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PubMed1989

[Population dynamics of Rhipicephalus pusillus Gil Collado, 1938 (Acarina, Ixodidae) in 1986-1987 in south-eastern Spain: modelling of the biological cycle].

The evolution of the Rhipicephalus pusillus population, a parasite of the european wild rabbit, Oryctolagus cuniculus, is studied in a locality of the Province of Granada (Spain), in 1986-1987. The moving average technique was applied to the sampling data (358 hosts), for each stage of the postembryonic cycle. This technique permitted us, together with the habitual usage of the statistics, to understand in a more complete manner, the evolution of daily changes which affect the average number of ticks over the population of the host rabbits. Various factors allowed us to envisage a strong dependency of the parasitism of the females and the larvae in relation with the developing environmental conditions, which determine the apparition and concentration of the parasites on the hosts. A very strong correlation between the parasitism by male ticks and that of the female ticks was observed for the two year duration of our investigation. However, the moment at which the distribution of the ectoparasites is contagious, the male abundance is nearly twice that of the females. The larvae respond to a similar pattern of distribution both years, but it is necessary to note a delay, which we can attribute to climatic changes registered from one year to the next. The nymphs, on the other hand, present a different distribution curve for each year. Their presence depends on climatic conditions and especially that of the situation of the ticks and hosts population in the moments proceeding: these conditions determine a deplacement of their apparition in one sense or another.

Analysis of Variance↗
PubMed1993

Short-term population dynamics of adult Aedes dorsalis (Diptera: Culicidae) in a northern California tidal marsh.

Short-term changes in the age structure and abundance of the host-seeking population of Aedes dorsalis (Meigen) females were studied in a Northern California tidal marsh by daily sampling from 25 July through 17 August 1990. The calculated numbers of nulliparous and parous females per day were used to estimate parity rates and duration of the gonotrophic cycle. The numbers of females collected per day ranged from 261 to 74,443, and daily parity rates ranged from 0 to 91%. The overall parity rate was 14%. Two peaks in nulliparous female abundance on days 7 and 12 were followed 5 d later by increases in the number of parous females, indicating that two cohorts had emerged with gonotrophic cycle lengths of approximately 5 d. This is consistent with the 5-d gonotrophic cycle length estimated using time series analysis of the same data sets. Peak host-seeking activity of nulliparous females in the two cohorts occurred 16 d after two marsh systems were flooded by monthly high tides. Survivorship was estimated to be 14% per gonotrophic cycle and 67% per day, although emigration may have caused the substantial underestimation of actual survivorship.

Aedes↗
PubMed2006

Effects of tick population dynamics and host densities on the persistence of tick-borne infections.

The transmission and the persistence of tick-borne infections are strongly influenced by the densities and the structure of host populations. By extending previous models and analysis, in this paper we analyse how the persistence of ticks and pathogens, is affected by the dynamics of tick populations, and by their host densities. The effect of host densities on infection persistence is explored through the analysis and simulation of a series of models that include different assumptions on tick-host dynamics and consider different routes of infection transmission. Ticks are assumed to feed on two types of host species which vary in their reservoir competence. Too low densities of competent hosts (i.e., hosts where transmission can occur) do not sustain the infection cycle, while too high densities of incompetent hosts may dilute the competent hosts so much to make infection persistence impossible. A dilution effect may occur also for competent hosts as a consequence of reduced tick to host ratio; this is possible only if the regulation of tick populations is such that tick density does not increase linearly with host densities.

Algorithms↗
PubMed1990

The interplay of population dynamics and the evolutionary process.

Long-term maintenance of genetic diversity is affected by ecological forces that are driven in turn by current levels of genetic variation. The strength of population regulation and the consequent patterns of population fluctuations determine the likelihood of genetic changes considered pivotal for rapid speciation. However, genetic diversity in the susceptibility to regulatory forces can reduce the magnitude of such fluctuations and minimize the likelihood of genetic revolutions. A group of populations that experiences local extinctions and recolonizations may hold lower levels of genetic diversity than in the absence of such extinctions, but local adaption, which provides enhanced genetic diversity, can reduce the likelihood of local extinctions. Tightly regulated populations experience different selection pressures than poorly regulated populations, although tighter regulation itself can evolve. When genotypic variation affects the outcome of interspecific interactions on a local scale, this effect, coupled with appropriate spatial variation, can enhance the resilience of the interactive system.

Animals↗
PubMed1999

A review of virus infections of cataceans and the potential impact of morbilliviruses, poxviruses and papillomaviruses on host population dynamics.

Viruses belonging to 9 families have been detected in cetaceans. We critically review the clinical features, pathology and epidemiology of the diseases they cause. Cetacean morbillivirus (family Paramyxoviridae) induces a serious disease with a high mortality rate and persists in several populations. It may have long-term effects on the dynamics of cetacean populations either as enzootic infection or recurrent epizootics. The latter presumably have the more profound impact due to removal of sexually mature individuals. Members of the family Poxviridae infect several species of odontocetes, resulting in ring and tattoo skin lesions. Although poxviruses apparently do not induce a high mortality, circumstancial evidence suggests they may be lethal in young animals lacking protective immunity, and thus may negatively affect net recruitment. Papillomaviruses (family Papovaviridae) cause genital warts in at least 3 species of cetaceans. In 10% of male Burmeister's porpoises Phocoena spinipinnis from Peru, lesions were sufficiently severe to at least hamper, if not impede, copulation. Members of the families Herpesviridae, Orthomyxoviridae and Rhabdoviridae were demonstrated in cetaceans suffering serious illnesses, but with the exception of a 'porpoise herpesvirus' their causative role is still tentative. Herpes-like viruses and caliciviruses (Caliciviridae) give rise to cutaneous diseases in Monodontidae and Delphinidae. Antibodies to several serotypes of caliciviruses were found in odontocetes and mysticetes. An unrecognized Hepadnaviridae was detected by serology in a captive Pacific white-sided dolphin Lagenorhynchus obliquidens with chronic persistent hepatitis. Adenoviruses (Adenoviridae) were isolated from the intestinal tracts of mysticeti and a beluga Delphinapterus leucas but were not associated with any pathologies. We discuss the potential impact of Paramyxoviridae, Poxviridae and Papovaviridae on the dynamics of several odontocete populations.

Adenoviridae↗
PubMed1987

The impact of sequential ultra-low volume ground aerosol applications of malathion on the population dynamics of Aedes aegypti (L.).

The efficacy of sequential, ultra-low volume ground aerosol applications of malathion at current U.S. label rates was evaluated as an emergency control measure for adult populations of Aedes aegypti (L.) in New Orleans, Louisiana. Replicates of 11 sequential aerosol treatments applied 12 hr apart during a 5.5-day period reduced mean adult captures and oviposition rates during the treatment period 73% and 75%, respectively. We hypothesize that oviposition was not completely suppressed because females with a developing egg burden remained sequestered during treatment periods or were more tolerant to the pesticide. We further concluded that adults could not be totally suppressed because of continued emergence. After treatment, adult densities recovered to pretreatment and control levels within approximately 1 week. A simulation study of the results suggested that, under the conditions of closely spaced housing and abundant vegetation that is typical of much of New Orleans, a single aerosol killed an average of 88% of the males and only 30% of the females present.

Aedes↗
PubMed1992

Population dynamics of adult Culex mosquitoes (Diptera: Culicidae) along the Kern River, Kern County, California, in 1990.

The temporal and spatial abundance, dispersal, survivorship, and density of Culex tarsalis Coquillett and Cx. quinquefasciatus Say populations were studied in riparian, agricultural, and residential habitats along the Kern River bed during the drought year of 1990. The temporal abundance of both species was related to cotton agricultural practices and peaked during intensive irrigation after cultivation was terminated in July. Cx. tarsalis peaked in abundance 2 wk earlier than Cx. quinquefasciatus, perhaps because of the advantage of autogenous oviposition, which shortened generation time. Although host-seeking females of both species were most abundant in the riparian habitat, more Cx. quinquefasciatus than Cx. tarsalis were collected in the residential habitat. Marked females released within the riparian habitat were recaptured most frequently within 1 km of the release point; however, flights as far as 12.6 km were documented within the 180-km2 study area. On average, marked Cx. quinquefasciatus dispersed farther and more rapidly than Cx. tarsalis and were recaptured more frequently within the residential habitat. Survivorship, estimated horizontally from the female recapture rate, ranged from 0.60 in May to 0.79 in July for Cx. tarsalis and from 0.74 in September to 0.84 in July for Cx. quinquefasciatus. The estimation of survivorship vertically from the parity rate was complicated by elevated autogeny rates in Cx. tarsalis and by the low parity rate in Cx. quinquefasciatus. Cx. tarsalis population density ranged from 125 females per km2 in May to 65,500 per km2 in August, and was well correlated with relative abundance. Collectively, these ecological data indicated that Cx. tarsalis may be important in disseminating arboviruses within the riparian habitat, but that Cx. quinquefasciatus may be important secondarily by disseminating virus from the riparian habitat to the adjacent residential habitat.

Animals↗
PubMed2002

Population dynamics of Frankliniella spp. and tomato spotted wilt incidence as influenced by cultural management tactics in tomato.

We investigated the effects of ultraviolet (UV)-reflective mulch and two rates of nitrogen fertilization on populations of Frankliniella spp. thrips and on the incidence of tomato spotted wilt in field-grown tomato in northern Florida. The higher of the two soil nitrogen fertilizer treatments significantly increased populations of Frankliniella occidentalis (Pergande), whereas mulch reflectance significantly decreased populations of F. occidentalis. Populations of Frankliniella tritici (Fitch) were decreased only by UV-reflective mulch. Decreased thrips populations in UV-reflective mulch plots were probably due to disruptions in host-finding behavior. Increased thrips populations in tomatoes treated with the higher nitrogen fertilization rate were probably due in part to increased nutrients available in flowers. Incidence of tomato spotted wilt was significantly decreased in tomatoes grown on UV-reflective mulch, whereas disease incidence was significantly greater in increased nitrogen-fertilized plots. This research reveals that cultural practices resulted in up to 45% reduction in the numbers of vector and nonvector species of flower thrips and up to 50% reduction in tomato spotted wilt.

Animals↗
PubMed2001

Population dynamics of Ornithodiplostomum ptychocheilus metacercariae in fathead minnows (Pimephales promelas) from four northern-Alberta lakes.

Annual, seasonal, and interlake variation in prevalence and intensity of Ornithodiplostomum ptychocheilus (Faust) metacercariae was assessed in populations of fathead minnows (Pimephales promelas) collected from 4 lakes in north-central Alberta. Mean metacercariae intensity in young-of-the-year minnows varied extensively (5-123 metacercariae/host) among year, month, and lakes. In 2 of the lakes, prevalence always reached 100%, and mean intensity always peaked in September or October. The high spatial and annual variation in metacercarial recruitment was partly attributable to variation in host size. but variation in water depth, temperature, snail densities, and bird visitation likely also played a role. A laboratory experiment demonstrated that host and metacercariae survival was intensity-independent during a period of simulated winter. Thus, metacercariae recruited in the fall survive until the following spring.

Alberta↗