James G. Surles

Model-Dependent Variance Inflation Factor Cutoff Values

When creating designed experiments, it is not always possible to run the experiment at the exact settings required to maintain orthogonal effects. However, this is not measurement error when precise measurements of the settings can be made once the experiment begins. A comparison is made for a 15-run Box–Behnken design using both the intended design settings and the actual design settings. Variance inflation factors are used to measure the induced collinearity in the effects. Two cutoff values are suggested for use to determine when an effects variance inflation factor is too large to keep that effect in the model.

Habitat Use by Migrant Shorebirds in Saline Lakes of the Southern Great Plains

Abstract Shorebirds migrating through the Southern Great Plains of North America use saline lakes as stopovers to rest and replenish energy reserves. To understand how availability of invertebrates, salinity, freshwater springs, vegetation, and water influence the value of saline lakes as migration stopovers, we compared lakes used and not used by migrant shorebirds. Shorebirds used lakes that had freshwater springs, mudflats and standing water, sparse vegetation (≤1% cover), low to moderate salinities (𝑥̄ = 30.87 g/L), and mean invertebrate biomass of 0.79 g/m2. Lakes that were not used were generally dry or had hypersaline water (𝑥̄ = 82.56 g/L), lacked flowing springs and vegetation, and had few or no invertebrates (𝑥̄ = 0.007 g/m2). Our results suggest that reduced spring flows and increased salinity negatively affect availability of shorebird habitats and aquatic invertebrates. We recommend preservation of the freshwater springs discharging in the saline lakes. Because the springs are discharged from the Ogallala aquifer, which is recharged through the playa wetlands, the entire complex of wetlands in the Great Plains and the Ogallala aquifer should be managed as an integral system.

Investigating relationships between internal marketing practices and employee organizational commitment in the foodservice industry

Purpose – The purpose of this study is to investigate the relationships between internal marketing practices, employee job satisfaction, organizational commitment and turnover intention in the foodservice industry. Design/methodology/approach – The target population was employees who were currently working at a restaurant in the USA. All respondents were recruited from different states for the generalization of the study results. A confirmatory factor analysis validated the measurement model, and subsequently, structural equation modeling tested the proposed model. Findings – Three internal marketing practices – vision, development and rewards – were good indicators for predicting employee job satisfaction, and two internal marketing practices – development and rewards – in addition to job satisfaction were significant predictors for employee organizational commitment. Finally, the findings indicated that job satisfaction and affective commitment had a significant impact on lowering employee turnover inte...

Foraging Ecology of Migrant Shorebirds in Saline Lakes of the Southern Great Plains

Abstract. Tens of thousands of shorebirds use saline lakes as migratory stopovers in the Southern Great Plains, USA. To assess their foraging strategies and understand how they replenish energy reserves during spring and summer/fall migrations, we examined diets, prey taxa selection, and prey size selection of American Avocets (Recurvirostra americana), Least Sandpipers (Calidris minutilla), Wilsons Phalaropes (Phalaropus tricolor), and Lesser Yellowlegs (Tringa flavipes). Migrant shorebirds foraged opportunistically by taking most prey taxa according to their availability. Least Sandpipers preferred small prey (2–5 mm), whereas American Avocet, Wilsons Phalaropes, and Lesser Yellowlegs generally preferred intermediate and large prey (6–20 mm). By consuming prey taxa according to their availability and prey sizes that require minimum energy to capture and ingest, shorebirds increase their ability to replenish energy reserves while migrating through interior North America. Drought and drying of freshwater springs will reduce availability of prey in saline lakes for migrating shorebirds. To preserve the saline lakes as important habitats where shorebirds replenish nutrient reserves while migrating through the Great Plains, it is important to conserve groundwater so that freshwater springs continue to discharge into the lakes.

Swift Fox Use of Black-Tailed Prairie Dog Towns in Northwest Texas

Abstract Biologists have suggested that prairie dog (Cynomys ludovicianus) towns provide important habitat for several prairie species including swift foxes (Vulpes velox). To examine this issue for swift foxes, we radiocollared and monitored 72 swift foxes in areas occupied by prairie dogs on the Rita Blanca National Grasslands and on fragmented private ranches in northwest Texas from January 2002 to April 2004. We overlaid swift fox locations on vegetation maps and found that swift foxes used prairie dogs towns proportionately less than expected (P < 0.001) in 5 of 6 comparisons based upon availability at both study sites. In one comparison swift foxes used prairie dog towns as expected. We also mapped swift fox den locations and found that den sites were located in prairie dog towns (2 of 106 den sites on national grasslands and 2 of 87 on private ranch for all years pooled) as expected based upon availability (P = 0.54 and P = 0.34). Previous research in these areas of Texas indicated that prairie dogs were a minor component of swift fox diet (<2%). Prairie dog towns do not appear to provide important habitat for swift foxes in northwest Texas or other similar sites because prairie dogs are not a significant source of food for swift foxes, because swift foxes generally avoid prairie dog towns during their normal activities, and because swift foxes only den in prairie dog towns in relation to their availability.

ESTIMATING WATERSHED AREA FOR PLAYAS IN THE SOUTHERN HIGH PLAINS, USA

Hydrologic budgets for depressional wetlands require estimates of runoff from watersheds. In the Southern High Plains, where there is little elevation relief, ground surveys provide accurate watershed estimates but are time-consuming and costly. Estimates can be derived at lower cost from DEMs (Digital Elevation Models) and topographical maps, but data resolution and interpretation introduces errors. Other computational methods provide alternatives for estimating watershed area. Two computational methods based on longitudinal distances and elevations are described; minimal distance method and weighted minimal distance method. Twenty playas were ground surveyed to obtain baseline estimates of watershed area. Watershed areas for these 20 playas were also estimated using topographic maps, DEMs, and the two computational methods. The DEM method was not subsequently included in analyses because they did not have sufficient resolution. There were small differences in bias among the other methods. However, comparing the three alternative methods to ground survey estimates revealed that errors for the minimal distance method were larger than topographic map and weighted minimal distance methods. For computational accuracy, topographic map and weighted minimal distance methods are preferred. For modeling and computational ease, the weighted minimal distance method provides a simple alternative for calculating watershed area of playas.

The professional development of graduate mathematics teaching assistants

There is significant interest around the world in all issues involving the recruitment and retention of students in mathematics and sciences at all levels. Because of this there is great need for programmes that focus on providing well-prepared and effective teachers of mathematics and science at all levels. In this article, we present sample programmes in the US that focus on the professional preparation of mathematics graduate student teaching assistants. We give a detailed description of one such programme along with an assessment of its effects on the graduate students’ teaching practice and philosophy.

The Effects of the Number of Scale Points and Non-Normality on the Generalizability Coefficient: A Monte Carlo Study

Increasingly, assessment practitioners use generalizability coefficients to estimate the reliability of scores from performance tasks. Little research, however, examines the relation between the estimation of generalizability coefficients and the number of rubric scale points and score distributions. The purpose of the present research is to inform assessment practitioners of (a) the optimum number of scale points necessary to achieve the best estimates of generalizability coefficients and (b) the possible biases of generalizability coefficients when the distribution of scores is non-normal. Results from this study indicate that the number of scale points substantially affects the generalizability estimates. Generalizability estimates increase as scale points increase, with little bias after scales reach 12 points. Score distributions had little effect on generalizability estimates.

Evaluation of adult quail and egg production following exposure to perchlorate‐treated water

Twenty-three adult female northern bobwhite (Colinus virginianus) quail were exposed to 0, 0.01, 0.1, and 1 mM ammonium perchlorate (AP) in drinking water for 30 d. Eggs laid in all treatment groups, including control, were collected, dated, given an identification number, and weighed. On day 30 of exposure, 10 birds were euthanized by carbon dioxide asphyxiation. Gross toxicological endpoints and thyroid histology were evaluated in 10 birds. Egg production and accumulation of perchlorate in the eggs (n = 10) and liver (n = 5) were determined. Perchlorate did not affect body or organ weights significantly; however, at 1 mM, AP caused alteration of thyroid gland morphology. Perchlorate did not affect egg production, but significant accumulation was observed in the eggs and livers of exposed birds.

Pullout Resistance Factors for Steel MSE Reinforcements Embedded in Gravelly Backfill

Abstract This paper presents results from a laboratory program of 287 pullout tests of galvanized steel reinforcements used in the construction of mechanically stabilized earth (MSE) walls. Results focus on the evaluation of pullout resistance factors for ribbed steel strip and welded steel grid reinforcement embedded in gravelly backfill. This project used Texas Tech University’s large-scale MSE test box with dimensions of 3.6 × 3.6 × 1.2 m and an applied overburden capacity equivalent to 12 m of soil fill. The research design evaluated pullout resistance factors for both ribbed strip and welded grid reinforcements for a variety of independent variables, including overburden pressure, reinforcement length, grid bar size, and grid geometry including both transverse and longitudinal bar spacing. Appropriate statistical analyses were used to interpret the data within the context of published design guidance for inextensible MSE reinforcements. The results show that pullout resistance factors for both ribb...