Добірка наукової літератури з теми "Malthusian behaviour"

Collective behaviours contributing to patterns of group formation and coordinated movement are common across many ecosystems and taxa. Their ubiquity is presumably due to altering interactions between individuals and their predators, resources and physical environment in ways that enhance individual fitness. On the other hand, fitness costs are also often associated with group formation. Modifications to these interactions have the potential to dramatically impact population-level processes, such as trophic interactions or patterns of space use in relation to abiotic environmental variation. In a wide variety of empirical systems and models, collective behaviour has been shown to enhance access to ephemeral patches of resources, reduce the risk of predation and reduce vulnerability to environmental fluctuation. Evolution of collective behaviour should accordingly depend on the advantages of collective behaviour weighed against the costs experienced at the individual level. As an illustrative case study, we consider the potential trade-offs on Malthusian fitness associated with patterns of group formation and movement by migratory Thomson's gazelles in the Serengeti ecosystem. This article is part of the theme issue ‘Collective movement ecology’.

The growth-fragmentation equation models systems of particles that grow and reproduce as time passes. An important question concerns the asymptotic behaviour of its solutions. Bertoin and Watson (2018) developed a probabilistic approach relying on the Feynman-Kac formula, that enabled them to answer to this question for sublinear growth rates. This assumption on the growth ensures that microscopic particles remain microscopic. In this work, we go further in the analysis, assuming bounded fragmentations and allowing arbitrarily small particles to reach macroscopic mass in finite time. We establish necessary and sufficient conditions on the coefficients of the equation that ensure Malthusian behaviour with exponential speed of convergence to the asymptotic profile. Furthermore, we provide an explicit expression of the latter.

Logistic equation with delay play important role in modelling of various biological processes. In this paper we study the behaviour of solutions of a logistic equation with two delays in a small neighbourhood of equilibrium. The main assumption is that Malthusian coefficient is large, so problem is singular perturbed. To study the local dynamics near points of bifurcation an analogues of normal form was constructed. Its coefficients depends on special bounded discontinues function, which takes all its values infinite number of times when large parameter increases to infinity. It is shown that the system under study has such dynamic effect as infinite process of direct and inverse bifurcations as the small parameter tends to zero.

A continuous-time network evolution model is considered. The evolution of the network is based on 2- and 3-interactions. 2-interactions are described by edges, and 3-interactions are described by triangles. The evolution of the edges and triangles is governed by a multi-type continuous-time branching process. The limiting behaviour of the network is studied by mathematical methods. We prove that the number of triangles and edges have the same magnitude on the event of non-extinction, and it is eαt, where α is the Malthusian parameter. The probability of the extinction and the degree process of a fixed vertex are also studied. The results are illustrated by simulations.

Delayed marriages played a very important role in slowing down population growth during the European Demographic Transition. Similarly, some developing countries have recently undergone even more rapid changes in marriage patterns, leading to declining levels of fertility. Curtailing marriage or entry into sexual unions is one of the "positive" checks posited by Malthusian theory and is worthy of some renewed attention because of the lack of decline in marital fertility in Pakistan. Several researchers have identified changes in nuptiality behaviour in Pakistan, in terms of a rise in both the average age at marriage [8; 11; 12] and changes in cohort nuptiality [7]. One researcher observed a slight decline in fertility and attributed it to a rise in the age at marriage in the late Seventies [1], but his observation was found to be an artefact of data and was, therefore, refuted (18] . Thus, nuptiality behaviour has been noted to have changed in Pakistan since the Fifties with no notable accompanying changes in marital fertility. This paper's primary objective is to explore the impact of modernization, particularly of expansion of education and modern sector employment, urbanization and migration, on proportions never married in various age groups.

The dynamics of a specific consumer-resource model for Daphnia magna is studied from a numerical point of view. In this study, Malthusian, chemostatic, and Gompertz growth laws for the evolution of the resource population are considered, and the resulting global dynamics of the model are compared as different parameters involved in the model change. In the case of Gompertz growth law, a new complex dynamic is found as the carrying capacity for the resource population increases. The numerical study is carried out with a second-order scheme that approximates the size-dependent density function for individuals in the consumer population. The numerical method is well adapted to the situation in which the growth rate for the consumer individuals is allowed to change the sign and, therefore, individuals in the consumer population can shrink in size as time evolves. The numerical simulations confirm that the shortage of the resource has, as a biological consequence, the effective shrink in size of individuals of the consumer population. Moreover, the choice of the growth law for the resource population can be selected by how the dynamics of the populations match with the qualitative behaviour of the data.

Abstract Consider a supercritical Crump‒Jagers process in which all births are at integer times (the lattice case). Let μ̂(z) be the generating function of the intensity of the offspring process, and consider the complex roots of μ̂(z)=1. The root of smallest absolute value is e-α=1∕m, where α>0 is the Malthusian parameter; let γ* be the root of second smallest absolute value. Subject to some technical conditions, the second-order fluctuations of the age distribution exhibit one of three types of behaviour: (i) when γ*>e-α∕2=m-1∕2, they are asymptotically normal; (ii) when γ*=e-α∕2, they are still asymptotically normal, but with a larger variance; and (iii) when γ*<e-α∕2, the fluctuations are in general oscillatory and (degenerate cases excluded) do not converge in distribution. This trichotomy is similar to what has been observed in related situations, such as some other branching processes and for Pólya urns. The results lead to a symbolic calculus describing the limits. The asymptotic results also apply to the total of other (random) characteristics of the population.

Complex socio-ecological systems like the food system are unpredictable, especially to long-term horizons such as 2050. In order to manage this uncertainty, scenario analysis has been used in conjunction with food system models to explore plausible future outcomes. Food system scenarios use a diversity of scenario types and modelling approaches determined by the purpose of the exercise and by technical, methodological and epistemological constraints. Our case studies do not suggest Malthusian futures for a projected global population of 9 billion in 2050; but international trade will be a crucial determinant of outcomes; and the concept of sustainability across the dimensions of the food system has been inadequately explored so far. The impact of scenario analysis at a global scale could be strengthened with participatory processes involving key actors at other geographical scales. Food system models are valuable in managing existing knowledge on system behaviour and ensuring the credibility of qualitative stories but they are limited by current datasets for global crop production and trade, land use and hydrology. Climate change is likely to challenge the adaptive capacity of agricultural production and there are important knowledge gaps for modelling research to address.

As recently as twenty-five years ago, there were virtually no demographers of China and there was little available data on Chinese demographic behavior. Thus in spite of intense interest in China's population dating back at least to Malthus (1766–1834), his initial understanding, or rather misunderstanding, of Chinese population dynamics remains dominant. While recent research on European population history has confirmed Malthus's observations that European, or at least English, population size was controlled largely by the preventive check, nuptiality, the absence of similar studies of Chinese population history ironically facilitated the persistence of a Malthusian hypothesis that Chinese population size was controlled largely by the positive check, mortality. It is a tribute to the elegance and power of the Malthusian orthodoxy that in spite of the lack of information on Chinese historic demographic behavior and economic performance, many of the most distinguished Western scholars of late imperial China continue to interpret social and economic processes in China during the last three hundred years in Malthusian or neo-Malthusian terms (Elvin 1973; Chao 1986; Huang 1990).

Le processus de Galton-Watson bi-sexué, introduit par Daley, est une extension du processus de Galton-Watson classique, décrivant l'accouplement de femelles et de mâles, formant des couples capables de se reproduire. Des propriétés telles que des conditions d'extinction et le comportement asymptotique ont été étudiées au cours des dernières années dans le cas uni-type, mais les versions multi-types n'ont été traitées que dans certains cas particuliers. Dans cette thèse, nous développons une version multidimensionnelle générale du modèle de Daley, où nous considérons différents types de femelles et de mâles, qui s'accouplent selon une “fonction d'appariement”. Nous supposons que cette fonction est superadditive, ce qui signifie simplement que deux groupes de femelles et de mâles forment un plus grand nombre de couples ensemble plutôt que séparément. L'une des principales difficultés dans l'étude de ce processus est que, contrairement au processus de Galton-Watson classique (asexué), l'opérateur associé au processus n'est pas linéaire mais concave. Pour surmonter ce problème, nous utilisons une théorie de Perron-Frobenius pour les opérateurs concaves, qui garantit l'existence d'éléments propres pour notre opérateur. Dans cette thèse, nous démontrons des lois des grands nombres et établissons des conditions nécessaires et suffisantes pour l'extinction presque sûre du processus. Nous étudions également, à travers l'identification d'une surmartingale, la convergence du processus en temps long dans le cas surcritique ainsi que l'existence de distributions quasi-stationnaires pour le régime sous-critique. Enfin, quelques extensions à des modèles avec une fonction d'appariement aléatoire et des modèles en temps continu sont traitées
The bisexual Galton-Watson process, introduced by Daley, is an extension of the classical Galton-Watson process, but taking into account the mating of females and males, which form couples that can accomplish reproduction. Properties such as extinction conditions and asymptotic behaviour have been studied in the past years in the single-type case, but multi-type versions have only been treated in some particular cases. In this thesis we deal with a general multi-dimensional version of Daley's model, where we consider different types of females and males, which mate according to a “mating function”. We consider that this function is superadditive, which in simple words implies that two groups of females and males will form a larger number of couples together rather than separate. One of the main difficulties in the study of this process is the absence of a linear operator that is the key to understand its behavior in the asexual case, but in our case it turns out to be only concave. To overcome this issue, we use a concave Perron-Frobenius theory which ensures the existence of eigen-elements for some concave operators. Using this tool, we find a necessary and sufficient condition for almost sure extinction as well as laws of large numbers. We also study the convergence of the process in the long-time through the identification of a supermartingale, and the existence of quasi-stationary distributions for the subcritical regime. Finally, some extensions to models with random mating function and models in continuous time are considered

This article focuses the theory of Malthus and the arguments of his Essay on the Principle of Population. This famous essay colored the thinking and actions of nineteenth-century householders and policy-makers. Vulgar Malthusian ideology missed the mark through an over-simplification of complex human behaviour, but general practice embodied his norms from 1760 to 1884. Even as the accuracy of the Malthusian model waned in terms of his description of marriage and reproduction at the end of the 1800s, its hold on the popular imagination persisted. Malthus bewitched the people with a picture. In 1798 Malthus proffered a schematic objection to their blueprints for perfecting humanity. Malthus postulated that the ‘passion between the sexes’ could unleash human ‘prolifick powers’ to reproduce at geometric rates, while technology generated merely arithmetic increases in the quantities of food necessary for human survival. An analysis of Malthusianism in practice concludes this article.

Abstract Throughout this book we have argued that sex for pleasure and sex for reproduction are conceptually distinct entities. With modern forms of birth control, wider acceptance of homosexual behavior, and advances in nonsexual reproductive techniques (e.g., artificial insemination), the perpetuation of this distinction seems assured. But does this mean that we are headed inexorably toward Aldous Huxley’s prophetic Brave New World, with its appropriately named Malthusian belts (containing an unspecified contraceptive) and its sex hormone chewing gum? That is, will the current trend continue unabated, the two functions of sexuality ultimately becoming completely divorced from one another? Or, as the conservative fundamentalist movement would have it, is the sexual liberation of the previous decades simply a fad, ready for reversal? What, in other words, is the future of sex?

Competition over natural resources has figured prominently among explanations of armed conflicts, from Malthusian fears of population growth and land scarcity to national security interests over resources defined as “strategic” because of their industrial or military use, such as oil and uranium. Access to natural resources and the transformation of nature into tradable commodities are deeply political processes, in which military force can play a role of domination or resistance. Armed separatism within Indonesia and Nigeria, annexation attempts on Kuwait and the Democratic Republic of the Congo, protracted civil wars in Angola and the Philippines, and coups d’état in Iran and Venezuela have all incorporated important resource dimensions. Arguably, the radical Islamic terrorism that has affected the United States since the early 1990s is to some extent an oil-related “blowback”: U.S. military deployment in Saudi Arabia, criticisms against the corruption of the Gulf regimes, and ironically, part of the funding made available to terrorist groups. This chapter examines relations between resources and armed conflicts, with a focus on commodities legally traded on international markets (thereby excluding drugs, as well as water and land involved, for example, in the Israeli-Palestinian conflict) and on extracted resources such as oil, minerals, and timber, in particular. Beyond a simple reading of so-called resource wars as violent modes of competitive behavior, this chapter argues that resource exploitation and the resource dependence of many producing countries play a role in shaping incentives and opportunities of uneven development, misgovernance, coercive rule, insurrection, and foreign interference. This relationship, however, is not systematic: history, political culture, institutions, and regional neighborhoods, as well as a country’s place in the international economy, all play a part these relations. The incorporation of resources into an armed conflict has also specific implications upon its course through their influence on the motivations, strategies, and capabilities of belligerents. Military targets often consist of commercial business opportunities rather than political targets, while the cost of engaging adversaries may be calculated in terms of financial reward.

According to Chesnais (1992), the fluctuation of human populations can be summarized into three broad categories: the pretransitional, transitional, and posttransitional cycles. In the pretransitional period before the Industrial Revolution, population fluctuations appear to reflect natural constraints of the environment. In more recent centuries, there were changes of the vital rates from high fertility-high mortality to low fertility-low mortality, which are referred to as demographic transitions. In this transitional period, because the decline of mortality usually leads that of fertility, fluctuations in the population age structure are a natural consequence of such a transition. After this transitional period, in many developed countries the mortality rate is stabilized, and female fertility becomes a typical family decision. Since family fertility decisions are related to other market institutions, the posttransitional population cycles have close interactions with these institutional elements. Although the population cycles can be separated into the three above-mentioned types, these cyclical movements share one common feature: the Malthusian environmental check always plays a direct or indirect role. In the next few chapters, I will discuss how the environmental checks interact with human decisions and institutions and how these interactions affect the cyclical movement of the population. Thomas Malthus argued that all populations are subject to environmental constraints and that these constraints operate through a variety of checks to population growth. If there are no such checks, we have a stationary branching process as described in chapters 2-6. In that case, the population will converge to a steady state under weak assumptions, and there are fluctuations only in the process of convergence. When there are environmental checks, the strength of the checks determines the speed with which the system tends toward equilibrium; this speed, relative to response lags that are intrinsic to the process, heavily influences the dynamic behavior of the economic-demographic system. When checks are weak, shocked populations tend to converge slowly without overshooting and to move in cycles one generation long (Lee, 1974). If checks arc stronger, overshooting may occur, and longer cycles of periodicity spanning two generations or more are possible, as population size and growth rates oscillate about their equilibrium values.

I mentioned in chapter 7 that the fluctuation of human population can be summarized into three broad categories: the pretransitional, transitional, and posttransitional cycles. Among these three categories, the last one has caught the attention of most demographic economists in the past thirty years. The main reason for this unbalanced research attention is that the posttransitional cycles appear only in developed countries, where high-quality data are available for empirical research. The recent development of advanced mathematical tools also facilitates the analysis of posttransitional density-dependent population dynamics. In this chapter we will provide a summary of the theoretical and empirical analyses of the most typical population fluctuations in the posttransitional period: the so-called Easterlin cycles. The well-known Easterlin cycles, named after the pioneer work by Richard Easterlin (1961, 1980), describe the observed two-generation-long birth cycles in the twentieth-century United States and in several other developed countries. Easterlin believed that there were two features associated with the observed cycles: they are related to the labor market, and they are more or less “self-generating” (Easterlin, 1961). The first feature implies that a complete theoretical framework should characterize how people’s fertility behavior is affected by the labor market and how the labor market is affected by the fertility pattern. The second feature addresses whether the theoretical framework can generate a persistent fertility fluctuation. An ideal theoretical framework should embody both of these features, and an ideal empirical analysis should also be compatible with these features. We start the background introduction by studying a Malthusian model presented by Lee (1974). Let us consider an overlapping-generation framework in which each individual lives one or two periods. The first period is childhood, the second period is adulthood, and all surviving adults will be in the labor force. Lee wrote down the following two equations: . . . W(t) = f(L(t)), (10.1). . . . . . b(t) = g(W(t)), (10.2). . . where W(t) is the wage rate (at time t), L is the size of the adult age group, b is the crude birth rate, and f(.) and g(.) are functions with f'(.) < 0 and g'(.) > 0.