Browsing by Author "Šćepanović, Julija"

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    Consequences for predator–prey dynamics caused by the presence of obstacles
    Šćepanović, Julija; Budinski-Petković, Ljuba; Jakšić, Zorica; Belić, Aleksandar; Vrhovac, Slobodan
    In order to understand how a heterogeneous habitat affects the population dynamics of the predator–prey system, a spatially explicit lattice model consisting of predators, prey and obstacles is constructed. The model includes smart pursuit (predators to prey) and evasion (prey from predators). Both species can affect their movement by visual perception within their finite sighting range. Non-conservative processes that change the number of individuals within the population, such as breeding and physiological dying, are implemented in the model. Obstacles are represented by non-overlapping lattice shapes that are randomly placed on the lattice. In the absence of obstacles, numerical simulations reveal regular, coherent oscillations with a nearly constant predator–prey phase difference. Numerical simulations have shown that changing the probabilities for non-conservative processes can increase or decrease the period of coherent oscillations in species abundances and change the relative lag between coherent components. After introducing obstacles into the model, we observe random transitions between coherent and non-coherent oscillating regimes. In the non-coherent regime, predator and prey abundances continue to oscillate, but without a well-defined phase relationship. Our model suggests that stochasticity introduced by density fluctuations of obstacles is responsible for the reversible shift from coherent to non-coherent oscillations.
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    Long-term effects of abrupt environmental perturbations in model of group chase and escape with the presence of non-conservative processes
    Šćepanović, Julija; Jakšić, Zorica; Budinski-Petković, Ljuba; Vrhovac, Slobodan
    This paper examines the influence of environmental perturbations on dynamical regimes of model ecosystems. We study a stochastic lattice model describing the dynamics of a group chasing and escaping between predators and prey. The model includes smart pursuit (predators to prey) and evasion (prey from predators). Both species can affect their movement by visual perception within their finite sighting range. Non-conservative processes that change the number of individuals within the population, such as breeding and physiological dying, are implemented in the model. The model contains five parameters that control the breeding and physiological dying of predators and prey: the birth and two death rates of predators and two parameters characterizing the birth and death of prey. We study the response of our model of group chase and escape to sudden perturbations in values of parameters that characterize the non-conservative processes. Temporal dependencies of the number of predators and prey are compared for various perturbation events with different abrupt changes of probabilities affecting the non-conservative processes.
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    Random sequential adsorption of lattice animals on a three-dimensional cubic lattice
    Lončarević, Ivana; Budinski-Petković, Ljuba; Šćepanović, Julija; Jakšić, Zorica; Vrhovac, Slobodan
    The properties of the random sequential adsorption of objects of various shapes on simple three-dimensional (3D) cubic lattice are studied numerically by means of Monte Carlo simulations. Depositing objects are "lattice animals," made of a certain number of nearest-neighbor sites on a lattice. The aim of this work is to investigate the impact of the geometrical properties of the shapes on the jamming density θJ and on the temporal evolution of the coverage fraction θ(t). We analyzed all lattice animals of size n=1, 2, 3, 4, and 5. A significant number of objects of size n≥6 were also used to confirm our findings. Approach of the coverage θ(t) to the jamming limit θJ is found to be exponential, θJ-θ(t)∼exp(-t/σ), for all lattice animals. It was shown that the relaxation time σ increases with the number of different orientations m that lattice animals can take when placed on a cubic lattice. Orientations of the lattice animal deposited in two randomly chosen places on the lattice are different if one of them cannot be translated into the other. Our simulations performed for large collections of 3D objects confirmed that σ≅mâ{1,3,4,6,8,12,24}. The presented results suggest that there is no correlation between the number of possible orientations m of the object and the corresponding values of the jamming density θJ. It was found that for sufficiently large objects, changing of the shape has considerably more influence on the jamming density than increasing of the object size.