Spatial variation in caddisfly grazing regimes within a northern California watershed

Ecologists seek better understanding of why species interactions change across space and time in natural communities. In streams, species effects on resources and community structure may change as physical characteristics of the stream environment change along drainage networks. We examined spatial and seasonal effects of armored grazers using a small-scale exclusion experiment that was replicated in streams of different drainage areas. Effects of grazing varied with stream size and were related to variation in grazer abundance and phenology. We identified three distinct grazing regimes and a stream size (drainage area [DA]) threshold corresponding to a shift from one to two functional trophic levels. In streams with DA < 1 km2, armored grazers did not reduce biomass of algal biofilms. In slightly larger streams (2-3 km2 DA), the armored grazer guild was dominated by bivoltine Glossosoma. These caddisflies persisted and limited algal biofilms throughout the summer in one of these streams. In the largest tributaries (DA > 10 km2), the grazer guild was dominated by univoltine caddisflies, and grazing limited algal biofilms in early summer, but not late summer, after caddisflies pupated. Drainage area is a useful predictor of spatial transitions in food web interactions within and among watersheds. Quantifying the drainage area threshold at which interactions change in catchments with differing geology, vegetation, hydrology, climate, land use, or species pools should help build the understanding we need to forecast ecological responses to environmental change.     

Quantitative threat analysis for management of an imperiled species: Chinook salmon (Oncorhynchus tshawytscha).

Chinook salmon (Oncorhynchus tshawytscha) have declined dramatically across the Pacific Northwest because of multiple human impacts colloquially characterized as the four "H's": habitat degradation, harvest, hydroelectric and other dams, and hatchery production. We use this conceptual framework to quantify the relative importance of major threats to the current status of 201 Chinook populations. Current status is characterized by two demographic indices: population density and trend. We employ path analytic models and information theoretic methods for multi-model inference. Our results indicate that dams most strongly affect variation in population density, while harvest and hatchery production most strongly affect variation in population trend. Comparable results arise when the sample size of the analysis is reduced to 22 Chinook populations within a smaller region typical of the scale at which salmon recovery planning is conducted. Results from these threat analyses suggest that recovery strategies targeting specific demographic indices, and those considering natural and human-mediated interdependencies of major threats, are most likely to succeed.     

A meta-BACI approach for evaluating management intervention on chronic wasting disease in mule deer.

Advances in acquiring and analyzing the spatial attributes of data have greatly enhanced the potential utility of wildlife disease surveillance data for addressing problems of ecological or economic importance. We present an approach for using wildlife disease surveillance data to identify areas for (or of) intervention, to spatially delineate paired treatment and control areas, and then to analyze these nonrandomly selected sites in a meta-analysis framework via before-after-control impact (BACI) estimates of effect size. We apply these methods to evaluate the effectiveness of attempts to reduce chronic wasting disease (CWD) prevalence through intensive localized culling of mule deer (Odocoileus hemionus) in north-central Colorado, USA. Areas where surveillance data revealed high prevalence or case clusters were targeted by state wildlife management agency personnel for focal scale (on average <17 km2) culling, primarily via agency sharpshooters. Each area of sustained culling that we could also identify as unique by cluster analysis was considered a potential treatment area. Treatment areas, along with spatially paired control areas that we constructed post hoc in a case-control design (collectively called "management evaluation sites"), were then delineated using home range estimators. Using meta-BACI analysis of CWD prevalence data for all management evaluation sites, the mean effect size (change of prevalence on treatment areas minus change in prevalence on their paired control areas) was 0.03 (SE = 0.03); mean effect size on treatment areas was not greater than on paired control areas. Excluding cull samples from prevalence estimates or allowing for an equal or greater two-year lag in system responses to management did not change this outcome. We concluded that management benefits were not evident, although whether this represented true ineffectiveness or was a result of lack of data or insufficient duration of treatment could not be discerned. Based on our observations, we offer recommendations for designing a management experiment with 80% power to detect a 0.10 drop in prevalence over a 6-12-year period.     

Occupational stressors identified by small-scale,independent commercial crab pot fishermen

IntroductionWe interviewed fishermen to identify jobs and/or tasks of concern in order to guide and inform current ergonomic interventions.MethodsWe administered surveys to two groups of southeastern US commercial crab fishermen: a cohort contacted by telephone and fishermen recruited at 11 local fish houses. Fishermen were asked to rate physical stress of selected work tasks and conditions on a scale from 0 (no problem) to 10 (major problem). Fishermen were also asked open-ended questions about other work-issues of concern.ResultsFishermen who completed the survey (n = 91) were predominantly male (90%), white (96%), and over 40 years of age (71%). The five most physically strenuous tasks and conditions as rated by fishermen were pulling pots by hand (mean 6.4), rough weather (6.1) or rough water (6.2), unloading without mechanical assistance (5.8), and long work days (5.3). Task stress ratings with the most variability measured by the inter-quartile range (IQR) included: pulling pots by hand (IQR = 5), unloading without mechanical assistance (IQR = 5), gear maintenance (IQR = 4.5), and moving boxes and baskets on board (IQR = 4.5). Other situations that fishermen identified as a problem included: economic, off-shore work, declining industry, mental stress, environment, regulation, conflict with other commercial or recreational fishermen, issues with crew, sun (glare or burn), and breaking up frozen bait.ConclusionsIn general, stressful tasks identified from previous research were rated similarly by the fishermen surveyed. Development and testing of ergonomic interventions is ongoing.     

Gainsharing and women's and men's relative pay satisfaction

There is some evidence that women have equal or higher pay satisfaction than similarly situated men, even though they may earn less than these men. Using Major's (1994) model of entitlement, this study examined gender differences in pay satisfaction in two companies before and after gainsharing bonus programmes were introduced. Results indicated that women had higher pay satisfaction than men prior to the introduction of gainsharing and there was some evidence that this difference was greater among lower‐paid employees. Women did not exhibit higher pay satisfaction after gainsharing was introduced. The potential association of gainsharing with changes in female–male pay satisfaction is discussed. Copyright © 1999 John Wiley & Sons, Ltd.     

Adverse effects of chromium on amino acid levels in freshwater fish Clarias batrachus (Linn.)

Various heavy metals released into the rivers and lakes affect aquatic fauna including Clarias batrachus. Elevated levels of chromium (Cr) in aquatic organisms, especially fish, represent an ecological and human concern. Amino acid levels were estimated in five tissues (gills, liver, kidneys, muscle, and brain) of C. batrachus after 28 days of exposure to Cr. This study showed that Cr elevated levels of free amino acids in organs of fish C. batrachus, indicating a compensatory mechanism to counter sublethal metallic stress. Data suggest that the measurement of amino acids may serve as a biomarker for Cr toxicity in fish.     

Mercury source zone identification using soil vapor sampling and analysis

Development and demonstration of reliable measurement techniques that can detect and help quantify the nature and extent of elemental mercury (Hg(0)) in the subsurface are needed to reduce uncertainties in the decision-making process and increase the effectiveness of remedial actions. We conducted field tests at the Y-12 National Security Complex in Oak Ridge, Tennessee, USA, to determine if sampling and analysis of Hg(0) vapors in the shallow subsurface (<0.3 m depth) can be used to as an indicator of the location and extent of Hg(0) releases in the subsurface. We constructed a rigid polyvinyl chloride push probe assembly, which was driven into the ground. Soil gas samples were collected through a sealed inner tube of the assembly and were analyzed immediately in the field with a Lumex and/or Jerome Hg(0) analyzer. Time-series sampling showed that Hg vapor concentrations were fairly stable over time, suggesting that the vapor phase Hg(0) was not being depleted and that sampling results were not sensitive to the soil gas purge volume. Hg(0) vapor data collected at over 200 push probe locations at 3 different release sites correlated very well to areas of known Hg(0) contamination. Vertical profiling of Hg(0) vapor concentrations conducted at two locations provided information on the vertical distribution of Hg(0) contamination in the subsurface. We conclude from our studies that soil gas sampling and analysis can be conducted rapidly and inexpensively at large scales to help identify areas contaminated with Hg(0).     

Self‐protective reactions to peer abusive supervision: The moderating role of prevention focus and the mediating role of performance instrumentality

Across 3 studies, we apply a self‐protection perspective of observed mistreatment to examine a moderated mediation model on “when” and “why” third parties are motivated by peer abusive supervision. We hypothesize that prevention‐focused third parties will increase their performance effort as a response to peer abusive supervision, and this effect is mediated by performance instrumentality. In a field study of working adults (Study 1) and an experimental study that manipulated peer abusive supervision (Study 2), we found that peer abusive supervision interacted with third parties' prevention focus to predict their performance effort such that peer abuse was positively related to third parties' performance effort only for those high on prevention focus. Results were replicated in a second field study of working adults (Study 3). Further, we found support for the mediating effect of performance instrumentality. The theoretical and practical implications of our results are discussed.     

Experimental and Numerical Verification of Similarity Concept for Dispersion of Car Exhaust Gases in Urban Street Canyons

In urban conditions, car exhaust gases are often emitted inside poorly ventilated street canyons. One may suppose however that moving cars can themselves produce a certain ventilation effect in addition to natural air motions. Such ventilation mechanism is not sufficiently studied so far. A similarity criterion relating the vehicle- and wind-induced components of turbulent motion in an urban street canyon was proposed in 1982 by E. J. Plate for wind tunnel modelling purposes. The present study aims at further evaluation of the criterion and its applicability for a variety of wind and traffic conditions. This is accomplished by joint analyses of data from numerical simulations and wind tunnel measurements.     

A dynamic model of the spatial spread of an infectious disease: the case of fox rabies in Illinois

A spatially explicit computer model is developed to examine the dynamic spread of fox rabies across the state of Illinois and to evaluate possible disease control strategies. The ultimate concern is that the disease will spread from foxes to humans through the pet population. Modeling the population dynamics of rabies in foxes requires comprehensive ecological and biological knowledge of the fox and pathogenesis of the rabies virus. Variables considered including population densities, fox biology, home ranges, dispersal rates, contact rates, and incubation periods, can greatly effect the spread of disease. Accurate reporting of these variables is paramount for realistic construction of a spatial model. The spatial modeling technique utilized is a grid-based approach that combines the relevant geographic condition of the Illinois landscape (typically described in a georeferenced database system) with a nonlinear dynamic model of the phenomena of interest in each cell, interactively connected to the other appropriate cells (usually adjacent ones). The resulting spatial model graphically links data obtained from previous models, fox biology, rabies information and landscape parameters using various hierarchical scales and makes it possible to follow the emergent patterns and facilitates experimental stimulus/result data collection techniques. Results of the model indicate that the disease would likely spread among the native healthy fox population from East to West and would occur in epidemiological waves radiating from the point of introduction; becoming endemic across the State in about 15 years. Findings also include the realization that while current hunting pressures can potentially wipe out the fox in the State, some level of hunting pressure can be effectively utilized to help control the disease. This revised version was published online in July 2006 with corrections to the Cover Date.