Using and interpreting diagnostic tests.

Diagnostic tests are invaluable to the practice of veterinary medicine. Using them correctly and interpreting the results appropriately depend on having a good understanding of the basic principles outlined in this article. Topics covered include sensitivity and specificity, agreement among tests, using multiple tests, and other issues related to the use and interpretation of diagnostic tests. The most important principle is recognition that the interpretation of test results varies across populations and requires an estimate of the prevalence of the infection (or disease) in the population being studied.     

Effect of Daily Soil Temperature Fluctuations on Soil Electrical Conductivity as Measured with the Geonics® EM-38

Soil electrical conductivity (EC_a) measured by electromagnetic induction (EM) using the EM-38 has shown promise as a soil survey tool. Soil temperature influences EC_a readings, and temperature can fluctuate considerably in the upper 10cm of the soil during a day. EC_a readings were taken in the horizontal and vertical dipole orientations once an hour from 8a.m. to 8p.m. at four sites on three separate days to determine if EC_a values were influenced by diurnal temperature variations. Soil temperature readings were taken at the same times at four depths. EM-38 readings remained steady at all four sites all 3days. Linear regression analysis when temperature in the upper 10cm was plotted against EC_a yielded low r ² values and slopes, indicating no correlation between soil temperature in the upper 10cm and EC_a values. Diurnal changes in soil temperature do not significantly influence soil EC_a readings obtained with the EM-38 under the conditions encountered during the study.     

Depletion of florfenicol amine in tilapia (Oreochromis sp.) maintained in a recirculating aquaculture system following Aquaflor®‐medicated feed therapy

Aquaflor^® [50% w w^?1 florfenicol (FFC)], is approved for use in freshwater‐reared warmwater finfish which include tilapia Oreochromis spp. in the United States to control mortality from Streptococcus iniae. The depletion of florfenicol amine (FFA), the marker residue of FFC, was evaluated after feeding FFC‐medicated feed to deliver a nominal 20 mg FFC kg^?1 BW d^?1 dose (1.33× the label use of 15 mg FFC kg^?1 BW d^?1) to Nile tilapia O. niloticus and hybrid tilapia O. niloticus × O. aureus held in a recirculating aquaculture system (RAS) at production‐scale holding densities. Florfenicol amine concentrations were determined in fillets taken from 10 fish before dosing and from 20 fish at nine time points after dosing (from 1 to 240 h post‐dosing). Water samples were assayed for FFC before, during and after the dosing period. Parameters monitored included daily feed consumption and biofilter function (levels of ammonia, nitrite and nitrate). Mean fillet FFA concentration decreased from 13.77 μg g^?1 at 1‐h post dosing to 0.39 μg g^?1 at 240‐h post dosing. Water FFC concentration decreased from a maximum of 1400 ng mL^?1 at 1 day post‐dosing to 847 ng mL^?1 at 240 h post‐dosing. There were no adverse effects noted on fish, feed consumption or biofilter function associated with FFC‐medicated feed administration to tilapia.     

Leaf gas exchange characteristics differ among Sonoran Desert riparian tree species

We investigated leaf gas exchange responses to leaf temperature, leaf-to-air vapor pressure deficit (VPD), and predawn and midday shoot water potential (psipd and psimd, respectively) of two native Sonoran Desert riparian tree species, Fremont cottonwood (Populus fremontii S. Wats.) and Goodding willow (Salix gooddingii Ball), and one exotic riparian tree species, saltcedar (Tamarix chinensis Lour. and related species). Measurements were made at two sites over 2 years that differed climatically. Because multiple linear regression models explained less than 29% of the variation in stomatal conductance (gs) and less than 48% of the variation in net photosynthetic rate (Pn) of all species, we used boundary-line analysis to compare gas exchange responses among species. Gas exchange rates were high in all species. The hyperbolic relationship between Pn and gs suggested that initial reductions in gs at high gs did not inhibit Pn. Reductions in gs of cottonwood and willow occurred at psimd values at or below previously reported xylem cavitation thresholds (-1.6 and -1.4 MPa, respectively), indicating tight stomatal regulation of water loss and a narrow cavitation safety margin. In contrast, reductions in gs of saltcedar occurred at psimd values well above the cavitation threshold (-7.0 MPa), but at much lower psimd values than in cottonwood and willow, suggesting a wider cavitation safety margin and less tight regulation of water loss in saltcedar. High VPD had a smaller effect on leaf gas exchange in willow than in cottonwood. In contrast, willow had a less negative psipd threshold for stomatal closure than cottonwood. Compared with cottonwood and willow, leaf gas exchange of saltcedar was more tolerant of high VPD and low psipd. These physiological characteristics of saltcedar explain its widespread success as an invader of riparian ecosystems containing native Fremont cottonwood and Goodding willow in the Sonoran Desert.     

Validating landtype associations using forest inventory and analysis data and neutral landscape models

One of the principal uses of land type associations (LTAs) is to provide information on ecological patterns and potentials useful for identifying alternatives and setting vegetation management objectives at landscape and watershed scales. Since LTA identification and delineation is an iterative process involving subjective decisions, it is imperative that LTAs accurately capture measurable distinctions in vegetation. In this study, we provided a framework for validating LTAs in Missouri’s. We chose a suite of variables from the Forest Inventory and Analysis database of the US Forest Service, an independent source, to capture a wide range of characteristics of the forest ecosystem. These variables included forest type, species composition, species diversity, species richness, site index, density of all trees 1 inch dbh and greater, and density of all trees 5 inch dbh and greater. First, the appropriateness of grouping LTAs into broader LTA types (identifications) was examined, and results suggest that species composition is more similar within LTA Type than among LTA Types. Second, a neutral model approach was used to evaluate the variables used in the study, and it was shown that forest type and the two density measures validated LTA adjacencies no more often than randomly delineated LTAs. Therefore, these three variables were removed from the analysis. Finally, comparisons of adjacent LTAs using statistical analysis of remaining variables resulted in the validation of 480 of the 623 compared adjacencies, showing a significant difference in at least one variable. Results of this study provide a quantitative measure of Missouri LTAs and reveal LTAs that have less distinction and need further refinements.     

Spatial pattern corrections and sample sizes for forest density estimates of historical tree surveys

The U.S. General Land Office land surveys document trees present during European settlement. However, use of these surveys for calculating historical forest density and other derived metrics is limited by uncertainty about the performance of plotless density estimators under a range of conditions. Therefore, we tested two plotless density estimators, developed by Morisita and Pollard, for two, three, and four trees per survey point under simulated ranges of tree densities, non-uniform densities, and different tree spatial distributions. Based on these results, we developed estimator corrections and determined number of survey points needed for reliable density estimates. The Morisita estimator was accurate for densities ranging from 5 to 1,000 trees per unit area, non-uniform densities, random and regular spatial distribution, and outperformed the Pollard estimator. Estimators using points with two or three trees did need a simple correction to account for overestimation. Likewise, for clustered distributions, depending on the number of trees per survey point and the amount of clustering, there should be adjustment for a range of under and overestimation. Sample sizes for survey points with three or four trees should be at least 200 survey points, and 1,000 survey points will have density estimates within ±10% tolerance range of actual density. For survey points with two trees, the minimum sample size should be 600 survey points, and 2,000 survey points should be the target value. These results provide guidelines for researchers to improve density estimates of historical forests.     

Detection of relative differences in phenology of forest species using Landsat and MODIS

Landsat imagery is routinely used to characterize stand-level forest communities, but low temporal resolution makes pixel-wise characterization of phenology difficult. This limitation can be overcome by using multi-year imagery, but organizing Landsat scenes by calendar date ignores phenological gradients across the landscape as well as inter-annual differences in both scene- and pixel-wise phenology. We demonstrate how a spatially generalizable, phenologically-informed approach for re-ordering Landsat pixels can be used to characterize spatial variations in autumn senescence in several forest tree species. Using end-of-season estimates derived from MODIS phenology data, we determined the “days left in season” (DLiS) across Landsat images to produce a synthesized phenological trajectory of the normalized difference infrared index (NDII). We used ground-based species composition data in conjunction with the NDII trajectories to model autumn senescence by species. Absolute phenology differed by one and a half to 3 weeks between northern and southern Wisconsin, USA, but we show that the relative timing of phenology for individual species differs across regions by only 1–3 days when considering senescence with respect to the local end of the season. The progression of species senescence was consistent in lowland stands, starting with green and black ash, followed by silver maple, yellow birch, red maple, and tamarack. The image analyses suggest that senescence progressed more rapidly in southern than northern Wisconsin, starting earlier but taking about ten more days in the north. Our results support the use of MODIS phenological data with multi-year Landsat imagery to detect species with unique phenologies and identify how these vary across the landscape.     

Scale-specific habitat relationships influence patch occupancy: defining neighborhoods to optimize the effectiveness of landscape-scale grassland bird conservation

Context

Beyond the recognized importance of protecting large areas of contiguous habitat, conservation efforts for many species are complicated by the fact that patch suitability may also be affected by characteristics of the landscape within which the patch is located. Currently, little is known about the spatial scales at which species respond to different aspects of the landscape surrounding an occupied patch.

Objectives

Using grassland bird point count data, we describe an approach to evaluating scale-specific effects of landscape composition on patch occupancy.

Methods

We used data from 793 point count surveys conducted in idle and grazed grasslands across Wisconsin, USA from 2012 to 2014 to evaluate scale-dependencies in the response of grassland birds to landscape composition. Patch occupancy models were used to evaluate the relationship between occupancy and landscape composition at scales from 100 to 3000 m.

Results

Bobolink (Dolichonyx oryzivorus) exhibited a pattern indicating selection for grassland habitats in the surrounding landscape at all spatial scales while selecting against other habitats. Eastern Meadowlark (Sturnella magna) displayed evidence of scale sensitivity for all habitat types. Grasshopper Sparrow (Ammodramus savannarum) showed a strong positive response to pasture and idle grass at all scales and negatively to cropland at large scales. Unlike other species, patch occupancy by Henslow’s Sparrow (A. henslowii) was primarily influenced by patch area.

Conclusions

Our results suggest that both working grasslands (pasture) and idle conservation grasslands can play an important role in grassland bird conservation but also highlight the importance of considering species-specific patch and landscape characteristics for effective conservation.

     

Predictors of the distribution of street and backyard vegetation in Montreal,Canada

Urban vegetation is shown to be unevenly distributed across cities and there is evidence of disparities in benefits provided by vegetation and of public health problems induced by urban heat islands. In order to improve vegetation cover, it remains crucial to understand the underpinning of such unevenness. In this paper, we investigate in Montreal (Canada) how the built environment, sociodemographic factors and administrative boroughs influence tree and lawn cover in public and residential land. The analysis was conducted at the dissemination area (DA) level, a Canadian census unit containing about 400–700 people. Six vegetation indicators were used as dependent variables: the proportion of a DA covered by trees/shrubs, lawn and total vegetation; the proportion of streets covered by trees/shrubs and the proportion of residential yards covered by trees/shrubs and total vegetation. Three sets of independent variables were studied: the built environment, sociodemographics and borough names. We used spatial autoregressive models to control for dependence and the spatial autoregressive term explained a large amount of variability in vegetation cover. The built-environment variables tend to have higher effects than the socio-demographic variables when predicting the three DA vegetation indicators, backyard vegetation, and to a lesser degree, street tree/shrub cover. In particular, population density is associated negatively to all indicators but positively to street tree cover. Socio-demographics are substantial in the explanation of the distribution of street trees, especially the presence of recent immigrants (negative effect) and of university degree holders (positive effect). These findings call for appropriate greening programs adapted to the local socio-demographic profile. The significance of boroughs also suggests the need for further research on the impact of within-city administrative hierarchies on the unevenness of urban vegetation.