scholarly journals A logistic-harvest model with allee effect under multiplicative noise

2021 ◽  
pp. 2150044
Author(s):  
Almaz Tesfay ◽  
Daniel Tesfay ◽  
James Brannan ◽  
Jinqiao Duan
Keyword(s):  
Population Size ◽  
Carrying Capacity ◽  
Noise Intensity ◽  
Allee Effect ◽  
Large Population ◽  
Logistic Growth ◽  
Maximum Point ◽  
Harvest Rate ◽  
Harvest Model ◽  
The Impact

This work is devoted to the study of a stochastic logistic growth model with and without the Allee effect. Such a model describes the evolution of a population under environmental stochastic fluctuations and is in the form of a stochastic differential equation driven by multiplicative Gaussian noise. With the help of the associated Fokker–Planck equation, we analyze the population extinction probability and the probability of reaching a large population size before reaching a small one. We further study the impact of the harvest rate, noise intensity and the Allee effect on population evolution. The analysis and numerical experiments show that if the noise intensity and harvest rate are small, the population grows exponentially, and upon reaching the carrying capacity, the population size fluctuates around it. In the stochastic logistic-harvest model without the Allee effect, when noise intensity becomes small (or goes to zero), the stationary probability density becomes more acute and its maximum point approaches one. However, for large noise intensity and harvest rate, the population size fluctuates wildly and does not grow exponentially to the carrying capacity. So as far as biological meanings are concerned, we must catch at small values of noise intensity and harvest rate. Finally, we discuss the biological implications of our results.

scholarly journals The spatial Muller’s ratchet: surfing of deleterious mutations during range expansion

2019 ◽  
Author(s):  
Félix Foutel-Rodier ◽  
Alison Etheridge
Keyword(s):  
Population Size ◽  
Range Expansion ◽  
Allee Effect ◽  
Large Population ◽  
Small Population ◽  
Deleterious Mutations ◽  
Muller's Ratchet ◽  
Muller’S Ratchet ◽  
Expansion Load ◽  
The Impact

AbstractDuring a range expansion, deleterious mutations can “surf” on the colonisation front. The resultant decrease in fitness is known as expansion load. An Allee effect is known to reduce the loss of genetic diversity of expanding populations, by changing the nature of the expansion from “pulled” to “pushed”. We study the impact of an Allee effect on the formation of an expansion load with a new model, in which individuals have the genetic structure of a Muller’s ratchet. A key feature of Muller’s ratchet is that the population fatally accumulates deleterious mutations due to the stochastic loss of the fittest individuals, an event called a click of the ratchet. We observe fast clicks of the ratchet at the colonization front owing to small population size, followed by a slow fitness recovery due to migration of fit individuals from the bulk of the population, leading to a transient expansion load. For large population size, we are able to derive quantitative features of the expansion wave, such as the wave speed and the frequency of individuals carrying a given number of mutations. Using simulations, we show that the presence of an Allee effect reduces the rate at which clicks occur at the front, and thus reduces the expansion load.

scholarly journals The influence of density in population dynamics with strong and weak Allee effect

2021 ◽  
Vol 29 (1) ◽  
Author(s):  
Kamrun Nahar Keya ◽  
Md. Kamrujjaman ◽  
Md. Shafiqul Islam
Keyword(s):  
Population Dynamics ◽  
Allee Effect ◽  
Global Bifurcation ◽  
Reaction Diffusion ◽  
Logistic Growth ◽  
Allee Effects ◽  
Reaction Diffusion Model ◽  
Positive Steady States ◽  
The Stability ◽  
The Impact

AbstractIn this paper, we consider a reaction–diffusion model in population dynamics and study the impact of different types of Allee effects with logistic growth in the heterogeneous closed region. For strong Allee effects, usually, species unconditionally die out and an extinction-survival situation occurs when the effect is weak according to the resource and sparse functions. In particular, we study the impact of the multiplicative Allee effect in classical diffusion when the sparsity is either positive or negative. Negative sparsity implies a weak Allee effect, and the population survives in some domain and diverges otherwise. Positive sparsity gives a strong Allee effect, and the population extinct without any condition. The influence of Allee effects on the existence and persistence of positive steady states as well as global bifurcation diagrams is presented. The method of sub-super solutions is used for analyzing equations. The stability conditions and the region of positive solutions (multiple solutions may exist) are presented. When the diffusion is absent, we consider the model with and without harvesting, which are initial value problems (IVPs) and study the local stability analysis and present bifurcation analysis. We present a number of numerical examples to verify analytical results.

scholarly journals Choosing Mutation and Crossover Ratios for Genetic Algorithms—A Review with a New Dynamic Approach

Information ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 390 ◽  
Author(s):  
Ahmad Hassanat ◽  
Khalid Almohammadi ◽  
Esra’a Alkafaween ◽  
Eman Abunawas ◽  
Awni Hammouri ◽  
...  
Keyword(s):  
Population Size ◽  
Optimization Problems ◽  
Large Population ◽  
Small Population ◽  
Mutation Rates ◽  
Mutation Operators ◽  
Tuning Methods ◽  
Two Parameters ◽  
The Impact ◽  
Crossover And Mutation

Genetic algorithm (GA) is an artificial intelligence search method that uses the process of evolution and natural selection theory and is under the umbrella of evolutionary computing algorithm. It is an efficient tool for solving optimization problems. Integration among (GA) parameters is vital for successful (GA) search. Such parameters include mutation and crossover rates in addition to population that are important issues in (GA). However, each operator of GA has a special and different influence. The impact of these factors is influenced by their probabilities; it is difficult to predefine specific ratios for each parameter, particularly, mutation and crossover operators. This paper reviews various methods for choosing mutation and crossover ratios in GAs. Next, we define new deterministic control approaches for crossover and mutation rates, namely Dynamic Decreasing of high mutation ratio/dynamic increasing of low crossover ratio (DHM/ILC), and Dynamic Increasing of Low Mutation/Dynamic Decreasing of High Crossover (ILM/DHC). The dynamic nature of the proposed methods allows the ratios of both crossover and mutation operators to be changed linearly during the search progress, where (DHM/ILC) starts with 100% ratio for mutations, and 0% for crossovers. Both mutation and crossover ratios start to decrease and increase, respectively. By the end of the search process, the ratios will be 0% for mutations and 100% for crossovers. (ILM/DHC) worked the same but the other way around. The proposed approach was compared with two parameters tuning methods (predefined), namely fifty-fifty crossover/mutation ratios, and the most common approach that uses static ratios such as (0.03) mutation rates and (0.9) crossover rates. The experiments were conducted on ten Traveling Salesman Problems (TSP). The experiments showed the effectiveness of the proposed (DHM/ILC) when dealing with small population size, while the proposed (ILM/DHC) was found to be more effective when using large population size. In fact, both proposed dynamic methods outperformed the predefined methods compared in most cases tested.

scholarly journals Carrying Capacity of a Population Diffusing in a Heterogeneous Environment

Mathematics ◽  
2020 ◽  
Vol 8 (1) ◽  
pp. 49 ◽  
Author(s):  
D.L. DeAngelis ◽  
Bo Zhang ◽  
Wei-Ming Ni ◽  
Yuanshi Wang
Keyword(s):  
Population Size ◽  
Carrying Capacity ◽  
Heterogeneous System ◽  
Total Population ◽  
Reaction Diffusion ◽  
Maximum Growth ◽  
Reaction Diffusion Equations ◽  
Logistic Growth ◽  
Chemostat Model ◽  
Total Population Size

The carrying capacity of the environment for a population is one of the key concepts in ecology and it is incorporated in the growth term of reaction-diffusion equations describing populations in space. Analysis of reaction-diffusion models of populations in heterogeneous space have shown that, when the maximum growth rate and carrying capacity in a logistic growth function vary in space, conditions exist for which the total population size at equilibrium (i) exceeds the total population that which would occur in the absence of diffusion and (ii) exceeds that which would occur if the system were homogeneous and the total carrying capacity, computed as the integral over the local carrying capacities, was the same in the heterogeneous and homogeneous cases. We review here work over the past few years that has explained these apparently counter-intuitive results in terms of the way input of energy or another limiting resource (e.g., a nutrient) varies across the system. We report on both mathematical analysis and laboratory experiments confirming that total population size in a heterogeneous system with diffusion can exceed that in the system without diffusion. We further report, however, that when the resource of the population in question is explicitly modeled as a coupled variable, as in a reaction-diffusion chemostat model rather than a model with logistic growth, the total population in the heterogeneous system with diffusion cannot exceed the total population size in the corresponding homogeneous system in which the total carrying capacities are the same.

scholarly journals ‘Stray Appetites’: A Socio-Ecological Analysis of Free-Ranging Dogs Living Alongside Human Communities in Bangalore, India

2020 ◽  
Author(s):  
Shireen Jagriti Bhalla ◽  
Roy Kemmers ◽  
Ana Vasques ◽  
Abi Tamim Vanak
Keyword(s):  
Population Size ◽  
Carrying Capacity ◽  
Population Control ◽  
Large Population ◽  
Food Sources ◽  
Effective Population ◽  
Management Options ◽  
Capture Recapture ◽  
Estimate Population Size ◽  
Free Ranging

AbstractAcross the developing world, humans and free-ranging domestic dogs share common spaces. The relationship between these dogs and humans can range from one of dependence, to apathy, to conflict. Given the high number of humans attacked by dogs every year in India, and the lack of an effective population control strategy, we seek to provide insights into the conflict and propose alternative population management options based on reducing the carrying capacity of the environment. We used a mixed methods approach to understand both ecological and sociological underpinnings of free-ranging dog-human relationships in Bangalore, India. We conducted a photographic capture-recapture survey of free-ranging dogs to estimate population size and linked it to the availability of potential food sources. We also conducted a qualitative survey to assess attitudes of residents towards the dog population. We found that dog population varied from 192 to 1888 per square kilometre across a gradient of housing densities. The density of houses, bakeries and garbage piles were significant predictors of dog population size. Crucially, as low as 10 to 18.3% of houses supported the large population of dogs, highlighting the need for residents to act responsibly towards the dogs. Further, we found that garbage, although significant, is a secondary food source to household-maintained dogs. Since on the whole, respondents expressed the desire for a reduction in dog population, we suggest decreasing the carrying capacity of the environment by targeting these three food sources.

Optimal Configuration of a Genetic Algorithm for Command Space Layout Analysis

2018 ◽  
Vol 62 (1) ◽  
pp. 383-387 ◽  
Author(s):  
Wenbi Wang
Keyword(s):  
Genetic Algorithm ◽  
Population Size ◽  
Simulation Experiment ◽  
Large Population ◽  
Spatial Layout ◽  
Search Efficiency ◽  
Medium Level ◽  
Military Command ◽  
Space Layout ◽  
The Impact

A genetic algorithm was developed to optimize the spatial layout of military command centres. This paper describes a simulation experiment in which the impact of key algorithm parameters on its search efficiency was examined. The results confirmed the benefit of a large population size and a long evolution process for improving the search effectiveness. For the parameter that controls the rate of introducing new solutions (i.e., probability of swap), a medium level configuration was found to be superior. Results of this study provide guidelines and heuristics for configuring key parameters of the proposed algorithm so that its search efficiency and computational expense are best balanced.

scholarly journals ‘Stray appetites’: a socio-ecological analysis of free-ranging dogs living alongside human communities in Bangalore, India

2021 ◽  
Author(s):  
Shireen Jagriti Bhalla ◽  
Roy Kemmers ◽  
Ana Vasques ◽  
Abi Tamim Vanak
Keyword(s):  
Population Size ◽  
Carrying Capacity ◽  
Population Control ◽  
Large Population ◽  
Food Sources ◽  
Effective Population ◽  
Management Options ◽  
Capture Recapture ◽  
Estimate Population Size ◽  
Free Ranging

AbstractAcross the developing world, humans and free-ranging domestic dogs share common spaces. The relationship between these dogs and humans can range from one of dependence, to apathy, to conflict. Given the high number of humans attacked by dogs every year in India, and the lack of an effective population control strategy, we seek to provide insights into the conflict and propose alternative population management options based on reducing the carrying capacity of the environment. We used a mixed methods approach to understand both ecological and sociological underpinnings of free-ranging dog-human relationships in Bangalore, India. We conducted a photographic capture-recapture survey of free-ranging dogs to estimate population size and linked it to the availability of potential food sources. We also conducted a qualitative survey to assess attitudes of residents towards the dog population. We found that dog population varied from 192 to 1888 per square kilometre across a gradient of housing densities. The density of houses, bakeries and garbage piles were significant predictors of dog population size. Crucially, as low as 10 to 18% of houses supported the large population of dogs, highlighting the need for residents to act responsibly towards the dogs. Further, we found that garbage, although significant, is a secondary food source to household-maintained dogs. Since on the whole, respondents expressed the desire for a reduction in dog population, we suggest decreasing the carrying capacity of the environment by targeting these three food sources.

scholarly journals Rapid increase in southern elephant seal genetic diversity after a founder event

2014 ◽  
Vol 281 (1779) ◽  
pp. 20133078 ◽  
Author(s):  
Mark de Bruyn ◽  
Malin L. Pinsky ◽  
Brenda Hall ◽  
Paul Koch ◽  
Carlo Baroni ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
Population Growth ◽  
Population Size ◽  
Large Population ◽  
Elephant Seal ◽  
Raw Material ◽  
Southern Elephant Seal ◽  
Mirounga Leonina ◽  
Approximate Bayesian ◽  
The Impact

Genetic diversity provides the raw material for populations to respond to changing environmental conditions. The evolution of diversity within populations is based on the accumulation of mutations and their retention or loss through selection and genetic drift, while migration can also introduce new variation. However, the extent to which population growth and sustained large population size can lead to rapid and significant increases in diversity has not been widely investigated. Here, we assess this empirically by applying approximate Bayesian computation to a novel ancient DNA dataset that spans the life of a southern elephant seal ( Mirounga leonina ) population, from initial founding approximately 7000 years ago to eventual extinction within the past millennium. We find that rapid population growth and sustained large population size can explain substantial increases in population genetic diversity over a period of several hundred generations, subsequently lost when the population went to extinction. Results suggest that the impact of diversity introduced through migration was relatively minor. We thus demonstrate, by examining genetic diversity across the life of a population, that environmental change could generate the raw material for adaptive evolution over a very short evolutionary time scale through rapid establishment of a large, stable population.

scholarly journals Does parental permissiveness toward cigarette smoking and alcohol use influence illicit drug use among adolescents? A longitudinal study in seven European countries

2021 ◽  
Author(s):  
Emina Mehanović ◽  
Federica Vigna-Taglianti ◽  
Fabrizio Faggiano ◽  
Maria Rosaria Galanti ◽  
Barbara Zunino ◽  
...  
Keyword(s):  
Alcohol Use ◽  
Drug Use ◽  
Cigarette Smoking ◽  
Longitudinal Data ◽  
Illicit Drug ◽  
Large Population ◽  
Illicit Drug Use ◽  
European Countries ◽  
The Impact

Abstract Purpose Adolescents’ perceptions of parental norms may influence their substance use. The relationship between parental norms toward cigarette and alcohol use, and the use of illicit substances among their adolescent children is not sufficiently investigated. The purpose of this study was to analyze this relationship, including gender differences, using longitudinal data from a large population-based study. Methods The present study analyzed longitudinal data from 3171 12- to 14-year-old students in 7 European countries allocated to the control arm of the European Drug Addiction Prevention trial. The impact of parental permissiveness toward cigarettes and alcohol use reported by the students at baseline on illicit drug use at 6-month follow-up was analyzed through multilevel logistic regression models, stratified by gender. Whether adolescents’ own use of cigarette and alcohol mediated the association between parental norms and illicit drug use was tested through mediation models. Results Parental permissive norms toward cigarette smoking and alcohol use at baseline predicted adolescents’ illicit drug use at follow-up. The association was stronger among boys than among girls and was mediated by adolescents’ own cigarette and alcohol use. Conclusion Perceived parental permissiveness toward the use of legal drugs predicted adolescents’ use of illicit drugs, especially among boys. Parents should be made aware of the importance of norm setting, and supported in conveying clear messages of disapproval of all substances.

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