Search results for "Population dynamic"
showing 10 items of 296 documents
Transient behavior of a population dynamical model
2005
The transient behavior of an ecosystem with N random interacting species in the presence of a multiplicative noise is analyzed. The multiplicative noise mimics the interaction with the environment. We investigate different asymptotic dynamical regimes and the role of the external noise on the probability distribution of the local field.
The bistable potential: An archetype for classical and quantum systems
2012
In this work we analyze the transient dynamics of three different classical and quantum systems. First, we consider a classical Brownian particle moving in an asymmetric bistable potential, subject to a multiplicative and additive noise source. We investigate the role of these two noise sources on the life time of the metastable state. A nonmonotonic behavior of the lifetime as a function of both additive and multiplicative noise intensities is found, revealing the phenomenon of noise enhanced stability. Afterward, by using a LotkaVolterra model, the dynamics of two competing species in the presence of Lévy noise sources is analyzed. Quasiperiodic oscillations and stochastic resonance pheno…
Abrupt Alnus population decline at the end of the first millennium CE in Europe - The event ecology, possible causes and implications
2019
The study, based on the examination of 70 published and unpublished pollen profiles from Poland and supplementary data from the surrounding regions, shows that an abrupt, episodic Alnus population decline at the end of the first millennium CE was a much more widespread event than has been previously reported, spanning large areas of the temperate and boreal zones in Europe. The data from Poland suggest that the decline was roughly synchronous and most likely occurred between the 9th and 10th centuries, with strong indications for the 10th century. The pollen data indicate that human impacts were not a major factor in the event. Instead, we hypothesize that one or a series of abrupt climatic…
Possible adverse impact of contaminants on Atlantic cod population dynamics in coastal ecosystems
2019
While many in-laboratory ecotoxicological studies have shown the adverse impact of pollutants to the fitness of an individual, direct evidence from the field on the population dynamics of wildlife animals has been lacking. Here, we provide empirical support for a negative effect of pollution on Atlantic cod ( Gadus morhua ) population dynamics in coastal waters of Norway by combining unique time series of juvenile cod abundance, body size, environmental concentration of toxic contaminants and a spatially structured population dynamics model. The study shows that mercury concentration might have decreased the reproductive potential of cod in the region despite the general decline in the env…
The use of Markovian metapopulation models: a comparison of three methods reducing the dimensionality of transition matrices.
2001
The use of Markovian models is an established way for deriving the complete distribution of the size of a population and the probability of extinction. However, computationally impractical transition matrices frequently result if this mathematical approach is applied to natural populations. Binning, or aggregating population sizes, has been used to permit a reduction in the dimensionality of matrices. Here, we present three deterministic binning methods and study the errors due to binning for a metapopulation model. Our results indicate that estimation errors of the investigated methods are not consistent and one cannot make generalizations about the quality of a method. For some compared o…
Territorial defense, territory size, and population regulation.
2005
The carrying capacity of an environment is determined partly by how individuals compete over the available resources. To territorial animals, space is an important resource, leading to conflict over its use. We build a model where the carrying capacity for an organism in a given environment results from the evolution of territorial defense effort and the consequent space use. The same evolutionary process can yield two completely different modes of population regulation. Density dependence arises through expanding and shrinking territories if fecundity is low, breeding success increases gradually with territory size, and/or defense is cheap. By contrast, when fecundity is high, breeding suc…
Nonmonotonic Pattern Formation in Three Species Lotka-Volterra System with Colored Noise
2005
A coupled map lattice of generalized Lotka-Volterra equations in the presence of colored multiplicative noise is used to analyze the spatiotemporal evolution of three interacting species: one predator and two preys symmetrically competing each other. The correlation of the species concentration over the grid as a function of time and of the noise intensity is investigated. The presence of noise induces pattern formation, whose dimensions show a nonmonotonic behavior as a function of the noise intensity. The colored noise induces a greater dimension of the patterns with respect to the white noise case and a shift of the maximum of its area towards higher values of the noise intensity.
Effects of forest patch size on physiological stress and immunocompetence in an area-sensitive passerine, the Eurasian treecreeper ( Certhia familiar…
2004
We manipulated the primary brood size of Eurasian treecreepers (Certhia familiaris) breeding in different sized forest patches (0.5-12.8 ha) in moderately fragmented landscapes. We examined the effects of brood size manipulation (reduced, control, enlarged) and forest patch size on physiological stress (heterophil-lymphocyte ratios; H/L), body condition and cell-mediated immunocompetence (phytohaemagglutinin test). Nestlings' H/L ratios were negatively related to forest patch area in control and enlarged broods, whereas no effects were found in reduced broods. The effects of forest patch area were strongest in enlarged broods, which had, in general, twofold higher H/L ratios than control an…
Modeling in Microbial Ecology
2014
SPE IPM; International audience; The bases and the principles of modeling in microbial community ecology and biogeochemistry are presented and discussed. Several examples are given. Among them, the fermentation process is largely developed, thus demonstrating how the model allows determining the microbial population growth rate, the death rate, and the maintenance rate. More generally, these models have been used to increase the development of bioenergetic formulations which are presently used in biogeochemical models (Monod, Droop, DEB models). Different types of interactions (competition, predation, and virus–bacteria) are also developed. For each topic, a complete view of the models used…
Optimal Control of the Lotka-Volterra Equations with Applications
2022
In this article, the Lotka-Volterra model is analyzed to reduce the infection of a complex microbiote. The problem is set as an optimal control problem, where controls are associated to antibiotic or probiotic agents, or transplantations and bactericides. Candidates as minimizers are selected using the Maximum Principle and the closed loop optimal solution is discussed. In particular a 2d-model is constructed with 4 parameters to compute the optimal synthesis using homotopies on the parameters.