Population dynamics in echinococcosis and cysticercosis: regulation ofTaenia hydatigenaandT. ovisin lambs through passively transferred immunity

SUMMARYA comparison has been made of the interactions between passively transferred and actively acquired immunity in regulating populations ofTaenia hydatigenaandT. ovis.When ewes were grazed prior to parturition under a high infection pressure, immunity was transferred to their offspring for up to 8 weeks. A qualititative difference between the species was the destruction of larvalT. ovisprior to their establishment (‘pre-encystment immunity’) and that ofT. hydatigenaafter they had become established (‘post-encystment immunity’) in the challenged lambs. The major difference in terms of population regulation between the two parasites was that infection occurred withT. hydatigenabut not withT. ovisin those lambs reared from birth for 16 weeks under high infection pressure. Passive, like active immunity, is a density-dependent constraint. It plays an important role in the population regulation ofT. ovis, but not ofT. hydatigena. This is discussed in terms of transmission in the natural environment, an hypothesis on humoral protection and the need to elucidate pathways of protection when immunization schedules are being evaluated for controlling the taeniid zoonoses.

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Establishment, survival and site selection of the cestode Eubothrium crassum in brown trout, Salmo trutta

Parasitology ◽

10.1017/s0031182000065872 ◽

1996 ◽

Vol 112 (3) ◽

pp. 347-355 ◽

Cited By ~ 5

Author(s):

C. R. Kennedy

Keyword(s):

Population Dynamics ◽

Site Selection ◽

Salmo Trutta ◽

Population Regulation ◽

Host System ◽

Mean Intensity ◽

Density Dependent ◽

Brown Trout Salmo Trutta ◽

Selection Of ◽

Heavy Mortality

SUMMARYPopulation dynamics, site selection, growth and maturation of the cestode Eubothrium crassum in a natural population of Salmo trutta in a small lake were studied over a period of 1 year, the life-span of a cohort in fish. Infection of fish commenced in spring but peaked in July. Small, plerocerciform parasites initially located in the intestine, but then some moved into the pyloric caecae whilst others, the majority in heavy infections, were lost from the fish causing a fall in abundance from 460 to 10 over 2 months. This mortality was density dependent. Initially, parasites were distributed more evenly throughout the caecae but as time increased larger parasites were found preferentially in the anterior caecae before moving back into the intestine when gravid, preparatory to being lost in the following summer. Only a small proportion of the infrapopulation became gravid. Although the proportion of caecae occupied was initially density dependent, by the time of maturation several preferred anterior caecae remained unoccupied and mean intensity always exceeded unity. Neither growth nor maturation was affected by intraspecific competition. It was concluded that caecal availability did not set a limit or threshold of infrapopulation density, and in this respect E. crassum–S. trutta differed from some acanthocephalan-fish systems but was similar to others. Heavy infection followed by heavy mortality appeared to be typical of this parasite-host system in other localities, and of several other cestode-fish systems. The implications of this for population regulation are discussed.

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Heterogeneity and the dynamics of host—parasitoid interactions

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.1990.0193 ◽

1990 ◽

Vol 330 (1257) ◽

pp. 203-220 ◽

Cited By ~ 58

Keyword(s):

Population Dynamics ◽

Continuous Time ◽

Population Regulation ◽

Host Density ◽

General Rule ◽

Field Studies ◽

Simple Description ◽

Density Dependent ◽

Total Heterogeneity ◽

Local Host

This paper is concerned with the dynamical effects of spatial heterogeneity in host-parasitoid interactions with discrete generations. We show that the dynamical effects of any pattern of distribution of searching parasitoids in such systems can be assessed within a common, simple framework. In particular, we describe an approximate general rule that the populations of hosts and parasitoids will be regulated if the coefficient of variation squared (CV 2 ) of the distribution of searching parasitoids is greater than one. This criterion is shown to apply both generally and in several specific cases. We further show that CV 2 may be partitioned into a density-dependent component (direct or inverse) caused by the response of parasitoids to host density per patch, and a density independent component. Population regulation can be enhanced as much by density independent as by density-dependent heterogeneity. Thus the dynamical effects of any pattern of distribution of searching parasitoids can be assessed within the same common framework. The paradoxical impact of density-independent heterogeneity on dynamics is especially interesting: the greater the density independence, and thus the more scattered the data of percent parasitism against local host density, the more stable the populations are likely to be. Although a detailed analysis of host-parasitoid interactions in continuous time has yet to be done, evidence does not support the suggestion of Murdoch & Oaten (1989) that non-random parasitism may have quite different effects on the dynamics of continuous-time interactions. There appears to be no fundamental difference in the role of heterogeneity in comparable discrete- or continuous-time interactions. A total of 65 data sets from field studies have been analysed, in which percentage parasitism in relation to local host density have been recorded. In each case, estimated values of have been obtained by using a maximum likelihood procedure. The method also allows us to partition the CV 2 into the density dependent and density-independent components mentioned above. In 18 out of the 65 cases, total heterogeneity was at levels sufficient (if typical of the interactions) to stabilize the interacting populations (i.e. CV 2 > 1). Interestingly, in 14 of these it is the host-density-independent heterogeneity that contributes most to the total heterogeneity. Although heterogeneity has often been regarded as a complicating factor in population dynamics that rapidly leads to analytical intractability, this clearly need not necessarily be so. The CV 2 > 1 rule explains the consequences of heterogeneity for population dynamics in terms of a simple description of the heterogeneity itself, and provides a rough rule for predicting the effects of different kinds of heterogeneity on population regulation.

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Increased natural mortality at low abundance can generate an Allee effect in a marine fish

Royal Society Open Science ◽

10.1098/rsos.140075 ◽

2014 ◽

Vol 1 (2) ◽

pp. 140075 ◽

Cited By ~ 10

Author(s):

Anna Kuparinen ◽

Jeffrey A. Hutchings

Keyword(s):

Population Dynamics ◽

Population Growth ◽

Density Dependence ◽

Gadus Morhua ◽

Allee Effect ◽

Population Regulation ◽

Atlantic Cod ◽

Adult Mortality ◽

Natural Mortality ◽

Density Dependent

Negative density-dependent regulation of population dynamics promotes population growth at low abundance and is therefore vital for recovery following depletion. Inversely, any process that reduces the compensatory density-dependence of population growth can negatively affect recovery. Here, we show that increased adult mortality at low abundance can reverse compensatory population dynamics into its opposite—a demographic Allee effect. Northwest Atlantic cod ( Gadus morhua ) stocks collapsed dramatically in the early 1990s and have since shown little sign of recovery. Many experienced dramatic increases in natural mortality, ostensibly attributable in some populations to increased predation by seals. Our findings show that increased natural mortality of a magnitude observed for overfished cod stocks has been more than sufficient to fundamentally alter the dynamics of density-dependent population regulation. The demographic Allee effect generated by these changes can slow down or even impede the recovery of depleted populations even in the absence of fishing.

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Population dynamics in echinococcosis and cysticercosis: mathematical model of the life-cycles of Taenia hydatigena and T. ovis

Parasitology ◽

10.1017/s0031182000053555 ◽

1987 ◽

Vol 94 (1) ◽

pp. 181-197 ◽

Cited By ~ 49

Author(s):

M. G. Roberts ◽

J. R. Lawson ◽

M. A. Gemmell

Keyword(s):

Population Dynamics ◽

Life Cycle ◽

New Zealand ◽

Equation Model ◽

Life Cycles ◽

Control Measures ◽

Taenia Hydatigena ◽

Infection Pressure ◽

Lower Infection ◽

Compare And Contrast

SUMMARYIt is shown that under the conditions that prevailed in New Zealand in the late 1950s, Taenia hydatigena was hyperendemic, the life-cycle being regulated by a density-dependent constraint in the form of acquired immunity, and T. ovis was rare. The control measures that caused Echinococcus granulosus, which was endemic at the time, to decline towards extinction reduced T. hydatigena and T. ovis to endemic status only. A non-linear integrodifferential equation model, which was previously linearized to describe the life-cycle of E. granulosus in dogs and sheep in New Zealand, is used to describe the life-cycles of T. hydatigena and T. ovis. The model is then used to compare and contrast the population dynamics of these three species. The model is used to demonstrate that the endemic steady state is structurally unstable, and may be asymptotically unstable to small perturbations. It is also shown that despite the lower infection pressure experienced by the intermediate host in the endemic state, the numbers of larvae in sheep may be higher than in the hyperendemic state. Finally it is shown that the partial success of the control measures against T. hydatigena may have caused an increase in the numbers and prevalence of T. ovis larvae in sheep due to the reciprocal immunity between the two species.

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GENETIC FEEDBACK AND SIMULATED ENVIRONMENTAL CATASTROPHES

The Canadian Entomologist ◽

10.4039/ent1071343-12 ◽

1975 ◽

Vol 107 (12) ◽

pp. 1343-1348 ◽

Cited By ~ 1

Author(s):

William J. Sydor ◽

David Pimentel

Keyword(s):

Population Dynamics ◽

Control System ◽

Population Regulation ◽

Feedback System ◽

Plant Population ◽

Common Occurrence ◽

Feedback Systems ◽

Population Mean ◽

Density Dependent ◽

The Impact

AbstractAn investigation was made of the impact of a series of environmental catastrophes upon herbivore population regulation through density-dependent genetic feedback interactions with simulated plants. Mean density and amplitude of fluctuation of the herbivore in the control system (only susceptible alleles in the plant population) were higher than in the genetic feedback system (3 resistant alleles and 3 susceptible alleles in the plant population). Mean density and amplitude of fluctuation of the herbivores in the catastrophic system (only susceptible alleles in the plant population and the herbivore population subject to a series of environmental catastrophes) were lower than in the control and genetic feedback systems, but both mean density and amplitude of fluctuation were higher than in the genetic feedback and catastrophic system (3 resistant and 3 susceptible alleles in the plant population and the herbivore population subject to a series of environmental catastrophes). The results of this experiment suggest that genetic feedback can exert a controlling influence in population dynamics even in systems where environmental catastrophes are a common occurrence.

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