Intermediate Density Research Articles

Topology optimization for harmonic vibration problems using a density-weighted norm objective function

The optimized design of structures subjected to harmonic excitation is of great interest, for both the suppression of the oscillatory response (minimization) and the design of resonant structures (maximization). This work proposes an objective function which can be used for both goals, can properly locate resonance even for large damping ratios, and can be tuned to avoid the presence of non-physical modes in regions with void or intermediate relative densities. The properties of the proposed formulation are shown using a traditional benchmark case and the formulation is compared with other two formulations presented in the literature: dynamic compliance and active power. The results show that the proposed formulation is simple to use, leading to well-defined topologies with extreme harmonic behavior, although not solving the well-known problem of discontinuous topologies.

Comparative Nanofabrication of PLGA-Chitosan-PEG Systems Employing Microfluidics and Emulsification Solvent Evaporation Techniques.

Poor circulation stability and inadequate cell membrane penetration are significant impediments in the implementation of nanocarriers as delivery systems for therapeutic agents with low bioavailability. This research discusses the fabrication of a biocompatible poly(lactide-co-glycolide) (PLGA) based nanocarrier with cationic and hydrophilic surface properties provided by natural polymer chitosan and coating polymer polyethylene glycol (PEG) for the entrapment of the hydrophobic drug disulfiram. The traditional emulsification solvent evaporation method was compared to a microfluidics-based method of fabrication, with the optimisation of the parameters for each method, and the PEGylation densities on the experimental nanoparticle formulations were varied. The size and surface properties of the intermediates and products were characterised and compared by dynamic light scattering, scanning electron microscopy and X-ray diffraction, while the thermal properties were investigated using thermogravimetric analysis and differential scanning calorimetry. Results showed optimal particle properties with an intermediate PEG density and a positive surface charge for greater biocompatibility, with nanoparticle surface characteristics shielding physical interaction of the entrapped drug with the exterior. The formulations prepared using the microfluidic method displayed superior surface charge, entrapment and drug release properties. The final system shows potential as a component of a biocompatible nanocarrier for poorly soluble drugs.

Facile synthesis of solar light-driven Z-scheme Ag2CO3/TNS-001 photocatalyst for the effective degradation of naproxen: Mechanisms and degradation pathways

The development of efficient solar light-driven catalyst materials is considered a promising strategy for the photocatalytic eradication of contaminants. Herein, a novel Z-scheme Ag2CO3/TNS-001 nanocomposite photocatalyst with excellent solar-light response was synthesized using a simple hydrothermal and deposition reaction. The morphology, chemical structure, and optical property of Z-scheme composites were systematically investigated by TEM, XRD, FI-IR, XPS, and UV–vis, etc. techniques. The Ag2CO3/TNS-001 exhibited superior photocatalytic activity for removal of naproxen (NAP) under solar light irradiation, demonstrating kinetics of 40.7, 23.9, and 6.9 times higher than that of Ag2CO3, P25, and TNS-001, respectively. This remarkably improved photocatalytic efficiency was attributed to the synergistic effects of highly active (001) facets, efficient solar light response, and enhanced separation of photogenerated carriers. The scavenging experiments indicated that h+ was the dominant species during the photocatalytic degradation of NAP. Together with the analyses of EPR and band structure, a potential Z-scheme mechanism was confirmed. Moreover, the degradation pathway of NAP was revealed via intermediate detection and density functional theory (DFT) calculations. The chlorella acute toxicity test further indicated that mineralization translated to a reduction in the toxicity of the NAP solution. This work offers a promising strategy for the design of efficient Z-scheme photocatalysts, while exploring new insights into the elimination of emerging organic pollutants.

Heavy elements nucleosynthesis on accreting white dwarfs: building seeds for the p-process

ABSTRACT The origin of the proton-rich trans-iron isotopes in the Solar system is still uncertain. Single-degenerate thermonuclear supernovae (SNIa) with n-capture nucleosynthesis seeds assembled in the external layers of the progenitor’s rapidly accreting white dwarf (RAWD) phase may produce these isotopes. We calculate the stellar structure of the accretion phase of five white dwarf (WD) models with initial masses ≥ 0.85 $\, \mathrm{M}_\odot$ using the stellar code mesa The near-surface layers of the 1, 1.26, 1.32 and 1.38 $\, \mathrm{M}_\odot$ models are most representative of the regions in which the bulk of the p nuclei are produced during SNIa explosions, and for these models we also calculate the neutron-capture nucleosynthesis in the external layers. Contrary to previous RAWD models at lower mass, we find that the H-shell flashes are the main site of n-capture nucleosynthesis. We find high neutron densities up to several 1015 cm−3 in the most massive WDs. Through the recurrence of the H-shell flashes these intermediate neutron densities can be sustained effectively for a long time leading to high-neutron exposures with a strong production up to Pb. Both the neutron density and the neutron exposure increase with increasing the mass of the accreting WD. Finally, the SNIa nucleosynthesis is calculated using the obtained abundances as seeds. We obtain solar to supersolar abundances for p-nuclei with A > 96. Our models show that SNIa are a viable p-process production site.

Morphological and functional reserves of the right middle lobe: Radiological analysis of changes after right lower lobectomy in healthy individuals

ObjectivesRemaining lung tissue after pulmonary resection can expand without decline in structural complexity and compensate for functional loss, showing morphological and functional reserves. However, the distribution of these reserves is unknown. This study examined the heterogeneity of morphological and functional reserves of the remaining lung tissue. MethodsWe retrospectively analyzed 53 donors who underwent right lower lobectomy for living-donor lobar lung transplantation. We examined morphometric changes in computed tomography images from 3 to 12 months after lobectomy. We assessed lung volume and structural complexity expressed as the fractal dimension. We also assessed effective lung volume (the volume of the lung with intermediate density) and volumetric fluctuation during respiration. Changes were compared between the right upper lobe, middle lobe, and left lung. ResultsThe expansion of lung tissue was greater in the middle lobe (130.9% ± 19.7%) than in the upper lobe (109.7% ± 9.2%; P < .001). The fractal dimension declined in the upper lobe (P < .001) but was maintained in the middle lobe (P = .39). The increase in effective lung volume was larger in the middle lobe (97.2 ± 73.5 mL) than in the upper lobe (62.7 ± 87.1 mL; P < .001), but not significantly different from that of the left lung (55.8 ± 186.3 mL; P = .052). A similar pattern was seen in respiratory fluctuation. ConclusionsMorphological and functional changes in lung tissue remaining after pulmonary resection were heterogeneous. The right middle lobe demonstrated morphological and functional reserves after right lower lobectomy.

Effects of different stocking densities on Nile tilapia performance and profitability of a biofloc system with a minimum water exchange

The determination of an optimum stocking density should be obtained according to a complex assessment, in which growth performance, water quality, animal welfare, and production costs need to be considered. In this context, the objective of this work was to evaluate different stocking densities of Nile tilapias in biofloc technology (BFT) with minimal water renewal. Six hundred masculinized Nile tilapia juveniles with an initial average weight of 133.91 g were evaluated at four different stocking densities (18.75, 37.50, 56.25, and 75.00 fish‧m−3) and four replications, during 260 days of trial. The increase in stocking density resulted in a reduction of DO and pH. The minimum water renewal at a rate of 5%‧day−1 promoted an average reduction of settleable solids in the system of 23.75% at each discharge. The final biomass followed a quadratic regression on the stocking density, with a maximum at 72.27 fish‧m−3 or 36.86 kg‧m−3. However, the greatest daily weight gain (2.84 g‧day−1) that resulted in the highest average final body weight (842.26 g) was obtained at the lowest stocking density. We did not obtain any significant differences in body composition. The biofloc, on the other hand, had lower ash content and higher gross energy in the high stocking densities. Regarding gill morphometry, we found a greater number of branchial lesions in the highest and lowest stocking density evaluated. By an economical assessment, if the sales price is influenced by the final body weight, the reduced average harvest weight in higher stocking densities could lead to low profitability or even financial loss. Therefore, it is concluded that the use of intermediate stocking density, around 33 fish‧m−3, has higher profitability since it produces a large proportion of harvested fish that reach high body weights, and possible high selling prices, combined with desirable biomass.

Simultaneous Magnetic and Structural Topology Optimization of Synchronous Reluctance Machine Rotors

This article presents the simultaneous magnetic and structural topology optimization of a transverse laminated synchronous reluctance machine rotor using a solid isotropic with material penalization (SIMP)-based approach with the globally convergent method of moving asymptotes (GCMMA) optimization algorithm. Magneto-structural single and multi-objective optimization formulations are presented. The single objective formulation maximizes the average torque subject to constraints on torque ripple, Von Mises stress, and compliance. The multiobjective formulation simultaneously maximizes average torque and minimizes compliance subject to constraints on torque ripple and Von Mises stress. In both optimization formulations, the electrical steel densities in the rotor mesh elements are the control variables. Including stress and compliance in the optimization formulation ensures a structurally feasible design. The design-dependent centripetal force contributed by each element in the rotor mesh is considered dependent on its density and mass. An intermediate density material issue is observed where the density of the material in a mesh element does not converge fully to air or electrical steel. This issue is addressed through the use of a thresholding mass function which forces the convergence of the mass but not the density. The two optimization formulations are compared for rotors operating at 4000 and 12 000 r/min. An initial magnetic only topology optimization is used to seed the magneto-structural topology optimization to decrease the computational time. The impact of the magnetic only seed and rotor mesh density on the optimization outcomes is also examined.

Population Density Effects on Carapace Growth in Clam Shrimp: Implications for Palaeontological Studies.

Fossil morphological data are time-averaged and generally reflect an overlap of different sources of carapace variability. To examine whether a proposed relationship between size and population density in fossil spinicaudatans is biologically meaningful, we set up rearing experiments involving two extant species: Eulimnadia texana and Eocyzicus argillaquus. Three and five days after hydration, clam shrimp were transferred into cups of various population densities that ranged between 1 and 15 inds/400 ml. Size and shape were measured 14 and 16 days after hydration, respectively. Every second day, we recorded length and sex of E. texana, which matured faster in lower-density cups. According to our growth model, population density and maximal carapace length follow a logarithmic relationship. At maturity, hermaphrodites yielded similar lengths across all population densities (~4.7 mm at 24°C), independent of age. Hence, clam shrimp can put off reproductive maturity as a response to decreased growth under higher density conditions. Growth rate generally decreases at maturity, but that effect is more pronounced in clam shrimp of high population densities, while low-density adults keep growing. For both species, multivariate analyses reveal that carapace size of low-density individuals is significantly larger than carapace size of higher-density individuals, while size values of intermediate densities cannot be distinguished. Shape distinction is strong in hermaphrodites of E. texana: 39.8% of the density-dependent shape variation is associated with relative umbo height, which is generally higher in individuals of smaller population densities. The H/L ratio, which is often used as a simple shape indicator, does not contribute to the main variation in shape, but it forms one of several ratios significant for 18.3% of the shape variability. In turn, the H/L ratio drives 30% of the shape variation in E. argillaquus. In addition, higher densities triggered shifts in ontogenetic growth trajectories in one third of the individuals, which led to aberrant morphologies. The present rearing experiment shows that some of the morphological variability on fossil bedding planes can be explained by population density. Also, it implies a considerable amount of ecophenotypic variability in Spinicaudata that affects our understanding of fossil taxonomy and palaeoecology.

Convergence of the direct limit analysis design method for discrete topology optimization

The present paper addresses the robustness and convergence behavior of the direct limit analysis (LA) based methodology developed for the topology design of continuum structures subject to prescribed statically and plastically admissible loads. The design methodology, based on a direct method formulation of the static LA problem, has recently been proposed for continuous topology optimization and its merits were highlighted. One of its remarkable features is the outstanding similarity of the topology design mathematical problem with its underlying direct static form of the LA problem. Subsequently, it has been extended to solve two dimensional discrete, i.e. black-and-white, topology design problems by modifying the objective function into a square root form in a way to penalize the intermediate densities and solving a sequence of conic quadratic programming problems of identical scale and algebraic structure as the continuous design problem, leaving a number of issues to be investigated, pertaining to convergence. In the present work different families of penalization function forms are proposed and assessed as alternatives to the original square root function. The performance is evaluated in terms of robustness, accuracy in the sense of closeness of the final design to a 0–1 topology and efficiency or number of approximate problems required for convergence. Convergence of the discrete topology design is shown to be improved using higher order power functions as well as trigonometric and exponential type penalty functions. The performance of the design method in solving example problems using the various penalization schemes is compared and the factors that affect it are analyzed.

How Different Stocking Densities Affect Growth and Stress Status of Acipenser baerii Early Stage Larvae.

Simple SummarySiberian sturgeon is a freshwater fish species currently at risk of extinction. Few studies have been performed on the environmental conditions during early larval stages, a phase of development where mortality rate is still relevant. In this study, we focused on assessing the impact of different rearing densities during the endogenous feeding stage of the Siberian sturgeon on growth, stress status, and muscle development, using a multidisciplinary approach. Results indicate that lower densities seem more advantageous in this stage of development in terms of growth rate and stress levels. However, rearing larvae at such low densities is not economically feasible in commercial hatcheries but it could be interesting, instead, in larvae production for repopulation purposes.In the present study, a multidisciplinary approach was used in order to evaluate growth, muscle development, and stress status in Siberian sturgeon Acipenser baerii larvae at schooling (T1) and complete yolk sac absorption (T2), reared at three stocking densities (low, medium, and high). Larvae growth, morphological muscle development, and whole-body cortisol levels were assessed. The expression of genes involved in the growth process (igf1 and igf2), in the myogenesis (myog), and in the regulation of cellular stress (glut1, glut2, glut4, and hsp70) was analyzed using a quantitative PCR. Larvae reared at lower densities showed a higher Specific Growth Rate and showed a physiological muscle development. Cortisol levels were low and did not differ significantly, both in different time sampling and across densities, suggesting that either the considered densities are not stressors in this species in the early stages of development or the hypothalamus-pituitary-adrenal (HPA) axis is not yet fully mature. Gene expression of glut1, igf1, and igf2 showed an up-regulation in both developmental stages at all the rearing densities considered, while myog significantly up-regulated at T1 at the highest density. Considering all of the results, it would seem that lower densities should be used in these stages of development, as these showed a higher growth rate, even if it is not economically feasible in commercial hatcheries. Therefore, choosing an intermediate stocking density could be a good compromise between larval performance and economical feasibility.

Piloting an integrated approach for estimation of environmental risk of Schistosoma haematobium infections in pre-school-aged children and their mothers at Barombi Kotto, Cameroon

Within schistosomiasis control, assessing environmental risk of currently non-treated demographic groups e.g. pre-school-aged children (PSAC) and their mothers is important. We conducted a pilot micro-epidemiological assessment at the crater lake of Barombi Kotto, Cameroon with GPS tracking and infection data from 12 PSAC-mother pairs (n = 24) overlaid against environmental sampling inclusive of snail, parasite and water-use information. Several high-risk locations or ‘hotspots’ with elevated water contact, increased intermediate snail host densities and detectable schistosome environmental DNA (eDNA) were identified. Exposure between PSAC and mother pairs was temporally and spatially associated, suggesting interventions which can benefit both groups simultaneously might be feasible. When attempting to interrupt parasite transmission in future, overlaid maps of snail, parasite and water contact data can guide fine-scale spatial targeting of environmental interventions.

Nonequilibrium continuous phase transition in colloidal gelation with short-range attraction

The dynamical arrest of attractive colloidal particles into out-of-equilibrium structures, known as gelation, is central to biophysics, materials science, nanotechnology, and food and cosmetic applications, but a complete understanding is lacking. In particular, for intermediate particle density and attraction, the structure formation process remains unclear. Here, we show that the gelation of short-range attractive particles is governed by a nonequilibrium percolation process. We combine experiments on critical Casimir colloidal suspensions, numerical simulations, and analytical modeling with a master kinetic equation to show that cluster sizes and correlation lengths diverge with exponents ~1.6 and 0.8, respectively, consistent with percolation theory, while detailed balance in the particle attachment and detachment processes is broken. Cluster masses exhibit power-law distributions with exponents −3/2 and −5/2 before and after percolation, as predicted by solutions to the master kinetic equation. These results revealing a nonequilibrium continuous phase transition unify the structural arrest and yielding into related frameworks.

Location and activity of VOx species on TiO2 particles for NH3-SCR catalysis

The role of anatase TiO2 on the performance of VOx-TiO2 is studied by in situ spectroscopies on a series of catalysts with 1.9–9.7 V at/nm2. At low coverages, VOx is preferentially located at defect sites, spreading on the main TiO2 {101} and {100} facets at intermediate coverages. Brønsted sites concentration is maximum around 6 V atoms/nm2, and EPR shows a significant amount of V4+ at intermediate VOx densities, indicating the influence of TiO2 on their reducibility. The activity is proportional to the square of the VOx density up to 5.8 V atoms/nm2. All catalysts show the same activation energy for NH3-SCR of 56.9 ± 1.0 kJ/mol in the temperature range 160−280 °C, indicating that the reaction path does not change in the studied V coverage range. The activity does not follow the observed trends for Brønsted acid sites or reducibility, and it seems that the ability to form V-pairs is the only requirement for catalytic activity.

Flammability thresholds or flammability gradients? Determinants of fire across savanna-forest transitions.

Vegetation-fire feedbacks are important for determining the distribution of forest and savanna. To understand how vegetation structure controls these feedbacks, we quantified flammability across gradients of tree density from grassland to forest in the Brazilian Cerrado. We experimentally burned 102 plots, for which we measured vegetation structure, fuels, microclimate, ignition success and fire behavior. Tree density had strong negative effects on ignition success, rate of spread, fire-line intensity and flame height. Declining grass biomass was the principal cause of this decline in flammability as tree density increased, but increasing fuel moisture contributed. Although the response of flammability to tree cover often is portrayed as an abrupt, largely invariant threshold, we found the response to be gradual, with considerable variability driven largely by temporal changes in atmospheric humidity. Even when accounting for humidity, flammability at intermediate tree densities cannot be predicted reliably. Fire spread in savanna-forest mosaics is not as deterministic as often assumed, but may appear so where vegetation boundaries are already sharp. Where transitions are diffuse, fire spread is difficult to predict, but should become increasingly predictable over multiple fire cycles, as boundaries are progressively sharpened until flammability appears to respond in a threshold-like manner.

In situ polarization study of zinc–cerium redox flow batteries

An in situ investigation of the sources of performance loss during discharge of a zinc-cerium redox flow battery (RFB) has been carried out. Polarization and electrochemical impedance spectroscopy (EIS) measurements on a bench-scale zinc-cerium RFB are combined to determine the overpotentials due to kinetic and ohmic effects and provide an estimate of the mass transfer losses. In order to further evaluate the source of these overpotentials, the contribution of each half-cell is evaluated by insertion of Ag/AgCl reference electrodes at each of the two inlets to the battery. Measurements reveal that most of the losses are due to the kinetic overpotential of the Zn/Zn2+ half-cell at low and intermediate current densities. Additionally, in situ kinetic analysis reveals that the exchange current density is ~7.4×10−3A cm−2 for Zn/Zn2+ oxidation and ~24.2×10−3A cm−2 for Ce4+ reduction. The difference in these values supports the conclusion that the slower kinetics at the negative electrode limits the performance at low and intermediate current densities. The effects of an alternative mixed sulfonate/chloride electrolyte to facilitate the kinetics of the Zn/Zn2+ redox couple and electrolyte flow rate to enhance the mass transfer at the positive electrode are also investigated through in situ polarization experiments.

Two-scale concurrent topology optimization of lattice structures with connectable microstructures

Two-scale concurrent design of lattice material microstructures and their macroscale distributions can effectively enlarge the design space, and thus achieve lightweight structures with desirable mechanical and multi-physics performances. Most of the existing inverse homogenization-based design methods do not take into consideration the connectivity issues of the microstructures. In practice, this may hinder the manufacturing and application of the optimized two-scale designs. To handle this issue, the present paper proposes a designable connective region method to obtain connectable microstructures in the context of two-scale concurrent structural topology optimization, considering structures composed of lattice materials with repetitive unit cells and prescribed porosity. On the microscale, the microstructures topologies are represented by the density model, and the effective material properties are computed with the homogenization method. On the macroscale, the distribution of different lattice materials is described with the discrete material optimization method, which can effectively reduce the amounts of macroscale elements with intermediate densities. The connectivity between any two types of the microstructures is naturally ensured by introducing pre-defined connective regions in the microstructural unit cells and keeping these regions sharing the same topology. This method can be conveniently implemented through microscale design variable linking and requires no evaluation of extra connectivity constraints and the corresponding sensitivities. It is exemplified by two-scale concurrent structural topology optimization for compliance minimization problems in two- and three-dimensional design domains. Numerical results show that this method is able to generate connectable lattice structures, which exhibits improved stiffness as compared with their uniform-lattice counterparts.

Effects of agrochemical pollution on schistosomiasis transmission: a systematic review and modelling analysis

BackgroundAgrochemical pollution of surface waters is a growing global environmental challenge, especially in areas where agriculture is rapidly expanding and intensifying. Agrochemicals might affect schistosomiasis transmission through direct and indirect effects on Schistosoma parasites, their intermediate snail hosts, snail predators, and snail algal resources. We aimed to review and summarise the effects of these agrochemicals on schistosomiasis transmission dynamics.MethodsWe did a systematic review of agrochemical effects on the lifecycle of Schistosoma spp and fitted dose-response models to data regarding the association between components of the lifecycle and agrochemical concentrations. We incorporated these dose-response functions and environmentally relevant concentrations of agrochemicals into a mathematical model to estimate agrochemical effects on schistosomiasis transmission. Dose-response functions were used to estimate individual agrochemical effects on estimates of the agrochemically influenced basic reproduction number, R0, for Schistosoma haematobium. We incorporated time series of environmentally relevant agrochemical concentrations into the model and simulated mass drug administration control efforts in the presence of agrochemicals.FindingsWe derived 120 dose-response functions describing the effects of agrochemicals on schistosome lifecycle components. The median estimate of the basic reproduction number under agrochemical-free conditions, was 1·65 (IQR 1·47–1·79). Agrochemical effects on estimates of R0 for S haematobium ranged from a median three-times increase (R0 5·05, IQR 4·06–5·97) to transmission elimination (R0 0). Simulations of transmission dynamics subject to interacting annual mass drug administration and agrochemical pollution yielded a median estimate of 64·82 disability-adjusted life-years (DALYs) lost per 100,000 people per year (IQR 62·52–67·68) attributable to atrazine use. In areas where aquatic arthropod predators of intermediate host snails suppress transmission, the insecticides chlorpyrifos (6·82 DALYs lost per 100,000 people per year, IQR 4·13–8·69) and profenofos (103·06 DALYs lost per 100,000 people per year, IQR 89·63–104·90) might also increase the disability burden through their toxic effects on arthropods.InterpretationExpected environmental concentrations of agrochemicals alter schistosomiasis transmission through direct and indirect effects on intermediate host and parasite densities. As industrial agricultural practices expand in areas where schistosomiasis is endemic, strategies to prevent increases in transmission due to agrochemical pollution should be developed and pursued.

Effects of Nanoscale Roughness on the Lubricious Behavior of an Ionic Liquid

AbstractWhile many mechanistic studies have focused on the lubricious properties of ionic liquids (ILs) on ideally smooth surfaces, little is known about the mechanisms by which ILs lubricate contacts with nanoscale roughness. Here, substrates with controlled density of nanoparticles are prepared to examine the influence of nanoscale roughness on the lubrication by 1‐hexyl‐3‐methyl imidazolium bis(trifluoromethylsulfonyl)imide. Atomic force microscopy is employed to investigate adhesion, hydrodynamic slip, and friction at the lubricated contact as a function of surface topography for the first time. This study reveals that nanoscale roughness has a significant influence on the slip along the surface and leads to a maximum slip length on the substrates with intermediate nanoparticle density. This coincides with the minimum friction coefficient at sufficiently small contact stresses, likely due to the lower resistance of the IL film to shear. However, at the higher pressures applied with a sharp tip, friction increases with nanoparticle density, indicating that the IL is not able to alleviate the increased dissipation due to roughness. The results of this work point toward a complex influence of the surface topology on friction. This study can help design ILs and nanopatterned substrates for tribological applications and nano‐ and microfluidics.

Resource segregation at fine spatial scales explains Karner blue butterfly (Lycaeides melissa samuelis) distribution

The resource concentration hypothesis predicts that herbivorous insect density scales positively with plant density because insects are better able to identify, and remain longer in, patches with denser plant resources. While some studies support this hypothesis, others do not. Different explanations have been proposed for this discrepancy, including variation in insect dispersal ability and diet breadth. We test the resource concentration hypothesis using the Karner blue butterfly (Lycaeides melissa samuelis), a specialist that relies on wild blue lupine (Lupinus perennis) as its sole host plant. We extended this hypothesis to test whether Karner blue density also scales positively with nectar plant resources. Our findings did not support the resource concentration hypothesis and demonstrate that the spatial segregation of nectar and host plant resources relative to each other can influence the location and abundance of Karner blues on the landscape. This is because the location of resources relative to each other influences the energy and time butterflies expend for flight activity, and thereby influences resource acquisition. During early summer when first brood Karner blues emerge, nectar and host plants were spatially segregated, and Karner blue density peaked at intermediate densities of nectar and host plants occurring at ratios approximately equal to 1:1. During late summer, we found no significant relationships between second brood Karner blues and nectar plants or host plants when there was no correlation between nectar and host plants. Conservation practitioners of specialist insects with low vagility can strategically manage the distribution of plant resources to minimize insect time and energy expenditure and promote resource acquisition for all of an insect’s life stages.

Tree plantations replacing natural grasslands in high biodiversity areas: How do they affect the mammal assemblage?

Monoculture plantations of fast-growing trees are increasing worldwide and, in many cases, these replace highly diverse natural environments. The Mesopotamian Savannas and the Iberá marshes ecoregions of northeastern Argentina are a mosaic of habitat types in which extensive areas of natural grasslands have been replaced by the planting of non-native pines (Pinus spp.). Their impact on the natural communities is unknown. We evaluated the effect of these plantations, the landscape configuration and the forestry management practices on the assemblages of medium to large-size terrestrial mammals of this region at landscape and stand levels. Camera-trap stations were deployed in three environments: 89 in natural grasslands, 54 in native forest patches, and 91 in tree plantations. At a landscape level, we evaluated the effect of the type of environment and of the extent of different land covers on mammal richness per station using GLM, and on species composition using one-way PERMANOVA and redundancy analysis. At a stand level, we assessed the effect of understory vegetation, and of the age and density of tree plantation stands, on the similarity in mammal species composition between tree plantations and native environments, using non-metric multidimensional scaling analyses and GLM. Species richness and species composition differed between native forests and other environments, but not between grasslands and plantations. The variations in composition between the environments differed among the two ecoregions: the species composition in the plantations was different from the grassland assemblage only in the Iberá marshes, which suggests that the impact of tree plantations depends on the local pool of species. Mammal assemblages were also affected by the proportion of forests and wetlands and the environmental heterogeneity in the landscape. The similarity between the mammal assemblages of pine plantations and those of native forests increased with the age of the stand and at intermediate tree densities. In this grassland-dominated but heterogeneous landscape, it seems that most medium and large grassland mammals do not perceive tree plantations as a barrier, regardless of their management. Actions at a stand level, such as planting at intermediate tree densities and promoting longer rotation times, are desirable to encourage the forest mammal assemblage to use the plantations. Forests and wetlands are acting as keystone habitats for many species that are clearly associated with the presence of these environments in the landscape. Keeping large areas of natural grasslands and wetlands sprinkled with forests is essential for the conservation of the mammal assemblages of this region.