Patterns of ash (Fraxinus excelsior L.) colonization in mountain grasslands: the importance of management practices

International audienceWoody colonization of grasslands is often associated with changes in abiotic or biotic conditions or a combination of both. Widely used as fodder and litter in the past traditional agro-pastoral system, ash (Fraxinus excelsior L.) has now become a colonizing species of mountain grasslands in the French Pyrenees. Its present distribution is dependent on past human activities and it is locally controlled by propagule pressure and abiotic conditions. However, even when all favourable conditions are met, all the potentially colonizable grasslands are not invaded. We hypothesize that management practices should play a crucial role in the control of ash colonization. From empirical field surveys we have compared the botanical composition of a set of grasslands (present and former) differing in management practices and level of ash colonization. We have displayed a kind of successional gradient positively linked to both ash cover and height but not to the age of trees. We have tested the relationships between ash presence in grassland and management types i.e. cutting and/or grazing, management intensity and some grassland communities' features i.e. total and local specific richness and species heterogeneity. Mixed use (cutting and grazing) is negatively linked to ash presence in grassland whereas grazing alone positively. Mixed use and high grazing intensity are directly preventing ash seedlings establishment, when low grazing intensity is allowing ash seedlings establishment indirectly through herbaceous vegetation neglected by livestock. Our results show the existence of a limit between grasslands with and without established ashes corresponding to a threshold in the intensity of use. Under this threshold, when ash is established, the colonization process seems to become irreversible. Ash possesses the ability of compensatory growth and therefore under a high grazing intensity develops a subterranean vegetative reproduction. However the question remains at which stage of seedling development and grazing intensity these strategies could occur

Mid-Tertiary elapid snakes (Squamata, Colubroidea) from Riversleigh, northern Australia: early steps in a continent-wide adaptive radiation

Abstract published in English and French French title: Serpents élapidés (Squamata, Colubroidea) du Tertiaire moyen de Riversleigh, Nord de l’Australie : étapes précoces d’une radiation adaptive répandue sur un continent entierVertebral and cranial remains of elapid snakes have been collected from fossil assemblages at Riversleigh, north-west Queensland, Australia; most are Miocene but one may be late Oligocene and another as young as Pliocene. The oldest specimen (probably the oldest elapid yet known anywhere) is a vertebra that can be referred provisionally to the extant taxon Laticauda (Hydrophiinae, sensu Slowinski and Keogh, 2000), implying that the basal divergences among Australasian hydrophiine lineages had occurred by the early Miocene, in contrast to most previous estimates for the age of this geographically isolated adaptive radiation. Associated vertebrae and jaw elements from a Late Miocene deposit are described as Incongruelaps iteratus nov. gen. et sp., which has a unique combination of unusual derived characters otherwise found separately in several extant hydrophiine taxa that are only distantly related. Associated vertebrae from other sites, and two parietals from a possibly Pliocene deposit, suggest the presence of several other taxa distinct from extant forms, but the amount of material (and knowledge of variation in extant taxa) is currently insufficient to diagnose these forms. The Tertiary elapids of Riversleigh thus appear to be relatively diverse taxonomically, but low in abundance and, with one exception, not referable to extant taxa below the level of Hydrophiinae. This implies that the present diversity of hydrophiine elapids (31 recognized terrestrial genera, and approximately 16 marine) represents the result of substantial extinction as well as the "cone of increasing diversity" that could be inferred from phylogenetic studies on extant forms. © 2003 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.John D. Scanlon, Michael S. Y. Lee and Michael Archerhttp://www.elsevier.com/wps/find/journaldescription.cws_home/622310/description#descriptio

Monte Carlo feature selection and interdependency discovery in supervised classification

Applications of machine learning techniques in Life Sciences are the main applications forcing a paradigm shift in the way these techniques are used. Rather than obtaining the best possible supervised classifier, the Life Scientist needs to know which features contribute best to classifying distinct classes and what are the interdependencies between the features. To this end we significantly extend our earlier work [Dramiński et al. (2008)] that introduced an effective and reliable method for ranking features according to their importance for classification. We begin with adding a method for finding a cut-off between informative and non-informative fea- tures and then continue with a development of a methodology and an implementa- tion of a procedure for determining interdependencies between informative features. The reliability of our approach rests on multiple construction of tree classifiers. Essentially, each classifier is trained on a randomly chosen subset of the original data using only a fraction of all of the observed features. This approach is conceptually simple yet computer-intensive. The methodology is validated on a large and difficult task of modelling HIV-1 reverse transcriptase resistance to drugs which is a good example of the aforementioned paradigm shift. We construct a classifier but of the main interest is the identification of mutation points (i.e. features) and their combinations that model drug resistance.feature selection, interdependency discovery, MCFS-ID, biological sequence analysi