ABSTRACT
Negative density-dependent recruitment of seedlings, that is, seeds of a given species are less likely to become established seedlings if the density of that species is high, has been proposed to be an important mechanism contributing to the extraordinary diversity of tropical tree communities because it can potentially prevent any particular species from usurping all available space, either in close proximity to seed sources or at relatively larger spatial scales. However, density-dependent recruitment does not necessarily enhance community diversity. Furthermore, although density-dependent effects have been found at some life stages in some species, no study has shown that density-dependent recruitment affects community diversity. Here we report the results of observations in a lowland, moist forest in the Republic of Panamá in which the species identities of 386,027 seeds that arrived at 200 seed traps were compared with the species identities of 13,068 seedlings that recruited into adjacent plots over a 4-year period. Across the 200 sites, recruit seedling diversity was significantly higher than seed diversity. Part of this difference was explained by interspecies differences in average recruitment success. Even after accounting for these differences, however, negative density-dependent recruitment contributes significantly to the increase in diversity from seeds to seedling recruits.
Subject(s)
Genetic Variation , Trees/genetics , Panama , Seeds , Tropical ClimateABSTRACT
OBJECTIVE: To clarify the effectiveness of amoxicillin prophylaxis in the prevention of catheter-related infections. METHOD: We performed a randomized, controlled, sequential, prospective trial in newborn infants undergoing percutaneous central venous catheterization. RESULTS: Seventy-five infants (median birth weight, 1240 gm; median age at catheter insertion, 3 days) received prophylactic amoxicillin (100 mg/kg per day); 73 infants in the control group (median birth weight, 1170 gm; median age, 2 days) received no routine prophylactic antibiotic treatment. No infant receiving amoxicillin had septicemia, whereas two infants (2.7%) in the control group did; suspected septicemia (positive clinical and laboratory findings but negative blood culture results) was found in 3 infants in the amoxicillin group and in 6 of the control group (not significantly). Bacterial contamination of the catheter tip at removal was significantly reduced in the amoxicillin group (13.3% vs 28.8% in control subjects; p < 0.05). Negligible differences were found in duration of catheterization (median, 15 days in both groups), or the number of thrombotic (9.3% vs 2.7% in control subjects) and other catheter-related complications between the groups. CONCLUSION: A low incidence of catheter-related infections can be achieved in neonates with central venous catheters without using prophylaxis with an antibiotic.