Seed predation by Neotropical rain forest mammals increases diversity in seedling recruitment

Seed dispersal and seedling recruitment (the transition of seeds to seedlings) set the spatiotemporal distribution of new individuals in plant communities. Many terrestrial rain forest mammals consume post-dispersal seeds and seedlings, often inflicting density-dependent mortality. In part because of density-dependent mortality, diversity often increases during seedling recruitment, making it a critical stage for species coexistence. We determined how mammalian predators, adult tree abundance, and seed mass interact to affect seedling recruitment in a western Amazonian rain forest. We used exclosures that were selectively permeable to three size classes of mammals: mice and spiny rats (weighing <1 kg), medium-sized rodents (1-12 kg), and large mammals (20-200 kg). Into each exclosure, we placed seeds of 13 tree species and one canopy liana, which varied by an order of magnitude in adult abundance and seed mass. We followed the fates of the seeds and resulting seedlings for at least 17 months. We assessed the effect of each mammalian size class on seed survival, seedling survival and growth, and the density and diversity of the seedlings that survived to the end of the experiment. Surprisingly, large mammals had no detectable effect at any stage of seedling recruitment. In contrast, small- and medium-sized mammals significantly reduced seed survival, seedling survival, and seedling density. Furthermore, predation by small mammals increased species richness on a per-stem basis. This increase in diversity resulted from their disproportionately intense predation on common species and large-seeded species. Small mammals thereby generated a rare-species advantage in seedling recruitment, the critical ingredient for frequency dependence. Predation by small (and to a lesser extent, medium-sized) mammals on seeds and seedlings significantly increases tree species diversity in tropical forests. This is the first long-term study to dissect the effects of various mammalian predators on the recruitment of a diverse set of tree species.     

A global evaluation of metabolic theory as an explanation for terrestrial species richness gradients

We compiled 46 broadscale data sets of species richness for a wide range of terrestrial plant, invertebrate, and ectothermic vertebrate groups in all parts of the world to test the ability of metabolic theory to account for observed diversity gradients. The theory makes two related predictions: (1) In-transformed richness is linearly associated with a linear, inverse transformation of annual temperature, and (2) the slope of the relationship is near -0.65. Of the 46 data sets, 14 had no significant relationship; of the remaining 32, nine were linear, meeting prediction 1. Model I (ordinary least squares, OLS) and model II (reduced major axis, RMA) regressions then tested the linear slopes against prediction 2. In the 23 data sets having nonlinear relationships between richness and temperature, split-line regression divided the data into linear components, and regressions were done on each component to test prediction 2 for subsets of the data. Of the 46 data sets analyzed in their entirety using OLS regression, one was consistent with metabolic theory (meeting both predictions), and one was possibly consistent. Using RMA regression, no data sets were consistent. Of 67 analyses of prediction 2 using OLS regression on all linear data sets and subsets, two were consistent with the prediction, and four were possibly consistent. Using RMA regression, one was consistent (albeit weakly), and four were possibly consistent. We also found that the relationship between richness and temperature is both taxonomically and geographically conditional, and there is no evidence for a universal response of diversity to temperature. Meta-analyses confirmed significant heterogeneity in slopes among data sets, and the combined slopes across studies were significantly lower than the range of slopes predicted by metabolic theory based on both OLS and RMA regressions. We conclude that metabolic theory, as currently formulated, is a poor predictor of observed diversity gradients in most terrestrial systems.     

Amending greenroof soil with biochar to affect runoff water quantity and quality

Numbers of greenroofs in urban areas continue to grow internationally; so designing greenroof soil to reduce the amount of nutrients in the stormwater runoff from these roofs is becoming essential. This study evaluated changes in extensive greenroof water discharge quality and quantity after adding biochar, a soil amendment promoted for its ability to retain nutrients in soils and increase soil fertility. Prototype greenroof trays with and without biochar were planted with sedum or ryegrass, with barren soil trays used as controls. The greenroof trays were subjected to two sequential 7.4cm/h rainfall events using a rain simulator. Runoff from the rain events was collected and evaluated. Trays containing 7% biochar showed increased water retention and significant decreases in discharge of total nitrogen, total phosphorus, nitrate, phosphate, and organic carbon. The addition of biochar to greenroof soil improves both runoff water quality and retention.     

Likelihood Ratio Analysis of Skin Cancer Prevalence Associated with Arsenic in Drinking Water in the USA

Several published studies have examined skin-cancer prevalence in regions of the USA that have concentrations of arsenic above the USA drinking-water standard. Those studies with adequate exposure and health outcome data did not report any skin cancer cases. Because the USA's arsenic concentrations are relatively low compared to some other countries and the study populations are small, the absence of reported skin-cancer cases could be due to an absence of risk in USA populations or random variability from a predicted risk. We used the current EPA arsenic cancer slope factor (CSF) model, which is derived from Taiwanese populations exposed to high levels of arsenic, to predict the expected number of skin cancers. We then conducted a likelihood ratio analysis, which showed that a null hypothesis (no additional skin cancer risk from arsenic) was approximately 2.2 times more likely than the hypothesis that ingested arsenic causes the predicted rate of skin cancers. Although based on small numbers, our analysis of USA populations indicates that the CSF derived from arsenic exposure in Taiwanese populations may be an overestimate when applied to USA populations.     

The Impact of a Building Implosion on Airborne Particulate Matter in an Urban Community

Abstract

In response to community concerns, the air quality impact of imploding a 22-story building in east Baltimore, MD, was studied. Time- and space-resolved concentrations of indoor and outdoor particulate matter (PM) (nominally 0.5–10 µm) were measured using a portable nephelometer at seven and four locations, respectively. PM₁₀ levels varied in time and space; there was no measurable effect observed upwind of the implosion. The downwind peak PM₁₀ levels varied with distance (54,000–589 µg/m³) exceeding pre-implosion levels for sites 100 and 1130 m 3000- and 20-fold, respectively. Estimated outdoor 24-hr integrated mass concentrations varied from 15 to 72 µg/m³. The implosion did not result in the U.S. Environmental Protection Agency (EPA) National Ambient Air Quality Standard (NAAQS) for PM₁₀ being exceeded. X-ray fluorescence analysis indicated that the elemental composition was dominated by crustal elements: calcium (57%), silicon (23%), aluminum (7.6%), and iron (6.1%). Lead was above background but at a low level (0.17 µg/m³). Peak PM₁₀ concentrations were short-lived; most sites returned to background within 15 min. No increase in indoor PM₁₀ was observed even at the most proximate 250 m location. These results demonstrate that a building implosion can have a severe but short-lived impact on community air quality. Effective protection is offered by being indoors or upwind.     

Periphyton as monitors for heavy metal pollution in the Calcasieu River estuary

The levels of copper, lead, chromium, zinc, cadmium, arsenic and silver were determined in periphyton specimens obtained with a diatometer collector. Stations selected were along three important bayous of the Calcasieu River system. Distributions of some metals in the organisms were similar to those found in sediment from the same locations, while other metals appeared to be similar to water concentrations. Concentration ratios of periphyton over sediment greatly exceeded one for the metals chromium, zinc, cadmium, arsenic and silver. The concentrations of heavy metals in the periphyton appeared to yield more information about pollutants than either water or sediment samples collected at the periphyton stations.     

First evaluation of the possibility of testing for drugged driving using exhaled breath sampling

Objective: Driving under the influence of psychoactive drugs causes an increased risk for accidents. In combating this, sobriety tests at the roadside are common practice in most countries. Sampling of blood and urine for forensic investigation cannot be done at the roadside and poses practical problems associated with costs and time. An alternative specimen for roadside testing is therefore warranted and the aerosol particles in exhaled breath are one such alternative.

Methods: The present study investigated how the exhaled breath sample compared with the routine legal investigations of blood and urine collected from suspects of drugged driving at 2 locations in Sweden. Exhaled breath was collected using a simple filter collection device and analyzed with state-of-the-art mass spectrometry technique.

Results: The total number of cases used for this investigation was 67. In 54 of these cases (81%) the results regarding a positive or negative drug test result agreed and in 13 they disagreed. Out of these, the report from the forensic investigation of blood/urine was negative in 21 cases. In 6 of these, analytical findings were made in exhaled breath and these cases were dominated by the detection of amphetamine. In 7 cases a positive drug test from the forensic investigation was not observed in the breath sample and these cases were dominated by detection of tetrahydrocannabinol in blood. In total, 45 samples were positive with breath testing and the number of positives with established forensic methods was 46.

Conclusion: The promising results from this study provide support to exhaled breath as a viable specimen for testing of drugged driving. The rapid, easy, and convenient sampling procedure offers the possibility to collect a drug test specimen at the roadside. The analytical investigation must be done in a laboratory at present because of the need for a highly sensitive instrument, which is already in use in forensic laboratories. The analytical work is not more challenging than for blood or oral fluid and should not cause an increase in cost. However, more studies need to be done before exhaled breath drug testing can be applied routinely for drugged driving investigation.