Function Of Population Density Research Articles

Regional density functions and growth patterns in major plains of China, 1982–1990

Abstract. This research analyzes the spatial patterns of regional development in China through the change of population density functions from 1982 to 1990, using several online digital data sets. To minimize the influence of physical environment on population densities, the study areas are limited to four major plains of China: the Northeast (Dongbei), North China (Huabei) and Hubei‐Hunan (Lianghu) Plains, and the Sichuan Basin. A gravity‐based delineation approach is used to delineate the influence regions of 17 cities. Regional densities in China decline with distance from a city, similar to western countries. In addition, areas close to central cities grew faster than remote areas, described as a trend of centralization. However, regions with strong core growth are generally associated with stagnant hinterlands ('core growth‐hinterland stagnation'); and regions with moderate core growth are usually matched by similar growth rates in the hinterlands ('spread through growth').

Mate choice games, context-dependent good genes, and genetic cycles in the side-blotched lizard, Uta stansburiana

According to mate choice models, a female should prefer males with traits that are reliable indicators of genetic quality which the sire can pass on to their progeny. However, good genes may depend on the social environment, and female choice for good genes should be context dependent. The side-blotched lizard, Uta stansburiana, exhibits genetically based throat colors (orange, blue, or yellow) that could be used as a sexually selected signal since they reliably predict the genetic quality of mates. The frequencies of male and female morphs cycle between years, and both male and female morphs have an advantage when rare; thus genetic quality will depend on morph frequency. A female should choose a sire that maximizes the reproductive success of both male and female progeny. We examine a game theoretical model that predicts female mate choice as a function of morph frequency and population density. The model predicts the following flexible mate choice rule: both female morphs should prefer rare males in ’boom years’ of the female cycle (e.g., ’rarest-of-N rule’), but prefer orange males in ’crash years’ of the female cycle (’orange-male rule’). Cues from the current social environment should be used by females to choose a mate that maximizes the future reproductive success of progeny, given the social environment of the next generation. We predict that the cue is the density of aggressive orange females. In the side-blotched lizard, cycling mate choice games and context-dependent mate choice are predicted to maintain genetic variation in the presence of choice for good genes.

Distribution-free estimation of the Gini inequality index: the kernel method approach

In this paper a non-parametric approach to the estimation of the Gini inequality index is introduced. The basic idea consists in taking first a preliminary estimation of the population density function, and then in computing the corresponding inequality index. Statistical properties of the estimator introduced are studied, with particular reference to the case of large samples (usually available from statistical agencies). As a by-product, approximated confidence intervals are obtained.

Variation of distal genitalia in the simultaneously hermaphroditic land snail Arianta arbustorum (Pulmonata, Stylommatophora) caused by sexual selection?

The most likely explanation for genitalic extravagance may be sexual selection acting either before, during, or after copulation. In promiscuous species, the intensity of postmating sexual selection may be a function of population density. In this study we examined the variability of the distal genitalia involved in spermatophore production, reception and manipulation of 113 adult individuals of the simultaneously hermaphroditic land snail Arianta arbustorum (L.) from six natural populations in the Eastern Alps (Gesause, Austria). We investigated the hypothesis that these genitalia increase in relation to shell size with increasing population density (range: 0.9 to 39.8 individuals/m2) and expected a higher variance of the genitalia compared to shell dimensions due to sexual selection. Genitalic size was unexpectedly inversely related to population density, probably due to increased inhibitory effects of snail mucus. Patterns of variation of female and male characters did not differ. Coefficients of variation of the genitalia were significantly higher than those of the shell dimensions as predicted. This was due to a higher dispersion around the regression lines rather than higher allometric values. However, the influence of sexual selection on genitalic size and variance cannot be unambiguously determined. We discuss different scenarios emphasizing the importance of sexual selection to differing degrees and conclude that sexual selection has probably played only a minor role.

Variation of distal genitalia in the simultaneously hermaphroditic land snail Arianta arbustorum (Pulmonata, Stylommatophora) caused by sexual selection?

The most likely explanation for genitalic extravagance may be sexual selection acting either before, during, or after copulation. In promiscuous species, the intensity of postmating sexual selection may be a function of population density. In this study we examined the variability of the distal genitalia involved in spermatophore production, reception and manipulation of 113 adult individuals of the simultaneously hermaphroditic land snail Arianta arbustorum (L.) from six natural populations in the Eastern Alps (Gesäuse, Austria). We investigated the hypothesis that these genitalia increase in relation to shell size with increasing population density (range: 0.9 to 39.8 individuals/m2) and expected a higher variance of the genitalia compared to shell dimensions due to sexual selection. Genitalic size was unexpectedly inversely related to population density, probably due to increased inhibitory effects of snail mucus. Patterns of variation of female and male characters did not differ. Coefficients of variation of the genitalia were significantly higher than those of the shell dimensions as predicted. This was due to a higher dispersion around the regression lines rather than higher allometric values. However, the influence of sexual selection on genitalic size and variance cannot be unambiguously determined. We discuss different scenarios emphasizing the importance of sexual selection to differing degrees and conclude that sexual selection has probably played only a minor role.

Catchability of Walleyes to Angling in Escanaba Lake, Wisconsin, 1980–1995

Abstract Angler catch rates were modeled as a nonlinear function of population density of adult walleyes Stizostedion vitreum to determine if walleye angling catchability was density dependent in Escanaba Lake, Wisconsin, during 1980–1995. Relations between angler catch rates (number fish/angler-hours) and catchability (q) of walleyes were modeled from data derived from compulsory creel censuses and mark–recapture estimates of walleye abundance (number/acre). For age-3 and older walleyes combined and for individual ages 3–8, angler catch rate was linearly related to population density, whereas catchability was not significantly related to population density. We conclude that angling catchability of walleyes in Escanaba Lake is not density dependent and therefore that angling can safely be regulated using indirect management strategies such as creel limits, size limits, and closed seasons.

Modelling heat transfer between solid particles

A population balance model is presented for describing the direct particle-to-particle heat transfer in fluid–solid processing systems. In developing the model, simple kinetic equations are assumed to describe the heat transfer process, but the particle–particle interactions are considered stochastic. A new approach is used to develop the population balance equation. The moment equations are derived and analysed. The time evolution of the population density function, determined by numerical solution of the integro-differential equation, is also presented.

SITE-DEPENDENT REGULATION OF POPULATION SIZE: REPLY

population regulation is how demographic parameters like birth and death rates change as a function of population size or density. In answering this question, it is important to know how habitats (sites?) of different qualities are distributed, how organisms find and defend high-quality habitats, and how the size and/or quality of occupied habitats changes in relationship to population size or density. To the extent that Rodenhouse et al. draw attention to this they have performed a useful service. However, redefining the classical concepts of density and density dependence so that they no longer exist does not seem to contribute to our understanding of the central question.

Estimating optimal population density for intermediate culture of scallops in spat collector bags

In a scallop restocking project in Îles-de-la-Madeleine, Québec, we investigated the spat growing within the collector bags, instead of using the usual pearl net method. To estimate optimal population density in the collector bags, we studied yield as a function of spat population density ( B– N curves) at three depths in the water column (10, 20, 30 m) and in a nearby lagoon. The B– N curves suggest that for 1-year-old spat, biomass at 10 m depth was maximum at ca. 1900 individual spat per bag. At higher population density, self-thinning occurred and yield decreased. The B– N curve for 20 m did not reach a maximum at the population densities encountered in the experiment. At population density ca. 2000 ind/bag, yield of individuals ≥2 cm shell height was greater at 20 m than at 10 m, apparently because of higher food availability at 20 m and presence of interspecific competitors at 10 m depth. Yields in the lagoon and at 30 m depth were not satisfactory. Intermediate culture should be done at 20 m depth, with at least 2000 ind/bag. The upper limit to this estimate could not be determined experimentally.

Studies on Instantaneous Characteristics of Er-Doped Fiber Laser

In this paper, instantaneous state characteristics of Er-doped fiber lasers (EDFLs) are studied. The fluctuation function of Er-doping ion and photon population density are solved under small pump perturbation. Furthermore, the damp and the resonance properties of the relaxation oscillation and relationships with EDFLs' parameters are discussed in detail.

Methane hydrate crystallization mechanism from in‐situ particle sizing

AbstractA new experimental setup that makes possible in‐situ determinations of the population density function of the methane hydrate particles during its crystallization in a pressurized reactor is used. Thanks to this equipment, new results can be obtained, in particular concerning the granular aspects of the crystallization processes and the influence of the stirring rate. These results are discussed in the framework of a model including gas absorption, primary and secondary nucleation, crystal growth, agglomeration, and breakage. From this discussion, the relevant processes and parameters of methane hydrate crystallization can be determined and quantified.

Density-dependent effects of a toxicant on life-history traits and population dynamics of a capitellid polychaete

The toxic effects of the widespread polycyclic aromatic hydrocarbon (PAH), fluoranthene (FLU), on life-history traits of Capitella sp. M as a function of population density were investigated in d life-table-response-experiment (LTRE) lasting 134 d. Animals from laboratory cultures were exposed to 6 different FLU concentrations (range 0 to 80 μg FLU [g dry wt sed] -1 , ppm) at 3 population densities (range 629 to 36 842 worms m -2 ), and survivorship, growth rate until maturity and reproductive parameters were recorded. Fluoranthene exposure significantly reduced juvenile survivorship in a concentration- tependent manner, whereas population density had no effect on this trait. In contrast, increasing density (= food limitation) was associated with significdnt decreases in body size at maturity and increased time to maturity, while FLU had no effect on these traits. Effects of FLU on time to first reproduction. % reproducing females, larvae per brood, broods per female and population growth rate (λ) varied in response to the intensity of density dependence. In general, interactions between FLU and density were compensatory (antagonistic) at low toxicant exposures, but synergistic at the highest. Population effects are summarised by effects on population growth rate. Our main result is that at low concentrations of FLU (0 to 40 ppm), increasing density alleviated FLU's effects on λ. Thus increasing FLU decreased λ at low density but had no effect at high density. At the highest concentrations of FLU, however, the reverse was the case ('synergistic effects') Here, the effect of increasing density is to exacerbate the effects of FLU. This result is particularly important because it demonstrates that LTREs carried out at low density (non-food limited), as most have been in the past, may seriously underestimate effects in the field, where densities are generally high and likely to produce food limitation, as here. Our results suggest that when food availability is limiting, the impact of low levels of toxicant stress on population dynamics may be marginal. By contrast at higher toxicant exposures, food limitation exacerbates toxicant effects and may increase the likelihood of extinction.

Taguchi and TQM

Abstract Industrial organisations, including manufacturers and users of surface coatings, are increasingly seeking to ensure conformance to target specifications and low variance; using measured variables in a product or process that can be used to assess quality, for example, using Taguchi's loss function. In a TQM environment, the drive is to constantly improve quality. However, an engineer may regard a system not exhibiting a normal distribution function as one lacking quality. We discuss how a “non-normal” physical phenomenon can be accepted as a “quality” system. One such system example is a coated cold forming tool. Using design of experiment techniques in an industrial environment, it has previously been shown that a TiN coating was only effective at reducing tool wear in a forming operation if it was combined with pre-polishing of the tool nose. Not only was the improvement quantifiable using the Weibull characteristic life, it also showed that the population density function changed dramatically, indicating that the failure mode had altered between the best and the rest of the tools – apparently increasing the variance as well as the mean response. This paper compares the previous analysis to one based on Taguchi's robust design ideas. The importance of choosing an applicable quality loss function is highlighted. The use of the Weibull characteristic life is proposed and demonstrated for the functional limit ( Δ 0 ) in the quality loss function. In this application it is shown that the relative loss of quality can be reduced by over 40% even considering a 25% increase in tool cost by using polished and coated forming tools compared to uncoated tools.

Dynamics of transitions between population interactions: a nonlinear interaction alpha-function defined

In nature, two populations may interact in different ways during their lifetime, and even undergo transitions from one type of interaction to another. A model for the dynamics of these transitions has been developed in this study. The interaction coefficients α i in the Lotka–Volterra equations are re-interpreted as nonlinear functions of population densities N i , N j , modulated by environmental parameters, which offers the possibility of a change in sign. Transitions can take place owing to variations in population density (endogenous effect), or in the environmental parameters (exogenous effect). Models for both facultative and obligate associations are examined. Graphical stability analyses show that multiple density equilibria are possible, accounting for the occurrence of the transitions.

Population Density in Suburban Chicago: A Bid-rent Approach

Bid-rent theory suggests that the dependent variable of a population density function is unobserved (or population equals zero) if land values are relatively low in residential use. If the errors of density and bid-rent function errors are correlated, bid-rent theory implies that OLS population density estimates are subject to selection bias. Combined land use and density estimates for suburban Chicago confirm these predictions. The results provide further evidence that Chicago cannot be modelled adequately as other than a polycentric city.

Relationship between bubble size distributions and chord-length distribution in heterogeneously bubbling systems

The probability relationships between bubble sizes and chord lengths in an heterogeneously bubbling system have been analyzed. A forward transform of chord length distribution for a given bubble size density distribution affecting the probe under a heterogeneously bubbling condition has been demonstrated. Three backward transform techniques, an analytical, a general, and a numerical, have been developed to infer bubble sizes from the chord length data in heterogeneously bubbling system. Both the analytical and the general backward transforms were based on the representation of the bubble population density function as a product of two functions which depend on bubble size and chord length. The techniques were tested and compared using Monte-Carlo simulations.

Allocation to Sexual versus Nonsexual Disease Transmission

Many diseases have both sexual and nonsexual transmission routes, and closely related diseases often differ in their degree of sexual transmission. We investigate the evolution of transmission mode as a function of host social and mating structure using a model in which disease transmission is explicitly dependent on the numbers of sexual and nonsexual contacts (which are themselves a function of population density) and per-contact infection probabilities. Most generally, and in the absence of trade-offs between the degree of sexual transmission and effects on host fecundity and mortality, nonsexual transmission is favored above the social-sexual crossover point (the host density at which the number of nonsexual contacts exceeds the number of sexual contacts), while sexual transmission is favored below this point. When changes in allocation to the two transmission modes are accompanied by changes in mortality or fecundity, both mixed and pure transmission strategies can be favored. If invading genotypes differ substantially from resident genotypes, genetic polymorphism in transmission mode is possible. The evolutionary outcomes are predictable from a knowledge of the equilibrium population sizes in relation to the social-sexual crossover point. Our results also show that predictions about dynamic outcomes, based on rates of invasion for single pathogens into healthy populations, do not adequately describe the resulting disease prevalence nor predict the subsequent evolutionary dynamics; once invasion of a pathogen has occurred, the conditions for spread of a second pathogen are themselves altered. If the host is considered as a single resource, our results show that two pathogens may coexist on a single resource if they use that resource differentially and have differential feedbacks on resource abundance; such resource feedback effects may be present in other biological systems.

Allocation to Sexual Versus Nonsexual Disease Transmission

Many diseases have both sexual and nonsexual transmission routes, and closely related diseases often differ in their degree of sexual transmission. We investigate the evolution of transmission mode as a function of host social and mating structure using a model in which disease transmission is explicitly dependent on the numbers of sexual and nonsexual contacts (which are themselves a function of population density) and per‐contact infection probabilities. Most generally, and in the absence of trade‐offs between the degree of sexual transmission and effects on host fecundity and mortality, nonsexual transmission is favored above the social‐sexual crossover point (the host density at which the number of nonsexual contacts exceeds the number of sexual contacts), while sexual transmission is favored below this point. When changes in allocation to the two transmission modes are accompanied by changes in mortality or fecundity, both mixed and pure transmission strategies can be favored. If invading genotypes differ substantially from resident genotypes, genetic polymorphism in transmission mode is possible. The evolutionary outcomes are predictable from a knowledge of the equilibrium population sizes in relation to the social‐sexual crossover point. Our results also show that predictions about dynamic outcomes, based on rates of invasion for single pathogens into healthy populations, do not adequately describe the resulting disease prevalence nor predict the subsequent evolutionary dynamics; once invasion of a pathogen has occurred, the conditions for spread of a second pathogen are themselves altered. If the host is considered as a single resource, our results show that two pathogens may coexist on a single resource if they use that resource differentially and have differential feedbacks on resource abundance; such resource feedback effects may be present in other biological systems.

A note on kernel density estimation with auxiliary information

It is well-known that the method of empirical likelihood can be employed to get sharper inferences on many functionals of the population distribution by making effective use of auxiliary information available in a nonparametric model. In this paper, we show that in the context of estimating a population density function, the modified kernel density estimator which makes use of the knowledge of auxiliary information does not sharpen our inferences on the population density function in the sense that the modified kernel density estimator is first order equivalent to the standard kernel density estimator which does not utilize auxiliary information.

Determinants of Density- and Frequency-Dependent Fitness in Competing Plant Pathogens

ABSTRACT Using mathematical models, we investigated how infection and sporulation characteristics of competing plant pathogens determine the density and frequency dependence of relative fitness. Two models, one for the infection stage and one for the sporulation stage of a pathogen's life cycle, describe reproductive output of pathogen strains in mixture as a function of the strains' population densities. Model parameters include infection and sporulation efficiencies, carrying capacities on leaves for sporulating lesions and spore production, and coefficients of interstrain competitive effects in both life cycle stages. Although the models were originally developed for rust fungi, they are generally applicable to any organism with distinct colonization (e.g., infection) and propagative (e.g., sporulation) life cycle stages. In this work, paired hypothetical strains were assigned equal baseline parameter values. Parameters were then altered one at a time for one or both strains, and relative fitness was calculated over a range of densities and strain frequencies. Except for infection efficiency, the fitness benefit conferred by an advantage in a single parameter was always density dependent. Relative fitness was frequency dependent whenever inter- and intrastrain competitive effects were not equal. These results suggest that the fitness of pathogens in nature is rarely fixed, but, rather, may typically be highly dependent on the densities and frequencies of all coexisting strains in a habitat.