University of Los Andes

About: University of Los Andes is a education organization based out in Bogotá, Colombia. It is known for research contribution in the topics: Population & Large Hadron Collider. The organization has 17616 authors who have published 25555 publications receiving 413463 citations.

Analysing Amazonian forest productivity using a new individual and trait-based model (TFS v.1)

Abstract: . Repeated long-term censuses have revealed large-scale spatial patterns in Amazon basin forest structure and dynamism, with some forests in the west of the basin having up to a twice as high rate of aboveground biomass production and tree recruitment as forests in the east. Possible causes for this variation could be the climatic and edaphic gradients across the basin and/or the spatial distribution of tree species composition. To help understand causes of this variation a new individual-based model of tropical forest growth, designed to take full advantage of the forest census data available from the Amazonian Forest Inventory Network (RAINFOR), has been developed. The model allows for within-stand variations in tree size distribution and key functional traits and between-stand differences in climate and soil physical and chemical properties. It runs at the stand level with four functional traits – leaf dry mass per area (Ma), leaf nitrogen (NL) and phosphorus (PL) content and wood density (DW) varying from tree to tree – in a way that replicates the observed continua found within each stand. We first applied the model to validate canopy-level water fluxes at three eddy covariance flux measurement sites. For all three sites the canopy-level water fluxes were adequately simulated. We then applied the model at seven plots, where intensive measurements of carbon allocation are available. Tree-by-tree multi-annual growth rates generally agreed well with observations for small trees, but with deviations identified for larger trees. At the stand level, simulations at 40 plots were used to explore the influence of climate and soil nutrient availability on the gross (ΠG) and net (ΠN) primary production rates as well as the carbon use efficiency (CU). Simulated ΠG, ΠN and CU were not associated with temperature. On the other hand, all three measures of stand level productivity were positively related to both mean annual precipitation and soil nutrient status. Sensitivity studies showed a clear importance of an accurate parameterisation of within- and between-stand trait variability on the fidelity of model predictions. For example, when functional tree diversity was not included in the model (i.e. with just a single plant functional type with mean basin-wide trait values) the predictive ability of the model was reduced. This was also the case when basin-wide (as opposed to site-specific) trait distributions were applied within each stand. We conclude that models of tropical forest carbon, energy and water cycling should strive to accurately represent observed variations in functionally important traits across the range of relevant scales.

ISPCAN child abuse screening tools retrospective version (ICAST-R): Delphi study and field testing in seven countries

Abstract: OBJECTIVES: To gain consensus among an ethnically and linguistically diverse group of international child protection experts on the structure and content of a new survey tool for retrospective measurement of child abuse, and to determine the performance of the instrument through an international field trial with young adults. METHODS: The questionnaire was developed through focus group discussions with international experts, and then subjected to a Delphi study in two waves to determine the perceived importance and translatability of items. The resultant questionnaire was translated into six languages and field tested in seven countries with convenient samples of young adults aged 18-26 years (N=842). RESULTS: Child maltreatment experts from 28 countries provided input to questionnaire development. Satisfactory agreement on draft item inclusion and exclusion and the translatability of items was gained. The tool includes 15 primary questions about potentially abusive physical, sexual and emotional events, with follow-up questions about perpetrator characteristics, frequency of acts and periods in childhood when the recalled abuse occurred. The field test revealed lifetime prevalence per item usually exceeded 10% (11/15 items; range 2.1-49.5%). Internal consistency (Cronbach's alpha) was moderate to high for each of three item sub-sets (between .61 and .82) and the rates of missing data were low (less than 1.5% for 14 of 15 items). The great majority of respondents nominated either peer and/or adult perpetrators (between 82.3% and 98.2% depending upon the item), and among these, child/adolescent peers and non-family adults (including teachers for emotional and physical acts) were nominated often. CONCLUSIONS: The ICAST-R is based on consensus from international experts, translates clearly and has satisfactory properties for adoption as a survey tool to estimate prevalence and describe perpetrators and other contextual aspects of child abuse. PRACTICE IMPLICATIONS: This tool can be utilized in a broad range of cultures and languages and may contribute to improved research practice. Although the core items are limited to just 15 acts of maltreatment, if these behaviorally specific questions are adopted as key indicators and incorporated into comprehensive local, national or regional surveys, eventually there should be greater comparability in survey estimates. Language: en

The Plant Pathogen Phytophthora andina Emerged via Hybridization of an Unknown Phytophthora Species and the Irish Potato Famine Pathogen, P. infestans

Abstract: Emerging plant pathogens have largely been a consequence of the movement of pathogens to new geographic regions. Another documented mechanism for the emergence of plant pathogens is hybridization between individuals of different species or subspecies, which may allow rapid evolution and adaptation to new hosts or environments. Hybrid plant pathogens have traditionally been difficult to detect or confirm, but the increasing ease of cloning and sequencing PCR products now makes the identification of species that consistently have genes or alleles with phylogenetically divergent origins relatively straightforward. We investigated the genetic origin of Phytophthora andina, an increasingly common pathogen of Andean crops Solanum betaceum, S. muricatum, S. quitoense, and several wild Solanum spp. It has been hypothesized that P. andina is a hybrid between the potato late blight pathogen P. infestans and another Phytophthora species. We tested this hypothesis by cloning four nuclear loci to obtain haplotypes and using these loci to infer the phylogenetic relationships of P. andina to P. infestans and other related species. Sequencing of cloned PCR products in every case revealed two distinct haplotypes for each locus in P. andina, such that each isolate had one allele derived from a P. infestans parent and a second divergent allele derived from an unknown species that is closely related but distinct from P. infestans, P. mirabilis, and P. ipomoeae. To the best of our knowledge, the unknown parent has not yet been collected. We also observed sequence polymorphism among P. andina isolates at three of the four loci, many of which segregate between previously described P. andina clonal lineages. These results provide strong support that P. andina emerged via hybridization between P. infestans and another unknown Phytophthora species also belonging to Phytophthora clade 1c.

An application of topological degree to the periodic competing species problem

Abstract: We consider the Volterra-Lotka equations for two competing species in which the right-hand sides are periodic in time. Using topological degree, we show that conditions recently given by K. Gopalsamy, which imply the existence of a periodic solution with positive components, also imply the uniqueness and asymptotic stability of the solution. We also give optimal upper and lower bounds for the components of the solution.