134 research outputs found
Cancellative actions
summary:The following problem is considered: when can the action of a cancellative semigroup on a set be extended to a simply transitive action of the universal group of on a larger set
A precedence theorem for semigroups
In a finite semigroup, the least element under a precedence order is an idempotent in the kernel
Commutative orders revisited
This article studies commutative orders, that is, commutative semigroups having a semigroup of quotients. In a commutative order S, the square-cancellable elements S(S) constitute a well-behaved separable subsemigroup. Indeed, S(S) is also an order and has a maximum semigroup of quotients R, which is Clifford.We present a new characterisation of commutative orders in terms of semilattice decompositions of S(S) and families of ideals of S. We investigate the role of tensor products in constructing quotients, and show that all semigroups of quotients of S are homomorphic images of the tensor product R âS(S) S. By introducing the notions of generalised order and semigroup of generalised quotients, we show that if S has a semigroup of generalised quotients, then it has a greatest one. For thiswe determine those semilattice congruences on S(S) that are restrictions of congruences on S
Characteristics of the yearly feeding activity of the Ocellated Lizard (Timon lepidus) based on faeces collected on Oleron Island (French Atlantic coast)
The pattern of the yearly feeding
activity of the Ocellated Lizard population on Oleron Island was studied during two one-year periods by
collecting the lizardsâ faeces along a transect. Collected faeces (753 in 2002, 646 in 2006) allowed understanding
in more detail the quantity of the lizardsâ food catch over a yearly cycle. Population feeding activity
starts in the second 10-day period of March and ends in the third 10-day period of October. The peak of feeding
activity was in May in 2002, and in June - July in 2006. This is explained mainly by the length of the day
and the average temperature, and to a much lesser extent by the amount of sunshine or rainfall (calculated
by multiple linear regression analysis). Findings were that in spite of the extreme geographical position of
the Oleron Island population, the pattern of feeding activity varies little from that observed in the Ocellated
Lizard populations in the south of France and central Spain. With some conditions, the faeces-collection
study method could be used for long-term population monitoringL'activité alimentaire du Lézard ocellé a été étudiée durant 2 années sur l'ßle d'Oléron, à partir de teces collectees le long d'un transect. La collecte de 753 teces en 2002 et 646 en 2006 permet de suivre avec précision
l'importance des prises alimentaires au cours du cycle annuel. L'activité alimentaire débute dans la deuxiÚme décade de mars et s'achÚve dans la troisiÚme décade d'octobre, avec un pic d'activité en mai en 2002 et en juin-juillet en 2006. Elle est principalement expliquée par la durée du
jour et par la tempĂ©rature moyenne ; peu par la pluviositĂ© (rĂ©gression multiple). Le rythme d'activitĂ© alimentaire de cette population diffĂšre peu de celui observĂ© dans les populations du sud de la France et du centre de l'Espagne malgrĂ© la position gĂ©ographique extrĂȘme de cette population.
Moyennant certaines prĂ©cautions, cette mĂ©thode pourrait ĂȘtre utilisĂ©e pour un suivi Ă long terme de la population
Modelling the distribution of the Ocellated Lizard in France : implications for conservation
The Ocellated Lizard, Timon lepidus (Daudin 1802) occupies the Mediterranean regions of southwestern Europe (Portugal, Spain, France, and the extreme northwest of Italy). Over the last decades, a marked decline in its population has been observed, particularly on the northern edge of its distribution. As a result, it is currently considered a threatened species, especially in France and Italy. In France, a national action plan for its conservation has been put in place. In this study, ecological niche modelling (ENM) was carried out over the entire area of France in order to evaluate the species' potential distribution, more accurately define its ecological niche, guide future surveys, and inform land use planning so this species can be better taken into consideration. The modelling used data representing 2,757 observation points spread over the known range of the species, and 34 ecogeographical variables (climate, topography, and vegetation cover) were evaluated. After removing correlated variables, models were fitted with several combinations of variables using eight species distribution model (SDM) algorithms, and then their performance was assessed using three model accuracy metrics. Iterative trials changing the input variables were used to obtain the best model. The optimized model included nine determining variables. The results indicate the presence of this species is linked primarily to three climate variables: precipitation in the driest month, precipitation seasonality, and mean temperature in the driest quarter. The model was checked by a sample dataset that was not used to fit the model, and this validation dataset represented 25% of the overall field observations. Of the known occurrence locations kept aside to check the results, 94% fell within the presence area predicted by the modelled map with a presence probability greater than 0.7, and 90% fell within the area with a presence probability ranging from 0.8 to 1, which represents a very high predictive value. These results indicate that the models closely matched the observed distribution, suggesting a low impact of either geographical factors (barriers to dispersal), historical factors (dispersal process), or ecological factors (e.g., competition, trophic resources). The overlap between the predicted distribution and protected areas for this species reveals that less than 1% of the potential distribution area is protected by strong regulatory measures (e.g., national parks and natural reserves). The knowledge obtained in this study allows us to recommend some guidelines that would favor the conservation of this species.Peer reviewe
A long-term monitoring program of the ocellated lizard (Timon lepidus) population on Oléron Island
The Ocellated Lizard Timon lepidus (Sauria ; Lacertidae) has declined throughout most of its range.
Today it is difficult to assess the extent of this decline. The Ocellated Lizard population of Oléron Island (Charente-
Maritime, France) is the subject of a long-term monitoring study established in 2007. This study is repeated every
3 years to follow the population evolution. The population is confined to a long-shore dune of 140 ha. The monitoring
method consists of 70 plots (50 x 50 m) randomly placed within a study area divided into six distinct zones. Three
surveys were conducted in the study area over the spring season (April, May and June). Results were analysed with
PRESENCE 3.0 (Beta) and R 2.8.1. The Ocellated Lizard has a highly heterogeneous distribution on Oléron Island.
The site-occupancy model allows us to conclude that the probability of detecting the species in the plots increases
over the field. In 2010, this probability was 0.78 in April and 0.97 in May and June. The estimated proportion
of occupied sites was 0.83 in 2010 and 0.76 in 2007. Colonization and local extinction are the consequences of
the evolution of available shelters (colonization if this resource increases and extinction if it disappears) and of
the coastal erosion (habitat loss). The relative abundance of Ocellated Lizards on the island (modeling with the
N-mixture model) can be principally explained by the presence of permanent shelters (used both during winter and
the lizardsâ active period), including rabbit and rodent burrows and artificial shelters. Rabbits are essential and their
maintaining is crucial for the Ocellated Lizard conservation. The Ocellated Lizard population size was estimated to
be 1025 individuals (95 % CI: 695-1355) in 2010. This monitoring survey will be replicated in 2013. Results will
help us in evaluating and guiding management and conservation measuresLe Lézard ocellé Timon lepidus subit un déclin marqué sur l'ensemble de son aire de répartition. Il est cependant difficile d'évaluer quantitativement ce déclin sans la mise en place de protocoles de suivi valides. Dans ce but, un
suivi à long terme a été initié en 2007 sur l'ßle d'Oléron. Celui-ci a été répété en 2010. La méthodologie retenue s'appuie sur la technique dite de « site occupancy ». Elle consiste à réaliser trois visites d'une heure au cours du printemps sur 70 placettes de suivi de 2500 m2 réparties
sur les 140 hectares de dunes occupés par l'espÚce. En 2010, la probabilité de détection de l'espÚce sur l'ensemble des placettes a été de 0,78 (0,05) pour la premiÚre visite puis de 0,97 (0,02) pour les deux suivantes. Le taux d'occupation des placettes a été de 0,76 (0,05) en 2007 et de
0,83 (0,04) en 2010. Les colonisations et extinctions locales du Lézard ocellé sur certaines placettes sont dues à l'évolution de la ressource en gßtes (terriers de lapins pour l'essentiel) et à l'érosion littorale (perte d'habitats favorables). Les gßtes permanents (terriers de lapins,
trous de rongeurs et gßtes artificiels) sont les variables environnementales qui expliquent le mieux les abondances du Lézard ocellé. Le Lapin de garenne joue donc un rÎle primordial dans le maintien de la population de lézards. L'estimation des effectifs de la population réalisée par la
technique de « site occupancy » donne des valeurs proches pour les deux périodes de suivi: 1018 (compris entre 602 et 1355) en 2007 et 1025 individus en 2010 (compris entre 695 et 1355). Une troisiÚme session du suivi sera réalisée en 2013. La méthodologie mise en place semble bien adaptée
aux objectifs poursuivis. Elle devrait permettre de mieux orienter les actions de gestion mises en Ćuvre depuis plusieurs annĂ©es sur cette population
Cadherin-23, myosin VIIa and harmonin, encoded by Usher syndrome type I genes, form a ternary complex and interact with membrane phospholipids
Cadherin-23 is a component of early transient lateral links of the auditory sensory cells' hair bundle, the mechanoreceptive structure to sound. This protein also makes up the upper part of the tip links that control gating of the mechanoelectrical transduction channels. We addressed the issue of the molecular complex that anchors these links to the hair bundle F-actin core. By using surface plasmon resonance assays, we show that the cytoplasmic regions of the two cadherin-23 isoforms that do or do not contain the exon68-encoded peptide directly interact with harmonin, a submembrane PDZ (post-synaptic density, disc large, zonula occludens) domain-containing protein, with unusually high affinity. This interaction involves the harmonin Nter-PDZ1 supramodule, but not the C-terminal PDZ-binding motif of cadherin-23. We establish that cadherin-23 directly binds to the tail of myosin VIIa. Moreover, cadherin-23, harmonin and myosin VIIa can form a ternary complex, which suggests that myosin VIIa applies tension forces on hair bundle links. We also show that the cadherin-23 cytoplasmic region, harmonin and myosin VIIa interact with phospholipids on synthetic liposomes. Harmonin and the cytoplasmic region of cadherin-23, both independently and as a binary complex, can bind specifically to phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2), which may account for the role of this phospholipid in the adaptation of mechanoelectrical transduction in the hair bundle. The distributions of cadherin-23, harmonin, myosin VIIa and PI(4,5)P2 in the growing and mature auditory hair bundles as well as the abnormal locations of harmonin and myosin VIIa in cadherin-23 null mutant mice strongly support the functional relevance of these interactions
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