1,721,338 research outputs found
Monitoring lichen diversity in Liguria: Critical notes on conservation planning
No full textA proper conservation plan for epiphytic lichens should take into account peculiar characteristics of these organisms and detailed informations about their distribution are needed. Bibliographic data and herbarium specimens are not sufficient to estimate rarity and vulnerability levels: they should be defined on the basis of probabilistic monitoring. In this work, some examples are provide to show how different methods for estimating Ligurian distribution of epiphytic lichens lead to different evaluations of conservation priorities. Further, main limits and advantages of these methods and urgent conservation strategies for lichens in Liguria are discussed
Indici di diversità funzionale nell'interpretazione dei dati di biomonitoraggio mediante licheni.
No full textThe influence of climate on the distribution of lichens: a case study in a borderline area (Liguria, NW Italy)
No full textThe purposes of this article are to quantify the relationship between epiphytic lichen distribution and macroclimatic variables in the study area and to provide a case study for evaluating the predictive role of epiphytic lichens as bioclimatic indicators. The study was carried out in the Liguria region (NWItaly), a small (5432 km2) borderline area, where phytoclimatic features range from the dry Mediterranean to the Alpine in a few kilometers. Epiphytic lichen diversity was sampled using a standardized protocol [Asta et al (2002) In: Nimis et al (eds) Monitoring with lichens: monitoring lichens. Kluwer, Dordrecht]. Abundance of the species in the sampling sites was related to macroclimatic parameters (yearly average temperature and rainfall) and non-parametric multivariate models were calculated to find significative relationships among predictive and response
variables. A total of 59 species showed highly significant relation with macroclimatic parameters. Four groups were selected, by means of a cluster analysis, related to four climatic niches (warm-humid, cold-humid, mesothermic-humid, warm-dry). Distributional pattern of the groups in the survey area showed a good correspondence with the bioclimatic units of Liguria region described by Nimis [(2003) Checklist of the Lichens of Italy 3.0. University of T r i e s t e , D e p t o f B i o l o g y . h t t p : / /
www.dbiodbs.univ.trieste.it. Cited 1 Jun 2006]. A significant subset of epiphytic lichen species in the study area have been proved to be efficient bioclimatic indicator and it is supposed to give good results to monitor climatic changes, in a long-term perspective
Variability of lichen diversity in a climatically heterogeneous area (Liguria, NW Italy)
No full textThe influence of environmental variables on epiphytic lichens in Liguria (NW Italy) was examined using two complementary approaches. Firstly, the variability of lichen vegetation in relation to environmental variables was investigated. Secondly, the variability of Lichen Biodiversity (LB) counts, used in biomonitoring studies, was analysed in relation to bioclimatic areas. Geomorphology strongly affects lichen vegetation. The coastal mountain ridge and the Tyrrhenian-Po valley watershed limit the distribution range of three different communities: a Parmelion community with a high frequency of coastal suboceanic species, a Parmelion community rich in oak wood species and the Parmelietum acetabuli association, situated beyond the Po Valley watershed. Substantial differences in the distribution of lichen communities related to a climatic gradient (from humid Mediterranean to dry sub-Mediterranean regions) are not matched by corresponding statistically significant differences in LB counts. More accurate studies are necessary to define homogeneous bioclimatic areas, in which LB values can be compared for biomonitoring purposes. © 2003 The British Lichen Society. Published by Elsevier Science Ltd. All rights reserved
New and interesting species to the Ligurian Lichen Flora
No full text27 species from various places in the Liguria region (Northern Italy) are reported. 13 of these are new to the region
Constrained Candecomp/Parafac via the Lasso
No full textThe Candecomp/Parafac (CP) model is a well-known tool for summarizing a three-way array by
extracting a limited number of components. Unfortunately, in some cases, the model suffers from the socalled
degeneracy, that is a solution with diverging and uninterpretable components. To avoid degeneracy,
orthogonality constraints are usually applied to one of the component matrices. This solves the problem
only from a technical point of view because the existence of orthogonal components underlying the data
is not guaranteed. For this purpose, we consider some variants of the CP model where the orthogonality
constraints are relaxed either by constraining only a pair, or a subset, of components or by stimulating
the CP solution to be possibly orthogonal. We theoretically clarify that only the latter approach, based
on the least absolute shrinkage and selection operator and named the CP-Lasso, is helpful in solving the
degeneracy problem. The results of the application of CP-Lasso on simulated and real life data show its
effectiveness
Candecomp/Parafac with ridge regularization
No full textThe Candecomp/Parafac (CP) model decomposes a three-way array through components. In the practical use of CP, degeneracymay arise, i.e. CP parametermatriceswith diverging, highly collinear and uninterpretable components. A frequently applied remedy to degeneracy is to fit a CPmodelwith orthogonality constraints on one of the componentmatrices. However, this does not guarantee that the so-extracted componentswell resemble the true ones because the occurrence of degeneracy does not imply the orthogonality of the true components. For this reason, a new CP method involving a particular ridge regularization term (hence, called CP-Ridge) is introduced. It solves the degeneracy problem admitting an overall maximum level of collinearity among the components. A simulation experiment is performed in order to illustrate the properties of CP-Ridge and to compare its performance with those of some other competitors available in the literature
Ridondanza funzionale nelle comunità licheniche in ambienti Mediterranei: relazioni spaziali e importanza del substrato.
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