Properties of Age Structure Models for Fish Populations

1974 ◽  
Vol 31 (6) ◽  
pp. 1119-1125 ◽  
Author(s):  
Robin L. Allen ◽  
Pereti Basasibwaki
Keyword(s):  
Age Structure ◽  
Egg Production ◽  
Sockeye Salmon ◽  
Necessary Conditions ◽  
Survival Function ◽  
Fish Populations ◽  
Simulation Methods ◽  
The Stability ◽  
Dynamic Population ◽  
Blue Pike

The behavior of a class of dynamic population models that can be described as a life table operating on a population with a stock recruit relation formed by the product of the egg production and a survival function was examined. A combination of analytical and simulation methods were used to find necessary conditions for the stability of equilibrium populations and the properties of fluctuations about the equilibrium. Regular oscillations that occurred in populations with an unstable equilibrium were of most interest and these were considered as possible causes of the regular fluctuations in populations of fish such as sockeye salmon, Oncorhynchus nerka, or blue pike, Stizostedion vitreum glaucum.

scholarly journals The Stability of the Aggregate Loss Distribution

Risks ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 91 ◽  
Author(s):  
Riccardo Gatto
Keyword(s):  
Stability Analysis ◽  
Survival Function ◽  
Saddlepoint Approximation ◽  
Computational Formula ◽  
Important Indicator ◽  
The Common ◽  
Infinitesimal Perturbation ◽  
Aggregate Loss ◽  
Aggregate Loss Distribution ◽  
The Stability

In this article we introduce the stability analysis of a compound sum: it consists of computing the standardized variation of the survival function of the sum resulting from an infinitesimal perturbation of the common distribution of the summands. Stability analysis is complementary to the classical sensitivity analysis, which consists of computing the derivative of an important indicator of the model, with respect to a model parameter. We obtain a computational formula for this stability from the saddlepoint approximation. We apply the formula to the compound Poisson insurer loss with gamma individual claim amounts and to the compound geometric loss with Weibull individual claim amounts.

A new approach to the stability analysis of thawing slopes

1980 ◽  
Vol 17 (4) ◽  
pp. 607-612 ◽  
Author(s):  
Luis E. Vallejo
Keyword(s):  
Stability Analysis ◽  
Water Content ◽  
Pore Water ◽  
Active Layer ◽  
Necessary Conditions ◽  
Mass Movements ◽  
New Approach ◽  
Pore Water Pressures ◽  
The Stability ◽  
Excess Pore

A new approach to the stability analysis of thawing slopes at shallow depths, taking into consideration their structure (this being a mixture of hard crumbs of soil and a fluid matrix), is presented. The new approach explains shallow mass movements such as skin flows and tongues of bimodal flows, which usually take place on very low slope inclinations independently of excess pore water pressures or increased water content in the active layer, which are necessary conditions in the methods available to date to explain these movements.

scholarly journals Hydrological stability and otter trophic diversity: a scale-insensitive pattern?

2008 ◽  
Vol 86 (10) ◽  
pp. 1152-1158 ◽  
Author(s):  
M. Clavero ◽  
J. Prenda ◽  
F. Blanco-Garrido ◽  
M. Delibes
Keyword(s):  
Iberian Peninsula ◽  
Fish Consumption ◽  
Aquatic Ecosystems ◽  
Fish Populations ◽  
Lutra Lutra ◽  
Mediterranean Streams ◽  
Diet Diversity ◽  
Trophic Diversity ◽  
Eurasian Otter ◽  
The Stability

Two recent works related Eurasian otter ( Lutra lutra (L., 1758)) trophic patterns over large areas with the stability of aquatic ecosystems. Higher levels of instability lead to reduced availability and (or) predictability of fish, and consequently, to a decrease in fish consumption by otters. The aim of the present study is to test these macrogeographical patterns in otter diet at regional and local scales. We analysed otter diet in Mediterranean streams in southwestern Iberian Peninsula where clear hydrological stability gradients (related to drainage area or distance to the sea) could be defined. Hydrological stability was directly related to fish consumption and inversely to otter diet diversity in terms of occurrence and biomass, both at regional and local scales. The level of stability of aquatic ecosystems appears to be a critical indirect factor that modulates otter diet through its effects on fish populations. The resulting trophic patterns are maintained from local to macrogeographical scales.

scholarly journals The Impact of Price on the Profits of Fishermen Exploiting Tritrophic Prey-Predator Fish Populations

2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Meriem Bentounsi ◽  
Imane Agmour ◽  
Naceur Achtaich ◽  
Youssef El Foutayeni
Keyword(s):  
Equilibrium Points ◽  
Price Change ◽  
Fishing Effort ◽  
Fish Populations ◽  
Bioeconomic Model ◽  
Top Predator ◽  
Nash Equilibrium Problem ◽  
Change Mechanism ◽  
The Stability ◽  
The Impact

We define and study a tritrophic bioeconomic model of Lotka-Volterra with a prey, middle predator, and top predator populations. These fish populations are exploited by two fishermen. We study the existence and the stability of the equilibrium points by using eigenvalues analysis and Routh-Hurwitz criterion. We determine the equilibrium point that maximizes the profit of each fisherman by solving the Nash equilibrium problem. Finally, following some numerical simulations, we observe that if the price varies, then the profit behavior of each fisherman will be changed; also, we conclude that the price change mechanism improves the fishing effort of the fishermen.

Secondary sexual characters, energy use, senescence, and the cost of reproduction in sockeye salmon

1999 ◽  
Vol 77 (11) ◽  
pp. 1663-1675 ◽  
Author(s):  
Andrew P Hendry ◽  
Ole K Berg
Keyword(s):  
Egg Production ◽  
Sockeye Salmon ◽  
Energy Use ◽  
Relative Size ◽  
Cost Of Reproduction ◽  
Bristol Bay ◽  
Secondary Sexual Characters ◽  
In The Wild ◽  
The Cost ◽  
Secondary Sexual

Reproductive development and energy stores were characterized for sockeye salmon (Oncorhynchus nerka) maturing in the wild (Pick Creek, Bristol Bay, Alaska). Between freshwater entry and the start of spawning, ovaries increased in mass by 87.1% and secondary sexual characters increased in linear dimension by 13.0-47.4%. Between the start of spawning and death, secondary sexual characters decreased in relative size by 3.3-12.7%. Mass-specific somatic energy declined from freshwater entry (6.7% fat, 20.6% protein, 6.6 kJ·g-1) to the start of spawning (1.6% fat, 18.0% protein, 4.5 kJ·g-1) and finally to death (0.1% fat, 14.4% protein, 2.9 kJ·g-1). Stored fat appeared to be used primarily for upriver migration and egg production, whereas stored protein appeared to be used primarily for the development of secondary sexual characters and metabolism during spawning. Most development of secondary sexual characters occurred late in maturation, perhaps to forestall deterioration of muscle tissue. Relative to populations with long freshwater migrations, Bristol Bay sockeye salmon stored less fat before entering fresh water and used less fat before death. The total energy cost of reproduction (freshwater entry until death, including gonad investment) was 74.1% for females and 66.1% for males, higher than levels typically reported for iteroparous salmonids.

Asymptotic stability of heteroclinic cycles in systems with symmetry

1995 ◽  
Vol 15 (1) ◽  
pp. 121-147 ◽  
Author(s):  
Martin Krupa ◽  
Ian Melbourne
Keyword(s):  
Asymptotic Stability ◽  
Ad Hoc ◽  
Necessary Conditions ◽  
Sufficient Conditions ◽  
Higher Dimensions ◽  
Systematic Investigation ◽  
Heteroclinic Cycles ◽  
General Sufficient Condition ◽  
Higher Dimensional ◽  
The Stability

AbstractSystems possessing symmetries often admit heteroclinic cycles that persist under perturbations that respect the symmetry. The asymptotic stability of such cycles has previously been studied on an ad hoc basis by many authors. Sufficient conditions, but usually not necessary conditions, for the stability of these cycles have been obtained via a variety of different techniques.We begin a systematic investigation into the asymptotic stability of such cycles. A general sufficient condition for asymptotic stability is obtained, together with algebraic criteria for deciding when this condition is also necessary. These criteria are always satisfied in ℝ3 and often satisfied in higher dimensions. We end by applying our results to several higher-dimensional examples that occur in mode interactions with O(2) symmetry.

scholarly journals Performance of obligations in modern civil law

2020 ◽  
pp. 414-417
Author(s):  
Marharyta Butsan
Keyword(s):  
Necessary Conditions ◽  
Civil Law ◽  
Demand Fulfillment ◽  
Mutual Interest ◽  
Injured Party ◽  
Contractual Obligations ◽  
The Stability ◽  
The Right ◽  
Property Performance ◽  
Proper Performance

The article considers the notion of performance. Treaty obligations were the most common in the civil turnover. Their performance depends to a large extent the stability of the economy and society as a whole. Of particular importance are norms of civil legislation implementing the Treaty obligation. They are used daily in practical activities of legal entities and citizens. The performance of an obligation – it is always a process that takes some period of time and consists of a series of actions of the debtor and the creditor. Debtor proposes the execution, the creditor accepts it. The article studies scientific approaches with respect to conditions of contractual obligations. practice shows that most contracts are careless, do not contain the necessary conditions to realization of the interests of the parties, do not include measures to ensure contractual obligations. During the execution of such contracts often have complications, different interpretations by the parties to the same conditions, and as a result, there has been a massive failure by the parties of their responsibilities, resulting in numerous conflicts. The most important task of modern legal science and practice – the creation of legal mechanisms, allowing most effectively to ensure the proper performance of contractual obligations and to compensate the injured party for the loss caused by their failure or improper performance. Mechanism of performance of the obligation is the mutual interest of the parties. In determining the obligations a list of specific actions that the debtor is obliged to make in favor of the lender, is limited to the indication of the transfer of property, performance of work and payment of money. Undoubtedly, the parties rely on bilateral compliance with the obligations under the contract, but obviously there are cases when under any circumstances one of the parties does not fulfill its obligations. Performance of the obligation should also be understood as certain acts by the debtor (or refraining from doing,) that is the obligation of the debtor. In this regard, it should be noted that the lender has the right to demand fulfillment of the obligation, but the debtor is involved in such actions. Moreover, under proper performance to understand the performance of an obligation by an appropriate person at the appropriate time a particular person under equal circumstances. The real is the performance of specific obligations, which is reflected in the implementation of certain actions.

scholarly journals Revisiting density-dependent fecundity in schistosomes using sibship reconstruction

2021 ◽  
Vol 15 (5) ◽  
pp. e0009396
Author(s):  
M. Inês Neves ◽  
Charlotte M. Gower ◽  
Joanne P. Webster ◽  
Martin Walker
Keyword(s):  
Statistical Power ◽  
Egg Production ◽  
High Sensitivity ◽  
Monitoring And Evaluation ◽  
Statistical Modelling ◽  
Dependent Manner ◽  
Density Dependent ◽  
Helminth Infections ◽  
Modelling Assumptions ◽  
The Stability

The stability of parasite populations is regulated by density-dependent processes occurring at different stages of their life cycle. In dioecious helminth infections, density-dependent fecundity is one such regulatory process that describes the reduction in egg production by female worms in high worm burden within-host environments. In human schistosomiasis, the operation of density-dependent fecundity is equivocal and investigation is hampered by the inaccessibility of adult worms that are located intravascularly. Current understanding is almost exclusively limited to data collected from two human autopsy studies conducted over 40 years ago, with subsequent analyses having reached conflicting conclusions. Whether egg production is regulated in a density-dependent manner is key to predicting the effectiveness of interventions targeting the elimination of schistosomiasis and to the interpretation of parasitological data collected during monitoring and evaluation activities. Here, we revisit density-dependent fecundity in the two most globally important human Schistosoma spp. using a statistical modelling approach that combines molecular inference on the number of parents/adult worms in individual human hosts with parasitological egg count data from mainland Tanzania and Zanzibar. We find a non-proportional relationship between S. haematobium egg counts and inferred numbers of female worms, providing the first clear evidence of density-dependent fecundity in this schistosome species. We do not find robust evidence for density-dependent fecundity in S. mansoni because of high sensitivity to some modelling assumptions and the lower statistical power of the available data. We discuss the strengths and limitations of our model-based analytical approach and its potential for improving our understanding of density dependence in schistosomiasis and other human helminthiases earmarked for elimination.

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