scholarly journals One out of ten: low sampling efficiency of cloth dragging challenges abundance estimates of questing ticks

2020 ◽  
Vol 82 (4) ◽  
pp. 571-585
Author(s):  
Siiri Nyrhilä ◽  
Jani J. Sormunen ◽  
Satu Mäkelä ◽  
Ella Sippola ◽  
Eero J. Vesterinen ◽  
...  
Keyword(s):  
Activity Rhythm ◽  
Mixed Forest ◽  
Initial Population ◽  
Sampling Efficiency ◽  
Forest Patch ◽  
Host Seeking ◽  
Abundance Estimates ◽  
Questing Ticks ◽  
Daily Activity Rhythm ◽  
Initial Population Size

AbstractHard ticks (Acari: Ixodidae) act as important vectors of zoonotic pathogens. For instance, Borrelia burgdorferi s.l. spirochetes pose a severe health risk as aetiological agents of Lyme borreliosis. Commonly, to study the abundance of questing (host-seeking) ticks, a 1 m2 piece of cloth is dragged over vegetation for a determined distance. Here, we designed a tick-sampling study to estimate the sampling efficiency of this standard method. We established 10 m dragging transects in a hemiboreal mixed forest patch in SW Finland for a 5-day monitoring period. Five of the transects were cloth-dragged 3× a day, whereas another five transects were dragged 6× a day in a manner that after each morning, midday and afternoon dragging, a second dragging was conducted on the same transect immediately. Captured Ixodes ricinus ticks were subsequently analysed for tick-borne pathogens. The initial population size of nymphal ticks on a transect was approximated by the accumulated nymph catch from the dragging sessions. The sampling efficiency of the cloth dragging was low, as a single dragging in a previously untouched vegetation strip always caught less than 12% (mean 6%) of the estimated population of active nymphs that were assumed to be questing during the study. Clear results were not found for daily activity rhythm, as ticks were caught in all daily dragging sessions. Approximately every third nymph and every second adult carried a pathogen, but nothing indicated that the occurrence of a pathogen affected the likelihood of the tick being caught by cloth dragging. Our results suggest that only a minority of active ticks can be caught by a single cloth dragging. The abundance estimates in many tick investigations might thus be downward biased.

scholarly journals Agglomeration economies, congestion diseconomies, and fertility dynamics in a two-region economy

2021 ◽  
Author(s):  
Madoka Muroishi ◽  
Akira Yakita
Keyword(s):  
Population Size ◽  
Stability Condition ◽  
Fertility Rate ◽  
Model Parameters ◽  
Initial Population ◽  
Interregional Migration ◽  
Stable Path ◽  
Regional Population ◽  
Initial Population Size

AbstractUsing a small, open, two-region economy model populated by two-period-lived overlapping generations, we analyze long-term agglomeration economy and congestion diseconomy effects of young worker concentration on migration and the overall fertility rate. When the migration-stability condition is satisfied, the distribution of young workers between regions is obtainable in each period for a predetermined population size. Results show that migration stability does not guarantee dynamic stability of the economy. The stationary population size stability depends on the model parameters and the initial population size. On a stable trajectory converging to the stationary equilibrium, the overall fertility rate might change non-monotonically with the population size of the economy because of interregional migration. In each period, interregional migration mitigates regional population changes caused by fertility differences on the stable path. Results show that the inter-regional migration-stability condition does not guarantee stability of the population dynamics of the economy.

scholarly journals The dynamics of questing ticks collected for 164 consecutive months off the vegetation of two landscape zones in the Kruger National Park (1988–2002). Part III. The less commonly collected species

2011 ◽  
Vol 78 (1) ◽  
Author(s):  
Gordon J. Gallivan ◽  
Andrea Spickett ◽  
Heloise Heyne ◽  
Arthur M. Spickett ◽  
Ivan G. Horak
Keyword(s):  
National Park ◽  
Development Stage ◽  
Kruger National Park ◽  
Ixodid Ticks ◽  
Limited Information ◽  
Host Seeking ◽  
Haemaphysalis Elliptica ◽  
Questing Ticks ◽  
Landscape Zone

Despite many studies regarding tick ecology, limited information on long-term changes in tick populations exist. This study assessed the long-term population dynamics of the less frequently collected questing ixodid ticks in the Kruger National Park (KNP). From 1988 to 2002, monthly dragging of the vegetation was performed in three habitats (grassland, woodland and gully) at two sites in the KNP (Nhlowa Road, Landscape Zone 17, and Skukuza, Landscape Zone 4). Amblyomma marmoreum and Rhipicephalus evertsi evertsi were collected as larvae most commonly. Most A. marmoreum larvae were collected at Skukuza and numbers peaked from March to July. More R. evertsi evertsi larvae were collected at Nhlowa Road and numbers peaked in summer and in winter, while at Skukuza there was a single peak in spring. Haemaphysalis elliptica, Rhipicephalus simus and Rhipicephalus turanicus were collected as adults most commonly. More Ha. elliptica and R. turanicus were collected at Nhlowa Road than at Skukuza, while R. simus numbers from the two sites were approximately equal. Ha. elliptica were collected most often between February and June, and R. simus and R. turanicus during February and March. All three species were collected more frequently in gullies than in grassland or woodland. Their numbers increased in 1994/1995 following an eruption of rodents, the preferred hosts of the immature stages. The different host-seeking strategies of ticks largely determine the development stage at which they are likely to be collected during vegetation dragging and reflect a complex interaction between ticks, their hosts and the environment.

Estimation of the parameters of a branching process from migrating binomial observations

1998 ◽  
Vol 30 (4) ◽  
pp. 948-967 ◽  
Author(s):  
C. Jacob ◽  
J. Peccoud
Keyword(s):  
Confidence Interval ◽  
Asymptotic Behaviour ◽  
Population Size ◽  
Branching Process ◽  
Total Population ◽  
Initial Population ◽  
Asymptotic Confidence Interval ◽  
Total Population Size ◽  
Initial Population Size ◽  
Watson Process

This paper considers a branching process generated by an offspring distribution F with mean m < ∞ and variance σ2 < ∞ and such that, at each generation n, there is an observed δ-migration, according to a binomial law Bpvn*Nnbef which depends on the total population size Nnbef. The δ-migration is defined as an emigration, an immigration or a null migration, depending on the value of δ, which is assumed constant throughout the different generations. The process with δ-migration is a generation-dependent Galton-Watson process, whereas the observed process is not in general a martingale. Under the assumption that the process with δ-migration is supercritical, we generalize for the observed migrating process the results relative to the Galton-Watson supercritical case that concern the asymptotic behaviour of the process and the estimation of m and σ2, as n → ∞. Moreover, an asymptotic confidence interval of the initial population size is given.

scholarly journals Experimental demonstration of a two-phase population extinction hazard

2011 ◽  
Vol 8 (63) ◽  
pp. 1472-1479 ◽  
Author(s):  
John M. Drake ◽  
Jeff Shapiro ◽  
Blaine D. Griffen
Keyword(s):  
Population Size ◽  
Time Distribution ◽  
Proportional Hazards ◽  
Initial Population ◽  
Extinction Time ◽  
Habitat Size ◽  
Two Phase ◽  
Population Extinction ◽  
Initial Population Size ◽  
Phase Population

Population extinction is a fundamental biological process with applications to ecology, epidemiology, immunology, conservation biology and genetics. Although a monotonic relationship between initial population size and mean extinction time is predicted by virtually all theoretical models, attempts at empirical demonstration have been equivocal. We suggest that this anomaly is best explained with reference to the transient properties of ensembles of populations. Specifically, we submit that under experimental conditions, many populations escape their initially vulnerable state to reach quasi-stationarity, where effects of initial conditions are erased. Thus, extinction of populations initialized far from quasi-stationarity may be exposed to a two-phase extinction hazard. An empirical prediction of this theory is that the fit Cox proportional hazards regression model for the observed survival time distribution of a group of populations will be shown to violate the proportional hazards assumption early in the experiment, but not at later times. We report results of two experiments with the cladoceran zooplankton Daphnia magna designed to exhibit this phenomenon. In one experiment, habitat size was also varied. Statistical analysis showed that in one of these experiments a transformation occurred so that very early in the experiment there existed a transient phase during which the extinction hazard was primarily owing to the initial population size, and that this was gradually replaced by a more stable quasi-stationary phase. In the second experiment, only habitat size unambiguously displayed an effect. Analysis of data pooled from both experiments suggests that the overall extinction time distribution in this system results from the mixture of extinctions during the initial rapid phase, during which the effects of initial population size can be considerable, and a longer quasi-stationary phase, during which only habitat size has an effect. These are the first results, to our knowledge, of a two-phase population extinction process.

scholarly journals Mutualistic cross-feeding in microbial systems generates bistability via an Allee effect

2019 ◽  
Author(s):  
Stefan Vet ◽  
Lendert Gelens ◽  
Didier Gonze
Keyword(s):  
Allee Effect ◽  
Positive Influence ◽  
Initial Population ◽  
Explicit Model ◽  
Experimental Parameters ◽  
Initial Population Size ◽  
Strong Allee Effect ◽  
Relationship Of ◽  
Microbial Systems ◽  
Explicit Relation

ABSTRACTMutualistic interactions are characterized by the positive influence that two species exert on each other. Such mutualism can lead to bistability. Depending on the initial population size species will either survive or go extinct. Various phenomenological models have been suggested to describe bistability in mutualistic systems. However, these models do not account for interaction mediators such as nutrients. In contrast, nutrient-explicit models do not provide an intuitive understanding of what causes bistability. Here, we reduce a theoretical nutrient-explicit model of two mutualistic cross-feeders in a chemostat, uncovering an explicit relation to a growth model with an Allee effect. We show that the dilution rate in the chemostat leads to bistability by turning a weak Allee effect into a strong Allee effect. This happens as long as there is more production than consumption of cross-fed nutrients. Thanks to the explicit relationship of the reduced model with the underlying experimental parameters, these results allow to predict the biological conditions that sustain or prevent the survival of mutualistic species.

The extinction time of a birth, death and catastrophe process and of a related diffusion model

1985 ◽  
Vol 17 (01) ◽  
pp. 42-52 ◽  
Author(s):  
P. J. Brockwell
Keyword(s):  
Population Size ◽  
Diffusion Processes ◽  
Death Process ◽  
Arbitrary Distribution ◽  
Initial Population ◽  
Extinction Time ◽  
Birth And Death Process ◽  
Expected Time ◽  
Time To Extinction ◽  
Initial Population Size

The distribution of the extinction time for a linear birth and death process subject to catastrophes is determined. The catastrophes occur at a rate proportional to the population size and their magnitudes are random variables having an arbitrary distribution with generating function d(·). The asymptotic behaviour (for large initial population size) of the expected time to extinction is found under the assumption that d(.) has radius of convergence greater than 1. Corresponding results are derived for a related class of diffusion processes interrupted by catastrophes with sizes having an arbitrary distribution function.

Population dynamics of Caladenia: Bayesian estimates of transition and extinction probabilities

2009 ◽  
Vol 57 (4) ◽  
pp. 351 ◽  
Author(s):  
Raymond L. Tremblay ◽  
Maria-Eglée Perez ◽  
Matthew Larcombe ◽  
Andrew Brown ◽  
Joe Quarmby ◽  
...  
Keyword(s):  
Life History ◽  
Vegetative State ◽  
Life History Strategies ◽  
Initial Population ◽  
Extinction Rate ◽  
Life History Stages ◽  
Threatened Plant Species ◽  
Initial Population Size ◽  
Transition Models ◽  
Disproportionate Number

A disproportionate number of threatened plant species in Australia are found in the genus Caladenia, although little has been published on their life history. Here we examine data from nine species to evaluate some of the basic life-history strategies in Caladenia, specifically the transitions between life-history stages. We constructed life-history transition models of the orchids by using a Bayesian approach, we evaluated the growth rate of populations, compared transition values among species and determined which stage influenced the population growth most. We assessed extinction likelihood and considered the effect of variation in transitions among states on the probability of extinction. Bayesian model selection showed differences between species regarding their life cycle. The probability of individuals flowering in two consecutive years is extremely rare and was found to be common in only one species, C. amoena. All other species had a high likelihood of returning to a vegetative state, and some were likely to enter dormancy after flowering. High elasticities in the transition from the dormant to dormant stage suggest that dormancy has a large impact on population persistence. The quasi-extinction rate suggests that C. rosella, C. clavigera, C. graniticola and C. macroclavia are most at risk when all species have an equal initial population size. Conservation management should focus on studies to identify cues that influence flowering in consecutive years, emergence from dormancy and increasing recruitment.

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