Mammifère marin | EPFL Graph Search

Un 'mammifère marin' est un mammifère inféodé à l'eau de mer, lié à un écosystème ou un biotope marin avec des caractéristiques hydromorphologiques spécifiques à cette vie aquatique. Comme chez les mammifères terrestres, la respiration est aérienne ; ils ne peuvent vivre sans venir respirer régulièrement à la surface. De plus, ils ont le sang chaud (homéotherme ou endotherme), portent leurs petits dans leur ventre (vivipare) et pour finir ils allaitent leurs petits. A l'exception des loutres ils possèdent, comme les poissons, des nageoires. Les biologistes dénombrent de mammifères marins dans le monde (dont 5 déjà éteintes). Ils sont presque tous et presque partout menacés ou en voie de régression. Des programmes de conservation ont été mis en place. Plusieurs aires marines protégées leur sont réservées, dont le sanctuaire Pelagos, qui résulte d'un accord signé en 1999 par la France, l'Italie et Monaco pour la protection des mammifères marins qui le fréquentent, de même que l'estua

Probable nature of higher-dimensional symmetries underlying mammalian grid-cell activity patterns

Alexander Mathis

Lattices abound in nature—from the crystal structure of minerals to the honey-comb organization of ommatidia in the compound eye of insects. These arrangements provide solutions for optimal packings, efficient resource distribution, and cryptographic protocols. Do lattices also play a role in how the brain represents information? We focus on higher-dimensional stimulus domains, with particular emphasis on neural representations of physical space, and derive which neuronal lattice codes maximize spatial resolution. For mammals navigating on a surface, we show that the hexagonal activity patterns of grid cells are optimal. For species that move freely in three dimensions, a face-centered cubic lattice is best. This prediction could be tested experimentally in flying bats, arboreal monkeys, or marine mammals. More generally, our theory suggests that the brain encodes higher-dimensional sensory or cognitive variables with populations of grid-cell-like neurons whose activity patterns exhibit lattice structures at multiple, nested scales. The brain of a mammal has to store vast amounts of information. The ability of animals to navigate through their environment, for example, depends on a map of the space around them being encoded in the electrical activity of a finite number of neurons. In 2014 the Nobel Prize in Physiology or Medicine was awarded to neuroscientists who had provided insights into this process. Two of the winners had shown that, in experiments on rats, the neurons in a specific region of the brain ‘fired’ whenever the rat was at any one of a number of points in space. When these points were plotted in two dimensions, they made a grid of interlocking hexagons, thereby providing the rat with a map of its environment. However, many animals, such as bats and monkeys, navigate in three dimensions rather than two, and it is not clear whether these same hexagonal patterns are also used to represent three-dimensional space. Mathis et al. have now used mathematical analysis to search for the most efficient way for the brain to represent a three-dimensional region of space. This work suggests that the neurons need to fire at points that roughly correspond to the positions that individual oranges take up when they are stacked as tight as possible in a pile. Physicists call this arrangement a face-centered cubic lattice. At least one group of experimental neuroscientists is currently making measurements on the firing of neurons in freely flying bats, so it should soon be possible to compare the predictions of Mathis et al. with data from experiments.

2015

Detecting animals in African Savanna with UAVs and the crowds

Stéphane Joost, Devis Tuia

Unmanned aerial vehicles (UAVs) offer new opportunities for wildlife monitoring, with several advantages over traditional field-based methods. They have readily been used to count birds, marine mammals and large herbivores in different environments, tasks which are routinely performed through manual counting in large collections of images. In this paper, we propose a semi-automatic system able to detect large mammals in semi-arid Savanna. It relies on an animal-detection system based on machine learning, trained with crowd-sourced annotations provided by volunteers who manually interpreted sub-decimeter resolution color images. The system achieves a high recall rate and a human operator can then eliminate false detections with limited effort. Our system provides good perspectives for the development of data-driven management practices in wildlife conservation. It shows that the detection of large mammals in semi-arid Savanna can be approached by processing data provided by standard RGB cameras mounted on affordable fixed wings UAVs.

Elsevier2017

Probable nature of higher-dimensional symmetries underlying mammalian grid-cell activity patterns

Alexander Mathis

2015