The indirect consequences of a mutualism: comparing positive and negative components of the net interaction between honeydew-tending ants and host plants.

1. In ecological webs, net indirect interactions between species are composed of interactions that vary in sign and magnitude. Most studies have focused on negative component interactions (e.

The relationship between the distribution of worker sizes and new worker production in the ant Formica neorufibarbis.

While it is commonly assumed that variation in worker sizes within a single ant colony increases colony efficiency, there is little causal evidence of a link between worker size variation and colony performance. I tested whether the range of worker sizes within colonies of the ant species Formica neorufibarbis affected new worker production. Removing large workers from colonies lowered the rate of new worker production.

Recruitment in the harvester ant, Pogonomyrmex occidentalis: effects of experimental removal.

We examined the importance of experimental removal of mature colonies on colony recruitment in the western harvester ant Pogonomyrmex occidentalis. To test the common assumption that established colonies suppress the establishment of new colonies we removed all colonies in ten 0.25 ha plots in 1996 and an additional five plots in 1997 and measured new colony recruitment in 1997, 1998, and 1999.

Nitrous acid interference with passive NO2 measurement methods and the impact on indoor NO2 data.

Recent research has demonstrated that nitrous acid (HONO) is produced in indoor environments by NO2 reacting with interior surfaces, and is also emitted directly by some combustion sources. We have recently characterized the interference by HONO to NO2 measurements made by several commonly used continuous NO2 monitors. This paper reports on the effect of HONO on NO2 measurements made by passive sampling devices.

The Boston residential nitrogen dioxide characterization study: classification and prediction of indoor NO2 exposure.

Many epidemiological studies have used house characteristics associated with indoor sources as simplified proxies for personal nitrogen dioxide (NO2) exposure. Stove type and presence of a pilot light often been used as the two key characteristics, but significant overlaps have remained in the NO2 concentrations in the exposed and unexposed groups. This has contributed to inconsistencies in epidemiological findings, due to potential misclassification of exposure.

Analysis of sampling strategies for estimating annual average indoor NO2 concentrations in residences with gas ranges.

Range gas consumption in households tends to follow an annual cycle resembling a sinusoid, with peak consumption during the winter. When outdoor NO2 concentrations have a constant or small impact, the resulting indoor NO2 concentrations also tend to resemble an annual sinusoid. Optimal monitoring strategies can be designed to take advantage of this knowledge to obtain a better estimate of the true annual average gas consumption or indoor NO2 concentration.

Causes and consequences of backdrafting of vented gas appliances.

House depressurization occurs when household equipment such as a kitchen or bathroom fan or a fireplace exhausts air from the house and lowers the pressure indoors with respect to the outside. The operation of air handlers for forced-air heating or cooling systems also can have a depressurization effect. This depressurization can hinder the natural draft from vented combustion appliances and lead to backdrafting, which in turn can result in combustion gases spilling into the indoor airspace.

California residential air exchange rates and residence volumes.

Unlabelled: Air exchange rate data from two residential indoor air quality studies are presented. In the first investigation, over 500 residences in Southern California were sampled for three one-week periods from 1984 to 1985. Those data provided seasonal information for a broad range of residential characteristics in a large metropolitan area.

Personal exposure to nitrogen dioxide in the Los Angeles Basin.

A large scale study of human exposure to nitrogen dioxide (NO2) was conducted in the Los Angeles Basin, the only metropolitan area in the United States that exceeds the NO2 NAAQS. Data are available for a population representative sample of 482 households and 682 individuals. Personal exposures, as well as indoor and outdoor home levels, were monitored using passive time-integrating filter badges.

Transformations, lifetimes, and sources of NO2, HONO, and HNO3 in indoor environments.

Recent research has demonstrated that nitrogen oxides are transformed to nitrogen acids in indoor environments, and that significant concentrations of nitrous acid are present in indoor air. The purpose of the study reported in this paper has been to investigate the sources, chemical transformations and lifetimes of nitrogen oxides and nitrogen acids under the conditions existing in buildings. An unoccupied single family residence was instrumented for monitoring of NO, NO2, NOy, HONO, HNO3, CO, temperature, relative humidity, and air exchange rate.

Wind velocity effects on sampling rate of NO2 badge.

The effects of wind velocity on a sampling rate of a nitrogen dioxide (NO2) diffusive badge were experimentally determined using a turntable. The use of a turntable permits the collection of the large amounts of data that are needed for statistically reliable results at several wind velocities in one experiment. The regression model for the wind effect determined by these experiments was closely correlated with data previously gathered from experiments using wind tunnels.

Sensitivity of trends in geometric mean blood levels to random measurement errors.

A statistical model is investigated that expresses observations, such as blood lead levels, as an additive function of true levels and random measurement errors. Both empirical results (obtained from a series of computer simulation experiments) and theoretical results indicate how certain summary statistics for the observations vary in response to random measurement errors. Such results are applied to a very large data base of pediatric blood lead levels collected in New York City during 1970-1976, and they indicate that the observed trends in geometric mean blood lead levels are not significantly altered by the possible presence of measurement errors.

Lead: a case study in interagency policy-making.

Exposures to low levels of lead in the environment are believed to have potentially significant health effects, especially in children; such exposures to the general population come from many sources. Responsibility for regulating lead exposures has been derived from a multitude of laws passed by the Congress, and thus ultimate protection of people depends on actions taken by several agencies of the federal government. For this reason, the history of efforts to reduce exposures to lead is an excellent case study in the way that federal agencies do or do not work well together.

Relation of pediatric blood lead levels to lead in gasoline.

Analysis of a large data set of pediatric blood lead levels collected in New York City (1970-1976) shows a highly significant association between geometric mean blood lead levels and the amount of lead present in gasoline sold during the same period. This association was observed for all age and ethnic groups studied, and it suggests that possible exposure pathways other than ambient air should be considered. Even without detailed knowledge of the exact exposure pathways, sufficient information now exists for policy analysis and decisions relevant to controls and standards related to lead in gasoline and its effect on subsets of the population.

Analysis of pediatric blood lead levels in New York City for 1970-1976.

A study was completed of more than 170,000 records of pediatric venous blood levels and supporting demographic information collected in New York City during 1970-1976. The geometric mean (GM) blood lead level shows a consistent cyclical variation superimposed on an overall decreasing trend with time for all ages and ethnic groups studied. The GM blood lead levels for blacks are significantly greater than those for either Hispanics or whites.

On the Calculation of Moments of Molecular Weight Distribution from Sedimentation Equilibrium Data.

In this paper we discuss a technique for calculating moments of polydisperse materials in terms of concentration readings along the cell. The proposed method minimizes dependence on data from the end points where they may be unreliable. An analysis is given of the errors involved in the use of the proposed method when the underlying molecular weight distribution is the Schulz distribution or the lognormal.

The Solution to a Nonlinear Lamm Equation in the Faxén Approximation.

An exact solution in the Faxén approximation is given for the Lamm equation in which the sedimentation coefficient is related to concentration as (1-). It is shown that the solution in this case can be expressed in terms of the solution to the linear case ( =0) with a modified argument. The boundary sharpening phenomenon expresses itself very clearly in the solution presented here.