Divergent composition but similar function of soil food webs of individual plants: plant species and community effects

Soils are extremely rich in biodiversity, and soil organisms play pivotal roles in supporting terrestrial life, but the role that individual plants and plant communities play in influencing the diversity and functioning of soil food webs remains highly debated. Plants, as primary producers and providers of resources to the soil food web, are of vital importance for the composition, structure, and functioning of soil communities. However, whether natural soil food webs that are completely open to immigration and emigration differ underneath individual plants remains unknown. In a biodiversity restoration experiment we first compared the soil nematode communities of 228 individual plants belonging to eight herbaceous species. We included grass, leguminous, and non-leguminous species. Each individual plant grew intermingled with other species, but all plant species had a different nematode community. Moreover, nematode communities were more similar when plant individuals were growing in the same as compared to different plant communities, and these effects were most apparent for the groups of bacterivorous, carnivorous, and omnivorous nematodes. Subsequently, we analyzed the composition, structure, and functioning of the complete soil food webs of 58 individual plants, belonging to two of the plant species, Lotus corniculatus (Fabaceae) and Plantago lanceolata (Plantaginaceae). We isolated and identified more than 150 taxa/groups of soil organisms. The soil community composition and structure of the entire food webs were influenced both by the species identity of the plant individual and the surrounding plant community. Unexpectedly, plant identity had the strongest effects on decomposing soil organisms, widely believed to be generalist feeders. In contrast, quantitative food web modeling showed that the composition of the plant community influenced nitrogen mineralization under individual plants, but that plant species identity did not affect nitrogen or carbon mineralization or food web stability. Hence, the composition and structure of entire soil food webs vary at the scale of individual plants and are strongly influenced by the species identity of the plant. However, the ecosystem functions these food webs provide are determined by the identity of the entire plant community.     

Marine Protected Area Design and the Spatial and Temporal Distribution of Cetaceans in a Submarine Canyon

Abstract: The Gully, the largest submarine canyon off the coast of eastern Canada, is currently under consideration as a marine conservation area, primarily because of the increasing interest in oil and gas production on the Scotian Shelf. Cetaceans, as a guild of abundant, large organisms that are relatively sensitive to such threats, provide a reliable means to determine the boundaries for a conservation area in this region. We compared the abundance of cetaceans between the Gully and other parts of the Scotian Shelf and Slope and found that abundance was higher in the Gully. We also assessed cetacean distribution and relative abundance within the Gully relative to search effort for several spatial and temporal parameters: depth, slope, sea surface temperature, and month. Distribution within the Gully was most strongly correlated with depth, but was also significantly correlated with sea surface temperature and month. Five of the 11 cetacean species commonly found in the Gully, and all those for which the Gully formed significant habitat on the Scotian Shelf, were concentrated in the deep (200–2000 m) mouth of the canyon. We suggest that a year-round marine protected area is necessary for the Gully. A core protection zone should be defined in the Gully based on depth and bounded by the 200-m isobath. A buffer zone around the core zone should be defined to provide protection from activities with further-reaching effects, such as noise, dredging, and chemical pollution.     

Hydrocarbon Production and Photochemical Ozone Formation in Forest Burn Plumes

The purpose of this paper is to describe ozone production in forest slash burn plumes. Plumes from controlled fires in the state of Washington were monitored using an instrumented aircraft. Ozone, oxides of nitrogen, condensation nuclei, and visual range (nephelometer) were measured continuously on board the plane. Airborne grab samples were collected for detailed hydrocarbon analysis.

The slash burn plumes were found to contain significant quantities of ozone. A buildup of 40–50 ppb above the ambient background ozone concentrations was not unusual. Hydrocarbon analyses revealed the presence of many photochemically reactive olefins in the plume. Hydrocarbon/NO _x ratios were favorable for photochemical oxidant production.     

Modeling the Effects of VOC/NOx Emissions on Ozone Synthesis in the Cascadia Airshed of the Pacific Northwest

ABSTRACT

A modeling system consisting of MM5, Calmet, and Calgrid was used to investigate the sensitivity of anthropogenic volatile organic compound (VOC) and oxides of nitrogen (NO_x) reductions on ozone formation within the Cascadia airshed of the Pacific Northwest. An ozone episode that occurred on July 11-14, 1996, was evaluated. During this event, high ozone levels were recorded at monitors downwind of Seattle, WA, and Portland, OR, with one monitor exceeding the 1 hr/120 ppb National Ambient Air Quality Standard (at 148 ppb), and six monitors above the proposed 8 hr/80 ppb standard (at 82-130 ppb). For this particular case, significant emissions reductions, between 25 and 75%, would be required to decrease peak ozone concentrations to desired levels. Reductions in VOC emissions alone, or a combination of reduced VOC and NO_x emissions, were generally found to be most effective; reducing NO_x emissions alone resulted in increased ozone in the Seattle area. When only VOC emissions were curtailed, ozone reductions occurred in the immediate vicinity of densely populated areas, while NO_x reductions resulted in more widespread ozone reductions.     

The Great Recession or progressive energy policies? Explaining the decline in US greenhouse gas emissions forecasts

This paper evaluates the causes of the 23% decline in 2030 US greenhouse gas emissions forecasts between 2007 and 2011. Dynamic regression modeling predicts that the Great Recession contributed to about 67% of the 2008–2009 emissions decline, but then fell to about an 18% share for the 2030 emissions forecast. An analysis of electricity generation forecasts show that switching from coal to gas contributed only 6% to the total 2030 decline. In contrast, regulatory impact assessments and policy analysis showed that state and federal policies were responsible for 46% of the 2030 decline in emissions.     

SOCPROG programs: analysing animal social structures

SOCPROG is a set of programs which analyses data on animal associations. Data usually come from observations of the social behaviour of individually identifiable animals. Associations among animals, sampling periods, restrictions on the data and association indices can be defined very flexibly. SOCPROG can analyse data sets including 1,000 or more individuals. Association matrices are displayed using sociograms, principal coordinates analysis, multidimensional scaling and cluster analyses. Permutation tests, Mantel and related tests and matrix correlation methods examine hypotheses about preferred associations among individuals and classes of individual. Weighted network statistics are calculated and can be tested against null hypotheses. Temporal analyses include displays of lagged association rates (rates of reassociation following an association). Models can be fitted to lagged association rates. Multiple association measures, including measures produced by other programs such as genetic or range use data, may be analysed using Mantel tests and principal components analysis. SOCPROG also performs mark-recapture population analyses and movement analyses. SOCPROG is written in the programming language MATLAB and may be downloaded free from the World Wide Web.     

The measurement of roadway PM10 emission rates using atmospheric tracer ratio techniques

In this work, stationary and mobile point source tracer release techniques have been used to determine PM₁₀ emission rates from four-lane commercial/residential paved roads under sanded and unsanded conditions, and from unpaved roads relative to site-specific vehicular and ambient parameters. Measured street (4 + lanes; ? 10,000 vehicles per day) emission factors for unsanded and sanded roads were 40 and 20% lower, respectively, than the EPA approved reference value. The sanded road emission factor was approximately 40% higher than that for the unsanded road. These results indicate a consistent relationship between PM₁₀ and relative humidity under unsanded conditions. There is some evidence to suggest that street sweeping has a measurable effect on PM,, emission reduction during periods of low relative humidity (i.e. ? 30%). Within the constraints imposed by the variable experimental conditions, the emission factors determined for unpaved roads agreed reasonably well with the unpaved road empirical formula. Limited correlations were observed with ambient meteorological parameters. The capability of the “upwind-dowiawind” concentration modeling method to predict accurate emission was tested using a Gaussian dispersion model (SIMFLUX). Predictions agreed well with the experimentally determined emission factors.     

Vocalizations of the North Atlantic pilot whale (Globicephala melas) as related to behavioral contexts

Summary Vocalizations of free-ranging North Atlantic pilot whales were studied in different behavioral contexts to gain insight into the function and biological significance of different sound types. Simple whistles (with no frequency inflections) were heard more frequently when whales were milling, a restful behavior type. During surface active behavior, energetic, often coordinated activity probably representing feeding, many sound types, especially complex whistles (with more frequency inflections) and pulsed sounds, occurred with greater frequency than when this behavior was absent. Greater numbers of most whistle types were produced when whales were spread over a larger area and when more subgroups were present. Thus, in pilot whales, there is a significant relationship between their sounds and their behavior, with vocalizations possibly serving to maintain contact and coordinate movements of the herd. Offprint requests to: L.S. Weilgart at the current address