1,720,963 research outputs found
Effect of dispersal in two-patch environment with Richards growth on population dynamics
Full text linkIn this paper, we consider a two-patch model coupled by migration terms, where each patch follows a Richards law. First, we prove the global stability of the model. Second, in the case when the migration rate tends to infinity, the total carrying capacity is given, which in general is different from the sum of the two carrying capacities and depends on the parameters of the growth rate and also on the migration terms. Using the theory of singular perturbations, we give an approximation of the solutions of the system in this case. Finally, we determine the conditions under which fragmentation and migration can lead to a total equilibrium population which might be greater or smaller than the sum of two carrying capacities and we give a complete classification for all possible cases. The total equilibrium population formula for a large migration rate plays an important role in this classification. We show that this choice of local dynamics has an influence on the effect of dispersal. Comparing the dynamics of the total equilibrium population as a function of the migration rate with that of the logistic model, we obtain the same behavior. In particular, we have only three situations that the total equilibrium population can occur: it is always greater than the sum of two carrying capacities, always smaller, and a third case, where the effect of dispersal is beneficial for lower values of the migration rate and detrimental for the higher values. We end by examining the two-patch model where one growth rate is much larger than the second one, we compare the total equilibrium population with the sum of the two carrying capacities
Effect of dispersal in single-species discrete diffusion systems with source-sink populations
No full textA multi-patch source-sink model with and without intraspecific competition in the sink patches is considered. First, we study the dynamics of the model when the matrix of migration is irreducible and reducible. We show that, there is a threshold number of source patches such that the population potentially becomes extinct below the threshold and established above the threshold. Next, used the theory of perturbation singular and theorem of Tikhonov, in the case of perfect mixing, i.e. when the diffusion rate tends to infinity, we calculate the equilibrium of the model and we give a good approximations of the solutions in this case. Second, we determine, in some particular cases, the conditions under which fragmentation and the existence of sinks patches can lead to a total equilibrium population greater or smaller than the sum of the carrying capacities of the source patches. Finally, we study the effect of the rapid growth source population and rapid death sink population on the dynamics of the total equilibrium population and on the coexistence of the species
Generalized logistic equation on Networks
No full textIn this paper, we consider a general single species model in a heterogeneous environment of n patches (n ≥ 2), where each patch follows a generalized logistic law. First, we prove the global stability of the model. Second, in the case of perfect mixing, i.e when the migration rate tends to infinity, the total population follows a generalized logistic law with a carrying capacity which in general is different from the sum of the n carrying capacities. Finally, we give some properties of the total equilibrium population and we compute its derivative at no dispersal. In some particular cases, we determine the conditions under which fragmentation and migration can lead to a total equilibrium population which might be greater or smaller than the sum of the n carrying capacities. Finally, we study an example of two-patch model where the first patch follows a logistic law and the second a Richard's law, we give a complete classification of the model parameter space as to whether dispersal is beneficial or detrimental to the sum of two carrying capacities
Effets de la migration et de l'hétérogénéité spatiale sur la dynamique d'une population et sur la coexistence des espèces
No full textThe main theme of this thesis it the dynamics of populations which are spatially structured in patches and coupled by migration processes between the patches. This dynamic can be interpreted as an isolated dynamic system problem ( on each of the patches) coupled by the terms of migration between the patches. The main results of this thesis can be found in Chapters 3 and 4. In Chapter 3 titled " The multi-patch logistic equation" we are interested in the effect of symmetric migration on the population dynamic. We study the model of n-patch model with migration terms, where each patch follows a logistic law. First, we give some properties of the total equilibrium population. In some particular cases, we determine the conditions under which fragmentation and migration can lead to a total equilibrium population which might be greater or smaller than the sum of the n carrying capacities. Second, in the case of perfect mixing, i.e when the migration rate tends to infinity, the total population follows a logistic law with a carrying capacity which in general is different from the sum of the n carrying capacities. Finally, for the three-patch model we show numerically that the increase in number of patches from two to three gives a new behavior for the dynamics of the total equilibrium population as a function of the migration rate.In Chapter 4 titled " The multi-patch logistic equation with asymmetric migration" we are interested in the effect of asymmetric migration on the dynamic of population and we generalize some results from symmetric case. We study a multi-patch model, where each patch follows a logistic law, and patches are coupled by asymmetrical migration terms. First, in the case of perfect mixing, the total population follows a logistic equation with a carrying capacity which in general is different from the sum of the n carrying capacities, and depends on the migration terms. Second, we determine, in some particular cases, the conditions under which fragmentation and asymmetrical migration can lead to a total equilibrium population greateror smaller than the sum of the carrying capacities.Finally, for the three-patch model, we show numerically the existence of least three critical value of the migration rate for which the total equilibrium population equals the sum of the carrying capacities.Le thème principal de cette thèse est l'étude des dynamiques de populations qui sont structurées spatialement, dans des sites liés par des processus de migration entre eux. Cette dynamique peut être interprétée comme un problème de système dynamique isolés (sur chacun des sites) couplés par les termes de migration entre les sites. Les résultats principaux de cette thèse se trouvent dans les chapitres 3 et 4. Dans le chapitre 3 intitulé " The multi-patch logistic equation", on s'intéresse à l'effet de la migration symétrique sur la dynamique d'une population.On étudie le modèle de n sites avec des termes de migration symétrique, où chaque site suit une loi logistique. Premièrement, nous donnons quelques propriétés de la population total à l'équilibre. Dans certains cas particuliers, nous déterminons les conditions dans lesquelles la fragmentation et la migration peuvent conduire à une population totale à l'équilibre qui peut être supérieure ou inférieure à la somme des n capacités de charge. Deuxièmement, dans le cas d'un mélange parfait, c'est à dire lorsque le taux de migration tend vers l'infini, la population totale suit une loi logistique avec une capacité de charge qui en général est différente de la somme des n capacités de charge. Enfin, pour le modèle de trois sites, nous montrons numériquement que l'augmentation du nombre de sites de deux à trois donne un nouveau comportement pourla dynamique de la population totale à l'équilibre en fonction du taux de migration.Dans le chapitre 4 intitulé " The multi-patch logistic equation with asymmetric migration", on s'intéresse à l'effet de la migration non symétrique sur la dynamique d'une population et on généralise quelques résultats sur la migration symétrique. Premièrement, dans le cas d'un mélange parfait, la population totale suit une loi logistique avec une capacité de charge qui en général est différente de la somme des n capacités de charge et dépend des termes de migration. Deuxièmement, et comme dans le cas symétrique, nous déterminons dans certains cas particuliers du modèle, les conditions dans lesquelles la fragmentation et la migration peuvent conduire à une population totale à l'équilibre qui peut être supérieure ou inférieure à la somme des n capacités de charge.Nous terminons en considérant le modèle de trois sites et nous montrons par des simulations numériques l'existence d'au moins trois valeurs critiques du taux de migration pour lesquelles la population totale à l'équilibre est égale à la somme des n capacités de charge
Generalized logistic equation on Networks
Full text linkIn this paper, we consider a general single species model in a heterogeneous environment of patches (), where each patch follows a generalized logistic law. First, we prove the global stability of the model. Second, in the case of perfect mixing, i.e. when the migration rate tends to infinity, the total population follows a generalized logistic law with a carrying capacity which in general is different from the sum of the carrying capacities. Next, we give some properties of the total equilibrium population and we compute its derivative at no dispersal. In some particular cases, we determine the conditions under which fragmentation and migration can lead to a total equilibrium population which might be greater or smaller than the sum of the carrying capacities. Finally, we study an example of two-patch model where the first patch follows a logistic law and the second a Richard’s law, we give a complete classification of the model parameter space as to whether dispersal is beneficial or detrimental to the sum of two carrying capacities
Generalized logistic equation on Networks
No full textIn this paper, we consider a general single species model in a heterogeneous environment of n patches (n ≥ 2), where each patch follows a generalized logistic law. First, we prove the global stability of the model. Second, in the case of perfect mixing, i.e when the migration rate tends to infinity, the total population follows a generalized logistic law with a carrying capacity which in general is different from the sum of the n carrying capacities. Finally, we give some properties of the total equilibrium population and we compute its derivative at no dispersal. In some particular cases, we determine the conditions under which fragmentation and migration can lead to a total equilibrium population which might be greater or smaller than the sum of the n carrying capacities. Finally, we study an example of two-patch model where the first patch follows a logistic law and the second a Richard's law, we give a complete classification of the model parameter space as to whether dispersal is beneficial or detrimental to the sum of two carrying capacities
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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