Biomedical subjects

Robert John

Publications and source records attributed to Robert John.

6 recordsLinked to original sources

PubMed2007

Soil nutrients influence spatial distributions of tropical tree species.

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.

Ecosystem↗

PubMed2006

Nonrandom processes maintain diversity in tropical forests.

An ecological community's species diversity tends to erode through time as a result of stochastic extinction, competitive exclusion, and unstable host-enemy dynamics. This erosion of diversity can be prevented over the short term if recruits are highly diverse as a result of preferential recruitment of rare species or, alternatively, if rare species survive preferentially, which increases diversity as the ages of the individuals increase. Here, we present census data from seven New and Old World tropical forest dynamics plots that all show the latter pattern. Within local areas, the trees that survived were as a group more diverse than those that were recruited or those that died. The larger (and therefore on average older) survivors were more diverse within local areas than the smaller survivors. When species were rare in a local area, they had a higher survival rate than when they were common, resulting in enrichment for rare species and increasing diversity with age and size class in these complex ecosystems.

Biodiversity↗

PubMed2004

Unreferred chronic kidney disease: a longitudinal study.

BACKGROUND: Chronic kidney disease (CKD) is a major health problem. A better understanding of the epidemiological characteristics of the different stages of CKD and the associated adverse outcomes is needed to establish and implement appropriate management strategies. METHODS: A serum creatinine (SCr) level of 2.03 mg/dL or greater (> or =180 micromol/L) in men and 1.53 mg/dL or greater (> or =135 micromol/L) in women was used to identify patients with moderate to severe CKD in a predominantly Caucasian area of the United Kingdom. Patients who were unknown to renal services were identified and followed up to establish survival, rate of referral, and change in glomerular filtration rate (GFR). RESULTS: The prevalence of CKD defined by SCr cutoff values was 5,554 per million population (pmp). Median calculated GFR of the cohort was 28.5 mL/min/1.73 m2 (range, 4.1 to 42.8 mL/min/1.73 m2), and median age was 83 years (range, 18 to 103 years). A total of 84.8% of patients were unknown to renal services. During a mean follow-up of 31.3 months, 8.1% of patients were referred. Median survival of the unreferred population was 28.1 months. Cardiovascular disease, cancer, and infection were the most common causes of death. Male sex, low GFR, and nonreferral were associated with poor outcome. The majority of unreferred patients had stable renal function. The incidence of new unreferred CKD during the first year of follow-up was 2,435 pmp, such that the prevalence remained stable at 4,910 pmp. Significant anemia (hemoglobin < 11 g/dL [<110 g/L]) was seen in 27.5% of the unreferred cohort. CONCLUSION: Referral of all patients with CKD is unrealistic and inappropriate. Management strategies aimed at improving adverse outcomes need to take account of this and be developed and implemented through collaboration between primary care and secondary care.

Adult↗

PubMed2003

Anger types and the use of cigarettes and smokeless tobacco among Native American adolescents.

BACKGROUND: Although tobacco use appears common among Native Americans, the study of dual use of cigarettes and smokeless tobacco has been neglected. The current study examines tobacco use among a sample of Native American adolescents. Also, it considers how the psychological factor of anger may relate to tobacco use. METHODS: The participants were 513 Native American students from a national sample in grades 6, 8, and 10 in the United States. Cluster analysis was used to identify anger types, and these types were compared on their tobacco use. RESULTS: Cluster analysis identified four anger types. One type was the Externalizing Type, characterized by the tendency to show externalizing behaviors such as fighting and yelling. This type had an elevated rate of tobacco use. In terms of an odds ratio, the Externalizing Type was about 10 times more likely to smoke, about 6 times more likely to use smokeless tobacco, and about 8 times more likely to show dual use. The majority of dual users were the Externalizing Type. CONCLUSIONS: The results suggest that externalizing anger types are more likely to use tobacco, and that smoking cessation programs for teens could be more effective when they address anger issues.

Adaptation, Psychological↗

PubMed2003

Patterns and impact of comorbidity and multimorbidity among community-resident American Indian elders.

PURPOSE: The purpose of this study is to suggest a new approach to identifying patterns of comorbidity and multimorbidity. DESIGN AND METHODS: A random sample of 1,039 rural community-resident American Indian elders aged 60 years and older was surveyed. Comorbidity was investigated with four standard approaches, and with cluster analysis. RESULTS: Most respondents (57%) reported 3 or more of 11 chronic conditions. Cluster analysis revealed a four-cluster comorbidity structure: cardiopulmonary, sensory-motor, depression, and arthritis. When the impact of comorbidity on four health-related quality of life outcomes was tested, the use of the clusters offered more explanatory power than the other approaches. IMPLICATIONS: Our study improves understanding of comorbidity within an understudied and underserved population by characterizing comorbidity in conventional and novel ways. The cluster approach has four advantages over previous approaches. In particular, cluster analysis identifies specific health problems that have to be addressed to alter American Indian elders' health-related quality of life.

Activities of Daily Living↗

PubMedDate not supplied

Evaluation of United States Department of Agriculture-sponsored consumer materials addressing food security.

PURPOSE: Food insecurity in the United States is a major public health issue. The main objective of this study was to evaluate the availability and quality of printed materials addressing food security targeted to special populations by the United States Department of Agriculture (USDA). DESIGN: Nutrition education resources addressing food security available from USDA websites were selected for analysis. SETTING: Not applicable. PARTICIPANTS: The review team consisted of project staff (n = 6), two of who were fluent in Spanish. METHOD: Selection criteria were established to identify the food-security materials, and a group of reviewers assessed the quality of each publication both quantitatively and qualitatively. A consensus meeting among the reviewers was held to make final determinations of the quality of the materials. The quantitative data analysis consisted of basic descriptive statistics. RESULTS: Among the 27 materials initially identified, 20 were either irrelevant or of low relevance to food security. Moreover, very few of them were intended for minority populations. The quality of most of the materials ranged from "average" to "good." Some of the major weaknesses include readability level, lack of cultural relevance, and inadequate coverage of food insecurity. CONCLUSION: Very few materials on food insecurity are of high quality. In the development of such materials, emphasis should be given to the readability level, content, and cultural relevance.

Access to Information↗