Search results for "complex"
showing 10 items of 5889 documents
The origin of two cryptic species of African desert jerboas (Dipodidae: Jaculus)
2011
The desert biota is exposed to extreme and variable conditions that shape its evolution and diversification processes. In this respect, the Jaculus jerboas have gained the attention of researchers as a result of their broad Saharan–Arabian distribution and their high and unexplained, morphological, anatomical, and molecular variation. In the present study, mitochondrial and nuclear genealogies where used to confirm monophyly of two cryptic species: Jaculus jaculus and Jaculus deserti. The reconstructed demography showed that the evolutionary histories of the species are markedly different and that the expansion into North-West Africa by J. deserti was more recent than that of J. jaculus. Th…
Multiple morphological characters needed for field identification of cryptic long‐eared bat species around the Swiss Alps
2010
The identification of cryptic species may significantly change our view about their distribution, abundance, ecology and therefore conservation status. In the European Alps, molecular studies have revealed the existence of three sibling species of plecotine bats Plecotus auritus, Plecotus austriacus and, very recently, Plecotus macrobullaris. Knowledge of the ecological niche partitioning of cryptic species is a requisite to develop sound conservation policies. Yet, this requests the development of unambiguous identification methods easily applicable in the field. This study investigates the reliability of several morphological methods used for species recognition and proposes a new identif…
'Niche Selection' and the evolution of a complex behavior in a changing environment--a simulation.
2000
One of the key problems in theoretical biology is the identification of the mechanisms underlying the evolution of complexity. This paper suggests that some difficulties in current models could be avoided by taking account of “niche selection” as proposed by Waddington [21] and subsequent authors [2]. Computer simulations, in which an evolving population of artificial organisms “selects” the niche(s) that maximize their fitness, are compared with a Control Model in which “Niche Selection” is absent. In the simulations the Niche Selection Model consistently produced a greater number of “fit” organisms than the Control Model; although the Niche Selection Model tended, in general, to produce o…
Soil microbial biomass and bacterial diversity in southern European regions vulnerable to desertification
2022
Abstract Soil functionality is strongly dependent on the soil microbiota, which in turn is affected by soil quality and climate. Among global change factors, desertification is the most threatening ecosystem change affecting southern Europe, but the effects on the soil microbiota are largely unknown. In this study, we investigated soil microbial biomass and bacterial diversity in regions of southern European countries (Spain, Portugal and Italy), most under desertification risk, and related to key soil chemical-physical indicators and land use. Soil microbial biomass was positively related, to soil organic carbon (SOC) but bacterial diversity was negatively correlated with it. pH was the mo…
A study of chemical characteristics of soil in relation to street trees status in Riga (Latvia)
2013
Abstract The chemical composition of soil and appropriate supply of nutrients are very important factors for normal plant growth and development. Lime tree ( Tilia x vulgaris H.), is a popular tree species used for urban landscaping in Europe. However, there is little information on the chemical element concentrations available to and recommended for T. x vulgaris in urban soils. The objectives of this study were: (1) to investigate the amount of nutrients, de-icing salts and heavy metals available for uptake by trees in the city centre on a seasonal scale; and (2) to assess the relationship between the vitality of T. x vulgaris and soil chemistry. The research was carried out in five stree…
Smithian Growth and Complexity
2016
In this paper we argue that Adam Smith’s theory of division and labor and economic growth, in particular through the developments of Alfred Marshall, Allyn Young and Nicholas Kaldor, has characteristics that allow to classify it in the realm of complexity economics. We support this claim by a historical reconstruction of the Smithian growth theory highlighting the characteristics that we show also characterize complex systems. We compare this perspective with the one developed by the traditional economic approach, rooted in general equilibrium, and describe a simple alternative model
The dynamic interdependence in the demand of primary and emergency secondary care: A hidden Markov approach
2021
This paper develops an extension of the class of finite mixture models for longitudinal count data to the bivariate case by using a trivariate reduction technique and a hidden Markov chain approach. The model allows for disentangling unobservable time-varying heterogeneity from the dynamic effect of utilisation of primary and secondary care and measuring their potential substitution effect. Three points of supports adequately describe the distribution of the latent states suggesting the existence of three profiles of low, medium and high users who shows persistency in their behaviour, but not permanence as some switch to their neighbour's profile.
Regression with imputed covariates: A generalized missing-indicator approach
2011
A common problem in applied regression analysis is that covariate values may be missing for some observations but imputed values may be available. This situation generates a trade-off between bias and precision: the complete cases are often disarmingly few, but replacing the missing observations with the imputed values to gain precision may lead to bias. In this paper, we formalize this trade-off by showing that one can augment the regression model with a set of auxiliary variables so as to obtain, under weak assumptions about the imputations, the same unbiased estimator of the parameters of interest as complete-case analysis. Given this augmented model, the bias-precision trade-off may the…
Do robots complement or substitute for older workers?
2021
Abstract The impact of robotization on labor market outcomes has been recently empirically investigated along several directions, including employment, wages and labor productivity. This work contributes to this literature by looking for heterogeneous effects of robots on the workforce, analyzed by age cohorts. Relying on a panel of data from IFR (2019) and EU KLEMS (2009) over the years 1994–2005, we find consistent evidence of higher complementarity between robots and older workers (hours worked by employees aged 50 and over), and a greater substitutability among robots and younger cohorts of the labor market. These findings are robust to age group disaggregation and specific capital pric…
Complexity in project co-creation of knowledge for innovation
2020
The European Union (EU) promotes collaboration across functions and borders in its funded innovation projects, which are seen as complex collaboration to co-create knowledge. This requires the engagement of multiple stakeholders throughout the duration of the project. To probe complexity in EU-funded innovation projects the research question is: How does complexity affect the co-creation of knowledge in innovation projects, according to project participants? The data for this study was collected from project experts in the form of short narratives, using a questionnaire based on the elements of complexity of Mitleton-Kelly (2003). The results indicate that complexity characterises the co-cr…