Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “population dynamics”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 631 records · Page 35Linked to original sources
PubMed2005

Influence of seasonal nitrogen nutrition fluctuations in orange and lemon trees on population dynamics of the glassy-winged sharpshooter (Homalodisca coagulata).

The glassy-winged sharpshooter (GWSS) is a xylem feeder that develops conspicuous, year-round populations in many citrus-producing regions of California. Field studies were conducted in a combined lemon and orange orchard to determine the influence of changing amino acid concentrations on relative densities of GWSS. Nineteen protein amino acids were detected in xylem fluid of both lemon and orange trees. Although annual profiles of total and essential amino acids were similar for each citrus species, mean concentrations were consistently higher in lemons than in oranges for most of the year, except for one critical period in late winter-early spring when concentrations were higher in oranges. Principal component analysis followed by factor analysis was performed individually on lemon and orange data sets to identify a reduced number of orthogonal factors composed of amino acids having similar seasonal profiles. Four factors were identified for each citrus species that accounted for 85% and 79% of the total variation in the orange and lemon analyses, respectively. These were then examined with respect to shifts in GWSS numbers that occurred asynchronously in lemons and oranges over the annual population cycle. Three distinctive number shifts were identified that included a peak in adult numbers in lemons during August 2001, significantly higher numbers in lemons relative to oranges during midwinter, and finally an increase in oranges of both adults and nymphs during spring 2002. Various groups of amino acids, i.e., factors, displayed peak annual or elevated levels during the intervals when shifts in GWSS numbers were occurring. Soluble protein levels in oranges and lemons did not correspond to shifting GWSS numbers as certain amino acids. However, soluble protein levels were higher in oranges during late winter/early spring when GWSS adults were sexually active. Potential roles of these amino acids and proteins in GWSS host selection are discussed.

Amino Acids↗
PubMed1994

The population dynamics of microparasites and vertebrate hosts: the importance of immunity and recovery.

The models of Anderson and May on the dynamics of vertebrate (1979, Nature 280, 361-367) and invertebrate (1981, Philos, Trans. R. Soc. 291, 451-524) populations and their microparasites have been extended and elaborated. Hence, in a series of models the effects of a range of biological factors have been considered. These models taken together clarify in particular the effects of recovery from the disease back to a state of susceptibility and the additional effects of recovery to a state of immunity. In general recovery increases both the threshold density and the equilibrium density but does not alter the prevalence of infection or the region in parameter space in which the host is regulated. Immunity causes a further increase in the equilibrium density, does not alter either the prevalence of infection or the threshold density, but reduces the region in which there is regulation. In both cases exceptions tend to occur when there is density dependence.

Animals↗
PubMed1975

Mass immigration and population dynamics in Israel.

Israel, in her 25 years of existence, received an unprecedented volume of immigration, which was the major source of her high population growth. This immigration was heavily concentrated in the first five years, 1948-1952; mass immigration of 711,000 supplemented an initial population of 630;000. Subsequently, since 1952, a very peculiar age-sex structure has developed: namely, instead of a pyramid, a wide rectangle for the younger age groups "topped" with a narrow pyramid for the older age groups. The peculiar age-sex dynamics is analyzed in relation to the volume of immigration with its uneven time distribution, the age selectivity of migrants and fertility-mortality patterns of migrants. It is concluded that the uneven time distribution of immigration and the higher fertility of migrants are jointly responsible for the development of Israel's peculiar age dynamics, and that the absence of either of these two factors alone would eliminate it. The peculiar dynamics has societal implications in the short and the long run, some of which are discussed.

Adolescent↗
PubMed2005

The impact of directed versus random movement on population dynamics and biodiversity patterns.

An improved understanding of dispersal behavior is needed to predict how populations and communities respond to habitat fragmentation. Most spatial dynamic theory concentrates on random dispersal, in which movement rates depend neither on the state of an individual nor its environment and movement directions are unbiased. We examine the neglected dispersal component of directed movement in which dispersal is a conditional and directional response of individuals to varying environmental conditions. Specifically, we assume that individuals bias their movements along local gradients in fitness. Random movers, unable to track heterogeneous environmental conditions, face source-sink dynamics, which can result in deterministic extinction or increase their vulnerability to stochastic extinction. Directed movers track environmental conditions closely. In fluctuating environments, random movers "spread their bets" across patches, while directed movers invest offspring in habitats currently enjoying propitious conditions. The autocorrelation in the environment determines each strategy's success. Random movers permeate entire landscapes, but directed movers are more geographically constrained. Local information constraints limit the ranges of directed movers and introduce a role for historical contingency in determining their ultimate distribution. These geographic differences have implications for biodiversity. Random movement maintains biodiversity through local coexistence, but directed movement favors a spatial partitioning of species.

Animal Migration↗
PubMed2006

Does the number of diapausing eggs laid on bark affect the population dynamics of the spider mite Panonychus mori?

We studied the relationship between number of diapausing eggs produced by the spider mite Panonychus mori and the subsequent population trend for a period of 3 years. Panonychus mori showed a single population density peak on its host plant moonseed, Cocculus trilobus. The position and height of this peak were correlated with the density of diapausing eggs around the moonseed leaf buds produced the winter before. In 1994 the density of diapausing eggs measured in February was 4.3/bud, which was 6-14 times higher than the density of diapausing eggs for the same period in 1995 (0.3/bud) and 1996 (0.7/bud). The subsequent population density peak in 1994 occurred in mid June and was about 2.5 times higher than the peaks in 1995 and 1996, which both occurred early September. Thus, the present study showed a positive correlation between the density of diapausing eggs on the host plant and the start and the extend of the population increase the next growing season. Predators associated with the spider mite population were phytoseiid mites, especially Amblyseius eharai was well synchronized with the spider mite density in 1994. Field observations revealed that P. mori produced diapausing eggs in response to short photoperiod in early October each year, which corresponded with the timing predicted by the critical photoperiod around 13 h at 18 degrees C, as assessed in laboratory trials. Diapause ended by early April when egg hatchability attained about 50% and eggs took 9 days to hatch at 25 degrees C and a 16L:8D photoperiod. Hatching in early April was twice faster than in late February.

Analysis of Variance↗
PubMed1997

Population dynamics inferred from temporal variation at microsatellite loci in the selfing snail Bulinus truncatus.

We analyzed short-term forces acting on the genetics of subdivided populations based on a temporal survey of the microsatellite variability in the hermaphrodite freshwater snail Bulinus truncatus. This species inhabits temporary habitats, has a short generation time and exhibits variable rates of selfing. We studied the variability over three sampling dates in 12 Sahelian populations (1161 individuals). Classical genetic parameters (estimators of Ho, He, f, selfing rate and Fst) showed limited change over time whereas important temporal changes of allelic frequencies were detected for 10 of the ponds studied. These variations are not easily explained by selection, sampling drift and genetic drift alone and may be due to periodic migration. Indeed the habitats occupied by the populations studied are subject to large temporal fluctuations owing to annual cycles of drought and flood. In such ponds our results support a demographic model of population expansions and contractions under which available habitats, after the rainy season, are colonized by individuals originating from a smaller number of refuges (areas that never dry out in the deepest parts of the ponds). In contrast, selfing appeared to be an important force affecting the genetic structure in permanent ponds.

Animals↗
PubMed2002

Population dynamics with a refuge: fractal basins and the suppression of chaos.

We consider the effect of coupling an otherwise chaotic population to a refuge. A rich set of dynamical phenomena is uncovered. We consider two forms of density dependence in the active population: logistic and exponential. In the former case, the basin of attraction for stable population growth becomes fractal, and the bifurcation diagrams for the active and refuge populations are chaotic over a wide range of parameter space. In the case of exponential density dependence, the dynamics are unconditionally stable (in that the population size is always positive and finite), and chaotic behavior is completely eradicated for modest amounts of dispersal. We argue that the use of exponential density dependence is more appropriate, theoretically as well as empirically, in a model of refuge dynamics.

Ecology↗
PubMed1995

A survey of structured cell population dynamics.

A survey of three types of cell population models is presented in this paper. The main issue in all the surveyed works is whether or not there exists a stable type distribution (s.t.d.). In the last few years, many efforts were directed towards describing the most general models which still exhibit s.t.d. Progress made in the case of size density models are discussed. A slightly extended version of a time continous daughter cell model, studied in Arino et al. (1991), is presented. Recently, some authors have undertaken the task of comparing models of various origins and types. Such works are alluded to in a discussion.

Cell Count↗
PubMed2000

Dispersal, Environmental Correlation, and Spatial Synchrony in Population Dynamics.

Many species exhibit widespread spatial synchrony in population fluctuations. This pattern is of great ecological interest and can be a source of concern when the species is rare or endangered. Both dispersal and spatial correlations in the environment have been implicated as possible causes of this pattern, but these two factors have rarely been studied in combination. We develop a spatially structured population model, simple enough to obtain analytic solutions for the population correlation, that incorporates both dispersal and environmental correlation. We ask whether these two synchronizing factors contribute additively to the total spatial population covariance. We find that there is always an interaction between these two factors and that this interaction is small only when one or both of the environmental correlation and the dispersal rate are small. The interaction is opposite in sign to the environmental correlation; so, in the normal case of positive environmental correlation across sites, the population synchrony will be lower than predicted by simply adding the effects of dispersal and environmental correlation. We also find that population synchrony declines as the strength of population regulation increases. These results indicate that dispersal and environmental correlation need to be considered in combination as explanations for observed patterns of population synchrony.

Moran effect↗
PubMed1970

Studies on the population dynamics of the housefly, Musca domestica L.

The population level and potential rate of increase of a population of houseflies, Musca domestica L., on Grand Turk Island was studied for about 2 years to determine what changes occurred when no control was applied (the first year) and when the population was totally suppressed by the application of chemosterilant baits (the second year). During the first year the population was relatively stable (the highest density occurred in June and the lowest in January) and the difference between the high and low levels was only 3-fold. When chemosterilant baits were applied over a 40-week period and total suppression was achieved, calculations based on the sterility achieved and the resulting control revealed that the population showed potential rates of increase ranging up to 4-fold during the period from June through October and from 4-fold to 11-fold from December through April. Thus, in the field, the potential rates of increase of the housefly are low despite its high biotic potential.

Animals↗
PubMed2000

Spatial coupling in cyclic population dynamics: models and data.

We use a dynamic random field to model a spatial collection of coupled oscillators with discrete time stochastic dynamics. At each time step the phase of each cyclic local population is subject to random noise, incremented by a common dynamic, and pulled by a coupling force in the direction of some collective mean phase. We define asynchrony and derive expressions for its measurement in this model. We describe robust methods for phase estimation of cyclic population time series, for estimating strength of coupling between local populations, and for measuring variance of locally acting noise from field data. Proposed methods allow intermittently acting phase synchronizing events operating over large spatial scales to be distinguished from more continuous and possibly locally acting coupling, both of which could result in elevated levels of phase synchronization. We demonstrate the utility of this approach by applying it to classical spatial time series data of Canadian lynx. Analysis confirms findings of previous studies and reveals evidence to suggest that interpopulation coupling was weaker over the 20th century than for the 1800s. Analysis supports the notion that synchrony in these populations is maintained by a continuous and locally acting coupling between adjacent regions with large phase adjustments occurring only infrequently. When this coupling is absent, asynchrony develops between populations.

Animals↗
PubMed2000

Population dynamics of the free-living stages of Amblyomma cajennense (Fabricius, 1787) (Acari: ixodidae) on pastures of Pedro Leopoldo, Minas Gerais State, Brazil.

A study on the population behavior of Amblyomma cajennense larvae, nymphs and adult free-living stages was carried out in Pedro Leopoldo County, Minas Gerais State, Brazil, from July 1995 to July 1997. Larvae were collected from pasture from April to October using the technique of drag sampling with flannelette. The maximal larval population was observed during autumn (May) representing, respectively, 48 and 82% of the total numbers recovered during the first and the second years of the experiment. Nymphs and adults were captured throughout the year by the use of traps with carbon dioxide as chemical attractant. The highest population of nymphs occurred during the winter (July), representing 39.5% of the total collected specimens. Adults had the highest population density on pasture during spring and summer, i.e., from August to May, with peaks in January and February, representing 46 and 38.3% of the total collected specimens during the first and the second year of study, respectively.

Animals↗
PubMed1985

Heterogeneity's ruses: some surprising effects of selection on population dynamics.

"As a cohort of people, animals, or machines ages, the individuals at highest risk tend to die or exit first. This differential selection can produce patterns of mortality for the population as a whole that are surprisingly different from the patterns for subpopulations or individuals. Naive acceptance of observed population patterns may lead to erroneous policy recommendations if an intervention depends on the response of individuals. Furthermore, because patterns at the individual level may be simpler than composite population patterns, both theoretical and empirical research may be unnecessarily complicated by failure to recognize the effects of heterogeneity."

Cohort Studies↗
PubMed1996

Human population dynamics revisited with the logistic model: how much can be modeled and predicted?

"We revive the logistic model, which was tested and found wanting in early-20th-century studies of aggregate human populations, and apply it instead to life expectancy (death) and fertility (birth)....For death...the logistic portrays the situation crisply. Human life expectancy is reaching the culmination of a two-hundred year-process that forestalls death until about 80 for men and the mid 80s for women. No breakthroughs in longevity are in sight unless genetic engineering comes to help. For birth, the logistic covers quantitatively its actual morphology. However, because we have not been able to model this essential parameter in a predictive way over long periods, we cannot say whether the future of human population is runaway growth or slow implosion... From a niche point of view, resources are the limits to numbers, and access to resources depends on technologies. The logistic makes clear that for homo faber, the limits to numbers keep shifting. These moving edges may most confound forecasting the long-run size of humanity."

Conservation of Natural Resources↗