropical plant-ants improves the fitness of a myrmecophyte

Myrmecophytes offer plant-ants a nesting place in exchange for protection from their enemies, particularly defoliators. These obligate ant-plant mutualisms are common model systems for studying factors that allow horizontally transmitted mutualisms to persist since parasites of ant-myrmecophyte mutualisms exploit the rewards provided by host plants whilst providing no protection in return. In pioneer formations in French Guiana, Azteca alfari and Azteca ovaticeps are known to be mutualists of myrmecophytic Cecropia (Cecropia ants). Here, we show that Azteca andreae, whose colonies build carton nests on myrmecophytic Cecropia, is not a parasite of Azteca-Cecropia mutualisms nor is it a temporary social parasite of A. alfari; it is, however, a temporary social parasite of A. ovaticeps. Contrarily to the two mutualistic Azteca species that are only occasional predators feeding mostly on hemipteran honeydew and food bodies provided by the host trees, A. andreae workers, which also attend hemipterans, do not exploit the food bodies. Rather, they employ an effective hunting technique where the leaf margins are fringed with ambushing workers, waiting for insects to alight. As a result, the host trees' fitness is not affected as A. andreae colonies protect their foliage better than do mutualistic Azteca species resulting in greater fruit production. Yet, contrarily to mutualistic Azteca, when host tree development does not keep pace with colony growth, A. andreae workers forage on surrounding plants; the colonies can even move to a non-Cecropia tree

Surveillance et contrôle des activités des navires en mer = Surveillance and Control of Vessel's Activities at Sea

Dossier : La sécurité globale. Menaces et réponses. Article disponible sur cette page = http://www.irit.fr/scanmaris/index.php?page=publicationsNational audienceTo guarantee good security conditions in the French national water and exclusive economic zone, the surveillance system is optimised in using various facilities: CROSS (Regional Operational Centres), a network of coastal semaphores, vessels and aircrafts from maritime administrations.. But information are acquired only over limited areas or time periods.Thus, the next solutions shall be global and permanent, and shall process all available information to better manage and control all activities at sea. To best achieve this global surveillance of wide maritime areas without constraining the free access and commercial activities, tools are to be developed to automatically combine and process various types of information collected to continuously monitor the ship's traffic, the good flows and to detect criminal activities and threats (illicit goods flows, clandestine immigrants, piracy, accidents, etc.), and regulation violations

Surveillance et contrôle des activités des navires en mer (REE nov. 2007)

Dossier : La sécurité globale. Menaces et réponses. Article disponible sur cette page = http://www.irit.fr/scanmaris/index.php?page=publicationsNational audienceTo guarantee good security conditions in the French national water and exclusive economic zone, the surveillance system is optimised in using various facilities: CROSS (Regional Operational Centres), a network of coastal semaphores, vessels and aircrafts from maritime administrations.. But information are acquired only over limited areas or time periods.Thus, the next solutions shall be global and permanent, and shall process all available information to better manage and control all activities at sea. To best achieve this global surveillance of wide maritime areas without constraining the free access and commercial activities, tools are to be developed to automatically combine and process various types of information collected to continuously monitor the ship's traffic, the good flows and to detect criminal activities and threats (illicit goods flows, clandestine immigrants, piracy, accidents, etc.), and regulation violations