Population-dynamics models and a sequential test in the analysis of the influence of household setting on the spread of Variola minor.
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Results for “population dynamics”
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Epizootiology of eastern equine encephalomyelitis virus in upstate New York, USA. II. Population dynamics and vector potential of adult Culiseta melanura (Diptera: Culicidae) in relation to distance from breeding site.
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Animals↗
Population dynamics of some Pakistan mosquitoes: temporal changes in reproductive status, age structure and survivorship of Anopheles culicifacies, An. stephensi and Culex tritaeniorhynchus.
The reproductive biology and age-structure of female Anopheles culicifacies, An. stephensi and Culex tritaeniorhynchus were studied at rural Punjabi villages near Lahore, Pakistan, during 1976-1980. Both Anopheles remained gonotrophically active throughout the year with blood-fed, gravid, parous and virgin females collected during all months. Culex tritaeniorhynchus populations bifurcated into reproductively active, non-overwintering and reproductively inactive, overwintering populations in October and/or November. Most female Cx. tritaeniorhynchus overwintered as inseminated nullipars with ovaries arrested at follicular State I; however, host-seeking and parous females were collected during every month of the year. Survivorship was calculated for each species by three methods and was negatively correlated with mean monthly ambient temperature. The ovarian tracheolation method provided inadequate estimates of parity for females collected at diurnal resting sites which refed the night of oviposition, but was suitable for Cx. tritaeniorhynchus females captured at bovid baits. The dilatation method of Polovodova was applied to all three species and yielded survivorship patterns which were constant with age and agreed well with a log-linear model. Anopheles culicifacies survived longer than did An. stephensi and thus was considered a better vector of malaria. Age-specific survivorship tables were constructed for all three species for those periods of the year when the gonotrophic rhythm was constant and generations were overlapping.
Animals↗
Intermittent chaos in population dynamics.
In modelling single species with discrete, non-overlapping generations, one usually assumes that the density at time t + .1 is a function of the density at time t: Nt+1 = f(Nt). The dynamical behaviour of this system depends on the parameters in the function f. It commonly changes, as a parameter increases, from a stable equilibrium through a series of bifurcations into stable cycles, to chaotic motion. It is implicit in the assumptions of the model that the population consists of identical individuals. In this paper it is shown that variation within the population can lead to a different route to chaos. Invasion of a mutant phenotype into a resident population can elicit intermittency. This kind of chaotic behaviour consists of regular motion most of the time with short intermittent periods in which the system fluctuates wildly.
Animals↗
A continuum formulation of the ideal free distribution and its implications for population dynamics.
The ideal free distribution is a description of how organisms would distribute themselves in space if they were free to move so as to maximize fitness. The standard formulation of the ideal free distribution envisions the environment as consisting of finitely many discrete habitats. In this paper, a version of the ideal free distribution is derived for the case where the environment is a continuum. The continuum formulation allows computation of average fitness at the population level by taking account of both local fitness and the spatial distribution of the population. An example shows that the average fitness may have a different form than the local fitness; in particular, if local fitness is described by a logistic equation at each location, the average fitness may obey the theta-logistic equation of F. J. Ayala et al. (1973, Theor. Popul. Biol. 4, 331-356). This gives a mechanistic derivation of the theta-logistic equation.
Animals↗
Do unusual site-specific population dynamics of rodent reservoirs provide clues to the natural history of hantaviruses?
Between January 1995 and November 1997, longitudinal mark-recapture studies of rodent hosts of hantaviruses in a disturbed microhabitat within a shortgrass prairie ecosystem in southeastern Colorado (USA) were conducted. The site was distinguished by edaphic and floristic characteristics unique to this area and associated with historical land use patterns, as well as the year-around availability of water from a functioning windmill. Populations of two common rodent species that are hosts for hantaviruses, Peromyscus maniculatus and Reithrodontomys megalotis, had unusually rapid turnover, a younger age structure, and a much lower prevalence of antibody to Sin Nombre virus than did populations at nearby sites in more typical shortgrass prairie and canyon habitats. Based on these findings, we suggest that a stable resident population of the reservoir is critical to the maintenance of hantaviruses at a given site, and we hypothesize that long-lived, persistently infected rodents are the principal transseasonal reservoir of hantaviruses.
Animals↗
[Evolution of rotifer population dynamics in a heterogeneous habitat: mathematical modeling].
We present the results of mathematical modeling of a rotifer species inhabiting two coupled habitats with different environmental conditions. We use the modified Consensus model and show that the exchange between the habitats can lead to chaotization of originally regular plankton dynamics and synchronization of plankton biomass oscillations. As a result, the invasion of a chaotic regime takes place.
Animals↗
Processes of pair formation leading to assortative mating in biological populations: dynamic interaction model.
A model of pair formation that treats mating between two individuals as a dynamic process rather than an instant event is suggested. A number of cases corresponding to polygamous and monogamous matings of individuals are considered. The individual mating preferences are represented in the model by a set of "compatibility probabilities." It is shown that the mating pattern (the distribution of characters among mating pairs) established in a population as a result of the process of pair formation does not uniquely reflect the pattern of mating preferences. Quite different mating patterns may occur in populations with very similar mating preferences, as well as similar mating patterns may occur in populations with different individual mating preferences. The model demonstrates that not only mating preferences of individuals but also specific mechanisms of pair formation play an important role in determining the mating pattern of a population.
Animals↗
Seagrass population dynamics and water quality in the Great Barrier Reef region: a review and future research directions.
Seagrasses in the Great Barrier Reef region, particularly in coastal habitats, act as a buffer between catchment inputs and reef communities and are important habitat for fisheries and a food source for dugong and green turtle. Within the Great Barrier Reef region there are four different seagrass habitat types now recognised. The spatial and temporal dynamics of the different types of seagrass habitat is poorly understood. In general seagrass growth is limited by light, disturbance and nutrient supply, and changes to any or all of these limiting factors may cause seagrass decline. The capacity of seagrasses to recover requires either recruitment via seeds or through vegetative growth. The ability of seagrass meadows to recover from large scale loss of seagrass cover observed during major events such as cyclones or due to anthropogenic disturbances such as dredging will usually require regeneration from seed bank. Limited research into the role of pollutants on seagrass survival suggests there may be ongoing impacts due to herbicides, pesticides and other chemical contaminants. Further research and monitoring of seagrass meadow dynamics and the influence of changing water quality on these is needed to enhance our ability to manage seagrasses on the Great Barrier Reef.
Animals↗
Microsatellite variation in solitary and social tuco-tucos: molecular properties and population dynamics.
Variation at 15 microsatellite loci was characterized for a population of the solitary Patagonian tuco-tuco (Ctenomys haigi) and a population of group-living colonial tuco-tuco (C. sociabilis), both of which were located in the Limay River Valley of south western Argentina. All loci examined were characterized by uninterrupted di- or trinucleotide repeats in both species; seven of these loci had been isolated from C. haigi and eight had been isolated from C. sociabilis. Across all loci, there was a significant tendency for both number of alleles and heterozygosity to be greater in C. haigi than in C. sociabilis. Cloning and sequencing of multiple PCR products per locus per population revealed no significant biases in allele length, suggesting that this difference in variability was not due to ascertainment bias or to population-wide differences in rates of microsatellite evolution. Instead, differences in microsatellite variation between C. haigi and C. sociabilis were more consistent with current demographic and suspected historical differences between these populations. In particular, interpopulation differences in the distribution of microsatellite allele sizes and allele frequencies suggested that C. sociabilis has been more subject to historical reductions in population size (e.g. population bottlenecks) than has C. haigi. These findings indicate that analyses of microsatellite structure can yield important insights into the population-level phenomena that contribute to diversity at these markers, including differences in population history that continue to influence levels of genetic variability.
Alleles↗
Natural population dynamics and expansion of pathogenic clones of Staphylococcus aureus.
The population structure of Staphylococcus aureus carried by healthy humans was determined using a large strain collection of nonclinical origin (n = 829). High-throughput amplified fragment length polymorphism (AFLP) analysis revealed 3 major and 2 minor genetic clusters of S. aureus, which were corroborated by multilocus sequence typing. Major AFLP cluster I comprised 44.4% of the carriage isolates and showed additional heterogeneity whereas major AFLP groups II and III presented 2 homogeneous clusters, including 47.3% of all carriage isolates. Coanalysis of invasive S. aureus strains and epidemic methicillin-resistant S. aureus (MRSA) revealed that all major clusters contained invasive and multiresistant isolates. However, clusters and subclusters with overrepresentation of invasive isolates were also identified. Bacteremia in elderly adults, for instance, was caused by a IVa cluster-derived strain significantly more often than by strains from other AFLP clusters. Furthermore, expansion of multiresistant clones or clones associated with skin disease (impetigo) was detected, which suggests that epidemic potential is present in pathogenic strains of S. aureus. In addition, the virulence gene encoding Panton-Valentine leukocidin was significantly enriched in S. aureus strains causing abscesses and arthritis in comparison with the carriage group. We provide evidence that essentially any S. aureus genotype carried by humans can transform into a life-threatening human pathogen but that certain clones are more virulent than others.
Cloning, Molecular↗
Non-invasive imaging of neuronal population dynamics in human thalamus.
Waveforms for early thalamic and cortical population responses to unilateral median nerve stimulation at the wrist were determined non-invasively for six subjects from 122-channel magnetoencephalographic data. Biphasic responses in contralateral ventral thalamus were obtained in 9 hemispheres similar to depth-electrode results reported for patients. Thalamic responses occurred at 15.1-17.4 and at 19.2-24 ms. Responses in contralateral sensorimotor cortex began at 16.3-18.8 ms.
Evoked Potentials↗
Seasonal and yearly population dynamics of two exotic helminths, Camallanus coti (Nematoda) and Bothriocephalus acheilognathi (Cestoda), parasitizing exotic fishes in Waianu Stream, O'ahu, Hawaii.
Exotic poeciliid fishes introduced into Hawaiian freshwaters are responsible for the introduction of several exotic parasites, of which the most important are Camallanus cotti and Bothriocephalus acheilognathi in terms of potential disease threat to native stream fishes. This roundworm and tapeworm are the most prevalent and abundant freshwater fish helminths in Hawaiian streams. This study examined the seasonal and yearly population structure of C. cotti and B. acheilognathi to determine if the tropical Hawaiian environment characterized by low climatic variability permits continuous opportunities for parasite transmission regardless of time of year. Camallanus cotti displayed seasonal differences in prevalence and mean abundance, whereas B. acheilognathi did not. Camallanus cotti prevalence and mean abundance were higher in the Hawaiian summer (47.7%, 0.79) than in winter (25.8%, 0.36). A seasonal relationship of C. cotti levels is likely explained by extensive rains associated with the Hawaiian winter season, which may act to decrease parasite transmission by flushing infected poeciliid hosts, intermediate copepod hosts, and possibly free-living infective worm stages downstream. Bothriocephalus acheilognathi displayed low prevalence and mean abundance in both summer (4.0%, 0.06) and winter (6.5%, 0.07), and it may be difficult to detect seasonal changes due to these low levels. Camallanus cotti prevalence and mean abundance remained relatively constant from the summer of 1995 to the summer of 1999, indicating that levels of this roundworm are stable in Waianu Stream. Whereas B. acheilognathi prevalence and mean abundance were low during the summer of 1995 and the summer of 1997, a dramatic peak in prevalence and mean abundance was observed in the summer of 1998 (41.2%, 1.06), with levels decreasing sharply in the summer of 1999 (4.4%, 0.07). It appears that B. acheilognathi also is present in stable populations at low levels, even though levels rose sharply during a single year.
Animals↗
[Population dynamics of the additive polygenic system under truncation selection].
Common features of the equations describing dynamics of the additive polygenic system under truncation selection are summarized. A combination of parameters playing the role of the effective selective pressure on the ith polygenic locus was revealed. The product of mean relative fitnesses of the individual polygenic loci, [formula: see text], was shown to play the role of relative mean fitness of the polygenic population. This value depends on the measurable parameters of the character distribution in the population: [formula: see text]. It was shown that under the constant population number during truncation selection, the characteristic of the best genotype increases, [formula: see text]; which is also a product of the frequencies of preferable genotypes at individual polygenic loci. This value plays the role of the proportion of the number of the best ("champion") genotype in the population. In fact, this is the champion genotype polygene consensus pattern frequency, which a priori indicates the possibility of the champion pattern fixation. The analogue of Haldane's dilemma for the polygenic system which restrict the number of polygenes simultaneously subjected to adaptive evolution [formula: see text] was obtained for the case of constant effective population number (Ne = const).
Genotype↗
Population dynamics of a naturally occurring heterogeneous mixture of Borrelia burgdorferi clones.
Two unique isolates of Borrelia burgdorferi, differing in plasmid content and outer surface protein C expression, were cultured on sequential captures of a single free-living Peromyscus leucopus mouse and were examined for differences in transmissibility. Both isolates were transmissible from inoculated C.B-17 mice to larval Ixodes scapularis ticks and, subsequently, from infected nymphal ticks to C3H/HeJ mice. Plasmid and protein analyses suggested that the original isolates were a mixed population of B. burgdorferi, and cloning by limiting dilution resulted in the identification of two clonal groups. In addition to being heterogeneous in plasmid and genomic macrorestriction analyses, the clones varied with respect to the electrophoretic mobilities and antigenicity of their OspC proteins, as shown by their reactivity to a panel of monoclonal antibodies. Plasmid analysis of sequential isolates from C3H mice experimentally infected with the primary isolate or various mixtures of its subclones showed an apparently random fluctuation in clonal dominance in the majority of mice. Surprisingly, mice infected with each subclone were permissive to superinfection with the heterologous subclone, despite the presence of anti-B. burgdorferi antibodies at the time of the secondary challenge. These results show conclusively that mice captured at Lyme disease enzootic sites may be infected by mixed populations of genetically and antigenically distinct B. burgdorferi clones and that these infections can be acquired by coinfection or by sequential infection. The lack of cross-immunization between clones existing within a naturally occurring population may play a role in the maintenance of the genetic heterogeneity of B. burgdorferi in nature.
Amino Acid Sequence↗
Population dynamics of flaviviruses revealed by molecular phylogenies.
The phylogeny of 123 complete envelope gene sequences was reconstructed in order to understand the evolution of tick- and mosquito-borne flaviviruses. An analysis of phylogenetic tree structure reveals a continual and asymmetric branching process in the tick-borne flaviviruses, compared with an explosive radiation in the last 200 years in viruses transmitted by mosquitoes. The distinction between these two viral groups probably reflects differences in modes of dispersal, propagation, and changes in the size of host populations. The most serious implication of this work is that growing human populations are being exposed to an expanding range of increasingly diverse viral strains.
Animals↗
[Seasonal variations of female aggressiveness and population dynamics of Culex quinquefasciatus Say 1823 in Abidjan (Republic of Côte d'Ivoire)].
Seasonal variations of Culex quinquefasciatus aggressiveness were studied in Abidjan where this mosquito is very harmful. Abidjan is crossed from East to West by the Ebrié lagoon, which is a vast expanse of brackish water (about 566 km2). In the North of this expanse of water lay continental plateaux and in the South lay low-plateaux. The city is composed of 10 districts, most of which are situated on the continental plateaux. Culex quinquefasciatus adult populations were caught monthly in 1989 on human bait traps in Abidjan 10 districts, one study place was located in each district. Captures took place outside the houses, in the dusk and during the first part of night, that is to say between 4 p.m. and 1 a.m. In Abidjan, Culex quinquefasciatus population density varies considerably within the city area. In the areas where the species is numerous, a high percentage of it seems to be developing all year through from breeding places which are, in most cases, permanent. Besides, the aggressiveness seasonal cycle which was registered in the above mentioned areas is particularly diversified.
Aggression↗
Population dynamics of B lymphocytes and their precursors: demonstration of high turnover in the central and peripheral lymphoid organs.
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Animals↗