Density-Dependent Population Growth

2020 ◽  
pp. 29-46
Author(s):  
Michael J. Fogarty ◽  
Jeremy S. Collie
Keyword(s):  
Population Density ◽  
Population Growth ◽  
Density Dependence ◽  
Multiple Equilibria ◽  
Dynamical Behavior ◽  
Logistic Growth ◽  
Density Dependent ◽  
Per Capita ◽  
Discrete Time Models ◽  
Complex Dynamical Behavior

The observation that no population can grow indefinitely and that most populations persist on ecological timescales implies that mechanisms of population regulation exist. Feedback mechanisms include competition for limited resources, cannibalism, and predation rates that vary with density. Density dependence occurs when per capita birth or death rates depend on population density. Density dependence is compensatory when the population growth rate decreases with population density and depensatory when it increases. The logistic model incorporates density dependence as a simple linear function. A population exhibiting logistic growth will reach a stable population size. Non-linear density-dependent terms can give rise to multiple equilibria. With discrete time models or time delays in density-dependent regulation, the approach to equilibrium may not be smooth—complex dynamical behavior is possible. Density-dependent feedback processes can compensate, up to a point, for natural and anthropogenic disturbances; beyond this point a population will collapse.

scholarly journals Trends of forest area and population and the impact of population on forest area per hectare in Serbia without APS

2012 ◽  
pp. 183-196
Author(s):  
Nenad Rankovic
Keyword(s):  
Population Density ◽  
Population Growth ◽  
Forest Cover ◽  
Forest Policy ◽  
Forest Area ◽  
Economic Changes ◽  
Policy Measures ◽  
Per Capita ◽  
The Impact

Socio-economic changes throughout history have shaped the attitude towards the forest and most significant ones are changes in terms of population. Over the centuries population and population density have had a significant impact on deforestation and the reduction of forest areas. Therefore, it is important to check what kind of trends are concerned and how population growth affects forest areas, forest cover and forest area per capita. These elements are important for assessing the direction, intensity of activity and the degree of success in the implementation of all forest policy measures in Serbia.

scholarly journals Increased natural mortality at low abundance can generate an Allee effect in a marine fish

2014 ◽  
Vol 1 (2) ◽  
pp. 140075 ◽  
Author(s):  
Anna Kuparinen ◽  
Jeffrey A. Hutchings
Keyword(s):  
Population Dynamics ◽  
Population Growth ◽  
Density Dependence ◽  
Gadus Morhua ◽  
Allee Effect ◽  
Population Regulation ◽  
Atlantic Cod ◽  
Adult Mortality ◽  
Natural Mortality ◽  
Density Dependent

Negative density-dependent regulation of population dynamics promotes population growth at low abundance and is therefore vital for recovery following depletion. Inversely, any process that reduces the compensatory density-dependence of population growth can negatively affect recovery. Here, we show that increased adult mortality at low abundance can reverse compensatory population dynamics into its opposite—a demographic Allee effect. Northwest Atlantic cod ( Gadus morhua ) stocks collapsed dramatically in the early 1990s and have since shown little sign of recovery. Many experienced dramatic increases in natural mortality, ostensibly attributable in some populations to increased predation by seals. Our findings show that increased natural mortality of a magnitude observed for overfished cod stocks has been more than sufficient to fundamentally alter the dynamics of density-dependent population regulation. The demographic Allee effect generated by these changes can slow down or even impede the recovery of depleted populations even in the absence of fishing.

scholarly journals Evolution of stochastic demography with life history tradeoffs in density-dependent age-structured populations

2017 ◽  
Vol 114 (44) ◽  
pp. 11582-11590 ◽  
Author(s):  
Russell Lande ◽  
Steinar Engen ◽  
Bernt-Erik Sæther
Keyword(s):  
Life History ◽  
Population Growth ◽  
Density Dependence ◽  
Population Size ◽  
Structured Populations ◽  
Environmental Stochasticity ◽  
Trade Off ◽  
Density Dependent ◽  
Fluctuating Environment ◽  
Stochastic Demography

We analyze the stochastic demography and evolution of a density-dependent age- (or stage-) structured population in a fluctuating environment. A positive linear combination of age classes (e.g., weighted by body mass) is assumed to act as the single variable of population size, N, exerting density dependence on age-specific vital rates through an increasing function of population size. The environment fluctuates in a stationary distribution with no autocorrelation. We show by analysis and simulation of age structure, under assumptions often met by vertebrate populations, that the stochastic dynamics of population size can be accurately approximated by a univariate model governed by three key demographic parameters: the intrinsic rate of increase and carrying capacity in the average environment, r0 and K, and the environmental variance in population growth rate, σe2. Allowing these parameters to be genetically variable and to evolve, but assuming that a fourth parameter, θ, measuring the nonlinearity of density dependence, remains constant, the expected evolution maximizes E[Nθ]=[1−σe2/(2r0)]Kθ. This shows that the magnitude of environmental stochasticity governs the classical trade-off between selection for higher r0 versus higher K. However, selection also acts to decrease σe2, so the simple life-history trade-off between r- and K-selection may be obscured by additional trade-offs between them and σe2. Under the classical logistic model of population growth with linear density dependence (θ=1), life-history evolution in a fluctuating environment tends to maximize the average population size.

scholarly journals Density dependence in the camelid Vicugna vicugna: the recovery of a protected population in Chile

Oryx ◽  
2002 ◽  
Vol 36 (2) ◽  
pp. 118-125 ◽  
Author(s):  
C. Bonacic ◽  
D. W. Macdonald ◽  
J. Galaz ◽  
R. M. Sibly
Keyword(s):  
Growth Rate ◽  
Population Growth ◽  
Density Dependence ◽  
Primary Productivity ◽  
Carrying Capacity ◽  
Population Growth Rate ◽  
Census Data ◽  
South American ◽  
Density Dependent ◽  
Vicugna Vicugna

The vicuña Vicugna vicugna is a wild South American camelid. Following over-exploitation, which brought the species to the brink of extinction in Chile in the 1960s, the population was protected. Since 1975 the population has been censused annually, generating one of the most extensive long-term census databases for any South American mammal. In this paper we use these data, and measures of environmental parameters, to describe the population growth trend of the species and to estimate carrying capacity. Our results indicate that the vicuña has been protected successfully in northern Chile. The census data reveal that, following protection, the population displayed logistic growth between 1975 and 1992. Population growth rate declined linearly with population size, which indicates a degree of density dependence. Density independent factors, such as rainfall, may also have been important. The principal density dependent effect observed was that birth rate declined in those family groups with the most breeding females. The carrying capacity of the study area was estimated from the census data and from models based on precipitation and local primary productivity. Using the census data, an estimation of carrying capacity as the asymptote of the fitted logistic curve suggested that the vicuña population should reach approximately 26,000 vicuñas, whereas estimation when the population growth rate was equated to zero gave a carrying capacity of c. 22,000. Coe's method based on local precipitation predicted 31,000 vicuña, whereas Lavenroth's method based on local primary productivity predicted 26,000 vicuña. In reality, the census data showed that the population peaked at 22,463 vicuñas in 1990. The results are discussed in relation to the need for better census techniques and the implications of density dependent effects for the management of the vicuña in Chile.

scholarly journals Population priorities: the challenge of continued rapid population growth

2009 ◽  
Vol 364 (1532) ◽  
pp. 2977-2984 ◽  
Author(s):  
Adair Turner
Keyword(s):  
Nineteenth Century ◽  
Population Density ◽  
Population Growth ◽  
Economic Performance ◽  
Developed Countries ◽  
Modern World ◽  
World Population ◽  
High Fertility ◽  
Rapid Population Growth ◽  
Per Capita

Rapid population growth continues in the least developed countries. The revisionist case that rapid population could be overcome by technology, that population density was advantageous, that capital shallowing is not a vital concern and that empirical investigations had not proved a correlation between high population growth and low per capita income was both empirically and theoretically flawed. In the modern world, population density does not play the role it did in nineteenth-century Europe and rates of growth in some of today's least developed nations are four times than those in nineteenth-century Europe, and without major accumulation of capital per capita , no major economy has or is likely to make the low- to middle-income transition. Though not sufficient, capital accumulation for growth is absolutely essential to economic growth. While there are good reasons for objecting to the enforced nature of the Chinese one-child policy, we should not underestimate the positive impact which that policy has almost certainly had and will have over the next several decades on Chinese economic performance. And a valid reticence about telling developing countries that they must contain fertility should not lead us to underestimate the severely adverse impact of high fertility rates on the economic performance and prospects of many countries in Africa and the Middle East.

scholarly journals Population regulation of African buffalo in the Mara–Serengeti ecosystem

2015 ◽  
Vol 42 (5) ◽  
pp. 382 ◽  
Author(s):  
Holly T. Dublin ◽  
Joseph O. Ogutu
Keyword(s):  
Land Use ◽  
Population Dynamics ◽  
Population Growth ◽  
Density Dependence ◽  
Food Limitation ◽  
Land Use Changes ◽  
African Buffalo ◽  
Regulatory Factor ◽  
Density Dependent ◽  
Serengeti Ecosystem

Context The processes regulating ungulate populations have been the focus of numerous studies. For the African buffalo (Syncerus caffer Sparrman) population inhabiting the Mara–Serengeti ecosystem, rinderpest was the primary regulatory factor up to the mid-1960s. Following reduction of rinderpest and buffalo population increase, interspecific competition for food, notably with cattle and wildebeest (Connochaetes taurinus Burchell), was thought to be the primary regulatory factor in the ecosystem. Aims We analysed buffalo population trends and the relationship between buffalo population growth and rainfall and density dependence in the Mara–Serengeti ecosystem and discuss the findings in the context of the key ecosystem processes governing buffalo population dynamics in African savannas, namely, food limitation, competition, predation, disease and land use changes. Methods We analysed buffalo population dynamics in the Mara–Serengeti ecosystem in relation to rainfall and density dependence feedback between 1984 and 2010. Key results Buffalo population growth was both significantly density-dependent and positively correlated with the dry season rainfall after, but not before, a severe drought in 1993. Buffalo numbers crashed by 48.6% in 1984–85 and by 76.1% in 1993–94 during severe droughts when food availability was lowest and competition with the more numerous cattle and wildebeest was highest. Conclusions Recovery of buffalo numbers to pre-drought levels took 8–9 years after the 1984–85 drought but was much slower, with buffaloes numbering merely 36% of their 1993 population (12 895 animals) 18 years after the 1993–94 drought despite intermittent periods of high rainfall, probably due to demographic and/or reproductive factors, heightened competition with livestock, land use changes in the adjoining pastoral ranches, lion predation and recurrent severe droughts. Implications Our findings demonstrate how food limitation caused by droughts associated with the hemispheric El Niño–Southern Oscillation can cause severe declines in and threaten the persistence of large ungulate populations. The findings also portray how density-dependent food limitation, competition, predation, land use changes and other factors can accentuate the effect of droughts and greatly prolong population recovery.

scholarly journals Two paradigms of population regulation

1995 ◽  
Vol 22 (1) ◽  
pp. 1 ◽  
Author(s):  
C. J. Krebs
Keyword(s):  
Population Density ◽  
Density Dependence ◽  
Population Regulation ◽  
Food Shortage ◽  
Holy Grail ◽  
Density Dependent ◽  
Movement Rates ◽  
Birth Death

No population increases without limit and ecologists have utilised two paradigms to find out why. The density-dependent paradigm assumes that birth, death and movement rates will be related to population density. In many cases they are not, and the search for density dependence has become a holy grail. A better approach is through the mechanistic paradigm which searches for relationships between birth, death and movement rates, and the mechanisms controlling populations, such as disease, predation, food shortage and territoriality. Seven suggestions are made for analysing the role of disease in population regulation in mammals. Useful progress will flow more quickly from the mechanistic paradigm without the need to search for density dependence.

scholarly journals Density-dependent selection and the limits of relative fitness

2017 ◽  
Author(s):  
Jason Bertram ◽  
Joanna Masel
Keyword(s):  
Population Density ◽  
Population Growth ◽  
Competitive Ability ◽  
Relative Fitness ◽  
Density Dependent ◽  
Volterra Models ◽  
Selection Behavior ◽  
Novel Model ◽  
Stable Populations ◽  
Density Dependent Selection

AbstractSelection is commonly described by assigning constant relative fitness values to genotypes. Yet population density is often regulated by crowding. Relative fitness may then depend on density, and selection can change density when it acts on a density-regulating trait. When strong density-dependent selection acts on a density-regulating trait, selection is no longer describable by density-independent relative fitnesses, even in demographically stable populations. These conditions are met in most previous models of density-dependent selection (e.g. “K-selection” in the logistic and Lotka-Volterra models), suggesting that density-independent relative fitnesses must be replaced with more ecologically explicit absolute fit-nesses unless selection is weak. Here we show that density-independent relative fitnesses can also accurately describe strong density-dependent selection under some conditions. We develop a novel model of density-regulated population growth with three ecologically intuitive traits: fecundity, mortality, and competitive ability. Our model, unlike the logistic or Lotka-Volterra, incorporates a density-dependent juvenile “reproductive excess”, which largely decouples density-dependent selection from the regulation of density. We find that density-independent relative fitnesses accurately describe strong selection acting on any one trait, even fecundity, which is both density-regulating and subject to density-dependent selection. Pleiotropic interactions between these traits recovers the familiarK-selection behavior. In such cases, or when the population is maintained far from demographic equilibrium, our model offers a possible alternative to relative fitness.

scholarly journals Population Trends and Urbanization: Simulating Density Effects Using a Local Regression Approach

2020 ◽  
Vol 9 (7) ◽  
pp. 454 ◽  
Author(s):  
Gloria Polinesi ◽  
Maria Cristina Recchioni ◽  
Rosario Turco ◽  
Luca Salvati ◽  
Kostas Rontos ◽  
...  
Keyword(s):  
Population Density ◽  
Population Growth ◽  
Growth Rates ◽  
European Regions ◽  
Density Dependent ◽  
Metropolitan Growth ◽  
Dependent Processes ◽  
Demographic Growth ◽  
Over Time

Density-dependent population growth regulates long-term urban expansion and shapes distinctive socioeconomic trends. Despite a marked heterogeneity in the spatial distribution of the resident population, Mediterranean European countries are considered more homogeneous than countries in other European regions as far as settlement structure and processes of metropolitan growth are concerned. However, rising socioeconomic inequalities among Southern European regions reflect latent demographic and territorial transformations that require further investigation. An integrated assessment of the spatio-temporal distribution of resident populations in more than 1000 municipalities (1961–2011) was carried out in this study to characterize density-dependent processes of metropolitan growth in Greece. Using geographically weighted regressions, the results of our study identified distinctive local relationships between population density and growth rates over time. Our results demonstrate that demographic growth rates were non-linearly correlated with other variables, such as population density, with positive and negative impacts during the first (1961–1971) and the last (2001–2011) observation decade, respectively. These findings outline a progressive shift over time from density-dependent processes of population growth, reflecting a rapid development of large metropolitan regions (Athens, Thessaloniki) in the 1960s, to density-dependent processes more evident in medium-sized cities and accessible rural regions in the 2000s. Density-independent processes of population growth have been detected in the intermediate study period (1971–2001). This work finally discusses how a long-term analysis of demographic growth, testing for density-dependent mechanisms, may clarify the intrinsic role of population concentration and dispersion in different phases of the metropolitan cycle in Mediterranean Europe.

scholarly journals Population Dynamics and Agglomeration Factors: A Non-Linear Threshold Estimation of Density Effects

2020 ◽  
Vol 12 (6) ◽  
pp. 2257 ◽  
Author(s):  
Mariateresa Ciommi ◽  
Gianluca Egidi ◽  
Rosanna Salvia ◽  
Sirio Cividino ◽  
Kostas Rontos ◽  
...  
Keyword(s):  
Population Density ◽  
Population Growth ◽  
Population Distribution ◽  
Negative Impact ◽  
Population Decline ◽  
Temporal Analysis ◽  
Time Interval ◽  
Density Dependent ◽  
Urban Dynamics ◽  
Population Growth Rates

Although Southern Europe is relatively homogeneous in terms of settlement characteristics and urban dynamics, spatial heterogeneity in its population distribution is still high, and differences across regions outline specific demographic patterns that require in-depth investigation. In such contexts, density-dependent mechanisms of population growth are a key factor regulating socio-demographic dynamics at various spatial levels. Results of a spatio-temporal analysis of the distribution of the resident population in Greece contributes to identifying latent (density-dependent) processes of metropolitan growth over a sufficiently long time interval (1961-2011). Identification of density-dependent patterns of population growth contributes to the analysis of socioeconomic factors underlying demographic divides, possibly distinguishing between the effects of population concentration and dispersion. Population growth rates were non-linearly correlated with population density, highlighting a positive (or negative) impact of urban concentration on demographic growth when population is lower (or higher) than a fixed threshold (2800 and 1300 inhabitants/km2 in 1961 and 2011, respectively). In a context of low population density (less than 20 inhabitants/km2), the relationship between density and growth was again negative, contrasting with the positive and linear relationship observed in denser contexts. This result evidences a sort of ‘depopulation’ trap that leads to accelerated population decline under a defined density threshold. An improved understanding of density-dependent mechanisms of population growth and decline contributes to rethinking strategies of sustainable development and social policies more adapted to heterogeneous regional contexts.

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