55 research outputs found
Habitat geometry, population viscosity and the rate of genetic drift
No full textIn all natural populations, individuals located close to one another tend to interact more than those further apart. The extent of population viscosity can have important implications for ecological and evolutionary processes. Here we develop a spatially explicit population model to examine how the rate of genetic drift depends upon both spatial population structure and habitat geometry. The results show that the time to fixation for a new and selectively neutral mutation is dramatically increased in viscous populations. Furthermore, in viscous populations the time to fixation depends critically on habitat geometry. Fixation time for populations of identical size increases markedly as landscape width decreases and length increases. We suggest that similar effects will also be important in metapopulations, with the spatial arrangement of subpopulations and their connectivity likely to determine the rate of drift. We argue that the recent increases in computer power should facilitate major advances in our understanding of evolutionary landscape ecology over the next few years, and suggest that the time is ripe for a unification of spatial population dynamics theory, landscape ecology and population genetics
The impact of habitat loss and fragmentation on genetic drift and fixation time
No full textIn this study, a simple genetic model is integrated with an established method from landscape ecology to investigate the effect of habitat geometry and availability on genetic drift. Previous ecological modelling has identified a sharp threshold in habitat availability for species' persistence, beyond which the species rapidly becomes extinct. This study demonstrates the existence of a similar threshold for fixation time of selectively neutral genotypes by genetic drift, the location of which is determined by habitat shape and spatial correlation of habitat loss. Time to fixation is greater for habitats if they are long and thin rather than square. Despite reductions in population size due to habitat loss, fixation time remains relatively constant until a pre-threshold value, beyond which there is often a substantial increase in time to fixation. Further habitat loss results in the percolation threshold being reached and beyond this point the time to fixation decreases very rapidly. This study reveals a complex relationship between habitat availability, habitat geometry and the process of genetic drift. Possible implications of our results for conservation are discussed. Further work is required to improve our understanding of the interaction between evolutionary, ecological and landscape processes
Jesus, moral regeneration and crime in the Gospel of John
No full textA structural and text-immanent approach to the Gospel of John reveals that Jesus of Nazareth came to earth to do the will of God his Father and to take away the sins of the world. The author/s makes/make it clear that Jesus taught Nicodemus that one needs to be born again in order to enter the kingdom of God. To be born again means that one must be born out of water and Spirit, that is, through becoming a follower or disciple of Jesus Christ, one’s life has to change. This change, also called regeneration, is, anthropologically-speaking, according to the rational-choice theory, a deliberate choice made by man to become a follower or disciple of Jesus and to do his Father’s will. The disciples are not called upon to be like robbers and thieves, focused on the accumulation of earthly wealth, but to love one another. Although Jesus was crucified because of an allegation of high treason, a crime against the state, He instructed his followers to forgive others and to remain in His love. In terms of the explicatio-applicatio model, the intended kerygmatic message of John to his intended readers is clear: he wants all people, including criminals, to believe in Jesus and to follow Him, because, according to the Johannine author/s, when one follows Jesus, one does not commit crime, because one has been morally regenerated.
Keywords: Jesus, moral regeneration, gospel of St John, crime, South Afric
Incorporating evolutionary processes into a spatially-explicit model: exploring the consequences of mink-farm closures in Denmark
No full textIn this paper, we present an individual-based cellular lattice model, which is based on a real landscape (Denmark). The model predicts the distribution of free-ranging mink from data collated on the geographic locations of fur farms, the number of breeding mink kept per farm, and a range of parameters regarding escape, reproduction, mortality, and dispersal. When evolution was incorporated in the model, the results showed that the degree of adaptation within the free-ranging mink population is likely to vary spatially, with lower adaptation in areas where farm mink density is highest (due to the greater number of escaping mink). We used the model to explore the potential consequences of closing mink farms, or limiting escapes from them, on the evolutionary ecology of the free-ranging population and found that depending upon the paramaterisation of the evolutionary processes, several different outcomes are possible. Closing mink farms may result in a crash of the free-ranging population, or alternatively it may result in the establishment of a better-adapted, truly feral population that may ultimately outnumber the population that was present before farm closures. The main purpose of this paper is to raise awareness of the potential importance of evolutionary processes for the naturalisation of mink in Denmark. and to highlight the need for further work. Future field studies should be targeted to reduce the uncertainty in key parameters, allowing the development of an improved version of this model that can be used to generate management recommendations. More generally, we believe. that further work linking evolutionary and population biology is required particularly in an applied context. There are likely to be many further scenarios where evolutionary processes may hold the key to understanding both population and community dynamics.</p
Du paradoxe à l’unité : la construction médiatique d’une jeunesse catholique. La réception de la JMJ par des médias québécois francophones
No full textEn explorant la réception médiatique de la Journée Mondiale de la jeunesse qui s’est tenue en juillet 2002 à Toronto (Canada), l’auteur tente d’esquisser le portrait des jeunes et de leurs rapports à la religion catholique que la médiatisation de l’événement a permis de construire. L’analyse d’une série d’articles parus dans deux grands quotidiens québécois permet d’identifier différentes visions de la jeunesse mise en avant-scène par les médias. On y constate que l’insistance de départ sur l’hétérogénéité de la jeunesse fait rapidement place à la présentation d’une jeunesse catholique homogène et unie autour de Jean-Paul II. Or, un tel rapport des jeunes au catholicisme va à l’encontre des principales conclusions de la recherche sur cette question. À cette réception de la JMJ par des médias québécois sont proposées certaines pistes d’explication concernant notamment le statut, le rôle et le fonctionnement des médias de masse dans nos sociétés.While examining the reception given by the media to the World Youth Day held in July 2002 in Toronto (Canada) as well as their promotion of the event, the author tries to draw the profile of the youth, and its links with catholic religion. The analysis of press articles published into two important Quebec daily newspapers allows the identification of different visions of the youth put forward by the media. It can be noticed that the emphasis put on youth heterogeneity at the beginning quickly moves to the presentation of a homogeneous youth united around Pope John-Paul II. However, such a relation of youth toward Catholicism goes against research major conclusions on this topic. To this reception of the WYD by Quebec media, several explanations about, among others, mass media status, role, and functioning in our society are proposed
An Open Source Simulation Model for Soil and Sediment Bioturbation
No full textBioturbation is one of the most widespread forms of ecological engineering and has significant implications for the structure and functioning of ecosystems, yet our understanding of the processes involved in biotic mixing remains incomplete. One reason is that, despite their value and utility, most mathematical models currently applied to bioturbation data tend to neglect aspects of the natural complexity of bioturbation in favour of mathematical simplicity. At the same time, the abstract nature of these approaches limits the application of such models to a limited range of users. Here, we contend that a movement towards process-based modelling can improve both the representation of the mechanistic basis of bioturbation and the intuitiveness of modelling approaches. In support of this initiative, we present an open source modelling framework that explicitly simulates particle displacement and a worked example to facilitate application and further development. The framework combines the advantages of rule-based lattice models with the application of parameterisable probability density functions to generate mixing on the lattice. Model parameters can be fitted by experimental data and describe particle displacement at the spatial and temporal scales at which bioturbation data is routinely collected. By using the same model structure across species, but generating species-specific parameters, a generic understanding of species-specific bioturbation behaviour can be achieved. An application to a case study and comparison with a commonly used model attest the predictive power of the approach
Approximation Schemes For Maximum Cardinality Matching
No full textLet G = (V ; E) be an undirected graph. Given an odd number k = 2l + 1, a matching M is said to be k-optimal if it does not admit an augmenting path of length less than or equal to k. We prove jMj jM j(l+ 1)=(l+ 2), where M is a maximum cardinality matching. If M is not already (k + 2)-optimal, using M, in O(jEj) time we compute a (k + 2)-optimal matching. We show that starting with any matching, repeated k-optimizations result in an optimal matching in O( p jM jjEj) time. This approximation scheme extends to the minimum weight perfect matching, and the minimum weight uncapacitated perfect 2-matching problems over complete graphs, and complete bipartite graphs with edge weights of one and two. In particular, we obtain a fast approximation algorithm for the traveling salesman problem over complete graphs with edge weights of one and two.Technical report lcsr-TR-24
Tree loss impacts on ecological connectivity : Developing models for assessment
No full textJMJT, RCH and SCFP were funded by NERC (NE/J008001/1). RJM was funded by the Scottish Government's Rural and Environment Science and Analytical Services (RESAS) research program. This project also benefited from funding provided by the Woodland Trust (A13246). KW was supported with funding from the Forestry Commission.Peer reviewe
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