RESUMEN
It is not known how school closure affected child maltreatment. We conducted a retrospective cohort, linear mixed-models study of 133 counties (comprising 8,582,479 children) in Virginia between 2018 and 2021. Exposure was the opening of schools at least 2 days a week. Outcomes were referrals and incidence of child maltreatment reported to the Department of Social Services. In 2020-2021, there were descriptively more referrals (in-person: 50.9 per 10,000 [95% CI: 47.9, 54.0]; virtual: 45.8 per 10,000 [95% CI: 40.7, 50.9]) and incidence (in-person: 3.7 per 10,000 [95% CI: 3.3, 4.2]; virtual: 2.9 per 10,000 [95% CI: 2.3, 3.5]) of child maltreatment in counties with in-person schooling, though these differences did not reach statistical significance. The referral rate variations (between pandemic and pre-pandemic eras) of counties with in-person schooling was significantly greater than rate changes in counties with virtual schooling during the summer period. There were no differences in incidence in any quarter. Higher poverty within a county was associated with both higher referrals and incidence. Our findings suggest that child maltreatment is driven primarily by underlying differences in counties (namely, poverty) rather than the type of schooling children receive.
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COVID-19 , Maltrato a los Niños , Instituciones Académicas , Humanos , Maltrato a los Niños/estadística & datos numéricos , COVID-19/epidemiología , COVID-19/prevención & control , Niño , Estudios Retrospectivos , Virginia/epidemiología , Femenino , Masculino , Incidencia , Preescolar , Adolescente , Derivación y Consulta/estadística & datos numéricosRESUMEN
The growth and survival of individual trees determine the physical structure of a forest with important consequences for forest function. However, given the diversity of tree species and forest biomes, quantifying the multitude of demographic strategies within and across forests and the way that they translate into forest structure and function remains a significant challenge. Here, we quantify the demographic rates of 1961 tree species from temperate and tropical forests and evaluate how demographic diversity (DD) and demographic composition (DC) differ across forests, and how these differences in demography relate to species richness, aboveground biomass (AGB), and carbon residence time. We find wide variation in DD and DC across forest plots, patterns that are not explained by species richness or climate variables alone. There is no evidence that DD has an effect on either AGB or carbon residence time. Rather, the DC of forests, specifically the relative abundance of large statured species, predicted both biomass and carbon residence time. Our results demonstrate the distinct DCs of globally distributed forests, reflecting biogeography, recent history, and current plot conditions. Linking the DC of forests to resilience or vulnerability to climate change, will improve the precision and accuracy of predictions of future forest composition, structure, and function.
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Cambio Climático , Clima Tropical , Biomasa , Demografía , EcosistemaRESUMEN
OBJECTIVE: To estimate the impact of the PediBIRN (Pediatric Brain Injury Research Network) 4-variable clinical decision rule (CDR) on abuse evaluations and missed abusive head trauma in pediatric intensive care settings. STUDY DESIGN: This was a cluster randomized trial. Participants included 8 pediatric intensive care units (PICUs) in US academic medical centers; PICU and child abuse physicians; and consecutive patients with acute head injures <3 years (n = 183 and n = 237, intervention vs control). PICUs were stratified by patient volumes, pair-matched, and randomized equally to intervention or control conditions. Randomization was concealed from the biostatistician. Physician-directed, cluster-level interventions included initial and booster training, access to an abusive head trauma probability calculator, and information sessions. Outcomes included "higher risk" patients evaluated thoroughly for abuse (with skeletal survey and retinal examination), potential cases of missed abusive head trauma (patients lacking either evaluation), and estimates of missed abusive head trauma (among potential cases). Group comparisons were performed using generalized linear mixed-effects models. RESULTS: Intervention physicians evaluated a greater proportion of higher risk patients thoroughly (81% vs 73%, P = .11) and had fewer potential cases of missed abusive head trauma (21% vs 32%, P = .05), although estimated cases of missed abusive head trauma did not differ (7% vs 13%, P = .22). From baseline (in previous studies) to trial, the change in higher risk patients evaluated thoroughly (67%â81% vs 78%â73%, P = .01), and potential cases of missed abusive head trauma (40%â21% vs 29%â32%, P = .003), diverged significantly. We did not identify a significant divergence in the number of estimated cases of missed abusive head trauma (15%â7% vs 11%â13%, P = .22). CONCLUSIONS: PediBIRN-4 CDR application facilitated changes in abuse evaluations that reduced potential cases of missed abusive head trauma in PICU settings. TRIAL REGISTRATION: ClinicalTrials.gov: NCT03162354.
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Maltrato a los Niños , Traumatismos Craneocerebrales , Niño , Maltrato a los Niños/diagnóstico , Traumatismos Craneocerebrales/diagnóstico , Cuidados Críticos , Humanos , Unidades de Cuidado Intensivo Pediátrico , Tamizaje MasivoRESUMEN
Resource allocation within trees is a zero-sum game. Unavoidable trade-offs dictate that allocation to growth-promoting functions curtails other functions, generating a gradient of investment in growth versus survival along which tree species align, known as the interspecific growth-mortality trade-off. This paradigm is widely accepted but not well established. Using demographic data for 1,111 tree species across ten tropical forests, we tested the generality of the growth-mortality trade-off and evaluated its underlying drivers using two species-specific parameters describing resource allocation strategies: tolerance of resource limitation and responsiveness of allocation to resource access. Globally, a canonical growth-mortality trade-off emerged, but the trade-off was strongly observed only in less disturbance-prone forests, which contained diverse resource allocation strategies. Only half of disturbance-prone forests, which lacked tolerant species, exhibited the trade-off. Supported by a theoretical model, our findings raise questions about whether the growth-mortality trade-off is a universally applicable organizing framework for understanding tropical forest community structure.
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Bosques , Clima Tropical , Especificidad de la Especie , ÁrbolesRESUMEN
Forest biomass is an essential indicator for monitoring the Earth's ecosystems and climate. It is a critical input to greenhouse gas accounting, estimation of carbon losses and forest degradation, assessment of renewable energy potential, and for developing climate change mitigation policies such as REDD+, among others. Wall-to-wall mapping of aboveground biomass (AGB) is now possible with satellite remote sensing (RS). However, RS methods require extant, up-to-date, reliable, representative and comparable in situ data for calibration and validation. Here, we present the Forest Observation System (FOS) initiative, an international cooperation to establish and maintain a global in situ forest biomass database. AGB and canopy height estimates with their associated uncertainties are derived at a 0.25 ha scale from field measurements made in permanent research plots across the world's forests. All plot estimates are geolocated and have a size that allows for direct comparison with many RS measurements. The FOS offers the potential to improve the accuracy of RS-based biomass products while developing new synergies between the RS and ground-based ecosystem research communities.
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Biomasa , Bosques , Tecnología de Sensores Remotos , Conservación de los Recursos Naturales , Monitoreo del Ambiente/métodosRESUMEN
CONTEXT: Pediatric burn patients warrant thorough evaluation because a sizeable proportion of pediatric burns are nonaccidental. DESIGN: A multidisciplinary method involving an internal child protection team (CPT) was developed and used to identify suspected nonaccidental pediatric burns in all pediatric burn patients 5 years of age or younger who were evaluated by the CPT and social workers at our institution over a 55-month period. RESULTS: We identified 343 cases for review that fit our age criteria, 6 of which we identified as cases of suspected abuse or neglect. On average, these patients were younger, suffered greater total body surface area burns (TBSA), and required a longer length of stay in the hospital than the total population. We have not had readmissions for repeat nonaccidental pediatric burn injuries in this group of patients since this model was implemented. CONCLUSIONS: Our multidisciplinary method might provide a more consistent and reliable method for identifying cases of suspected abuse.
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Quemaduras/etiología , Maltrato a los Niños/diagnóstico , Protección a la Infancia , Modelos Teóricos , Accidentes , Factores de Edad , Quemaduras/patología , Servicios de Protección Infantil , Preescolar , Hospitalización , Humanos , Lactante , Recién Nacido , Pediatría , Mejoramiento de la Calidad , Índice de Severidad de la Enfermedad , Trabajadores SocialesRESUMEN
OBJECTIVE: To characterize racial and ethnic disparities in the evaluation and reporting of suspected abusive head trauma (AHT) across the 18 participating sites of the Pediatric Brain Injury Research Network (PediBIRN). We hypothesized that such disparities would be confirmed at multiple sites and occur more frequently in patients with a lower risk for AHT. STUDY DESIGN: Aggregate and site-specific analysis of the cross-sectional PediBIRN dataset, comparing AHT evaluation and reporting frequencies in subpopulations of white/non-Hispanic and minority race/ethnicity patients with lower vs higher risk for AHT. RESULTS: In the PediBIRN study sample of 500 young, acutely head-injured patients hospitalized for intensive care, minority race/ethnicity patients (n = 229) were more frequently evaluated (P < .001; aOR, 2.2) and reported (P = .001; aOR, 1.9) for suspected AHT than white/non-Hispanic patients (n = 271). These disparities occurred almost exclusively in lower risk patients, including those ultimately categorized as non-AHT (P = .001 [aOR, 2.4] and P = .003 [aOR, 2.1]) or with an estimated AHT probability of ≤25% (P <.001 [aOR, 4.1] and P <.001 [aOR, 2.8]). Similar site-specific analyses revealed that these results reflected more extreme disparities at only 2 of 18 sites, and were not explained by local confounders. CONCLUSION: Significant race/ethnicity-based disparities in AHT evaluation and reporting were observed at only 2 of 18 sites and occurred almost exclusively in lower risk patients. In the absence of local confounders, these disparities likely represent the impact of local physicians' implicit bias.
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Maltrato a los Niños/etnología , Traumatismos Craneocerebrales/etnología , Etnicidad/estadística & datos numéricos , Disparidades en Atención de Salud/etnología , Notificación Obligatoria , Población Blanca/estadística & datos numéricos , Sesgo , Niño , Maltrato a los Niños/diagnóstico , Maltrato a los Niños/terapia , Preescolar , Traumatismos Craneocerebrales/diagnóstico , Traumatismos Craneocerebrales/terapia , Cuidados Críticos , Hospitalización , Humanos , Lactante , Recién Nacido , Grupos Minoritarios/estadística & datos numéricos , Estados UnidosRESUMEN
BACKGROUND: Intramuscular (IM) ziprasidone is often used to manage acute agitation. Limited data exist on the pediatric dosing of ziprasidone in the emergency department (ED). OBJECTIVE: To characterize the mg/kg dosing differences between pediatric ED patients who respond to an initial dose of ziprasidone versus patients who do not. METHODS: This was a retrospective, observational study of 5- to 18-year-old patients who were treated with IM ziprasidone in the pediatric ED from 2007 to 2015. Medical records were reviewed to determine demographic and clinical information. Patients were deemed responders to ziprasidone if they required no additional rescue medication for acute agitation within 30 minutes of the initial dose. RESULTS: Forty children received 50 doses of IM ziprasidone. Twenty-seven (68%) patients responded to the initial ziprasidone dose, requiring no further medication intervention for their acute agitation. Responders were given a mean initial dose of 0.19 ± 0.1 mg/kg, while nonresponders were given an initial mean dose of 0.13 ± 0.06 mg/kg ( P = .03). CONCLUSION: A significant dose difference exists between patients who required only one initial dose of ziprasidone compared to those who required additional medication. As a result, an initial dose of 0.2 mg/kg of IM ziprasidone may be considered when managing acutely agitated pediatric patients in the ED.
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Antipsicóticos/administración & dosificación , Servicio de Urgencia en Hospital , Piperazinas/administración & dosificación , Agitación Psicomotora/tratamiento farmacológico , Tiazoles/administración & dosificación , Adolescente , Niño , Relación Dosis-Respuesta a Droga , Femenino , Humanos , Inyecciones Intramusculares , Masculino , Agitación Psicomotora/diagnóstico , Agitación Psicomotora/psicología , Estudios RetrospectivosRESUMEN
Global change is impacting forests worldwide, threatening biodiversity and ecosystem services including climate regulation. Understanding how forests respond is critical to forest conservation and climate protection. This review describes an international network of 59 long-term forest dynamics research sites (CTFS-ForestGEO) useful for characterizing forest responses to global change. Within very large plots (median size 25 ha), all stems ≥ 1 cm diameter are identified to species, mapped, and regularly recensused according to standardized protocols. CTFS-ForestGEO spans 25 °S-61 °N latitude, is generally representative of the range of bioclimatic, edaphic, and topographic conditions experienced by forests worldwide, and is the only forest monitoring network that applies a standardized protocol to each of the world's major forest biomes. Supplementary standardized measurements at subsets of the sites provide additional information on plants, animals, and ecosystem and environmental variables. CTFS-ForestGEO sites are experiencing multifaceted anthropogenic global change pressures including warming (average 0.61 °C), changes in precipitation (up to ± 30% change), atmospheric deposition of nitrogen and sulfur compounds (up to 3.8 g N m(-2) yr(-1) and 3.1 g S m(-2) yr(-1)), and forest fragmentation in the surrounding landscape (up to 88% reduced tree cover within 5 km). The broad suite of measurements made at CTFS-ForestGEO sites makes it possible to investigate the complex ways in which global change is impacting forest dynamics. Ongoing research across the CTFS-ForestGEO network is yielding insights into how and why the forests are changing, and continued monitoring will provide vital contributions to understanding worldwide forest diversity and dynamics in an era of global change.
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Cambio Climático , Conservación de los Recursos Naturales , Monitoreo del Ambiente , BosquesRESUMEN
BACKGROUND AND OBJECTIVE: To reduce missed cases of pediatric abusive head trauma (AHT), Pediatric Brain Injury Research Network investigators derived a 4-variable AHT clinical prediction rule (CPR) with sensitivity of .96. Our objective was to validate the screening performance of this AHT CPR in a new, equivalent patient population. METHODS: We conducted a prospective, multicenter, observational, cross-sectional study. Applying the same inclusion criteria, definitional criteria for AHT, and methods used in the completed derivation study, Pediatric Brain Injury Research Network investigators captured complete clinical, historical, and radiologic data on 291 acutely head-injured children <3 years of age admitted to PICUs at 14 participating sites, sorted them into comparison groups of abusive and nonabusive head trauma, and measured the screening performance of the AHT CPR. RESULTS: In this new patient population, the 4-variable AHT CPR demonstrated sensitivity of .96, specificity of .46, positive predictive value of .55, negative predictive value of .93, positive likelihood ratio of 1.67, and negative likelihood ratio of 0.09. Secondary analysis revealed that the AHT CPR identified 98% of study patients who were ultimately diagnosed with AHT. CONCLUSIONS: Four readily available variables (acute respiratory compromise before admission; bruising of the torso, ears, or neck; bilateral or interhemispheric subdural hemorrhages or collections; and any skull fractures other than an isolated, unilateral, nondiastatic, linear, parietal fracture) identify AHT with high sensitivity in young, acutely head-injured children admitted to the PICU.
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Maltrato a los Niños/diagnóstico , Maltrato a los Niños/estadística & datos numéricos , Traumatismos Craneocerebrales/diagnóstico , Traumatismos Craneocerebrales/epidemiología , Técnicas de Apoyo para la Decisión , Preescolar , Estudios Transversales , Femenino , Humanos , Lactante , Recién Nacido , Unidades de Cuidado Intensivo Pediátrico/estadística & datos numéricos , Masculino , Tamizaje Masivo/estadística & datos numéricos , Admisión del Paciente/estadística & datos numéricos , Estudios Prospectivos , Sensibilidad y Especificidad , Estados UnidosRESUMEN
OBJECTIVE: Teen dating violence (TDV) is associated with multiple sequelae including substance use. The objective of this study was to determine the prevalence and association between levels of dating violence and substance use among urban adolescents presenting at a pediatric emergency department (ED). METHODS: As part of standard practice, 282 adolescents were screened for relationship status, producing 135 dating violence screens. Scales from the Revised Conflict Tactics Scale and the Youth Risk Behavior Survey were used to capture variables of interest. Logistic regression was performed to test the influence of levels of dating violence on substance use, while controlling for gender, race, age, sexual orientation, and psychiatric symptoms. RESULTS: Over one-quarter of those teens (27.3%) within a current relationship reported experiencing any dating violence, 26.1% experienced psychological violence, and 11.9% experienced physical violence. Teens experiencing psychological violence were at twice the risk for any substance use (alcohol, marijuana, and tobacco use) and specifically for alcohol and marijuana, whereas no increased risk was found for teens experiencing physical violence. CONCLUSIONS: This study contributes to the understanding of TDV within the context of high-risk, urban adolescents presenting at a pediatric ED. Identifying levels of TDV and understanding the association with substance use can provide an important foundation for prevention and early intervention for urban youth.
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Conducta del Adolescente , Relaciones Interpersonales , Conducta Sexual/estadística & datos numéricos , Trastornos Relacionados con Sustancias/epidemiología , Población Urbana/estadística & datos numéricos , Violencia/estadística & datos numéricos , Adolescente , Niño , Servicio de Urgencia en Hospital/estadística & datos numéricos , Femenino , Humanos , MasculinoRESUMEN
BACKGROUND: Currently there are few data that brief violence intervention (BVI) and community case management services (CCMS) are effective for trauma patients admitted for interpersonal violence in terms of recidivism, service utilization, or alcohol abuse. The objective of this study is to assess outcomes for a cohort of young trauma patients in a prospective, randomized trial comparing BVI with BVI + CCMS. METHODS: Intentionally injured patients, aged 10 years to 24 years, admitted to a Level I trauma center were randomized to receive a brief in-hospital psychoeducational violence intervention alone (Group I) or in combination with a 6 months wraparound CCMS (Group II) that included vocational, employment, educational, housing, mental health, and recreational assistance. Recidivism, alcohol use, and hospital and community service utilization were assessed at 6 weeks (6W) and 6 months (6M). RESULTS: Seventy-five of 376 eligible injured patients were randomized into Group I and II. The two groups had similar demographics, injuries, and clinical outcomes. After discharge, percent clinic visits maintained was 57% in both the groups. Group II showed better hospital service utilization, CMS, and risk factor reduction at 6W and 6M. One patient in each group sustained a reinjury at 6M. CONCLUSIONS: In-hospital BVI with community wraparound case management interventions can improve hospital and community service utilization both short- and long-term for high-risk injured patients. Longer follow-up is needed to show sustained reduction.
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Manejo de Caso/organización & administración , Bienestar Social , Centros Traumatológicos , Violencia/prevención & control , Heridas y Lesiones/prevención & control , Adolescente , Adulto , Niño , Femenino , Estudios de Seguimiento , Humanos , Incidencia , Masculino , Estudios Prospectivos , Medición de Riesgo , Factores de Riesgo , Violencia/estadística & datos numéricos , Virginia/epidemiología , Heridas y Lesiones/epidemiología , Heridas y Lesiones/etiología , Adulto JovenRESUMEN
Long-term studies have revealed that the structure and dynamics of many tropical forests are changing, but the causes and consequences of these changes remain debated. To learn more about the forces driving changes within tropical forests, we investigated shifts in tree species composition over the past 25 years within the 50-ha Forest Dynamics Plot on Barro Colorado Island (BCI), Panama, and examined how observed patterns relate to predictions of (1) random population fluctuations, (2) carbon fertilization, (3) succession from past disturbance, (4) recovery from an extreme El Niño drought at the start of the study period, and (5) long-term climate change. We found that there have been consistent and directional changes in the tree species composition. These shifts have led to increased relative representations of drought-tolerant species as determined by the species' occurrence both across a gradient of soil moisture within BCI and across a wider precipitation gradient from a dry forest near the Pacific coast of Panama to a wet forest near its Caribbean coast. These nonrandom changes cannot be explained by stochastic fluctuations or carbon fertilization. They may be the legacy of the El Niño drought, or alternatively, potentially reflect increased aridity due to long-term climate change. By investigating compositional changes, we increased not only our understanding of the ecology of tropical forests and their responses to large-scale disturbances, but also our ability to predict how future global change will impact some of the critical services provided by these important ecosystems.
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Ecosistema , Árboles , Clima Tropical , El Niño Oscilación del Sur , Geografía , Modelos Biológicos , Panamá , Especificidad de la Especie , Factores de TiempoRESUMEN
In Amazonian tropical forests, recent studies have reported increases in aboveground biomass and in primary productivity, as well as shifts in plant species composition favouring fast-growing species over slow-growing ones. This pervasive alteration of mature tropical forests was attributed to global environmental change, such as an increase in atmospheric CO2 concentration, nutrient deposition, temperature, drought frequency, and/or irradiance. We used standardized, repeated measurements of over 2 million trees in ten large (16-52 ha each) forest plots on three continents to evaluate the generality of these findings across tropical forests. Aboveground biomass increased at seven of our ten plots, significantly so at four plots, and showed a large decrease at a single plot. Carbon accumulation pooled across sites was significant (+0.24 MgC ha(-1) y(-1), 95% confidence intervals [0.07, 0.39] MgC ha(-1) y(-1)), but lower than reported previously for Amazonia. At three sites for which we had data for multiple census intervals, we found no concerted increase in biomass gain, in conflict with the increased productivity hypothesis. Over all ten plots, the fastest-growing quartile of species gained biomass (+0.33 [0.09, 0.55] % y(-1)) compared with the tree community as a whole (+0.15 % y(-1)); however, this significant trend was due to a single plot. Biomass of slow-growing species increased significantly when calculated over all plots (+0.21 [0.02, 0.37] % y(-1)), and in half of our plots when calculated individually. Our results do not support the hypothesis that fast-growing species are consistently increasing in dominance in tropical tree communities. Instead, they suggest that our plots may be simultaneously recovering from past disturbances and affected by changes in resource availability. More long-term studies are necessary to clarify the contribution of global change to the functioning of tropical forests.
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Árboles/fisiología , Clima Tropical , Biodiversidad , Evolución Biológica , Biomasa , Ecosistema , Ambiente , Monitoreo del Ambiente , Agricultura Forestal , Malasia , Panamá , Puerto Rico , Sri Lanka , Tailandia , Factores de Tiempo , Árboles/crecimiento & desarrolloRESUMEN
OBJECTIVE: To determine whether a transport team composed of advanced practice nurses could function as effectively as a physician-nurse team, as measured by patient outcome. DESIGN: Observational cohort study. SETTING: The interfacility transport team at a tertiary care children's hospital. PATIENTS AND OTHER PARTICIPANTS: Fourteen transport nurses and 539 patients. METHODS: A transport team was studied during a previously planned change in composition from a physician-nurse team to a nurse-nurse team. Data were recorded by transport nurses and by subsequent review of the medical record during two 4-month periods, 1 before and 1 after the team change. Pediatric risk of mortality scores (a marker for degree of illness) were assigned for the periods before, during, and after transport. Transport time intervals, demographic data, and patient outcomes were also recorded. Data were assessed using frequency tables for discrete variables, as well as mean and standard deviation for continuous variables. For identification of group differences, chi test was used. MAIN OUTCOME MEASURES: Mortality, transport-related morbidity, overall transport times and interval times, and outcome of procedures performed by transport nurses. RESULTS: Five hundred thirty-nine data sheets were received: 228 before (group 1) and 311 after (group 2) the team change. Physicians attended 128 (56.1%) group 1 transports and 15 (4.82%) group 2 transports. There were no significant differences in mean pediatric risk of mortality scores between group 1 and group 2 patients. Mortality was equivalent. Group 2 transport times were significantly shorter than group 1 times. Transport nurses performed 8 intubations; all were successful. CONCLUSIONS: Outcomes for the 2 types of teams were equivalent. Nonphysician teams responded more quickly and spent less time at the referring facility.
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Grupo de Atención al Paciente/organización & administración , Gestión de la Calidad Total , Transporte de Pacientes/organización & administración , Adulto , Preescolar , Estudios de Cohortes , Femenino , Hospitales Pediátricos , Humanos , Lactante , Recién Nacido , Unidades de Cuidado Intensivo Neonatal , Unidades de Cuidado Intensivo Pediátrico , Masculino , Enfermeras Clínicas , Rol de la Enfermera , Grupo de Enfermería/organización & administración , Enfermería Pediátrica , Rol del Médico , Estados UnidosRESUMEN
The importance of niche vs. neutral assembly mechanisms in structuring tropical tree communities remains an important unsettled question in community ecology [Bell G (2005) Ecology 86:1757-1770]. There is ample evidence that species distributions are determined by soils and habitat factors at landscape (<10(4) km(2)) and regional scales. At local scales (<1 km(2)), however, habitat factors and species distributions show comparable spatial aggregation, making it difficult to disentangle the importance of niche and dispersal processes. In this article, we test soil resource-based niche assembly at a local scale, using species and soil nutrient distributions obtained at high spatial resolution in three diverse neotropical forest plots in Colombia (La Planada), Ecuador (Yasuni), and Panama (Barro Colorado Island). Using spatial distribution maps of >0.5 million individual trees of 1,400 species and 10 essential plant nutrients, we used Monte Carlo simulations of species distributions to test plant-soil associations against null expectations based on dispersal assembly. We found that the spatial distributions of 36-51% of tree species at these sites show strong associations to soil nutrient distributions. Neutral dispersal assembly cannot account for these plant-soil associations or the observed niche breadths of these species. These results indicate that belowground resource availability plays an important role in the assembly of tropical tree communities at local scales and provide the basis for future investigations on the mechanisms of resource competition among tropical tree species.
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Suelo/análisis , Árboles/fisiología , Clima Tropical , Ecosistema , Concentración de Iones de Hidrógeno , Dinámica Poblacional , América del SurRESUMEN
In large samples of trees > or = 1 cm dbh (more than 1 million trees and 3000 species), in six lowland tropical forests on three continents, we assigned species with >30 individuals to one of six classes of stature at maturity (SAM). We then compared the proportional representation of understory trees (1-2 cm dbh) among these classes. The understory of the three Asian sites was predominantly composed of the saplings of large-canopy trees whereas the African and American sites were more richly stocked with trees of the smaller SAM classes. Differences in class representation were related to taxonomic families that were present exclusively in one continent or another. Families found in the Asian plots but not in the American plot (e.g., Dipterocarpaceae, Fagaceae) were predominantly species of the largest SAM classes, whereas families exclusive to the American plots (e.g., Melastomataceae sensu stricto, Piperaceae, and Malvaceae [Bombacacoidea]) were predominantly species of small classes. The African plot was similar to Asia in the absence of those American families rich in understory species, while similar to America in lacking the Asian families rich in canopy species. The numerous understory species of Africa were chiefly derived from families shared with Asia and/or America. The ratio of saplings (1-2 cm dbh) to conspecific canopy trees (>40 cm dbh) was lower in American plots than in the Asian plots. Possible explanations for these differences include phenology, moisture and soil fertility regimes, phyletic constraints, and the role of early successional plants in forest development. These results demonstrate that tropical forests that appear similar in tree number, basal area, and the family taxonomy of canopy trees nonetheless differ in ecological structure in ways that may impact the ecology of pollinators, dispersers, and herbivores and might reflect fundamental differences in canopy tree regeneration.
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Ecosistema , Árboles/clasificación , Árboles/fisiología , Biodiversidad , Densidad de Población , Lluvia , Análisis de Regresión , Clima TropicalRESUMEN
Most ecological hypotheses about species coexistence hinge on species differences, but quantifying trait differences across species in diverse communities is often unfeasible. We examined the variation of demographic traits using a global tropical forest data set covering 4500 species in 10 large-scale tree inventories. With a hierarchical Bayesian approach, we quantified the distribution of mortality and growth rates of all tree species at each site. This allowed us to test the prediction that demographic differences facilitate species richness, as suggested by the theory that a tradeoff between high growth and high survival allows species to coexist. Contrary to the prediction, the most diverse forests had the least demographic variation. Although demographic differences may foster coexistence, they do not explain any of the 16-fold variation in tree species richness observed across the tropics.
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Biodiversidad , Ecosistema , Árboles , África , Américas , Asia , Teorema de Bayes , Ambiente , India , Modelos Estadísticos , Distribución Normal , Estaciones del Año , Árboles/crecimiento & desarrollo , Tiempo (Meteorología)RESUMEN
The theory of metabolic ecology predicts specific relationships among tree stem diameter, biomass, height, growth and mortality. As demographic rates are important to estimates of carbon fluxes in forests, this theory might offer important insights into the global carbon budget, and deserves careful assessment. We assembled data from 10 old-growth tropical forests encompassing censuses of 367 ha and > 1.7 million trees to test the theory's predictions. We also developed a set of alternative predictions that retained some assumptions of metabolic ecology while also considering how availability of a key limiting resource, light, changes with tree size. Our results show that there are no universal scaling relationships of growth or mortality with size among trees in tropical forests. Observed patterns were consistent with our alternative model in the one site where we had the data necessary to evaluate it, and were inconsistent with the predictions of metabolic ecology in all forests.