scholarly journals Resident-invader dynamics of similar strategies in fluctuating environments

2020 ◽  
Vol 81 (4-5) ◽  
pp. 907-959
Author(s):  
Yuhua Cai ◽  
Stefan A. H. Geritz
Keyword(s):  
Relative Size ◽  
Environmental Stochasticity ◽  
Total Size ◽  
Relative Population ◽  
Resident Population ◽  
Structured Population Models ◽  
Time Scale Separation ◽  
Long Run ◽  
Fluctuating Environments ◽  
Invasion Criteria

Abstract We study resident-invader dynamics in fluctuating environments when the invader and the resident have close but distinct strategies. First we focus on a class of continuous-time models of unstructured populations of multi-dimensional strategies, which incorporates environmental feedback and environmental stochasticity. Then we generalize our results to a class of structured population models. We classify the generic population dynamical outcomes of an invasion event when the resident population in a given environment is non-growing on the long-run and stochastically persistent. Our approach is based on the series expansion of a model with respect to the small strategy difference, and on the analysis of a stochastic fast-slow system induced by time-scale separation. Theoretical and numerical analyses show that the total size of the resident and invader population varies stochastically and dramatically in time, while the relative size of the invader population changes slowly and asymptotically in time. Thereby the classification is based on the asymptotic behavior of the relative population size, and which is shown to be fully determined by invasion criteria (i.e., without having to study the full generic dynamical system). Our results extend and generalize previous results for a stable resident equilibrium (particularly, Geritz in J Math Biol 50(1):67–82, 2005; Dercole and Geritz in J Theor Biol 394:231-254, 2016) to non-equilibrium resident population dynamics as well as resident dynamics with stochastic (or deterministic) drivers.

scholarly journals DOES THE BALASSA–SAMUELSON THEORY EXPLAIN THE LINK BETWEEN RELATIVE POPULATION GROWTH AND PURCHASING POWER PARITY?

2013 ◽  
Vol 58 (01) ◽  
pp. 1350007 ◽  
Author(s):  
A. F. M. KAMRUL HASSAN ◽  
RUHUL SALIM
Keyword(s):  
Exchange Rate ◽  
Population Growth ◽  
Purchasing Power Parity ◽  
Panel Cointegration ◽  
Least Square ◽  
Power Parity ◽  
Relative Population ◽  
Relative Prices ◽  
Stable Relationship ◽  
Long Run

Relative population growth affects relative prices through the so-called Balassa–Samuelson (BS) mechanism and that in turn impacts PPP. This paper empirically investigates the relationship between the PPP exchange rate and relative population growth in a panel of 80 selected countries. Following the BS hypothesis, this paper argues that relative population growth affects nominal wages that impact price levels and thereby impacts PPP. Using panel cointegration and fully modified ordinary least square (FMOLS), the empirical results show that there is a stable relationship between PPP exchange rate and relative population growth in the long run. These empirical findings suggest that population growth have an important role in exchange rate determination through PPP.

scholarly journals Evidence for r - and K -selection in a wild bird population: a reciprocal link between ecology and evolution

2016 ◽  
Vol 283 (1829) ◽  
pp. 20152411 ◽  
Author(s):  
Bernt-Erik Sæther ◽  
Marcel E. Visser ◽  
Vidar Grøtan ◽  
Steinar Engen
Keyword(s):  
Density Dependence ◽  
Population Size ◽  
Clutch Size ◽  
Balancing Selection ◽  
Empirical Support ◽  
Small Population ◽  
Environmental Stochasticity ◽  
Fluctuating Environments ◽  
Population Sizes ◽  
Large Clutch

Understanding the variation in selection pressure on key life-history traits is crucial in our rapidly changing world. Density is rarely considered as a selective agent. To study its importance, we partition phenotypic selection in fluctuating environments into components representing the population growth rate at low densities and the strength of density dependence, using a new stochastic modelling framework. We analysed the number of eggs laid per season in a small song-bird, the great tit, and found balancing selection favouring large clutch sizes at small population densities and smaller clutches in years with large populations. A significant interaction between clutch size and population size in the regression for the Malthusian fitness reveals that those females producing large clutch sizes at small population sizes also are those that show the strongest reduction in fitness when population size is increased. This provides empirical support for ongoing r - and K -selection in this population, favouring phenotypes with large growth rates r at small population sizes and phenotypes with high competitive skills when populations are close to the carrying capacity K . This selection causes long-term fluctuations around a stable mean clutch size caused by variation in population size, implying that r - and K -selection is an important mechanism influencing phenotypic evolution in fluctuating environments. This provides a general link between ecological dynamics and evolutionary processes, operating through a joint influence of density dependence and environmental stochasticity on fluctuations in population size.

scholarly journals Effect of a quality-improving cod end on size selectivity and catch patterns of cod in bottom trawl fishery

2019 ◽  
Vol 76 (11) ◽  
pp. 2110-2120 ◽  
Author(s):  
Jesse Brinkhof ◽  
Bent Herrmann ◽  
Roger B. Larsen ◽  
Tiago Veiga-Malta
Keyword(s):  
Gadus Morhua ◽  
Barents Sea ◽  
Relative Size ◽  
Bottom Trawl ◽  
Size Selectivity ◽  
Total Size ◽  
Trawl Fishery ◽  
The Barents Sea ◽  
Sea Bottom ◽  
Significant Difference

A new cod-end concept developed and tested exhibited significantly improved quality of caught cod (Gadus morhua) compared with that of the conventional cod end used in the Barents Sea bottom trawl fishery. However, the design of the new quality-improving cod end raised concerns about its size selectivity and the possibility that higher retention probability could negatively impact the catch pattern by increasing the proportion of undersized cod. Therefore, the goal of this study was to quantify and compare the size selectivity and catch pattern for cod when deploying, respectively, the conventional and new quality-improving cod end in the Barents Sea bottom trawl fishery. The new quality-improving cod end had significantly lower relative size selectivity than the conventional cod end, but no significant difference in the catch patterns was detected in the trawl. Further, estimation of the total size selectivity in the trawl revealed that the increased retention of small cod when using the quality-improving cod end was minor. Hence, despite the reduced selectivity, the quality-improving cod end can be used with low risk of retaining small cod.

scholarly journals The hitch-hiking effect of a favourable gene

1974 ◽  
Vol 23 (1) ◽  
pp. 23-35 ◽  
Author(s):  
John Maynard Smith ◽  
John Haigh
Keyword(s):  
Population Size ◽  
Large Population ◽  
Natural Populations ◽  
Population Changes ◽  
Average Heterozygosity ◽  
Gene Frequencies ◽  
Total Size ◽  
Long Run ◽  
Selective Substitution ◽  
Aggregate Effect

SummaryWhen a selectively favourable gene substitution occurs in a population, changes in gene frequencies will occur at closely linked loci. In the case of a neutral polymorphism, average heterozygosity will be reduced to an extent which varies with distance from the substituted locus. The aggregate effect of substitution on neutral polymorphism is estimated; in populations of total size 106 or more (and perhaps of 104 or more), this effect will be more important than that of random fixation. This may explain why the extent of polymorphism in natural populations does not vary as much as one would expect from a consideration of the equilibrium between mutation and random fixation in populations of different sizes. For a selectively maintained polymorphism at a linked locus, this process will only be important in the long run if it leads to complete fixation. If the selective coefficients at the linked locus are small compared to those at the substituted locus, it is shown that the probability of complete fixation at the linked locus is approximately exp (− Nc), where c is the recombinant fraction and N the population size. It follows that in a large population a selective substitution can occur in a cistron without eliminating a selectively maintained polymorphism in the same cistron.

Reproductive value and analyses of population dynamics of age-structured populations

2021 ◽  
pp. 285-298
Author(s):  
Bernt-Erik Sæther ◽  
Steinar Engen
Keyword(s):  
Growth Rate ◽  
Population Dynamics ◽  
Age Structure ◽  
Good Description ◽  
Age Distribution ◽  
Reproductive Rate ◽  
Environmental Stochasticity ◽  
Reproductive Value ◽  
Long Run ◽  
Age Structured

Many populations of especially long-lived species show large temporal variation in age structure, which can complicate estimating of important population parameters. This occurs because it can be difficult to disentangle whether variation in numbers is due to fluctuations in the environment or caused by changes in the age distribution. This chapter shows that fluctuations in the total reproductive value of the population, that is, the sum of all individual reproductive values, often provide a good description of the population dynamics but still is not confounded by fluctuations in age structure. Because the change in the total reproductive rate is exactly equal to the growth rate of the population, this quantity enables decomposition of the long-run growth rate into stochastic components caused by age-specific variation in demographic and environmental stochasticity. The chapter illustrates the practical application of this approach in stochastic demography by analyses of the dynamics of several populations of birds and mammals. It puts a strong focus on these methods being particularly useful in viability analyses of small populations of vulnerable or endangered species.

scholarly journals International trade with pensions and demographic shocks

2017 ◽  
Vol 18 (1) ◽  
pp. 140-164
Author(s):  
IGOR FEDOTENKOV ◽  
BAS VAN GROEZEN ◽  
LEX MEIJDAM
Keyword(s):  
International Trade ◽  
Relative Size ◽  
Pension Scheme ◽  
Demographic Changes ◽  
Central Question ◽  
Production Factors ◽  
Pension Schemes ◽  
Long Run ◽  
Capital Intensive

AbstractThe central question of this paper is how international trade and specialization are affected by different designs of pension schemes and asymmetric demographic changes. In a model with two goods, two countries and two production factors, we find that countries with a relatively large unfunded pension scheme will specialize in the production of labour intensive goods. If these countries are hit by a negative demographic shock, this specialization will intensify in the long run. Eventually, these countries may even completely specialize in the production of those goods. The effects spill over to other countries, which will move away from complete specialization in capital intensive goods as the relative size of their labour intensive goods sector will also increase.

scholarly journals The Enduring Impact of the American Dust Bowl: Short- and Long-Run Adjustments to Environmental Catastrophe

2012 ◽  
Vol 102 (4) ◽  
pp. 1477-1507 ◽  
Author(s):  
Richard Hornbeck
Keyword(s):  
Agricultural Land ◽  
Land Values ◽  
Dust Bowl ◽  
Population Declines ◽  
Relative Population ◽  
Long Run ◽  
The 1950S ◽  
Initial Difference

The 1930s American Dust Bowl was an environmental catastrophe that greatly eroded sections of the Plains. The Dust Bowl is estimated to have immediately, substantially, and persistently reduced agricultural land values and revenues in more-eroded counties relative to less-eroded counties. During the Depression and through at least the 1950s, there was limited relative adjustment of farmland away from activities that became relatively less productive in more-eroded areas. Agricultural adjustments recovered less than 25 percent of the initial difference in agricultural costs for more-eroded counties. The economy adjusted predominantly through large relative population declines in more-eroded counties, both during the 1930s and through the 1950s. (JEL N32, N52, Q15, Q18, Q54)

Dates Are Not Just Data: Paleolithic Settlement Patterns in Siberia Derived from Radiocarbon Records

2005 ◽  
Vol 70 (4) ◽  
pp. 773-789 ◽  
Author(s):  
Yaroslav V. Kuzmin ◽  
Susan G. Keates
Keyword(s):  
Population Size ◽  
Russian Far East ◽  
Far East ◽  
Relative Size ◽  
Time Range ◽  
Relative Population ◽  
Radiocarbon Dates ◽  
Time Period ◽  
The Last Glacial Maximum ◽  
The Last Glacial

The large radiocarbon database now established for Paleolithic sites in Siberia and the Russian Far East can be used to build up a picture of relative population size in these regions. We consider the time period of ca. 46,000 to 12,000 B.P. for which we have assembled and critically studied 437 radiocarbon dates. All dates from individual sites that fall within 1,000 14C years are considered as a single event and called occupation episode. The results of our analysis show that the number of 14C dates until ca. 28,000 B.P. is small and increases at ca. 28,000–20,000 B.P, and dates decrease in frequency for the ca. 20,000–16,000 B.P. time range. It is after ca. 16,000 B.P. that we see a substantial rise in the number of 14C dates. In terms of the relative size of Siberian Paleolithic populations based on the frequency of occupation episodes, population density was small until ca. 36,000 B.P. Subsequently, population size increased gradually at ca. 36,000–16,000 B.P., and the growth rate became almost exponential at ca. 16,000–12,000 B.P. The number of occupations from ca. 20,000 to 18,000 B.P. did not decrease, running counter to arguments that Siberia was completely or considerably depopulated during the Last Glacial Maximum.

Interpreting HVEM of muscle-cell impulse networks

1992 ◽  
Vol 50 (1) ◽  
pp. 126-127
Author(s):  
Paul DeCosta ◽  
Kyugon Cho ◽  
Stephen Shemlon ◽  
Heesung Jun ◽  
Stanley M. Dunn
Keyword(s):  
Structural Analysis ◽  
Muscle Cell ◽  
Electron Micrographs ◽  
Relative Size ◽  
Automatic Classification ◽  
Nerve Fibers ◽  
Analysis Algorithm ◽  
Structural Networks

Introduction: The analysis and interpretation of electron micrographs of cells and tissues, often requires the accurate extraction of structural networks, which either provide immediate 2D or 3D information, or from which the desired information can be inferred. The images of these structures contain lines and/or curves whose orientation, lengths, and intersections characterize the overall network.Some examples exist of studies that have been done in the analysis of networks of natural structures. In, Sebok and Roemer determine the complexity of nerve structures in an EM formed slide. Here the number of nodes that exist in the image describes how dense nerve fibers are in a particular region of the skin. Hildith proposes a network structural analysis algorithm for the automatic classification of chromosome spreads (type, relative size and orientation).

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