Carboplatin is active against low-grade gliomas. Further evaluation of the role of carboplatin in the preirradiation treatment of children with low-grade gliomas of the optic pathway is currently underway in a clinical trial.

Patterns of size inequality in crowded plant populations are often taken to be indicative of the degree of size asymmetry of competition, but recent research suggests that some of the patterns attributed to size-asymmetric competition could be due to spatial structure. To investigate the theoretical relationships between plant density, spatial pattern, and competitive size asymmetry in determining size variation in crowded plant populations, we developed a spatially explicit, individual-based plant competition model based on overlapping zones of influence. The zone of influence of each plant is modeled as a circle, growing in two dimensions, and is allometrically related to plant biomass. The area of the circle represents resources potentially available to the plant, and plants compete for resources in areas in which they overlap. The size asymmetry of competition is reflected in the rules for dividing up the overlapping areas. Theoretical plant populations were grown in random and in perfectly uniform spatial patterns at four densities under size-asymmetric and size-symmetric competition. Both spatial pattern and size asymmetry contributed to size variation, but their relative importance varied greatly over density and over time. Early in stand development, spatial pattern was more important than the symmetry of competition in determining the degree of size variation within the population, but after plants grew and competition intensified, the size asymmetry of competition became a much more important * E-mail: jw@kvl.dk. † E-mail: stoll@sgi.unibe.ch. ‡ E-mail: helene@eno.princeton.edu. § E-mail: ajasen@concentric.net. source of size variation. Size variability was slightly higher at higher densities when competition was symmetric and plants were distributed nonuniformly in space. In a uniform spatial pattern, size variation increased with density only when competition was size asymmetric. Our results suggest that when competition is size asymmetric and intense, it will be more important in generating size variation than is local variation in density. Our results and the available data are consistent with the hypothesis that high levels of size inequality commonly observed within crowded plant populations are largely due to size-asymmetric competition, not to variation in local density.Keywords: asymmetric competition, individual-based models, population structure, size inequality, spatial effects, zone of influence.Competition among individuals usually increases size variation within plant populations, but there is controversy over the mechanisms through which this occurs. This controversy reflects a fundamental disagreement about the nature of competition among individual plants. Some studies have concluded that a major factor generating size variation in crowded plant populations is the "size asymmetry" of competition: larger plants have a disproportionate advantage (for their relative size) in competition with smaller plants, suppressing their growth (Begon 1984;Weiner 1990;Schwinning and Weiner 1...

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Objective In Nicaragua, an epidemic of chronic kidney disease (CKD) with unknown aetiology has been described primarily among young, male sugarcane workers. Our goals were to characterise the type of kidney damage and evaluate the potential role of occupational factors. Methods Our study population included 284 sugarcane workers, 51 miners, 60 construction workers, and 53 port workers in Western Nicaragua. For sugarcane workers in seven jobs (e.g. cane cutters, pesticide applicators, etc.), blood and urine samples were collected at the beginning and end of the 6-month sugarcane harvest. One round of samples were also collected from workers who were employed in the other three industries (but had never worked in the sugarcane industry). Biomarkers of kidney injury included serum creatinine, urinary albumin, and urinary neutrophil gelatinase-associated lipocalin (NGAL). Linear regression models were used to determine whether biomarkers of kidney injury increased during the harvest and/or varied by job. Results Biomarkers of kidney injury were significantly different by sugarcane job and estimated glomerular filtration rate (eGFR) declined significantly during the harvest among those engaged in the most strenuous work tasks, while urine albumin remained low in all groups. Compared to factory workers, eGFR was lowest among cane cutters (p = 0.006) and urinary NGAL was highest among cane cutters (p = 0.04). Workers in other industries also had higher than expected prevalence of eGFR <60 mL/min/1.73 m2. Conclusions Our results provide evidence that the type of kidney damage occurring in sugarcane workers, as well as among workers in other industries, is primarily tubulointerstitial (and not glomerular) in nature. Biomarkers of kidney injury varied by job and were highest among workers engaged in more strenuous physical labour. If acute kidney damage is on the causal pathway to CKD, heat or other work-related exposures may be contributing to this epidemic.