Difference In Mean Density Research Articles

Multiphase simulations of nonlinear fluids with SPH

A modified apparent viscosity approach has been implemented for a weakly compressible SPH scheme for two-phase flows where a nonlinear phase must yield under erosive dynamics but also maintain a pseudosolid behaviour under the right conditions. The final purpose is to provide a means to model both dam-break dynamics and erosive interactions between different phases simultaneously while also keeping smooth pressure fields in spite of discontinuities introduced by viscosity variations of a nonlinear phase along with significant differences in mean density. Key contributions include purposeful avoidance of nonphysical elastic behaviour and the integration of a specific particle shifting technique that allows for proper replication of erosion and scouring. In this work, the method is validated by applying it to model a silted-up dam that collapses over a static water bed, effectively including all main elements of interest. Although the formulation is inherently three dimensional, validation is done by direct comparison with data from physical experiments of a dominant two-dimensional nature, assuming variable yield stress of medium-grain quartz sand according to the Drucker–Prager equation. Overall results show most of the expected interface dynamics, such as erosion and transportation of the nonlinear phase, sustained piling of the non-yielded volume of silt, and good correspondence of both granular and water surface position with experimental data. Finally, a series of modelling assumptions and implications for future developments are explicitly stated because of their direct impact on stability and versatility for multiphase, nonlinear flows in general.

Can virtual non-contrast imaging replace true non-contrast imaging in multiphase scanning of the neck region?

Dual-energy computed tomography (DECT) is an advanced imaging method that enables reconstruction of virtual non-contrast (VNC) images from a contrast-enhanced acquisition. This has the potential to reduce radiation exposure by eliminating the need for a true non-contrast (TNC) phase. The purpose is to evaluate the feasibility of VNC images in the neck region. A total of 100 patients underwent a DECT scan as part of diagnostic workup of primary hyperparathyroidism. VNC images were reconstructed from 30s (arterial) and 50s (venous) post-contrast scans. Regions of interest (ROIs) were placed in thyroid tissue, lymph node, carotid artery, jugular vein, fat, and sternocleidomastoid muscle. Mean densities of all anatomical structures were compared between VNC and TNC images. For all anatomical structures except the thyroid gland, the difference in mean density between TNC and VNC images was less than 15 HU. The mean difference in density between TNC and VNC images of the thyroid was 53.2 HU (95% CI 46.8; 59.6, p = <0.001). This study demonstrated an acceptable agreement in density between true non-contrast and virtual non-contrast images for most anatomical structures in the neck region. Therefore, VNC images may have the potential to replace TNC images in the neck. However, due to significant differences in CT density of thyroid tissue, true non-contrast imaging cannot be directly substituted by virtual non-contrast imaging when examining the thyroid and its surrounding tissue.

Reviewing the knowledge on the genus Patella in the Mediterranean Sea: testing the effect of protection on the mean abundance and size of Patella ferruginea

Increasing human pressure has strongly impacted the littoral environment, altering the habitats and population parameters of some species. The Mediterranean Sea is one of the regions that have been highly affected by these events. In response to these events, marine protected areas (MPAs) have emerged as one of the main conservation tools for marine habitats and species. In this regard, harvesting of limpets (Patella spp.) is a good example of the impact of human activity on the coast. Limpets are mollusks that are collected as food or fishing bait, and their exploitation causes an immediate decrease in the density and size structure of individuals. In the Mediterranean Sea, the genus Patella is represented by five species: Patella rustica, P. caerulea, P. ulyssiponensis, P. ferruginea, and P. depressa. To verify the effectiveness of the MPAs, a deep review of 75 studies on Patella spp. in the Mediterranean Sea was conducted to analyze the spatial and temporal distribution of studies. Data extracted from these articles were used to assess the effect of protection on the density and size of P. ferruginea. Regarding spatial distribution, the studies reviewed were performed at 67 sites in 13 countries, of which 23 were in MPAs and 44 in non-protected or control areas. The findings of this study show that P. ferruginea is the species most studied, because it is one of the most threatened marine invertebrates in the Mediterranean Sea. This explains the temporal distribution of the studies, which coincides with the establishment of the conservation status and the concern about the population status of P. ferruginea. Analysis of the effect of protection on the density and mean size of P. ferruginea individuals revealed no significant difference in mean density between the control sites and MPAs. However, mean size between individuals was significantly higher in MPAs than control sites. This pattern may be related to intra- and interspecific competition between individuals.

Subantarctic Mode Water Biogeochemical Formation Properties and Interannual Variability

AbstractSubantarctic mode water (SAMW) is a key water mass for the transport of nutrients, oxygen, and anthropogenic carbon into the ocean interior. However, a lack of biogeochemical observations of SAMW properties during wintertime formation precluded their detailed characterization. Here we characterize for the first time SAMW properties across their entire wintertime formation regions based primarily on biogeochemical profiling floats. Observations show that the SAMW properties differ between the two main formation regions in the Pacific and Indian sectors of the Southern Ocean. SAMW formed in the Pacific is colder, fresher, and higher in oxygen, nitrate, and dissolved inorganic carbon (DIC) than its Indian Ocean counterpart. The relationship between potential density and biogeochemical water properties is nearly identical between the two formation regions; property differences thus predominantly reflect the difference in mean densities of SAMW formed in each region. SAMW is undersaturated in oxygen during formation, which will impact calculations of derived quantities that assume preformed oxygen saturation. SAMW is at or above atmospheric pCO2 during wintertime and therefore not a direct sink of contemporary carbon dioxide during the formation period. Results from the Biogeochemical Southern Ocean State Estimate suggest anti‐correlated interannual variability of DIC, nitrate, and oxygen between the central and southeastern Pacific formation regions similar to previously established patterns in mixed layer physical properties. This indicates that the mean properties of SAMW will vary depending on which sub‐region has a stronger formation rate, which is in turn linked to the Southern Annual Mode and the El‐Niño Southern Oscillation.

Population Density and Reproductive Seasonality of Tryonia cheatumi (Gastropoda: Cochliopidae), the Phantom Tryonia

We studied population density, population size, and reproductive seasonality of the Phantom Tryonia, Tryonia cheatumi (Pilsbry, 1935). This endangered freshwater snail is found only in the San Solomon Spring system, a cienega, or karst-based, arid-land freshwater spring system, in western Texas, USA. We sampled populations at seven locations in the system seasonally over a 2-yr period. San Solomon Spring, the system's largest spring and modified into a swimming pool, had the largest population of T. cheatumi, with an estimated 49 million individuals and a mean density as high as 23,626 ± 39,030 (individuals/m2 ± SD). There were seasonal differences in mean density (up to 25-fold) and median snail size at all sites, but consistent seasonal patterns of mean density or size were not observed. Median snail size among samples was not related to water temperature, and juveniles were present in most samples in all seasons. These results support continuous, aseasonal reproduction, as expected in thermally stable habitats, but differences in median size and mean density among seasons and sites suggest that other factors affect reproduction and seasonal variation in population size of T. cheatumi.

On Replicates for Comparing Species Densities in Space and Time

ABSTRACT Because benthic foraminifera exhibit spatial heterogeneity, a number of replicates or multiple biological samples are necessary to estimate population densities. In this study, we empirically examine the efficacy of taking four or fewer replicates to differentiate among mean densities in location and time using p-values as a metric for strength of evidence against the null hypothesis of no difference in taxon density. For spatial analyses, four stations along a traverse with four replicates per station were compared with ANOVA within Mission Bay, Texas, using the four most abundant taxa. The p-values for comparing mean densities among stations increased markedly for all taxa, as the number of samples per station decreased from four to two. Using a test level of 0.05, four replicates per station resulted, on average, in significant differences for three of four taxa, three replicates distinguished two of four taxa, and two replicates detected only one difference. For temporal analyses, a single station was sampled in the Indian River Lagoon, Florida, seasonally over four years. Again, p-values increased markedly as the number of samples per station decreased. Using a test level of 0.05, both four- and three-replicate groups were found to separate mean densities among the four years for three of four taxa, two replicates distinguished one taxon, and use of only one replicate could not detect any difference in mean densities among the four years. Based on these and previous field results, we recommend at least four replicates per station for environmental monitoring. However, when examining mean densities within larger ecological entities such as biofacies, just one sample at each station along a single traverse containing four stations in each bay could delineate Mission, Copano, and Mesquite bays in Texas.

Impact of combining indoor residual spraying and long-lasting insecticidal nets on Anopheles arabiensis in Ethiopia: results from a cluster randomized controlled trial

BackgroundIndoor residual house spraying (IRS) and long-lasting insecticidal nets (LLINs) are the key front-line malaria vector interventions against Anopheles arabiensis, the sole primary malaria vector in Ethiopia. Universal coverage of both interventions has been promoted and there is a growing demand in combinations of interventions for malaria control and elimination. This study compared the impact on entomological outcomes of combining IRS and LLINs with either intervention alone in Adami Tullu district, south-central Ethiopia. The epidemiological outcomes were recently published on a separate paper.MethodsThis factorial, cluster-randomized, controlled trial randomized villages to four study arms: IRS + LLIN, IRS, LLIN, and control. LLINs (PermaNet 2.0) were provided free of charge. IRS with propoxur was applied before the main malaria transmission season in 2014, 2015 and 2016. Adult mosquitoes were collected in randomly selected villages in each arm using CDC light trap catch (LTC) set close to a sleeping person, pyrethrum spray catch (PSC), and artificial pit shelter (PIT), for measuring mosquito host-seeking density (HSD), indoor resting density (IRD), and outdoor resting density (ORD), respectively. Human landing catch (HLC) was performed in a sub-set of villages to monitor An. arabiensis human biting rates (HBR). Mean vector densities and HBR were compared among study arms using incidence rate ratio (IRR) calculated by negative binomial regression.ResultsThere were no significant differences in mean densities (HSD, IRD, ORD) and HBR of An. arabiensis between the IRS + LLIN arm and the IRS arm (p > 0.05). However, mean HSD, IRD, ORD, and HBR were significantly lower in the IRS + LLIN arm than in the LLIN alone arm (p < 0.05). All An. arabiensis tested for malaria infection were negative for Plasmodium species. For this reason, the entomological inoculation rate could not be determined.ConclusionsThe IRS + LLIN were as effective as IRS alone in reducing densities and HBR of An. arabiensis. However, the effectiveness of the two interventions combined was higher than LLINs alone in reducing densities and HBR of the vector. Added impact of the combination intervention against malaria infectivity rates of An. arabiensis compared to either intervention alone remains unknown and warrants further research.Trial registration PACTR201411000882128. Registered 8 September 2014, https://trialsjournal.biomedcentral.com/articles/10.1186/s13063-016-1154-2

Impact of land use and tenure changes on the Kitenden wildlife corridor, Amboseli Ecosystem, Kenya

AbstractThis study assesses the ecological pressure exerted by changing land use and tenure on the Kitenden wildlife corridor, a critical cross‐border link between the Amboseli and Kilimanjaro national parks. The implications on viability of the two high‐value protected areas and their respective dispersal areas are both negative and serious. The extent of land use change and its impacts were assessed through household and vegetation surveys, while wildlife abundance was measured using transect walks. Approximately 30% of the study area has shifted from community to private land ownership over the last two decades. Except for baboon and vervet monkey, most wildlife avoided the cultivated area. Vegetation composition on the noncultivated area has been greatly altered by intense wildlife and livestock use, where mean herbaceous vegetation cover differed significantly among range‐plant categories (F3, 524 = 29.015, p &lt; 0.05). The frequency of increaser I (21.4%) differs greatly from that of decreaser and forbs, at 8.3% and 7.4%, respectively Tree recruitment was low, with a significant difference in mean density among age classes (F2, 110 = 3.663, p &lt; 0.05). Only through land leasing agreements between landowners and conservation organisations, and a widely supported land use plan, can the spread of cultivation be controlled and complete cessation of wildlife movement be prevented.

Effects of Planetesimal Accretion on the Thermal and Structural Evolution of Sub-Neptunes

Abstract A remarkable discovery of NASA’s Kepler mission is the wide diversity in the average densities of planets of similar mass. After gas disk dissipation, fully formed planets could interact with nearby planetesimals from a remnant planetesimal disk. These interactions would often lead to planetesimal accretion due to the relatively high ratio between the planet size and the hill radius for typical planets. We present calculations using the open-source stellar evolution toolkit mesa (Modules for Experiments in Stellar Astrophysics) modified to include the deposition of planetesimals into the H/He envelopes of sub-Neptunes (∼1–20 M ⊕). We show that planetesimal accretion can alter the mass–radius isochrones for these planets. The same initial planet, as a result of the same total accreted planetesimal mass, can have up to ≈5% difference in mean densities approximately several gigayears after the last accretion due to the inherent stochasticity of the accretion process. During the phase of rapid accretion, these differences are more dramatic. The additional energy deposition from the accreted planetesimals increase the ratio between the planet’s radius to that of the core during rapid accretion, which in turn leads to enhanced loss of atmospheric mass. As a result, the same initial planet can end up with very different envelope mass fractions. These differences manifest as differences in mean densities long after accretion stops. These effects are particularly important for planets that are initially less massive than ∼10 M ⊕ and with envelope mass fractions less than ∼10%, thought to be the most common type of planets discovered by Kepler.

Month-to-Month Variations in Densities and Dominance of Birds Breeding in an Extensive Pine Forest

Abstract Month-to-month changes in avian assembages are considerable in forest habitats. In this study such changes were studied by means of the line transect method (eight transect with total length of 77.7 km) in lowland coniferous forest in SW Poland (dominant forest type in Central European Plain), in three consecutive spring months: April, May and June. Shannon’s diversity index varied between 1.31 and 2.25 in particular month, while Simpson’s diversity index and Pielou’s evenness index were almost identical everywhere: H′ = 0.92-0.93 and J′ = 0.74-0.78, respectively. In overall, the differences in mean densities of breeding species between three months on all transects pooled were not statistically significant, as were also not statistically significant such differences on particular transects. Month-to-month variations in densities in all transects pooled were statistically significant in the case of 26 out of 54 species (48.1 %). Month-to-month changes in population densities recorded on transects, only partly conform to the arrival patterns. Two counts, instead of three, would sufficed for precise estimation of bird population densities in Central European lowland pine forests: one count should be conducted in April, to register mainly resident species, and the second one in May to count mainly the migrant species.

DINÂMICA DA CHUVA DE SEMENTES EM REMANESCENTE DE FLORESTA ESTACIONAL SUBTROPICAL

O presente estudo teve por objetivo avaliar a dinâmica da chuva de sementes em dois agrupamentos florísticos formados em um remanescente de Floresta Estacional Subtropical. Os agrupamentos foram caracterizados pelo estágio sucessional da floresta, denominados de grupo I (Floresta Secundária em Estágio Médio - FSEM), com predomínio de espécies secundárias iniciais; e o grupo II (Floresta Secundária em Estágio Avançado - FSEA), com predomínio de espécies secundárias tardias. A chuva de sementes (CS) foi avaliada em 70 coletores de 1 m², distribuídos de forma aleatória nos dois agrupamentos, sendo que no grupo I foram instalados 15 coletores e no grupo II, por apresentar maior área, 55 coletores. O material depositado foi coletado mensalmente, no período de outubro de 2008 a outubro de 2010. A dinâmica da CS foi avaliada pela densidade de sementes de cada espécie, síndrome de dispersão e sazonalidade da produção. Utilizou-se o teste não paramétrico da Soma das Ordens de Wilcoxon (W) para verificar diferenças estatísticas nas médias de densidade de sementes em cada ano de avaliação para cada trecho de floresta. A chuva de sementes do remanescente estudado, durante os três anos de estudo, foi representada por 114 espécies e a maior produção de sementes ocorreu em 2008 (1632 sem.m-² no grupo I e 1270 sem.m-² no grupo II), principalmente devido à ocorrência da alta produção de Chusquea ramosissima Lindm., Dasyphyllum spinescens (Less.) Cabrera, Vernonanthura discolor (Spreng.) H.Rob. Somente no segundo ano (2009) observaram-se diferenças estatísticas nas médias de densidade entre os dois grupos analisados (FSEM=565,6 sem.m-2 e FSEA=274 sem.m-2; Z tabelado =1,96 e W FSEM x FSEA = 2,248). As espécies zoocóricas predominaram na área de estudo, e os períodos de maior produção de sementes foram o inverno e a primavera. A CS mostrou-se importante mecanismo de regeneração natural para o remanescente de floresta, sendo afetado pelas condições climáticas e estágio sucessional da floresta.

Agreement and precision of periprosthetic bone density measurements in micro-CT, single and dual energy CT.

The objective of this study was to test the precision and agreement between bone mineral density measurements performed in micro CT, single and dual energy computed tomography, to determine how the keV level influences density measurements and to assess the usefulness of quantitative dual energy computed tomography as a research tool for longitudinal studies aiming to measure bone loss adjacent to total hip replacements. Samples from 10 fresh-frozen porcine femoral heads were placed in a Perspex phantom and computed tomography was performed with two acquisition modes. Bone mineral density was calculated and compared with measurements derived from micro CT. Repeated scans and dual measurements were performed in order to measure between- and within-scan precision. Mean density difference between micro CT and single energy computed tomography was 72 mg HA/cm3 . For dual energy CT, the mean difference at 100 keV was 128 mg HA/cm3 while the mean difference at 110-140 keV ranged from -84 to -67 mg HA/cm3 compared with micro CT. Rescanning the samples resulted in a non-significant overall between-scan difference of 13 mg HA/cm3 . Bland-Altman limits of agreement were wide and intraclass correlation coefficients ranged from 0.29 to 0.72, while 95% confidence intervals covered almost the full possible range. Repeating the density measurements for within-scan precision resulted in ICCs >0.99 and narrow limits of agreement. Single and dual energy quantitative CT showed excellent within-scan precision, but poor between-scan precision. No significant density differences were found in dual energy quantitative CT at keV-levels above 110 keV. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1470-1477, 2017.

Waterbird response to management practices in rice fields intended to reduce greenhouse gas emissions

There are many benefits of agricultural landscapes for wildlife. In California's Central Valley, post-harvest flooding of rice fields increases the decomposition of rice stubble and provides habitat for over 50 species of waterbirds. These fields are also flooded during planting, providing habitat for spring migrants and locally breeding birds. Because California has lost over 90% of its historic wetlands, flooded rice is critical wildlife habitat, providing 80% of the total flooded habitat in the Sacramento Valley. Flooding rice fields, however, contributes to greenhouse gas (GHG) emissions. Several rice field management practices may reduce methane emissions including reduced flooding in winter, removal of rice straw after harvest (baling), and drill seeding during planting. During the winters of 2011–2012 and 2012–2013, we compared waterbird use in four combinations of post-harvest practices: baled/flooded, baled/non-flooded, non-baled/flooded, and nonbaled/non-flooded. We found significantly higher dabbling duck and shorebird densities in the non-baled/flooded practice compared to the other three practices. During the spring of 2012 and 2013, we compared waterbird use of drill-seeded fields (reduced GHG) with flooded fly-on seeded fields (status quo GHG). We found no significant differences in mean density between the two seeding practices for waterbirds. Our study found evidence that some post-harvest practices (reduced winter flooding, baling) that reduce GHG emissions from rice also reduce use by waterbirds. While reducing GHG is globally necessary to minimizing the impacts of climate change, doing so in an area of hemispheric importance for waterbirds should be done with caution.

Further expansion of the invasive musselSinanodonta woodiana(Lea, 1834) in Poland – establishment of a new locality and population features

The increasingly frequent appearance of invasive species of mussels is a common phenomenon nowadays. Their rapid expansion is a significant component of the global changes that pose a great ecological impact and a serious threat to the diversity of native fauna. This study documents new localities of occurrence of Sinanodonta woodiana in Poland. We also attempted to determine its density, biomass, morphometric features and age structure. We found that its presence is clearly related to temperature and that the current range of its occurrence in Poland mostly overlaps with the areas with the highest average annual temperatures. The study showed significant differences in mean density between the fishponds: on particular sites the density amounted to 9 individuals/m2 and their biomass exceeded 3000 g/m2 . ANOVA revealed significant differences in the mean dimensions of the shells between the three fishponds related to their height and width. Seven-year-old individuals were the most numerous while one-, two-, five- and six-year-old specimens were the most numerous in pond 2. In our opinion, S. woodiana has created a permanent population that is probably able to breed. This is confirmed by the appearance of one-year-old individuals as well as the other younger age classes.

Post-fire regeneration dynamics of tree species in a tropical dry deciduous forest, Western Ghats, India

This study was aimed to understand the effect of repeated fire on tropical dry deciduous forest in Mudumalai Tiger Reserve (MTR), Western Ghats. Tropical dry deciduous forests are prone to forest fire owing to high fuel load and long dry season. Fire frequency map of the study area was prepared for 15years from 1999 to 2013 using annual burn maps. Study area was stratified as B1 to B6 (one to six times burned) and compared to control (B0 – unburned during 1999–2013). Three plots were randomly laid in each stratum and seedlings; saplings and trees present in each plot were recorded. Species diversity indices showed increase in dominance and decrease in diversity with increasing fire frequency. Results showed that overall stem density (>1cm DBH) ranged from 576 (SD 112.69) (B1) to 236 (SD 20) individual ha−1 (B6). The basal area ranged from 36.8 (SD 2.19) m2ha−1 (B0) to 12.12 (SD 2.69) m2ha−1 (B5). Fire promoted seedling density from B0 to B2 and after that it started decreasing whereas sapling density was poor in all classes and recorded least in B6. Stem density of trees did not vary much up to B3 and started decreasing after that. Number of species decreased linearly with increasing fire frequency. In the analysis of dominant species, Tectona grandis showed a very significant mean difference in seedling, sapling and tree population whereas Terminalia cranulata did not show significant difference in mean densities of seedling, sapling or trees. It is found that fire with long interval can promote seedlings density but species diversity decreases with increasing fire frequency.

Natural Circulation Cooling Scram Transient Analysis in Advanced BWRs: Buoyancy Effects

In this study, the transient characteristics of a two-phase natural circulation core cooling in advanced boiling water reactors is investigated during a scram scenario. The natural circulation is controlled by the mean density difference between the coolant inside and outside of the core. The Boussinesq approximation was applied in the momentum equations for two-phase flow analysis that considers the buoyancy force, which is related with thermal effects. The results obtained in transient with the buoyancy force in the core were compared with the standard approximation. The found results for scram transient indicate that, for time–scale, a small trend is practically the same between Boussinesq and standard approximation, where the difference between them is small. However, for higher simulation time (8 to 12 s) the consequences of the drive force effects are appreciable.

A reproducible automated segmentation algorithm for corneal epithelium cell images from in vivo laser scanning confocal microscopy

To evaluate an automated process to find borders of corneal basal epithelial cells in pictures obtained from in vivo laser scanning confocal microscopy (Heidelberg Retina Tomograph III with Rostock corneal module). On a sample of 20 normal corneal epithelial pictures, images were segmented through an automated four-step segmentation algorithm. Steps of the algorithm included noise reduction through a fast Fourier transform (FFT) band-pass filter, image binarization with a mean value threshold, watershed segmentation algorithm on distance map to separate fused cells and Voronoi diagram segmentation algorithm (which gives a final mask of cell borders). Cells were then automatically counted using this border mask. On the original image either with contrast enhancement or noise reduction, cells were manually counted by a trained operator. The average cell density was 7722.5 cells/mm(2) as assessed by automated analysis and 7732.5 cells/mm(2) as assessed by manual analysis (p=0.93). Correlation between automated and manual analysis was strong (r=0.974 [0.934-0.990], p<0.001). Bland-Altman method gives a mean difference in density of 10 cells/mm(2) and a limits of agreement ranging from -971 to +991 cells/mm(2) . Visually, the algorithm correctly found almost all borders. This automated segmentation algorithm is worth for assessing corneal epithelial basal cell density and morphometry. This procedure is fully reproducible, with no operator-induced variability.

Natural Circulation Core Cooling Steady State Analysis in Advanced BWRs

In this study, the steady-state characteristics of two-phase natural circulation core cooling in advanced boiling water reactors is investigated. The natural circulation is controlled by the mean density difference between the coolant inside and outside of the core. The Boussinesq approximation was applied in the momentum equations for two-phase flow analysis that considers the buoyancy force, which is related with thermal effects. The results obtained in steady state with the buoyancy force in the core were compared with the standard approximation. It was found that the buoyancy effects in two-phase flow can be important in the nuclear design of advanced boiling water reactors, due to the fact that nuclear parameters, such as thermal-hydraulics and neutronic, power, void fraction, fuel temperature, heat flux, mass flow rate in the core (superficial velocities), feedwater flow, and main steam flow, are appreciably influenced by this physical phenomena.

Breeding bird assemblage dynamics of a primaeval temperate mixed forest in the Western Carpathians (Slovakia): support for pluralistic community concept

Structure and dynamics of breeding bird assemblages of primaeval beech-fir forest in the Šrámková National Nature Reserve, the Malá Fatra Mts., Slovakia were studied during ten consecutive years 1997–2006. Bird abundances were estimated by the combined ver-sion of the mapping method in the 27.5 ha forest interior study plot. Determination of for-aging guild structure was done by a posteriori approach by a numerical analysis of ran-dom point observations of foraging birds. In total, 53 bird species were recorded as breed-ers in the study plot, averaging 39.0 species per year. Mean value of population variability coefficient (PV) of density of the 22 most numerous species was 0.33 ± 0.14 SD (CV = 42.05%) indicating a mean difference in density among years of 33%. The highest fluctu-ations were detected in plant eaters (PV = 0.47, N = 3) followed by flycatchers (PV = 0.44, N = 3), herb layer foragers (PV = 0.33, N = 2), trunk foragers (PV = 0.33, N = 2), foliage gleaners (PV = 0.29, N = 8) and litter foragers (PV = 0.21, N = 4). Cluster analysis of the Pearson’s correlation coefficient of species densities showed no consistent grouping ac-cording to wintering areas or guild membership. Only seven of 26 simulations by binary null models (9 algorithms, 3 indices) on assemblage level indicated negative associations. None of 9 null model simulations of density assemblage matrix (3 algorithms, 3 indices) or null model analysis of foraging guilds showed negative species associations. The re-sults do not provide evidence for competition in the structuring of this bird assemblage, but instead support a pluralistic model of community functioning.

Spatiotemporal Distributions of Threadfin Shad in Tropical Reservoirs

AbstractEffective predator management requires accurate knowledge of prey availability and dynamics, yet prey species are rarely studied as intensely as their predatory counterparts. Almost nothing is known about the biology or behavior of threadfin shad Dorosoma petenense in tropical environments, despite that this species is the primary prey in many systems. The goals of this study were to examine spatial and temporal patterns in threadfin shad abundance in tropical reservoirs and to refine protocols for sampling this species. A custom, 3 × 3‐m frame trawl was used to sample four reservoirs in Puerto Rico every 3 months for 1 year. Samples were stratified by longitudinal section (upper and lower lake) and by depth strata (0–3, 3–6, 6–9 m). Threadfin shad densities varied markedly among seasons, reservoirs, longitudinal sections, and depth (overall model: F 36, 188 = 32.0, P &lt; 0.001, coefficient of variation [CV] = 22.1%, r 2 = 0.86). Density estimates from samples were highest in spring and winter when there was substantially more larval production, and density fluctuated as much as 42‐fold among seasons within reservoirs. Differences in mean density were as much as 23 times greater in productive reservoirs than in the least productive reservoir during the same season. Longitudinal variability was substantial between upper and lower reservoir sections (mean percent difference = 70%), but patterns were not consistent among reservoirs or seasons. Threadfin shad showed clear preference for shallow depth strata where 75.4% of fish were collected in the 0–3‐m stratum, and only 2.4% collected in the 6–9‐m stratum. Oxygen profiles suggested that threadfin shad selected shallow depths even when dissolved oxygen levels were suitable in deeper depth strata. Understanding spatiotemporal patterns in threadfin shad distributions will improve sampling programs in terms of timing and frequency of sampling, longitudinal and vertical sampling design, and sample size requirements.Received March 19, 2012; accepted June 2, 2012