University of Los Andes, Colombia
Cardenas J.C.,University of Los Andes, Colombia |
Mantilla C.,Institute for Advanced Study in Toulouse
Frontiers in Behavioral Neuroscience | Year: 2015
We report the results of a new public goods experiment with an intra-group cooperation dilemma and inter-group competition. In our design subjects receive information about their relative individual and group performance after each round with non-incentivized and then incentivized group competition. We found that, on average, individuals with low relative performance reduce their contributions to the public good, but groups with low performance increase theirs. With incentivized competition, where the relative ranking of the group increases individual payoffs, the reaction to relative performance is larger with individuals contributing more to the group; further, we observe that the variance of strategies decreases as individual and group rankings increase. These results offer new insights on how social comparison shapes similar reactions in games with different incentives for group performance and how competition and cooperation can influence each other. © 2015 Cárdenas and Mantilla.
Stevenson P.R.,University of Los Andes, Colombia
Biotropica | Year: 2011
Ateline monkeys, the largest primates in the Neotropics, may disperse more than one million seeds/km 2/d at sites where they are abundant, but it is unclear whether a reduction in their populations can alter plant diversity patterns. The species richness and composition of regenerating plants as a proxy of future plant communities were studied by comparing 16 sites with different ateline abundance in three countries in northwestern South America. A total of 3658 plots included 94,340 regenerating plants, which were assigned to species or morphospecies. Paired t-tests comparing sites in the same region but with different densities of atelines, and regression analyses showed a consistent positive relationship between ateline density and plant diversity. These results were due to the larger number of stems per area and higher evenness at sites with more atelines, suggesting higher recruitment rates for dispersed seeds. Differences were also found in plant composition, as canopy, endozoochorous, and medium seed size plants were consistently more abundant in sites with more ateline monkeys than in sites with less atelines. The findings of this study suggest that these primates play a key role in plant regeneration. In order to maintain the diversity and plant composition of tropical forests for future generations, conservation of these large frugivores and other key game species is imperative. © 2010 The Author(s). Journal compilation © 2010 by The Association for Tropical Biology and Conservation.
Kelkar N.G.,University of Los Andes, Colombia
Acta Physica Polonica B | Year: 2015
Even if the theoretical definition of an unstable state is straightforward, its experimental identification often depends on the method used in the analysis and extraction of data. A good example is the case of eta-mesic nuclei where strong hints of their existence led to about three decades of extensive theoretical and experimental searches. Considering the still undecided status of these states and the limitations in the understanding of the eta-nucleon as well as the eta-nucleus interaction, the present article tries to look back at some unresolved problems in the production mechanism and final state interaction of the eta mesons and nuclei. An unconventional perspective which provides a physical insight into the nature of the eta-nucleus interaction is also presented using quantum time concepts. © 2015 ACTA PHYSICA POLONICA B.
Rodriguez-R L.M.,University of Los Andes, Colombia
BMC microbiology | Year: 2012
The genus Xanthomonas comprises several plant pathogenic bacteria affecting a wide range of hosts. Despite the economic, industrial and biological importance of Xanthomonas, the classification and phylogenetic relationships within the genus are still under active debate. Some of the relationships between pathovars and species have not been thoroughly clarified, with old pathovars becoming new species. A change in the genus name has been recently suggested for Xanthomonas albilineans, an early branching species currently located in this genus, but a thorough phylogenomic reconstruction would aid in solving these and other discrepancies in this genus. Here we report the results of the genome-wide analysis of DNA sequences from 989 orthologous groups from 17 Xanthomonas spp. genomes available to date, representing all major lineages within the genus. The phylogenetic and computational analyses used in this study have been automated in a Perl package designated Unus, which provides a framework for phylogenomic analyses which can be applied to other datasets at the genomic level. Unus can also be easily incorporated into other phylogenomic pipelines. Our phylogeny agrees with previous phylogenetic topologies on the genus, but revealed that the genomes of Xanthomonas citri and Xanthomonas fuscans belong to the same species, and that of Xanthomonas albilineans is basal to the joint clade of Xanthomonas and Xylella fastidiosa. Genome reduction was identified in the species Xanthomonas vasicola in addition to the previously identified reduction in Xanthomonas albilineans. Lateral gene transfer was also observed in two gene clusters.
Reyes J.C.,University of Los Andes, Colombia |
Chopra A.K.,University of California at Berkeley
Earthquake Engineering and Structural Dynamics | Year: 2011
The modal pushover analysis (MPA) procedure, presently restricted to one horizontal component of ground motion, is extended to three-dimensional analysis of buildings-symmetric or unsymmetric in plan-subjected to two horizontal components of ground motion, simultaneously. Also presented is a variant of this method, called the practical modal pushover analysis (PMPA) procedure, which estimates seismic demands directly from the earthquake response (or design) spectrum. Its accuracy in estimating seismic demands for very tall buildings is evaluated, demonstrating that for nonlinear systems this procedure is almost as accurate as the response spectrum analysis procedure is for linear systems. Thus, for practical applications, the PMPA procedure offers an attractive alternative whereby seismic demands can be estimated directly from the (elastic) design spectrum, thus avoiding the complications of selecting and scaling ground motions for nonlinear response history analysis. © 2010 John Wiley & Sons, Ltd.
Stevenson P.R.,University of Los Andes, Colombia
Oecologia | Year: 2011
Seed dispersal is a mutualistic interaction in which frugivores gain nutrients and plants gain when seeds are transported to adequate places for establishment. However, this relationship is prone to deceit, for example, when frugivores spit-out seeds in the proximity of parental trees. Still, few hypotheses have offered explanations on why deceiving strategies are not widespread. In this study, I explore the importance of how difficult it is to mechanically separate the nutritious pulp from the seeds, as a factor that can explain the chance a seed has of being dispersed by woolly monkeys (Lagothrix lagothricha). I completed 1,440 h of focal animal follows during 2 years in order to quantify the chances plant species have of being dispersed. To do so, I evaluated the residuals from the relationship between the number of seeds manipulated and seeds dispersed by a population of woolly monkeys in Tinigua Park (Colombia). For 74 fruit species, I estimated how difficult it is to separate pulp from seeds as the time needed to separate the parts. An exponential model showed that this variable was able to predict 38% of the variation on dispersal probability, demonstrating that, when it is difficult to separate the pulp from the seeds, the probability of legitimate dispersal increases. However, when fruit parts were easy to separate, there was more variation in the outcome. My results suggest that many plants have evolved mechanisms (e. g., small seeds embedded in pulp, strong attachment, irregular seed surface, and thin pulp layer) that preclude deceit by frugivores. © 2011 Springer-Verlag.
Meesters R.J.,University of Los Andes, Colombia
Bioanalysis | Year: 2013
The quantitative analysis of free amino acids in human plasma has become an important and essential analysis parameter in different areas of life sciences. Free amino acid concentrations in human plasma samples are generally determined by means of GC or LC after chemical derivatization followed by UV, fluorescent or MS detection of the amino acid derivatives. Derivatization of free amino acids is done either pre-or post-column, and the amino acid derivatives obtained posess improved chromatographic behavior, increased detection sensitivity and selectivity compared with non-derivatized free amino acids. This work gives an overview of different chemical derivatization methods applied and their liquid separation techniques in bioanalytical assays for quantitative free amino acid analysis in human plasma samples. Important plasma preparation procedures, pre-and post-column derivatization, and different LC separation techniques are presented. © 2013 Future Science Ltd.
Van Hoof B.,University of Los Andes, Colombia
Journal of Cleaner Production | Year: 2014
Cleaner Production was heralded as a promising concept for improving the environmental performance; however it has largely focused on technical aspects, which has limited its expected implementation. This article integrates organizational studies into cleaner production. A Mexican Sustainable Supply Chain Programme designed to improve environmental performance of small- and medium-sized firms provided the empirical setting for analysis. Organizational learning in cleaner production was measured by accessing differential performance among suppliers in their implementation of cleaner production projects. The findings revealed how the organizational characteristics, such as supply sector, firm size, and type of supplier, influenced organizational learning of preventive environmental practices in small firms. The participating managers' characteristics had substantial influence on the learning levels within and among firms; managers who combined both technical and administrative backgrounds fostered catalyzed higher learning levels among their employees than those with single technical, or single administrative, profiles. The conclusions of this study highlight that organizational learning is a crucial element of successful implementation of cleaner production. The recommendations emphasized that a blended learning method and supply networks are valuable dissemination approaches for stimulating of the implementation of cleaner production through organizational learning in small firms in emerging markets. © 2013 Elsevier Ltd. All rights reserved.
Cardenas J.C.,University of Los Andes, Colombia
Environmental and Resource Economics | Year: 2011
Behavior in the local commons is usually embedded within a context of incentives, regulations and social norms for the group of resource users. Standard environmental economics has tended mostly to focus on the material incentives and regulations that transform the relative material costs and benefits of various/specific/certain actions. However, there exist behavioral aspects and social norms that affect how individuals value material and non-material incentives, and thus determine their decision to either cooperate or over-extract resources from a common-pool. This paper discusses the importance of social norms in shaping behavior in the commons through the lens of experiments-in particular, experiments conducted in the field with exactly those people who usually face these social dilemmas in their daily lives. Using a large sample of experimental sessions inclusive of around one thousand people, both villagers and students, I test some hypotheses about behavior in the commons, wherein regulations and social norms constrain people's choices. The results suggest that people evaluate several components of intrinsic and material motivations in deciding whether or not to cooperate. While responding in the expected direction to an imperfectly monitored fine for over extraction, the valuation of the private net cost of violating the regulation is not a sufficient explanation for participants' changes in behavior in the experiments. Even when violations have zero cost, people may react positively to an external regulator who issues a normative statement about a rule aimed at solving a particular social dilemma. © 2011 Springer Science+Business Media B.V.
Gonzalez-Caro S.,University of Los Andes, Colombia
PloS one | Year: 2012
Patterns of phylogenetic structure of assemblages are increasingly used to gain insight into the ecological and evolutionary processes involved in the assembly of co-occurring species. Metrics of phylogenetic structure can be sensitive to scaling issues and data availability. Here we empirically assess the sensitivity of four metrics of phylogenetic structure of assemblages to changes in (i) the source of data, (ii) the spatial grain at which assemblages are defined, and (iii) the definition of species pools using hummingbird (Trochilidae) assemblages along an elevational gradient in Colombia. We also discuss some of the implications in terms of the potential mechanisms driving these patterns. To explore how source of data influence phylogenetic structure we defined assemblages using three sources of data: field inventories, museum specimens, and range maps. Assemblages were defined at two spatial grains: coarse-grained (elevational bands of 800-m width) and fine-grained (1-km(2) plots). We used three different species pools: all species contained in assemblages, all species within half-degree quadrats, and all species either above or below 2000 m elevation. Metrics considering phylogenetic relationships among all species within assemblages showed phylogenetic clustering at high elevations and phylogenetic evenness in the lowlands, whereas those metrics considering only the closest co-occurring relatives showed the opposite trend. This result suggests that using multiple metrics of phylogenetic structure should provide greater insight into the mechanisms shaping assemblage structure. The source and spatial grain of data had important influences on estimates of both richness and phylogenetic structure. Metrics considering the co-occurrence of close relatives were particularly sensitive to changes in the spatial grain. Assemblages based on range maps included more species and showed less phylogenetic structure than assemblages based on museum or field inventories. Coarse-grained assemblages included more distantly related species and thus showed a more even phylogenetic structure than fine-grained assemblages. Our results emphasize the importance of carefully selecting the scale, source of data and metric used in analysis of the phylogenetic structure of assemblages.