Density dependence

The local densities of heterospecifics and conspecifics are known to have profound effects on the dynamics of many benthic species, including rates of settlement and early post-settlement survivorship. We described the early life history of the Caribbean coral, Siderastrea radians by tracking the population dynamics from recently settled planulae to juveniles. Through three years of observation, settlement correlated with the abundance of other benthic organisms, principally turf algae (negatively) and crustose coralline algae (positively). In addition, adult density showed independent effects on coral settlement and early post-settlement survivorship. Settlement rates increased across low levels of adult cover and saturated at a maximum around 10% cover. Early post-settlement survivorship decreased with adult cover, revealing structuring density dependence in coral settlers. The earliest life stages of corals are defined by low survivorship, with survivorship increasing appreciably with colony size. However, recent settlers (one-polyp individuals, ,1 year old) are more likely to grow into two-polyp juveniles than older single polyps (.1 year old) that were delayed in their development. The early benthic phase of corals is defined by a severe demographic bottleneck for S. radians, with appreciable density-dependent and density-independent effects on survivorship. For effective management and restoration of globally imperiled coral reefs, we must focus more attention on this little studied, but dynamic, early life history period of corals.

Conidial anastomosis tubes (CATs) can be recognized in 73 species of filamentous fungi covering 21 genera, and develop in culture and in host-pathogen systems. They have been shown to be morphologically and physiologically distinct from germ tubes in Colletotrichum and Neurospora, and under separate genetic control in Neurospora. CATs are short, thin, usually unbranched and arise from conidia or germ tubes. Their formation is conidium-density dependent, and CATs grow towards each other. MAP kinase mutants of Neurospora are blocked in CAT induction. Nuclei pass through fused CATs and are potential agents of gene exchange between individuals of the same and different species. CAT fusion may also serve to improve the chances of colony establishment.

Using time-domain Terahertz spectroscopy we performed direct studies of the photoinduced suppression and recovery of the superconducting gap in a conventional BCS superconductor. Both processes are found to be strongly temperature and excitation density dependent. The analysis of the data with the established phenomenological Rothwarf-Taylor model enabled us to determine the bare recombination rate of quasiparticles, the Cooper pair-breaking rate and the electron-phonon coupling constant, $\lambda=1.1\pm0.1,$ which is in excellent agreement with theoretical estimates.

Fruit-eating animals deposit viable seeds in patterns that determine the conditions under which seeds and seedlings live or die. Many tree species are scatter-dispersed by birds, bats, or other small frugivores that regurgitate, defecate, or drop seeds singly or in pairs. These scatterdispersed plant species normally recruit as isolated individuals, and are unlikely to evolve exceptional resistance to herbivores, pathogens, or to other sources of density-dependent seed or seedling mortality. Other tree species are clump-dispersed by larger terrestrial or arboreal frugivores that defecate seeds in masses which produce bouquets of seedlings. Because their seeds invariably germinate in close proximity to other seedlings, clump-dispersed species necessarily evolve chemical or mechanical defenses against seed predators, pathogens, and herbivores that act in a densitydependent manner.

The generation of terahertz (THz) transients in photoconductive emitters has been studied by varying the spatial extent and density of the optically excited photocarriers in asymmetrically excited, biased low-temperature-grown GaAs antenna structures. We find a pronounced dependence of the THz pulse intensity and broadband (>6.0 THz) spectral distribution on the pump excitation density and simulate this with a three-dimensional carrier dynamics model. We attribute the observed variation in THz emission to changes in the strength of the screening field.

Competition between contest and scramble strategists was examined using two strains of Callosobruchus maculatus, the contest strain (iQ.) and the scramble strain (tQ). The direct larval interference experiment within each strain showed that the contest strain performed strong direct interference throughout its larval stage against the conspecific opponent(s). The scramble strain also performed its interference, but only during the 3rd and the 4th larval stages. The inter-strain larval competition experiments inside a large and small mung bean (Vigna radiata) showed that the contest strain was, in general, superior to the scramble strain in competition, but the competition results were density-and frequency-dependent. In the large beans, the proportion of adult emergence of the contest strain increased with the increase of its own initial density but decreased as the initial density of the scramble strain increased. The shape of the proportion of adult emergence became nonlinear in the small beans. The cause of the complexity of inter-strain competition results was discussed in the light of the difference in larval interference ability between the two strains.

We conducted an experiment to test competing hypotheses regarding the effects of hunting on American black bear (Ursus americanus) demographic parameters. Specifically, we tested for the existence and the relative influence of sexually selected infanticide (SSI) and density dependence in regulating demographic parameters. We monitored 290 bears in 2 hunted areas and an adjoining unhunted area in the boreal forest of Alberta, Canada, during a 4-year study (2002)(2003)(2004)(2005). We manipulated the areas using a modified before-after control-impact (BACI) design whereby bait sites for hunting were closed in 1 of the 2 hunted areas in years 3 and 4 and adult males in the unhunted area were removed in year 3. Results did not support a significant influence of SSI, if it occurs, on population parameters compared with the effects of density dependence. We found lower cub survival (66% versus 83%) and older age of first reproduction in the unhunted, higher-density area than in the lower-density, hunted area. We found no difference in body condition of males and females between areas, suggesting that if SSI restricted females to suboptimal areas, the effect was not strong enough to affect reproduction. We did not detect an influx of new males or a change in cub survival after removal of adult males from the unhunted area (66% before versus 73% after). Our results suggest that SSI does not affect the population growth rate of hunted black bear populations, and that target hunting quotas do not require including potential effects of SSI in population projections. However, SSI should be considered in unhunted or lightly hunted populations approaching carrying capacity (K). We advocate the inclusion of density dependence in population projection models for bear populations. However, for specific cases where harvesting maintains a population size well below K, density-dependent effects are predicted to be negligible due to the non-linear relationship between demographic parameters and density.

In this communication, experimental measurements and thermodynamic modeling of solubilities of methane and a hydrocarbon gas mixture (94% methane + 4% ethane + 2% n-butane) in water at low temperature conditions are reported. Methane solubility measurements have been conducted at a temperature range of 275.11-313.11 K and pressures up to 18 MPa. The solubility of the individual components in the gas mixture was measured from 278.14 to 313.12 K and pressures up to 14.407 MPa. A static-analytic apparatus, taking advantage of a pneumatic capillary sampler is used for fluid sampling. The Valderrama modification of the Patel-Teja equation of state combining with non-density dependent mixing rules were used for modeling gas solubilities in water. The data generated in this work are compared with the literature data and the predictions of the thermodynamic model, demonstrating the reliability of the techniques used in this work.

Changing climate may impact wildlife populations in national parks and conservation areas. We used logistic and non-linear matrix population models and 35 years of historic weather and population data to investigate the effects of climate on the population dynamics of elk in Rocky Mountain National Park (RMNP), Colorado, U.S.A. We then used climate scenarios derived from Hadley and Canadian Climate Center (CCC) global climate models to project the potential impact of future climate on the elk population. All models revealed density-dependent effects of population size on growth rates. The best approximating logistic population model suggested that high levels of summer precipitation accelerated elk population growth, but higher summer minimum temperatures slowed growth. The best approximating non-linear matrix model indicated that high mean winter minimum temperatures enhanced recruitment of juveniles, while high summer precipitation enhanced the survival of calves. Warmer winters and wetter summers predicted by the Hadley Model could increase the equilibrium population size of elk by about 100%. Warmer winters and drier summers predicted by the CCC Model could raise the equilibrium population size of elk by about 50%. Managers of national parks have relied on effects of weather, particularly severe winters, to regulate populations of native ungulates and prevent harmful effects of overabundance. Our results suggest that these regulating effects of severe winter weather may weaken if climate changes occur as those that are widely predicted in most climate change scenarios.

Fluorescence molecular imaging is rapidly increasing its popularity in image guided surgery applications. To help develop its full surgical potential it remains a challenge to generate dual-emissive imaging agents that allow for combined visible assessment and sensitive camera based imaging. To this end, we now describe multispectral InP/ZnS quantum dots (QDs) that exhibit a bright visible green/yellow exciton emission combined with a long-lived far red defect emission. The intensity of the latter emission was enhanced by X-ray irradiation and allows for: 1) inverted QD density dependent defect emission intensity, showing improved efficacies at lower QD densities, and 2) detection without direct illumination and interference from autofluorescence.

We estimated carrying capacity for sea otters (Enhydra lutris) in the coastal waters of British Columbia, Canada, by characterizing habitat according to the complexity of nearshore intertidal and sub-tidal contours. We modeled the total area of complex habitat on the west coast of Vancouver Island by first calculating the complexity of the Checleset Bay-Kyuquot Sound (CB-KS) region, where sea otters have been at equilibrium since the mid-1990s. We then identified similarly complex areas on the west coast of Vancouver Island (WCVI model), and adapted the model to identify areas of similar complexity along the entire British Columbia coast (BC model). Using survey data from the CB-KS region, we calculated otter densities for the habitat predicted by the 2 models. The density estimates for CB-KS were 3.93 otters/km 2 and 2.53 otters/km 2 for the WCVI and BC models, respectively, and the resulting 2 estimates of west coast of Vancouver Island complex habitat carrying capacity were not significantly different (WCVI model: 5,123, 95% CI ¼ 3,337-7,104; BC model: 4,883, 95% CI ¼ 3,223-6,832). The BC model identified the region presently occupied by otters on the central British Columbia coast, but the amount of coast-wide habitat it predicted (5,862 km 2 ) was relatively small, and the associated carrying capacity estimate (14,831, 95% CI ¼ 9,790-20,751) was low compared to historical accounts. We suggest that our model captured a type of high-quality or optimum habitat prevalent on the west coast of Vancouver Island, typified by the CB-KS region, and that suitable sea otter habitat elsewhere on the coast must include other habitat characteristics. We therefore calculated a linear, coast-wide carrying capacity of 52,459 sea otters (95% CI ¼ 34,264-73,489)-a more realistic upper limit to sea otters in British Columbia. Our carrying capacity estimates are helping set population recovery targets for sea otters in Canada, and our habitat predictions represent a first step in Critical Habitat identification. This habitat-based approach to estimating carrying capacity is likely suitable for other nonmigratory, density-dependent species.

In organic farming, weeds are one of the threats that limit crop yield. An early prediction of weed effect on yield loss and the size of late weed populations could help farmers and advisors to improve weed management. Numerous studies predicting the effect of weeds on yield have already been conducted, but the level of uncertainty about weed effect is expected to be very high in organic crops. It is thus more appropriate to provide farmers and advisors with distributions of possible production levels, rather than with point values. The purpose of this study was to estimate the effect of early weed density at the end of the tillering stage of organic winter wheat on subsequent yield and on late weed density at flowering, by using quantile regression. Results showed that this method can be applied to a hyperbolic model and to an allometric density-dependent model, to describe the distribution of yield values and of late weed density respectively, as functions of early weed density measurements. Mechanical weed control showed no significant effect on the relationship between early weed density and grain yield, but it decreased late weed density. Yield and late weed density distributions derived by quantile regression provided sound information on the possible effect of weeds on organic winter wheat production.

We develop an approach for studying population dynamics resulting from mutualism by employing functional responses based on density-dependent benefits and costs. These functional responses express how the population growth rate of a mutualist is modified by the density of its partner. We present several possible dependencies of gross benefits and costs, and hence net effects, to a mutualist as functions of the density of its partner. Net effects to mutualists are likely a monotonically saturating or unimodal function of the density of their partner. We show that fundamental differences in the growth, limitation, and dynamics of a population can occur when net effects to that population change linearly, unimodally, or in a saturating fashion. We use the mutualism between senita cactus and its pollinating seed-eating moth as an example to show the influence of different benefit and cost functional responses on population dynamics and stability of mutualisms. We investigated two mechanisms that may alter this mutualism's functional responses: distribution of eggs among flowers and fruit abortion. Differences in how benefits and costs vary with density can alter the stability of this mutualism. In particular, fruit abortion may allow for a stable equilibrium where none could otherwise exist.

Rebuilding depleted fishery resources is a worldwide problem. In the U.S., the Magnuson Stevens Fishery Conservation and Management Reauthorization Act (MSRA) of 2007 requires that "Conservation and management measures shall prevent overfishing while achieving, on a continuing basis, the optimum yield from each fishery.. .". However, translating this legal mandate into tangible goals and actions presents several technical challenges, especially for resources that have been chronically over-exploited. For example, maximum sustainable yields and biomass reference points are poorly estimated for stocks that have been overfished for a long period of time and are poorly defined unless sufficient data are available from periods of low-fishing mortality rates and relatively high-stock sizes. The conundrum of how to set meaningful rebuilding goals given limited information on the population dynamics and trophic interactions of a rebuilt stock can generally be addressed through adaptive management procedures incorporating learning about density-dependent population dynamics. Monitoring changes in life history parameters and recruitment is critical for successful rebuilding strategies realizing the full yield potential of rebuilt stocks while periodic re-evaluation of rebuilding targets is also needed to address uncertainties due to density dependence, trophic interactions or environmental factors. This paper summarizes the development and implementation of goals and strategies to rebuild New England groundfish stocks over the past decade. Management is particularly challenging because the true yield and population size potentials of these interacting stocks is unknown due to chronic overfishing throughout the modern history of the fishery, uncertainty in compensatory/depensatory population dynamics and in the degree of stationarity in environmental control of groundfish recruitment.

The classic fur trade records on Canadian lynx (Lynx canadensis) have rarely been analysed in direct conjunction with data on its principal prey, the snowshoe hare (Lepus americanus). Comparable long-term data for hare exist only for a region south of Hudson Bay. We fitted a bivariate log-linear time-series model to this hare and lynx data to disentangle the within-and between-population interactions of these species. To reduce problems with fur returns being non-normal and non-linearly related to abundance, we transformed the fur returns to a normal distribution based on sample quantiles. The estimated effect on next year's lynx abundance of a 1% increase in current hare abundance was a 0.23% (SE = 0.05) increase in lynx. Conversely, a 1% increase in current lynx abundance corresponded to a 0.46% (SE = 0.12) decrease in next year's hare abundance. This contrasts with some earlier studies. However, these studies mixed hare data from south of Hudson Bay with lynx totals for all of Canada. Despite this asymmetry of interaction strengths, coefficients of determination were similar for hare versus lynx and lynx versus hare, because hare abundance varies more than lynx. Both species showed clear intraspecific density-dependence of about equal strength. A 1% increase in current abundance increased next year's abundance by about 0.75%.

In this chapter, the main features of current models for predicting the dynamics of house mice ( Mus domesticus ) populations are reviewed and an assessment made of their data requirements and their ability to contribute to the effective management of mice in Australia. In addition, recent progress with quantifying aspects of the dynamics of mouse populations in the Mallee

The Casentinesi Forests, in the northern Apennines, harbour a rich community of wild ungulates, with the wolf representing the largest predator in the area. Between 1993 and 2000, wolf pack distribution in the area was monitored and estimates of pack size were obtained by wolf-howling surveys, snow-tracking, and occasional observations. Three to five packs were detected yearly, with sizes averaging 4.2 AE 0.9 wolves (maximum 7). The overall density in the area was 4.7 wolves per 100 km 2 with an average distance between adjacent packs of 11.1 km. The high wolf density in the Casentinesi Forests is mostly related to abundance and size of wild prey. In this, like in other areas at low latitudes, wolf density depends mainly on the number of packs, as pack size is rather small and recruitment limited by early dispersal and high mortality. Three homesites used in several years by resident packs were discovered. Homesite fidelity and pack reproductive success were higher in fully protected rather than harvested areas. Establishing a network of protected areas with high ungulate diversity and abundance is proposed as the main factor for allowing a full recovery of the wolf population in Italy.

Intraspecific, negative density dependence may contribute to the maintenance of diversity by limiting the dominance of common species. Shorea quadrinervis Slooten (Dipterocarpaceae) is one of the dominant canopy trees in a species-rich tropical rain forest in Southeast Asia. We test whether juvenile density and performance and overall population growth rate of S. quadrinervis decline with increasing local abundance of conspecific adult trees.

The ozonized sunflower oil product (Oleozon Ò ) was investigated to explore its cytotoxic activity on Giardia duodenalis in vitro cultivated trophozites. Oleozon Ò produced inactivation of Giardia trophozoites in a dose-and cell density-dependent manner. Thirty microliter of Oleozon Ò with peroxide index value of 500 equivalent-mmol of activated oxygen per kilogram were used to achieve a 100% inhibition (<À4.00 log unit) of trophozoites from an initial inoculum of 15 Â 10 4 cells. This potent effect was confirmed by transmission electron microscopy where morphological deterioration of superficial structures mainly in the ventral disc, and formation of a great number of micro vesicles in the cytoplasm were found. We concluded that a direct chemical-oxidation attack by the active substances from Oleozon Ò is one of the causes of the parasitocidal effect of this product. We suggest that the dose and cell density-dependent effect must be taken into account when prescription of this product for giardiasis treatment in humans.

We investigate loss mechanisms in 1.55-m In-GaAsP-InP multiquantum-well ridge-waveguide laser diodes at room temperature. The common method of measuring light versus current curves and plotting the inverse slope efficiency versus laser length is employed to extract the internal optical loss i and the differential internal efficiency i . This method neglects the dependence of both the parameters on the laser cavity length L. We analyze physical mechanisms behind these loss parameters and their length dependence using the commercial laser simulation software PICS3D. Internal optical losses are dominated by carrier density dependent absorption. The differential internal efficiency above threshold is found to be mainly restricted by carrier recombination losses within the quantum wells, i.e., Fermi level pinning is not observed. Both loss mechanisms are enhanced with shorter cavity length due to the higher quantum well carrier density. For the shortest device measured (L = 269 m), we extract i = 20 cm 01 and i = 66%. With increasing cavity length, the loss parameters approach i = 15 cm 01 and i = 70%. From the inverse slope efficiency versus cavity length plot, we obtain i = 14 cm 01 and i = 67% independent of laser length.

Kinetics of N-methyl pyrrolidone evaporation from swollen photo-crosslinked polyacrylate was monitored thermogravimetrically at temperatures ranging from 323 to 398 K. Crosslink density dependence of evaporation kinetics was investigated in photo-crosslinked polyacrylates with crosslinked density ranging from &1.2 9 10 2 to &1.7 9 10 4 mol m-3 and number of main chain atoms between crosslinks ranging from &70 atoms to &6 atoms, respectively. As was shown, evaporation kinetics was controlled by the solvent diffusion in polymer. Activation energies of evaporation (diffusion) were deduced from the rate measurements at different temperatures. Apparent activation energy of evaporation decreased from 48.7 to 31.1 kJ mol-1 with crosslink density increase. Activation energy of pure N-methyl pyrrolidone evaporation was 50.6 kJ mol-1. Decrease of the rate of solvent diffusion and unexpected decrease of diffusion activation energy with increase of crosslink density of swollen polymer matrix was explained by decrease in polymer chain segments mobility, as indicated by Eyring's approach to diffusion in polymers.

Proteus mirabilis colonies exhibit striking geometric regularity. Basic microbiological methods and imaging techniques were used to measure periodic macroscopic events in swarm colony morphogenesis. We distinguished three initial phases (lag phase, first swarming phase, and first consolidation phase) followed by repeating cycles of subsequent swarming plus consolidation phases. Each Proteus swarm colony terrace corresponds to one swarming-plus-consolidation cycle. The duration of the lag phase was dependent upon inoculation density in a way that indicated the operation of both cooperative and inhibitory multicellular effects. On our standard medium, the second and subsequent swarm phases displayed structure in the form of internal waves visible with reflected and dark-field illumination. These internal waves resulted from organization of the migrating bacteria into successively thicker cohorts of swarmer cells. Bacterial growth and motility were independently modified by altering th...

Mutualisms provide benefits to interacting species, but they also involve costs. If costs come to exceed benefits as population density or the frequency of encounters between species increases, the interaction will no longer be mutualistic. Thus curves that represent benefits and costs as functions of interaction frequency are important tools for predicting when a mutualism will tip over into antagonism. Currently, most of what we know about benefit and cost curves in pollination mutualisms comes from highly specialized pollinating seed-consumer mutualisms, such as the yucca moth-yucca interaction. There, benefits to female reproduction saturate as the number of visits to a flower increases (because the amount of pollen needed to fertilize all the flower's ovules is finite), but costs continue to increase (because pollinator offspring consume developing seeds), leading to a peak in seed production at an intermediate number of visits. But for most plant-pollinator mutualisms, costs to the plant are more subtle than consumption of seeds, and how such costs scale with interaction frequency remains largely unknown. Here, we present reasonable benefit and cost curves that are appropriate for typical pollinator-plant interactions, and we show how they can result in a wide diversity of relationships between net benefit (benefit minus cost) and interaction frequency. We then use maximum-likelihood methods to fit net-benefit curves to measures of female reproductive success for three typical pollination mutualisms from two continents, and for each system we chose the most parsimonious model using information-criterion statistics. We discuss the implications of the shape of the net-benefit curve for the ecology and evolution of plant-pollinator mutualisms, as well as the challenges that lie ahead for disentangling the underlying benefit and cost curves for typical pollination mutualisms.

Cavia intermedia may be the mammal with the smallest geographical distribution in the world, because it is endemic to a 10-ha island and therefore vulnerable to extinction. The objective of this study was to understand the population dynamics of C. intermedia in order to define its conservation status and to provide information for its management. The population was sampled monthly using capture-mark-recapture methods and radiotelemetry for 16 months, between March 2004 and June 2005. A total of 5,530 trap-nights resulted in 665 captures of 141 individuals. The population exhibited the main demographic characteristics of the insular syndrome, such as high and stable density, small home ranges, stable age structure composed mostly of adults, and high survival rates. The population dynamics were characterized by density-dependent effects on mortality. C. intermedia can be considered one of the rarest species on the planet because of its limited geographic distribution and very small population size (average estimated population of 42 individuals). We recommend that it be listed as Critically Endangered.

Human encroachment on wildlife habitats has contributed to the emergence of several zoonoses. Pathogenic hantaviruses are hosted by rodents and cause severe diseases in the Americas and Eurasia. We reviewed several factors that potentially drive prevalence (the proportion of infected rodents) in host populations. These include demography, behavior, host density, small mammal diversity, predation, and habitat and landscape characteristics. This review is the first to include a quantitative summary of the literature investigating hantavirus prevalence in rodents. Demographic structure and density were investigated the most and predation the least. Reported effects of demographic structure and small mammal diversity were consistent, whereby reproductive males were most likely to be infected and prevalence decreased with small mammal diversity. The influences of habitat and landscape properties are often complex and indirect. The relationship between density and prevalence merits more investigation. Most hantavirus hosts are habitat generalists and their control is challenging. Incorporating all potential factors and their interactions is essential to understanding and controlling infection in host populations.

Molecular dynamics simulations of a Lennard-Jones fluid under negative pressure are carried out to Ž . investigate the inception of vapor phase in the liquid i.e., cavitation and properties of liquid under negative pressure. The pressure of the system is reduced by uniform system expansion. In the case of larger expansion ratios, the nuclei of bubbles immediately appear, whereas finite waiting time is observed in case of smaller expansion ratio. This means the system reaches a kinetic limit of metastability. The nucleation rate calculated with the waiting time is 8 orders of magnitude larger than that of classical nucleation theory. Isothermal compressibility is also obtained and its density dependence is discussed. q 1998 Elsevier Science B.V.

Increased micronutrient density in grain destined for human consumption may alleviate micronutrient de®ciencies (Fe, Zn, Cu, and I) in human populations around the world. The review of literature indicates that fertilization with inorganic and organic forms of micronutrients has a potential to increase their concentrations in grain. The most effective fertilization could be via soil (for Zn and, to some extent, Cu), foliarly (for Fe) and by adding fertilizers to the irrigation water (for iodine). Care should be exercised not to overfertilize crops with micronutrients because of consequent toxicity and losses in quality and quantity of grain yield. Effectiveness of various agricultural measures in increasing micronutrient density depends on soil type, crop, cultivar, rotation, and environmental and other factors, thus necessitating development of a speci®c set of measures for individual regions. Agricultural measures would need to be supplemented with appropriate changes in the milling technology to ascertain that increased micronutrient concentrations in some grain parts are passed into the food chain. # 0378-4290/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. P I I : S 0 3 7 8 -4 2 9 0 ( 9 8 ) 0 0 1 3 1 -2

We present a review of recent applications of self-consistent relativistic mean-field models to exotic nuclear structure. Based on concepts of non-renormalizable effective relativistic field theories and density functional theory, these models provide a rich theoretical framework for studies of nuclei along the valley of β-stability, exotic nuclei with extreme ground-state isospin values and close to the particle drip lines. A quantitative microscopic description of ground states and properties of excited states in nuclei far from stability necessitates a unified description of mean-field and pairing correlations. The relativistic Hartree-Bogoliubov (RHB) model has been employed in studies of structure phenomena that include: the description of the neutron drip-line in light nuclei and the microscopic mechanism for the formation of neutron halos; the reduction of the effective spin-orbit interaction and the resulting modification of surface properties in drip-line nuclei; the suppression of shell effects and the onset of deformation and shape coexistence in neutron-rich nuclei; nuclei at the proton drip-line and ground-state proton emitters in the region of deformed rare-earth nuclei; shape coexistence phenomena in neutron-deficient nuclei.

Interactions among sympatric large predators and their prey and how they respond to conservation measures are poorly known. This study examines predictions concerning the effects of establishing a protected area in Nepal on tigers (Panthera tigris), leopards (Panthera pardus), and their ungulate prey. Within a part of the park, after 22 years the total density of wild ungulates had increased fourfold, to ca. 200 animals/km 2 , almost exclusively due to a remarkable increase in chital deer (Axis axis). Tiger density also increased markedly to nearly 20 animals/100 km 2 , whereas leopard density did not and was ca. 5 animals/ 100 km 2 . The prediction that grazers should increase more than browsers was only partially supported. The prediction of positive density dependence in prey selection was not supported. Instead, the most abundant species (chital and hog deer, Axis porcinus) were killed less frequently than expected, whereas the lower-density wild boar (Sus scrofa) was preferred. Predictions that (i) initially rare species suffer highest predation was partially supported, that (ii) predation is highest among the most abundant prey was not supported, and that (iii) predation is highest among the most preferred prey independently of their densities was supported. Clearly, the conservation efforts adopted in Bardia were successful, as both tigers and their natural prey base increased. However, the positive numerical response of tigers limited and depressed the abundance of some prey species. Thus, conservation activities aimed at restoring large predators are likely to change in the composition of the overall mammal community, potentially eliminating rare but preferred prey species.

In the Drosophila literature, selection for faster development and selection for adapting to high density are often confounded, leading, for example, to the expectation that selection for faster development should also lead to higher competitive ability. At the same time, results from experimental studies on evolution at high density do not agree with many of the predictions from classical density-dependent selection theory. We put together a number of theoretical and empirical results from the literature, and some new experimental results on Drosophila populations successfully subjected to selection for faster development, to argue for a broader interpretation of density-dependent selection. We show that incorporating notions of α-selection, and the division of competitive ability into effectiveness and tolerance components, into the concept of density-dependent selection yields a formulation that allows for a better understanding of the empirical results. We also use this broader formulation to predict that selection for faster development in Drosophila should, in fact, lead to the correlated evolution of decreased competitive ability, even though it does lead to the evolution of greater efficiency and higher population growth rates at high density when in monotypic culture. [Joshi A., Prasad N. G. and Shakarad M. 2001 K-selection, α-selection, effectiveness, and tolerance in competition: densitydependent selection revisited. J. Genet. 80, [63][64][65][66][67][68][69][70][71][72][73][74][75] Much of what we have to say is not new. However, most of the theoretical and experimental elements that we wish to weave together into an argument were originally presented in diverse contexts and, in some cases, seem to have escaped the attention of several subsequent workers

Intrusion of seawater into coastal aquifers is considered one of the most important processes that degrade water-quality by raising the salinity to levels exceeding acceptable drinking standards. Therefore saltwater intrusion should be prevented or at least controlled to protect groundwater resources. This paper presents a cost-effective method to control seawater intrusion in coastal aquifers. This methodology ADR (Abstraction, Desalination and Recharge) includes; abstraction of saline water and recharge to the aquifer after desalination. A coupled transient density-dependent finite element model is developed for simulation of fluid flow and solute transport and used to simulate seawater intrusion. The simulation model has been integrated with an optimization model to examine three scenarios to control seawater intrusion including; abstraction, recharge and a combination system, ADR. The main objectives of the models are to determine the optimal depths, locations and abstraction/recharge rates for the wells to minimize the total costs for construction and operation as well as salt concentrations in the aquifer. A comparison between the combined system (ADR) and the individual abstraction or recharge system is made in terms of total cost and total salt concentration in the aquifer and the amount of repulsion of seawater achieved. The results show that the proposed ADR system performs significantly better than using abstraction or recharge wells alone as it gives the least cost and least salt concentration in the aquifer. ADR is considered an effective tool to control seawater intrusion and can be applied in areas where there is a risk of seawater intrusion.

The biological theory of adaptive dynamics proposes a description of the long-term evolution of a structured asexual population. It is based on the assumptions of large population, rare mutations and small mutation steps, that lead to a deterministic ODE describing the evolution of the dominant type, called the 'canonical equation of adaptive dynamics'. Here, in order to include the effect of stochasticity (genetic drift), we consider self-regulated randomly fluctuating populations subject to mutation, so that the number of coexisting types may fluctuate. We apply a limit of rare mutations to these populations, while keeping the population size finite. This leads to a jump process, the so-called 'trait substitution sequence', where evolution proceeds by successive invasions and fixations of mutant types. Then we apply a limit of small mutation steps (weak selection) to this jump process, that leads to a diffusion process that we call the 'canonical diffusion of adaptive dynamics', in which genetic drift is combined with directional selection driven by the gradient of the fixation probability, also interpreted as an invasion fitness. Finally, we study in detail the particular case of multitype logistic branching populations and seek explicit formulae for the invasion fitness of a mutant deviating slightly from the resident type. In particular, second-order terms of the fixation probability are products of functions of the initial mutant frequency, times functions of the initial total population size, called the invasibility coefficients of the resident by increased fertility, defence, aggressiveness, isolation, or survival.

a b s t r a c t [6] demonstrated that the solubility of a substance in a supercritical fluid (SCF) can be correlated with the density of the pure supercritical gas. Therefore, Chrastil's equation permits calculation of the supercritical phase composition of binary SCF + substance mixture based on the knowledge of the supercritical gas density and avoiding the use of equation of state based models.

The optical absorption of a many (continuum) polaron gas is derived in the framework of a variational approach at zero temperature and weak or intermediate electron-phonon coupling strength. We derive a compact formula for the optical conductivity of the many-polaron system taking into account many-body effects in the electron or hole system. Within the method presented here, these effects are contained completely in the dynamical structure factor of the electron or hole system. This allows to build on well-established studies of the interacting electron gas. Based on this approach a novel feature in the absorption spectrum of the many-polaron gas, related to the emission of a plasmon together with a phonon, is identified. As an application and illustration of the technique, we compare the theoretical many-polaron optical absorption spectrum as derived in the present work with the `d-band' absorption feature in Nd$_{2}$CuO$_{2}$. Similarities are shown between the theoretically and the experimentally derived first frequency moment of the optical absorption of a family of differently doped Nd$_{2-x}$Ce$_{x}$CuO$_{4-y}$ materials.

Current data finds that the atmospheric neutrino anomaly is best explained with n m - n t neutrino oscillations. However, there is motivation for the Mass Varying Neutrino (MaVaN) model as an explanation for the presence of dark energy and the results of LSND. A possible consequence of said model is a bias in the neutrino mass from the electron density r e of the matter a neutrino passes through. Using the data from Super-Kamiokande-I, n m - n t oscillation models whose mass differences are proportional to (r e ) n are applied to the Monte Carlo predictions for several different n values. A constant mixing angle in all densities is assumed. For each density dependence hypothesis, two sets of models are applied, which do not or do account for the air pathlength. In all of the specific models tested, the density dependent oscillations are disfavored at greater than a 3s level compared with 2-flavor oscillations with a fixed mass in all environments. In addition, a separate analysis which assumes maximal mixing finds that a best-fit 2-flavor oscillation of varying density dependence is consistent with no dependence on electron density within 1s.

It is well understood that populations cannot grow without bound and that it is competition between individuals for resources which restricts growth. Despite centuries of interest, the question of how best to model density dependent population growth still has no definitive answer. We address this question here through a number of individual based models of populations expressed using the process algebra WSCCS. The advantage of these models is that they can be explicitly based on observations of individual interactions. From our probabilistic models we derive equations expressing overall population dynamics, using a formal and rigorous rewriting based method. These equations are easily compared with the traditionally used deterministic Ordinary Differential Equation models and allow evaluation of those ODE models, challenging their assumptions about system dynamics. Further, the approach is applied to epidemiology, combining population growth with disease spread.

We argue that population growth rate is the key unifying variable linking the various facets of population ecology. The importance of population growth rate lies partly in its central role in forecasting future population trends; indeed if the form of density dependence were constant and known, then the future population dynamics could to some degree be predicted. We argue that population growth rate is also central to our understanding of environmental stress: environmental stressors should be defined as factors which when first applied to a population reduce population growth rate. The joint action of such stressors determines an organism's ecological niche, which should be defined as the set of environmental conditions where population growth rate is greater than zero (where population growth rate = r = log e (N tϩ1 /N t )). While environmental stressors have negative effects on population growth rate, the same is true of population density, the case of negative linear effects corresponding to the well-known logistic equation. Following Sinclair, we recognize population regulation as occurring when population growth rate is negatively density dependent. Surprisingly, given its fundamental importance in population ecology, only 25 studies were discovered in the literature in which population growth rate has been plotted against population density. In 12 of these the effects of density were linear; in all but two of the remainder the relationship was concave viewed from above.

We synthesize results from existing models of marine reserves to identify key theoretical issues that appear to be well understood, as well as issues in need of further exploration. Models of marine reserves are relatively new in the scientific literature; 32 of the 34 theoretical papers we reviewed were published after 1990. These models have focused primarily on questions concerning fishery management at the expense of other objectives such as conservation, scientific understanding, recreation, education, and tourism. Roughly one-third of the models analyze effects on cohorts while the remaining models have some form of complete population dynamics. Few models explicitly include larval dispersal. In a fisheries context, the primary conclusion drawn by many of the complete population models is that reserves increase yield when populations would otherwise be overfished. A second conclusion, resulting primarily from single-cohort models, is that reserves will provide fewer benefits for species with greater adult rates of movement. Although some models are beginning to yield information on the spatial configurations of reserves required for populations with specific dispersal distances to persist, it remains an aspect of reserve design in need of further analysis. Other outstanding issues include the effects of (1) particular forms of density dependence, (2) multispecies interactions, (3) fisher behavior, and (4) effects of concentrated fishing on habitat. Model results indicate that marine reserves could play a beneficial role in the protection of marine systems against overfishing. Additional modeling and analysis will greatly improve prospects for a better understanding of the potential of marine reserves for conserving biodiversity.