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[Effect of solar and geomagnetic activity on population dynamics among residents of Russia].

Basing on the annual data of mortality and birth-rate in Russia in 1867-1897 an attempt to evaluate the role of solar (sunspot number W) and geomagnetic activity (Kp-index) in the population was made. It was shown that mortality is affected by the solar activity and by the absolute value of geomagnetic activity deviation from the mean level: Mi = 3.29 + 0.0044Wi + 1 + 0.030 delta Kp,i (r = 0.78). For the birth-rate the following expression was obtained: Bi = 5.00-0.049 delta Kp,i + 1-0.0012Wi + 3; (r = -0.67). The correlation coefficients between the observed variations of the mortality (and birth-rate) and indices Mi and Bi amounts the values 0.78 and -0.67 correspondingly.

Birth Rate↗
PubMed1993

Does migration stabilize local population dynamics? Analysis of a discrete metapopulation model.

A discrete model for a metapopulation consisting of two local populations connected by migration is described and analyzed. It is assumed that the local populations grow according to the logistic law, that both populations have the same emigration rate, and that migrants choose their new habitat patch at random. Mathematically this leads to a coupled system of two logistic equations. A complete characterization of fixed point and two-periodic orbits is given, and a bifurcation analysis is performed. The region in the parameter plane where the diagonal is a global attractor is determined. In the symmetric case, where both populations have the same growth rate, the analysis is rigorous with complete proofs. In the nonsymmetric case, where the populations grow at different rates, the results are obtained numerically. The results are interpreted biologically. Particular attention is given to the sense in which migration has a stabilizing and synchronizing effect on local dynamics.

Animals↗
PubMed2001

Population dynamics: Poisson approximation and its relation to the Langevin process.

We discuss how to simulate a stochastic evolution process in terms of difference equations with Poisson distributions of independent events when the problem is naturally described by discrete variables. For large populations the Poisson approximation becomes a discrete integration of the Langevin approximation [T. G. Kurtz, J. Appl. Prob. 7, 49 (1970); 8, 344 (1971)]. We analyze when the latter gives a reasonable representation of the original evolution for finite size systems. A simple example of an epidemic process is used to organize the discussion and to perform statistical tests that underline the goodness of the proposed method.

Poisson Distribution↗
PubMed1997

[Implications of spatial aggregation of parasites for the population dynamics in host-parasite interaction].

Some aspects of the widely observed over-dispersed pattern of the distribution of parasites within the host population are examined. It has been established in the parasitological literature that most hosts usually harbour few parasites, while only few hosts harbour a large proportion of the parasite population. Factors that may influence the pattern of distribution of parasites, the relation between the level of parasite aggregation and the prevalence of infection, and changes in this level of aggregation as a function of host age are analysed. Factors which determine the diversity of species in parasite communities are presented, and aspects of exploitative and interference competition among parasites and their relations with biological control procedures are also considered. Attention is also focused on the regulatory and destabilizing processes influencing the dynamic behaviour of host-parasite population interactions.

Age Factors↗
PubMed1995

Evolutionary cycling in predator-prey interactions: population dynamics and the red queen.

This paper describes the coevolution of phenotypes in a community comprising a population of predators and of prey. It is shown that evolutionary cycling is a likely outcome of the process. The dynamical systems on which this description is based are constructed from microscopic stochastic birth and death events, together with a process of random mutation. Births and deaths are caused in part by phenotype-dependent interactions between predator and prey individuals and therefore generate natural selection. Three outcomes of evolution are demonstrated. A community may evolve to a state at which the predator becomes extinct, or to one at which the species coexist with constant phenotypic values, or the species may coexist with cyclic changes in phenotypic values. The last outcome corresponds to a Red Queen dynamic, in which the selection pressures arising from the predator-prey interaction cause the species to evolve without ever reaching an equilibrium phenotypic state. The Red Queen dynamic requires an intermediate harvesting efficiency of the prey by the predator and sufficiently high evolutionary rate constant of the prey, and is robust when the model is made stochastic and phenotypically polymorphic. A cyclic outcome lies outside the contemporary focus on evolutionary equilibria, and argues for an extension to a dynamical framework for describing the asymptotic states of evolution.

Animals↗
PubMed2005

Population dynamics of cotton rats (Sigmodon hispidus) inhabiting abandoned petroleum landfarms in Oklahoma, USA.

Previous work by our group has shown bioaccumulation of contaminants and alterations in the immune system of hispid cotton rats (Sigmodon hispidus) inhabiting petrochemical waste sites (landfarms). We studied populations of cotton rats inhabiting petrochemical landfarms or uncontaminated reference sites. Cotton rat populations inhabiting abandoned landfarms experienced reduced summer population densities and lower mean monthly survival, with maximum densities 65% that of populations inhabiting non-contaminated grassland (reference) sites. Survival was lower in populations from landfarms (0.62+/-0.04) compared to reference sites (0.75+/-0.04), with differences most notable during summer months. Cotton rat populations sampled from landfarms had even sex ratios and a lower proportion of juveniles compared to populations from reference sites. No differences were observed in the weight of epididymides, testes, uteri, or ovaries, and no differences in fecundity were detected among sites.

Animals↗
PubMed2006

Historical population dynamics and demography of the Eastern Atlantic pomacentrid Chromis limbata (Valenciennes, 1833).

Recent studies have focused on the relationship between the marine fauna of the Eastern Atlantic and the Mediterranean Sea, but within the Atlantic, little is known about genetic relationships between populations of the Macaronesian islands. In this study, we tested whether the paleo-climatology and paleo-oceanography of the region could predict the genetic relationships among three Eastern Atlantic populations (Azores, Madeira, and Canaries) of a damselfish, Chromis limbata, and compared our results with its Mediterranean and adjacent Atlantic sister species, Chromis chromis. We combined phylogeographic and coalescent approaches using the fast evolving mitochondrial control region gene. No population structure was found for the three archipelagos. The coalescence time estimated for C. limbata (0.857-1.17 Mya) was much greater than that estimated for C. chromis. We propose that this difference reflects differences in glaciating extents in the Northeastern Atlantic and the Mediterranean. Diversity indexes (Hd and genetic distances) together with historical demographic parameters of C. limbata (Theta and g) revealed a more stable population history when compared to C. chromis. Our results suggest that the Macaronesian populations of C. limbata have probably been less affected by the last glaciation than the Mediterranean populations of C. chromis. Migration across the three archipelagos was estimated and a prevailing northwest trend was detected. This result supports the idea of a colonization of the Azores by warm water fish from Madeira or the westernmost Canary islands which acted as major glacial refugia for the tropical and subtropical marine fauna during the glaciations.

Animals↗
PubMed2005

Effects of the pyrethroid esfenvalerate on life-cycle traits and population dynamics of Chironomus riparius--importance of exposure scenario.

Field populations of aquatic organisms, particularly those inhabiting flowing waters, likely are exposed to short pulses of pesticides following periods of spray drift, surface runoff, or drain flow. In the present study, we investigated the effect of pulse exposures of a pyrethroid insecticide, esfenvalerate, on survival, development, and reproduction of the midge, Chironomus riparius. The first experiment was designed to simulate the exposure of settling larvae to a waterborne pulse of esfenvalerate. A second experiment simulated exposure of larvae entering a sediment that had been exposed previously to a waterborne pulse of esfenvalerate. A third experiment simulated exposure of sediment-inhabiting larval populations to a waterborne pulse of esfenvalerate and examined whether population density influenced the response of C. riparius. Our results indicate that even very brief (i.e., 1-h) exposures to environmentally realistic concentrations of esfenvalerate during early larval life can have measurable effects on larval survival and developmental rates. For those individuals that survived a pulse exposure early in life, however, there appeared to be no lasting effects of esfenvalerate on their subsequent egg laying or egg viability. Thus, brief exposure to environmentally realistic concentrations of pesticides can have measurable effects on freshwater invertebrate populations, but whether such effects occur depends on the details of the exposure regime. In addition, population density may influence the responses of life-cycle traits and, thereby, population-level impacts of pesticides.

Animals↗
PubMed2003

The influence of antibiotic production and pre-emptive colonization on the population dynamics of Pantoea agglomerans (Erwinia herbicola) Eh1087 and Erwinia amylovora in planta.

Stigma colonization by Erwinia amylovora is the crucial first step in the development of most fire blight infections in apple and pear trees. Suppression at this point of the disease process by antagonists of E. amylovora, such as Pantoea agglomerans (Erwinia herbicola) strain Eh1087, is a rational approach to control fire blight. We tested the hypothesis that the ability of E. amylovora to compete with Eh1087 for colonization of a stigma is reduced by the potential for Eh1087 to produce the phenazine antibiotic, d-alanylgriseoluteic acid (AGA). In competition experiments on the stigmas of apple flowers, E. amylovora was significantly less successful against Eh1087 (AGA+) than against EhDeltaAGA (AGA-). Further experiments to test the importance of pre-emptive colonization of the stigma by either the pathogen or the antagonist suggested that AGA production significantly enhanced the competitiveness of Eh1087 when it was applied at the same time or 24 h before the pathogen. We also found that pre-emptive stigma colonization by either the pathogen or the antagonist resulted in a population that was resilient to subsequent invasion by a second species suggesting that niche exclusion has a dominant influence on the dynamics of bacterial populations on stigmas.

Anti-Bacterial Agents↗
PubMed1998

Population dynamics of resource limited plants and their pollinators.

In this paper we build upon and generalize an earlier model of the interactions between a plant and its pollinator (Ingvarsson and Lundberg, 1995). In this model we assume that the performance of the pollinator population is directly linked to the size of the plant population. To avoid the problem of both populations growing exponentially we have, without loss of generality, assumed the plant population to be resource limited. Analysis of the system shows that there exists either two or no internal equilibrium points. The case with no equilibrium points corresponds to the trivial case where the system cannot persist, resulting in the extinction of both the plant and pollinator population. When the two internal equilibrium points do exist, one of them will always be unstable. This unstable equilibrium can be viewed as an equivalent of the threshold criteria derived in Ingvarsson and Lundberg (1995) in the sense that whenever the system is initiated above the unstable equilibrium point, persistence of the system is assured, while both species will go extinct whenever the system is initiated below the unstable equilibrium point. The analytical results were verified by numerical simulations of the system. We conclude that the existence of a threshold criteria, below which the system cannot persist is a general feature of plant-pollinator systems. We discuss how the existence of the threshold criteria will affect the persistence of plant-pollinator systems in light of, for instance, habitat fragmentation or stochastic reductions in the densities of either the plant or pollinator population. We further highlight some recent empirical studies that indicate the existence of a threshold in natural populations below which extinction is inevitable.

Animals↗
PubMed1997

Population dynamics and their impact on adolescents in the ESCAP region.

"This study examines the impact on adolescents of the dramatic demographic, social and economic changes currently taking place in the ESCAP region. Among the aspects it considers are the growth of the adolescent population, their age at marriage and fertility, educational developments, labour force participation, and the effects of poverty, globalization and urbanization on this segment of the population. It concludes by drawing out the implications of the research for policy and programme purposes."

Adolescent↗