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A challenge for introductory students in conservation biology is to understand how different environmental and human factors – in particular, density-dependent and density-independent factors – can interact to increase extinction risk in species. To enhance students' processing of sometimes dry and challenging material, we use a kinetic exercise in which students become an endangered animal, move around their environment, and act out a series of scenarios that highlight how species can be driven down a path toward extinction.

HighlightsReal-time, free-space transmission measurements of relative complex permittivity in unshelled peanuts during dryingDynamic application: temperature, density and moisture content changing during dryingThree density-independent calibration functions evaluated for accuracy in real-time moisture content determinationReal-time moisture content determination with standard error of performance (SEP) = 0.55% moisture content for all calibration functionsCalibration function most commonly used with microwave moisture sensor was determined to be most accurate; SEP = 0.448% moisture contentAbstract. A microwave moisture sensor, developed within USDA ARS, has been used to determine moisture content in unshelled peanuts during drying. Relative complex permittivities of the peanuts obtained from free-space transmission measurements at 5.8 GHz are used for the moisture determination. Due to variations in density caused by drying, it is advantageous to estimate moisture content independent of bulk density. Therefore, moisture content was estimated with three density-independent calibration functions to assess which one provided optimal accuracy. One of the functions is based on the measured attenuation and phase shift, and the other two are permittivity based (one of which is commonly used with the microwave moisture sensor). The sensor was calibrated for peanut pod moisture content determination over a temperature range of 10°C to 40°C and a moisture content range of 6.5% to 19% wet basis (w.b.). Statistical analysis showed high coefficients of determination (r2), = 0.97 for the calibration with each function. Peanut pod moisture content was determined with the sensor in real-time as peanuts dried, and estimated moisture content was compared to the reference oven drying method. While the standard error of performance (SEP) for the three functions was = 0.55% moisture content, the calibration function most commonly used with the microwave sensor was observed to be the most accurate (SEP = 0.448% moisture content). Microwave sensing is a viable solution for nondestructive, real-time determination of moisture content in peanuts in dynamic situations such as drying. Keywords: Complex permittivity, Dielectric properties, Free-space measurements, Microwave sensing, Moisture content, Peanut drying.

Beverton and Holt’s (1957. On the dynamics of exploited fish populations. UK Ministry of Agriculture, Fisheries and Food. Fisheries Investigations, 2: 533 pp.) monograph contributed a widely used stock–recruitment relationship (BH-SRR) to fisheries science. However, because of variation around a presumed relationship between spawning biomass and recruits, the BH-SRR is often considered inadequate and approached merely as a curve-fitting exercise. The commonly used and simplified version of the BH-SRR has eclipsed the fact that in their classic monograph, the derivation accounted for mechanistic recruitment processes, including multi-stage recruitment with explicit cohort-dependent and -independent mortality terms that represent competition between recruits and extrinsic, cohort-independent factors such as the environment or predation as two independent sources of mortality. The original BH-SRR allows one to recreate recruitment patterns that correspond to observed ones. Doing so shows that variation in density-independent mortality increases the probability of overlooking an underlying stock–recruitment relationship. Intermediate coefficients of variation in mortality (75–100%) are sufficient to mask stock–recruitment relationships and recreate recruitment time series most similar to empirical data. This underlines the importance of variation in survival for recruitment and that Beverton and Holt’s work still provides a fundamental and useful tool to model the dynamics of populations.

International audience; In this paper, we propose a contribution in the field of Reinforcement Learning (RL) with continuous state space. Our work is along the line of previous works involving a vector quantization algorithm for learning the state space representation on top of which a function approximation takes place. In particular, our contribution compares the performances of the Kohonen SOM and the Rougier DSOM with the Göppert function approximation scheme on both the mountain car problem. We give a particular focus to DSOM as it is less sensitive to the density of inputs and opens interesting perspectives in RL.

Intraspecific competition in large aggregations of animals should generate density-dependent effects on foraging patterns. To test how large differences in colony size affect foraging movements, we tracked seasonal movements of the African straw-coloured fruit bat ( Eidolon helvum ) from four colonies that range from 4000 up to 10 million animals. Contrary to initial predictions, we found that mean distance flown per night (9–99 km), number of nightly foraging sites (2–3) and foraging and commuting times were largely independent of colony size. Bats showed classic central-place foraging and typically returned to the same day roost each night. However, roost switching was evident among individuals in three of the four colonies especially towards the onset of migration. The relatively consistent foraging patterns across seasons and colonies indicate that these bats seek out roosts close to highly productive landscapes. Once foraging effort starts to increase due to local resource depletion they migrate to landscapes with seasonally increasing resources. This minimizes high intraspecific competition and may help to explain why long-distance migration, otherwise rare in bats, evolved in this highly gregarious species.

We study N-particle systems in $$\mathbb {R}^d$$ whose interactions are governed by a hypersingular Riesz potential $$|x-y|^{-s}$$ , $$s>d$$ , and subject to an external field. We provide both macroscopic results as well as microscopic results in the limit as $$N\rightarrow \infty $$ for random point configurations with respect to the associated Gibbs measure at scaled inverse temperature $$\beta $$ . We show that a large deviation principle holds with a rate function of the form ‘ $$\beta $$ -Energy + Entropy’, yielding that the microscopic behavior (on the scale $$N^{-1/d}$$ ) of such N-point systems is asymptotically determined by the minimizers of this rate function. In contrast to the asymptotic behavior in the integrable case $$sd$$ is strongly $$\beta $$ -dependent.

Due to strong spatial interplays between intraspecific interactions and environmental forcing, both density-dependent and density-independent processes can affect spatio-temporal dynamics of fish populations in a spatially explicit fashion. To this end, this study investigated the underlying mechanisms of spatio-temporal dynamics of Atlantic cod (Gadus morhua) in the Gulf of Maine (GoM). Based on the data from the Northeast Fisheries Science Center (NEFSC) bottom-trawl surveys in spring and fall from 1982 to 2013, empirical cumulative distribution function (ECDF) curves and geographic distribution indices were used to examine the species–environment and abundance–occupancy relationship, respectively. Then, a variable-coefficient generalized additive model was constructed to quantify the simultaneous effects of environmental variables and population size on the spatio-temporal dynamics of cod distribution. Area occupied remained relatively high through the late 1990s, but underwent a pronounced contraction into the western GoM (WGoM) for the reminder of the time-series. The model results suggest that the spatio-temporal dynamics of GoM cod have been driven by complex interactions of density-dependent and density-independent factors over the past three decades. Better knowledge of these dynamics can improve our understanding of the causality of abundance–occupancy and species–environment relationships and help to reduce error estimates for survey-based indices.

With efficiencies of industrial type PERC solar cells exceeding 22% and reduced electrical and optical losses in these high efficiency cells, it becomes more and more important for manufacturers to rely on high quality silicon wafers. In this contribution, we present data of the bulk excess carrier lifetime τ bulk and a doping density independent material quality parameter at maximum power point, the material saturation current density j 0,mat , of different p-type monocrystalline silicon materials. These values are obtained by measuring the effective carrier lifetime of neighbouring wafers of different thickness and thus eliminating the surface recombination contribution. We show that j 0,mat is an adequate parameter to evaluate the bulk quality of a given material. To further validate these findings, we compare the results to PERC cell efficiencies obtained with the same material.

Empirical evidence suggests that carry-over effects (COEs) can have a strong influence on the time evolution of populations. Here, COEs are defined as any event or process in one season that affects individual performance in a non-lethal manner during the following seasons. Our results have the potential to explain previously reported experimental results and to provide new biological phenomena. The population response to COEs is typically considerably more complicated than previously believed. We found that COEs that reduce the reproduction rates always decrease the population density. However, in the case of COEs that reduce the survival rates, there could be an increase in the population size. Regarding the dynamical behaviour, the impact of COEs is primarily associated with a stabilizing role in ecological research. However, this response is guaranteed only in COEs affecting the reproduction rate when the survival is density independent (or has a negligible density-dependent component). Interestingly, COEs have the potential to create bi-stability scenarios, particularly in COEs across multiple seasons.

Transmission is central to our understanding and efforts to control the spread of infectious diseases. Because transmission generally requires close contact, host movements and behaviors can shape transmission dynamics: random and complete mixing leads to the classic density-dependent model, but if hosts primarily interact locally (e.g., aggregate) or within groups, transmission may saturate. Manipulating host behavior may thus change both the rate and functional form of transmission. We used the ranavirus-wood frog (Lithobates sylvaticus) tadpole system to test whether transmission rates reflect contacts, and whether the functional form of transmission can be influenced by the distribution of food in mesocosms (widely dispersed, promoting random movement and mixing vs. a central pile, promoting aggregations). Contact rates increased with density, as expected, but transmission rapidly saturated. Observed rates of transmission were not explained by observed contact rates or the density-dependent model, but instead transmission in both treatments followed models allowing for heterogeneities in the transmission process. We argue that contacts were not generally limiting, but instead that our results are better explained by heterogeneities in host susceptibility. Moreover, manipulating host behavior to manage the spread of infectious disease may prove difficult to implement.

Life history theory predicts that resource competition increases as a population increases, leading to changes in life history traits such as growth, survival, and reproduction. The Northwest Atlantic (NWA) harp seal population has increased from a low of 1.1 million animals in 1971 to over 7 million animals in 2014. Given this 7-fold increase in abundance, we hypothesized that density-dependent regulation might be reflected by changes in body growth. Gompertz curves fitted to size at age data for harp seals collected in the Gulf of St Lawrence over a 40 year period show a decline in female asymptotic length and mass. Body mass and condition were negatively related to reproductive rates the previous year, while a quadratic relationship (‘inverse u’) was observed between body measures and the ratio of the March:April first year ice cover, a measure of ice breakup. Condition was also negatively related to January ice cover. At high densities, reproduction is likely to be relatively more expensive for Northwest Atlantic harp seals, underlining the importance of females being able to access high energy food during the winter foraging period to build-up condition prior to pupping. A complex relationship between condition and the timing of ice-breakup likely reflects the influence of the timing of ice retreat on food resources and hence female ability to rebuild energy stores prior to moulting.

Microplastics have been detected in aquatic sediments around the world, highlighting the propensity of this matrix to serve as a sink for these structural pollutants. More reliable and reproducible extraction protocols for microplastics would facilitate comparisons across studies. A number of different extraction techniques are currently used to separate microplastics from sediment and almost exclusively employ density-based separations, which take advantage of the inherent densities of plastic particles. Some of these techniques are cost-effective but fail to fully recover all plastic types. Other techniques may recover most plastic types, but are more costly and/or hazardous to human or environmental health. We present here a novel, cost-effective oil extraction protocol (OEP) that provides an alternative to density-based approaches by taking advantage of the oleophilic properties of microplastics. Using this technique, we counted microplastic particles in spiked sediment samples using light microscopy and observed 96.1% ± 7.4 recovery for total microplastics, with recovery rates of 92.7% ± 4.3 for fibers and 99% ± 1.4 for particles. Subsequent analysis with Fourier-Transform Infrared Spectrometry (FTIR) revealed that the oil interfered with the FTIR spectrum of microplastics, but that an additional, post-extraction clean-up step using ethyl alcohol (90%) removed residual traces of oil and eliminated the FTIR spectral interference. The application of this new technique to shoreline sediment samples collected from sites in urban Vancouver, British Columbia, Canada, and a remote beach on Vancouver Island, as well as bulk seawater, demonstrated that the oil extraction protocol is effective for environmental samples. This novel OEP represents a cost-effective and reliable alternative to leading density-based techniques.

A systematic study of the central depletion of proton density has been performed in the isotonic chains of nuclei with neutron numbers $N = 20$ and $28$ using different variants of the relativistic mean-field (RMF) models. These models include either the non-linear contributions from the mesons with the coupling constants being density independent or the non-linearity of the mesonic fields realized through the density dependent coupling strengths. The central depletion in deformed nuclei tends to disappear irrespective of the occupancy of $2s_{1/2}$ state in contrast to the spherical nuclei in which the unoccupancy of $2s_{1/2}$ state leads to the central depletion. Due to the differences in the strength of spin-orbit potentials in these models, the central depletions are found to be model dependent. The influence of the central depletion on the neutron-skin thickness is also investigated. It appears that the effects of the central depletion do not percolate far enough to display its finger prints on the trends of the neutron-skin thickness., 17 pages, 9 figures, Accepted in Journal of Physics G: Nuclear and Particle Physics

People counting in high density crowds is emerging as a new frontier in crowd video surveillance. Crowd counting in high density crowds encounters many challenges, such as severe occlusions, few pixels per head, and large variations in person's head sizes. In this paper, we propose a novel Density Independent and Scale Aware model (DISAM), which works as a head detector and takes into account the scale variations of heads in images. Our model is based on the intuition that head is the only visible part in high density crowds. In order to deal with different scales, unlike off-the-shelf Convolutional Neural Network (CNN) based object detectors which use general object proposals as inputs to CNN, we generate scale aware head proposals based on scale map. Scale aware proposals are then fed to the CNN and it renders a response matrix consisting of probabilities of heads. We then explore non-maximal suppression to get the accurate head positions. We conduct comprehensive experiments on two benchmark datasets and compare the performance with other state-of-theart methods. Our experiments show that the proposed DISAM outperforms the compared methods in both frame-level and pixel-level comparisons. © 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.

Weather has been recognized as a density independent factor influencing the abundance, distribution, and behavior of vertebrates. Male wild turkeys’ (Meleagris gallopavo) breeding behavior includes vocalizations and courtship displays to attract females, the phenology of which can vary with latitude. State biologists design spring turkey-hunting season frameworks centered on annual vocalization patterns to maximize hunter engagement. The Mississippi Department of Wildlife, Fisheries, and Parks has traditionally instituted a statewide, 7-week, spring harvest season. However, hunters routinely argue that different peaks in gobbling activity across the state exist. The objective of this study was to determine whether differences in peak gobbling activity existed across a latitudinal gradient of Mississippi and assess the effect of weather on gobbling. During 2008 and 2009, we conducted a statewide gobbling survey. We used generalized additive mixed models to describe the probability and frequency of gobbling activity within northern and southern regions of the state. We also investigated the effect of daily weather conditions on gobbling activity. Our results revealed an approximate 10–14-day difference in peak gobbling activity between southern and northern Mississippi. The majority of all gobbling activity occurred within the current spring harvest framework. Perhaps more importantly, gobbling activity was more prevalent on days of regionally dry conditions (i.e., less humid) according to the Spatial Synoptic Classification. Our results provide information on gobbling activity phenology relative to hunting-season dates and weather-response information. Our approach may be particularly applicable in states with relatively shorter seasons or highly variable daily weather conditions that moderate gobbling frequency.

Three density-independent calibration functions expressed in term of the attenuation, phase shift and the dielectric properties were investigated for moisture prediction in flowing grain and seed samples. The flowing-grain system was calibrated by using static samples placed in a chute between two patch antennas operating at 5.8 GHz and connected to a vector network analyzer. Measurements at room temperature (22 oC) on flowing grain and seed samples showed that moisture content can be predicted with these algorithms with a standard error of calibration of less than 1% moisture content.

At present, the giant impact (GI) is the most widely accepted model for the origin of the Moon. Most of the numerical simulations of GI have been carried out with the smoothed particle hydrodynamics (SPH) method. Recently, however, it has been pointed out that standard formulation of SPH (SSPH) has difficulties in the treatment of a contact discontinuity such as a core-mantle boundary and a free surface such as a planetary surface. This difficulty comes from the assumption of differentiability of density in SSPH. We have developed an alternative formulation of SPH, density independent SPH (DISPH), which is based on differentiability of pressure instead of density to solve the problem of a contact discontinuity. In this paper, we report the results of the GI simulations with DISPH and compare them with those obtained with SSPH. We found that the disk properties, such as mass and angular momentum produced by DISPH is different from that of SSPH. In general, the disks formed by DISPH are more compact: while formation of a smaller mass moon for low-oblique impacts is expected with DISPH, inhibition of ejection would promote formation of a larger mass moon for high-oblique impacts. Since only the improvement of core-mantle boundary significantly affects the properties of circumplanetary disks generated by GI and DISPH has not been significantly improved from SSPH for a free surface, we should be very careful when some conclusions are drawn from the numerical simulations for GI. And it is necessary to develop the numerical hydrodynamical scheme for GI that can properly treat the free surface as well as the contact discontinuity., Comment: Accepted for publication in Icarus

Habitat use of aquatic organisms is essential to evaluate effects of many environmental challenges like effects of hydro-power regulation, where stranding may occur under hydropeaking (rapid dewatering of shallow river areas). Experimental studies as well as observations from nature with juvenile Atlantic salmon (Salmo salar) show that the proportion of the population that uses shallow depth was both independent of population density and decreasing with fish size. Experiments were conducted both in the presence and in absence of older fish, during day and night, and during all four seasons. Juvenile salmon from deep areas may therefore distribute into the shallow areas even when fish density becomes reduced. Thus, low density does not lead to reduced stranding risk and shallow areas may therefore function as a sink in a within-generation source-sink dynamic under a repeated hydropeaking scenario. The sink effect of rapid dewatering in shallow areas may be mitigated by e.g. seasonal and diurnal regulation of hydropeaking activity, but dewatering may still result in extinction of weak populations. habitat use, hydropeaking, intracohort competition, intercohort competition, microhabitat use, stranding Copyright the Author. Published by NRC Research Press (Canadian Science Publishing). This Just-IN manuscript is the accepted manuscript prior to copy editing and page composition. It may differ from the final official version of record.

Effects of density dependent as well as independent dispersal modes between a harvested patch and a protected area on the maximum sustainable yield and population abundance are studied. Without dispersal, the Gordon-Schaefer harvesting model predicts that as the protected area increases, population abundance increases too but the maximum sustainable yield (MSY) decreases. This article shows that dispersal can change this prediction. For density independent balanced and fast dispersal, neither the MSY, nor population abundance depends on the protected area. For fast and unbalanced dispersal both the MSY and equilibrium population abundance are unimodal functions of the protected area size. For density dependent dispersal which is in direction of increasing fitness predictions depend on whether individuals react to mortality risk in harvested patch. When animals disregard harvesting risk, the results are similar to the case of density independent and balanced dispersal. When animals do consider harvesting risk, the results are similar to the case without dispersal. The models considered also show that dispersal reduces beneficial effect of protected areas, because population abundance is smaller when compared with no dispersal case.

Vincent (2014, this issue) questions our paper (Gazey et al. 2008) with respect to three issues: (1) the statistical support for density-dependent mortality (because our model does not account for ...

Faced with a strong and sudden deterioration of environment, a population encounters two possible options — adapt or perish. In general, it is not known which of those outcomes the environmental changes will lead to. Building on experimental research, we introduce a discrete-space, discrete-time model for environmental rescue based on the influence of population dispersal, as well as, potentially beneficial mutations. Numerical results obtained by the model are shown to correspond well to experimentally obtained data.

Natural mortality (M) rates are difficult to measure empirically and are often specified in stock assessments based on life history characteristics. More recently, these specifications have included M as a function of the size or age of a fish. However, natural mortality is a dynamic parameter that will change with the suite of predators and, thus, indirectly with cohort size and age. As an alternative, a density-dependent M rate function is derived and compared with the commonly used Lorenzen model, where M at age forms an allometric relationship with weight-at-age. The density-dependent model expresses M as a function of two parameters: one density dependent and one density independent. Properties of the two models (size-based vs. density-dependent) were explored to indicate conditions where the results are and are not similar. Associated catch equations, equilibrium analyses, and non-linear replacement lines in stock–recruitment theory are examined. Just as with density-independent values of M, most assessment data are not sufficient to provide precise estimates of density-dependent M parameters. However, the density-dependent model provides a basis for incorporating ecological variability into single-species assessments, noting the differing dynamics between short- and long-lived species. The incorporation of dynamic natural mortality has implications when estimating abundance trends and stock status, and ultimately setting management reference points.

We use highly accurate ab initio calculations of binding enthalpies and entropies of gas phase clusters of alcohols to demonstrate how they can be used to obtain association parameters for PC-SAFT. The thermochemical results demonstrate that cooperativity effects and state dependent cluster distributions cause a strongly varying average enthalpy and entropy per bond as function of temperature and density for alcohols. In contrast to this, the two association parameters of PC-SAFT lead to density independent bond enthalpy and entropy and are thus effective parameters. Therefore, we choose to compute the cluster distribution at a universal state point and show that the thus obtained association parameters can be used to reduce the number of adjustable parameters from 5 to 3 with only a marginal loss of accuracy for most of the studied systems, and even an estimation of thermodynamic properties without adjusted parameters is possible. The ab initio calculations suggest that the 2B association scheme is more appropriate for 1-alkanols than the 3B one.

Globally, salmon populations are under pressure and in those where numbers are severely depleted, density independent factors such as the accumulation of fine sediment and subsequent mortality of incubating embryos are critical factors in their conservation. Although progress has been made in identifying the processes by which fine sediment can lead to embryo mortality, this has focussed on the physical blockage of gravel pores. This paper presents new knowledge on the role of sediment-associated organic matter in controlling the supply of dissolved oxygen to incubating salmon embryos within gravel river beds. We report a new approach to the measurement of sediment oxygen demand (SOD) from interstitial sediments accumulated within salmon redds and demonstrate this across a range of salmon river types. The effects of varying SOD on dissolved oxygen supply to incubating salmon embryos are quantified for the first time, using the physically based Sediment Intrusion and Dissolved Oxygen (SIDO-UK) model. The results reveal the importance of the mass of accumulating sediment and sediment consumption rates (sediment oxygen consumption [SOC]), which constitute the overall SOD over time for a particular sediment sample. Higher SOC result in reductions in dissolved oxygen that are deleterious to salmonids; however, these are subordinate to the effects of sediment mass. Larger quantities of sediment accumulating within the redd not only create a higher SOD but also physically block the pores within the gravels, leading to a more drastic decline in oxygen supply through the combined effects of reduced seepage velocity and dissolved oxygen concentration. We seek to generalize the results by exploring the influence of catchment characteristics on field measures of SOD and SOC. This work makes a significant and novel contribution to improving our fundamental understanding of hyporheic processes within salmonid spawning gravels whilst providing resource managers with evidence of the deleterious effects of sediment-associated organic matter on salmon recruitment.

We propose density independent hydrodynamics model (DIHM) which is a novel and automatic method for coherency detection in crowded scenes. One of the major advantages of the DIHM is its capability to handle changing density over time. Moreover, the DIHM avoids oversegmentation and thus achieves refined coherency detection. In the proposed DIHM, we first extract a motion flow field from the input video through particle initialization and dense optical flow. The particles of interest are then collected to retain only the most motile and informative particles. To represent each particle, we accumulate the contribution of each particle in a weighted form, based on a kernel function. Next, the smoothed particle hydrodynamics (SPH) is adopted to detect coherent regions. Finally, the detected coherent regions are refined to remove the effects of oversegmentation. We perform extensive experiments on three benchmark datasets and compare the results with 10 state-of-the-art coherency detection methods. Our results show that DIHM achieves superior coherency detection and outperforms the compared methods in both pixel level and coherent region level average particle error rates (PERs), average coherent number error (CNE) and F-score. © 2018. This is the authors’ accepted and refereed manuscript to the article. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/

Summary 1. The chief objectives were as follows: (i) to describe and compare quantitatively the life cycles of the summer and overwintering generations of Baetis rhodani, including laboratory experiments to determine the number of eggs laid per female and the number of larval instars; (ii) to test Dyar’s hypothesis; and (iii) to test for density dependence in the life cycle. Samples of larvae and downstream-drifting adults (newly emerged subimagines and spent female imagines) and counts of egg masses were taken every 2 weeks over 39 months in a small stony stream. 2. Although females from the summer generation were smaller than those from the overwintering generation and laid fewer eggs, the relationship between the number of eggs laid by a female and body length was the same for both generations, being described by a power function. An exponential equation described the relationship between the mean body length of each instar and instar number; hence, Dyar’s hypothesis was validated. Adult males emerged after 17 or 18 larval instars and females after 18 or 19 instars in the summer generation, with higher values of 25 or 26 instars for males and 26 or 27 instars for females in the overwintering generation. Mean instar body length in the summer generation was always larger than that in the overwintering generation, but this did not produce larger final instar larvae because the fewer instars resulted in males and females being smaller on emergence than in the overwintering generation. 3. Male subimagines started to emerge before females, and their emergence patterns indicated that there were two cohorts in each generation. Ovipositing females in the first cohort were always larger than those in the second cohort. Therefore, four mean values for eggs/female (=eggs/egg mass) were used to convert egg masses per m2 to eggs laid per m2. Larvae were divided into six stages: I = instar 1, II = instars 2–5, III = instars 6–10, IV = instars 11–16, V = instars 17–24 (overwintering generation only) and VI = final instars prior to emergence. There were two clear modal densities for each larval stage in each generation, confirming the presence of two cohorts. 4. These modal densities were used to estimate loss rates between successive larval stages, and ‘k-factor analysis’ was used to examine the relationship between loss rates for a particular larval stage and the modal value for eggs or larvae at the start of that stage. Loss rates in larval stage II were density dependent and were when population regulation occurred. For all other larval stages, loss rates were density independent and fairly constant with no significant differences between the two generations. Life tables were constructed for egg densities close to the range of modal values found in the stream (1332–11 512 m−2). The egg density that yielded the maximum number of final instar larvae, and hence adults, was 2700–2750 m−2 with poorer survival for initial egg densities below and above these values. 5. This study has shown that (i) the mechanism for population regulation was density-dependent survival in larval stage II (instars 2–5); (ii) the importance of obtaining information on egg densities and their role in density-dependent processes; (iii) the necessity of frequent sampling for a quantitative description of complex life cycles of aquatic insects.

It has been proposed that selenium, an element chemically similar to sulfur, can participate in some of the same biological pathways as sulfur, although only a few studies have been confirmed this. In this study, we investigated the relationship between selenium and sulfur-dependent luminescence in Vibrio fischeri. The luminescence of V. fischeri was induced by the addition of sulfur-containing compounds such as Na₂SO₄ and L-cystine, and their luminescence was suppressed, in a dose-dependent manner, by the addition of the selenium-containing compounds Na₂SeO₄ and L-selenocystine. Since the viability of V. fischeri was not affected by the addition of low concentration of selenium-containing compounds, the decrease in luminescence intensity cannot be explained by cell death. Kinetic analysis performed using Lineweaver-Burk plots demonstrate that Na₂SeO₄ and L-selenocystine act as competitive suppressors in inorganic sulfur (Na₂SeO₄)-dependent luminescence. In contrast, these selenium-containing compounds act as uncompetitive suppressors in organic sulfur (L-cystine)-dependent luminescence.

Several large epidemiologic studies have shown an association between chronic obstructive pulmonary disease (COPD) and osteoporosis. Recent studies have further implied an emphysema-specific association with low bone mineral density independent of obstruction severity.This review will outline the studies demonstrating an independent association between radiographic emphysema and decreased bone mineral density and will discuss potential disease mechanisms, including systemic inflammation and immune-mediated factors, linking these disease processes.Radiographic emphysema should be considered an independent risk factor in studies examining the mechanisms underlying COPD-related bone loss. Future research focused on the relationship between emphysema and low bone mineral density could provide mechanistic insight and result in the development of targeted therapies designed to halt progression of both disease processes.

Knowledge of density-dependent processes and how they are mediated by environmental factors is critically important for understanding population and community ecology of insects, as well as for mitigating harmful insect-borne diseases. Here, we tested whether the oviposition of chironomids (Diptera: Chironomidae; non-biting midges), known to carry the Cholera pathogen Vibrio cholerae, is density dependent and if it is mediated by habitat availability. We used two multiple choice experiments in habitat-limited and habitat-unlimited environments and performed isodar analysis on counts of egg batches after controlling the polarization of light reflected from the habitats, which is known to affect their attractiveness to ovipositing chironomids. We found that, when habitats are limited, egg batch isodars indicate that chironomid selection is density dependent. Although a greater number of individuals selected to oviposit in highly polarized sites, oviposition was also common in sites with low polarization. When habitats are unlimited, chironomid selection is either weakly density dependent, or completely density independent. Chironomids oviposit to a very large extent in sites with high level of polarization, oviposit to a small extent in sites with medium level of polarization, and almost completely disregard unpolarized sites. We suggest that ovipositing females consider the availability of habitats in their surroundings when they choose an oviposition site. When high quality habitats are scarce, more females opt to breed in low quality sites. These findings may be used to limit the spread of Cholera by controlling the habitats available for chironomid oviposition.

Tamdrari, H., Castonguay, M., Brêthes, J-C., and Duplisea, D. 2010. Density-independent and -dependent habitat selection of Atlantic cod (Gadus morhua) based on geostatistical aggregation curves in the northern Gulf of St Lawrence. – ICES Journal of Marine Science, 67: 1676–1686. Relationships were sought between local density and population abundance of Atlantic cod (Gadus morhua) in the northern Gulf of St Lawrence (Canada) over its entire area (4RS) and also within a subarea (4R) where the stock has concentrated since it collapsed during the early 1990s. Relationships were analysed using geostatistical aggregation curves computed within the two areas between years of contrasting abundance levels. The curves were interpreted in terms of four conceptual models of spatial dynamics: models D1 and D2, forced mainly by environmental heterogeneity, and models D3 and D4, in which individual behaviour is influenced by local density. Over the entire area, the cod population follows the D2 model for all years and age groups, and it is influenced by abiotic factors. Within the subarea, all four models applied, and the density-dependent basin model (D4) dominated from 2006 to 2008. The year 2006 seems to be pivotal because it coincides with the expansion of the cod population into its former area in the western Gulf (4S).

Density-independent high moisture content measurement is required in actual production line. In this paper, the experimental results for high moisture content measurement using microwave free-space technique are presented. The method is based on a ratio of phase shifts at two microwave frequencies after propagating through a sample. The experiments were performed with three kinds of sawdust named Momizai, Cedar and Douglas Fir. In the high moisture content above 130%, the root mean square error (RMSE) of moisture determination by the method for three kinds of sawdust are 9.0%, 17.0%, 22.8%, respectively.

Breast cancer risk assessment is becoming increasingly important in clinical practice. It has been suggested that features that characterize mammographic texture are more predictive for breast cancer than breast density. Yet, strong correlation between both types of features is an issue in many studies. In this work we investigate a method to generate texture features and/or scores that are independent of breast density. The method is especially useful in settings where features are learned from the data itself. We evaluate our method on a case control set comprising 394 cancers, and 1182 healthy controls. We show that the learned density independent texture features are significantly associated with breast cancer risk. As such it may aid in exploring breast characteristics that are predictive of breast cancer irrespective of breast density. Furthermore it offers opportunities to enhance personalized breast cancer screening beyond breast density.

The northern abalone, Haliotis kamtschatkana, fisheries in British Columbia (BC) were closed in 1990 because of substantial declines in the stock biomass. Abalone biomass has remained low since the fishery closure. We used abalone survey data and established growth models to study the stock-recruitment (SR) relationships, estimate mortality rates, and simulate population growth trajectories at various mortality levels for abalone populations in the Queen Charlotte Islands and the Central Coast of BC. The fitted SR curves were flat and near linear, indicating a lack of productivity in the abalone populations. At low spawning stock biomass (

A wide variety of environmental stresses can cause density-independent mortality in species populations. One example is cooling-water withdrawals, which kill or injure many aquatic organisms near power plants and other industrial facilities. In the United States alone, hundreds of facilities withdraw trillions of gallons from inland and coastal waters every year to cool turbines and other manufacturing equipment. A number of detailed, site-specific studies of the effects of such cooling-water withdrawals have been conducted over the last 30 years, but only a few generalizations have been proposed in the peer-reviewed literature. In this paper we use a series of basic theoretical models to investigate the potential effects of density-independent mortality on species populations and ecosystems, with particular focus on the effects of cooling-water withdrawals on fish populations, fisheries, and aquatic communities. Among other results, we show that the effects of cooling-water withdrawals on a species will depend on the magnitude of other co-occurring stressors, environmental variability, the nature of the management regime in the associated fisheries, and the position of the species in the food web. The general models in this paper can provide a starting point for further empirical case studies and some preliminary conceptual guidance for decision makers who must choose between alternative policy options for controlling cooling-water withdrawals.

A quasi-optical resonator is implemented to characterize low loss polymer powders at mm waves. Based on the suggested resonator configuration, density-independent moisture measurements have been carried out in W-band. The resonant frequencies and Q factor were measured to reconstruct the real and imaginary parts of a dielectric constant to be used for moisture determination. The model needed to describe this quasi-optical resonator including the reconstructing algorithm has also been developed. An example illustrating the method proposed is reported.

In this paper, we study two-species predator–prey Lotka–Volterra-type dispersal system with periodic coefficients, in which the prey species can disperse among n-patches, but the predator species which is density-independent is confined to some patches and cannot disperse. By utilizing the analytic method, sufficient and realistic conditions on the boundedness, permanence, extinction, and the existence of positive periodic solution are established. The theoretical results are confirmed by a special example and numerical simulations.

A population of booted eagles (Hieraaetus pennatus) consisting of 21–29 pairs was studied for 7 years (1998–2004) in a forested mountainous region of southeastern Spain. The average egg-laying time was 25 April (earliest 31 March, latest 26 May). Sixty-eight percent of territorial pairs produced eggs, and 81% of reproductive pairs successfully raised at least one offspring. Mean clutch size was 1.91 eggs, and 84% hatched. The survival rate of chicks was high, with only 17% dying. The major known cause of nestling mortality was predation, mainly by the Eurasian eagle owl (Bubo bubo). The mean number of flying offspring was 0.91 per territorial pair, 1.29 per reproductive pair and 1.65 per successful pair. All population breeding parameters analysed were density independent, but most showed a significantly negative relationship with mean laying date.