Possible evidence for mortality induced by the parasite Apatemon gracilis in a population of brook sticklebacks (Culaea inconstans)

Parasitology ◽  
1982 ◽  
Vol 84 (1) ◽  
pp. 41-47 ◽  
Author(s):  
D. M. Gordon ◽  
M. E. Rau
Keyword(s):  
Frequency Distribution ◽  
Parasite Burden ◽  
Fish Population ◽  
Fish Host ◽  
Culaea Inconstans ◽  
The Mean ◽  
Over Dispersion

SUMMARYRegular samples made on the 1978 cohort of brook sticklebacks (Culaea inconstans) from a swamp in Ile Perrot, Quebec, Canada were examined for Apatemon gracilis metacercariae. The prevalence of the parasite rapidly reached 100% in the fish population. The mean parasite burden increased from zero to a plateau of about 44 parasites/fish. Over-dispersion of the frequency distribution of parasites in the fish host, as measured by variance to mean ratios, increased to a peak and then decreased significantly while the mean parasite burden remained constant. The effects of parasite burden on the survival of the stickleback host are discussed, as well as the validity of the use of changes in over-dispersion for demonstrating parasite-induced mortality.

The use of frequency distributions in an attempt to detect host mortality induced by infections of diplostomatid metacercariae

Parasitology ◽  
1984 ◽  
Vol 89 (2) ◽  
pp. 209-220 ◽  
Author(s):  
C. R. Kennedy
Keyword(s):  
Small Sample Size ◽  
Parasite Burden ◽  
Fish Host ◽  
Small Sample ◽  
Host Age ◽  
Parasite Abundance ◽  
Frequency Distributions ◽  
Host Mortality ◽  
The Mean ◽  
Over Dispersion

SummaryFollowing recent suggestions that a peaked host age–parasite abundance curve, concomitant with a decline in the degree of dispersion of parasites in the older age classes of hosts, can provide evidence of parasite-induced host mortality, the changes in mean abundance and over-dispersion of metacercarial stages of Diplostomum spathaceum, D. gasterostei, Tylodelphys clavata and T. podicipina in relation to fish age were studied in a field locality. The mean parasite burden of D. spathaceum, D. gasterostei and T. clavata increased with host age and the maximum mean burden was found in the oldest hosts. The variance to mean ratio also increased in D. gasterostei, but decreased in the oldest hosts in D. spathaceum and T. clavata. It is concluded that this decrease could be due to parasite-induced host mortality but could equally be due to death of parasites within the host or to changes in infection rate or could be a reflection of the small sample size of the oldest fish. The mean burden of T. podicipina declined gradually with host age, but the variance to mean ratio remained constant and it is concluded that this could be explained by death of the parasites within the host. None of these data or data from other localities provided clear and unambiguous evidence of host mortality induced by heavy infections of any of the four species, although they are consistent with such mortality and do not refute such a possibility. It is concluded that it may be just as difficult to detect and unequivocally demonstrate parasite-induced host mortality in metacercarial digenean–fish host systems as in any other parasite–host systems.

Bias in Using an Age–Length Key to Estimate Age-Frequency Distributions

1978 ◽  
Vol 35 (2) ◽  
pp. 184-189 ◽  
Author(s):  
S. J. Westrheim ◽  
W. E. Ricker
Keyword(s):  
Frequency Distribution ◽  
Age Distribution ◽  
Length Distribution ◽  
Fish Population ◽  
Systematic Bias ◽  
Parental Age ◽  
Frequency Distributions ◽  
Class Strength ◽  
Key Words Age ◽  
Age Frequency Distribution

Consider two representative samples of fish taken in different years from the same fish population, this being a population in which year-class strength varies. For the "parental" sample the length and age of the fish are determined and are used to construct an "age–length key," the fractions of the fish in each (short) length interval that are of each age. For the "filial" sample only the length is measured, and the parental age–length key is used to compute the corresponding age distribution. Trials show that the age–length key will reproduce the age-frequency distribution of the filial sample without systematic bias only if there is no overlap in length between successive ages. Where there is much overlap, the age–length key will compute from the filial length-frequency distribution approximately the parental age distribution. Additional bias arises if the rate of growth if a year-class is affected by its abundance, or if the survival rate in the population changes. The length of the fish present in any given part of a population's range can vary with environmental factors such as depth of the water; nevertheless, a sample taken in any part of that range can be used to compute age from the length distribution of a sample taken at the same time in any other part of the range, without systematic bias. But this of course is not likely to be true of samples taken from different populations of the species. Key words: age–length key, bias, Pacific ocean perch, Sebastes alutus

PARAMETER ESTIMATION ON HURDLE POISSON REGRESSION MODEL WITH CENSORED DATA

2012 ◽  
Vol 57 (1) ◽  
Author(s):  
SEYED EHSAN SAFFAR ◽  
ROBIAH ADNAN ◽  
WILLIAM GREENE
Keyword(s):  
Regression Model ◽  
Count Data ◽  
Poisson Regression ◽  
Goodness Of Fit ◽  
Poisson Model ◽  
Likelihood Method ◽  
Poisson Regression Model ◽  
Response Variable ◽  
The Mean ◽  
Over Dispersion

A Poisson model typically is assumed for count data. In many cases, there are many zeros in the dependent variable and because of these many zeros, the mean and the variance values of the dependent variable are not the same as before. In fact, the variance value of the dependent variable will be much more than the mean value of the dependent variable and this is called over–dispersion. Therefore, Poisson model is not suitable anymore for this kind of data because of too many zeros. Thus, it is suggested to use a hurdle Poisson regression model to overcome over–dispersion problem. Furthermore, the response variable in such cases is censored for some values. In this paper, a censored hurdle Poisson regression model is introduced on count data with many zeros. In this model, we consider a response variable and one or more than one explanatory variables. The estimation of regression parameters using the maximum likelihood method is discussed and the goodness–of–fit for the regression model is examined. We study the effects of right censoring on estimated parameters and their standard errors via an example.

scholarly journals Seasonal Variation and Frequency Distribution of Ectoparasites in Crossbreed Cattle in Southeastern Brazil

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Maria do Socorro Ferraz da Costa ◽  
Marcos Pezzi Guimarães ◽  
Walter dos Santos Lima ◽  
Ana Julia Ferraz da Costa ◽  
Elias Jorge Facury Filho ◽  
...  
Keyword(s):  
Seasonal Variation ◽  
Frequency Distribution ◽  
Minas Gerais ◽  
Climatic Conditions ◽  
Climatic Factor ◽  
Boophilus Microplus ◽  
Field Conditions ◽  
Southeastern Brazil ◽  
Minas Gerais State ◽  
The Mean

The aims of this study were to evaluate the seasonal variation and frequency distribution of Rhipicephalus (Boophilus) microplus, Haematobia irritans, and Dermatobia hominis on crossbred heifers under field conditions in the northeast of Minas Gerais state, southeastern Brazil. From November 2007 to September 2009 (23 months), 40 heifers aged 16.6±2.4 months were divided into groups A (1/4 Holstein × 3/4 Gir) and B (1/2 Holstein × 1/2 Gir) and had the monthly infestation estimated along with the climatic conditions. The mean maximum and minimum temperatures were 28.5 and 19°C, respectively. The ectoparasites were present on animals in all months of the year. The levels of ticks on the animals were low (3.0±0.2 ticks/animal), with the highest density in midwinter. The temperature was the climatic factor that most influenced the tick levels. The population of H. irritans (13.9±0.3 flies/animal) and D. hominis (1.5±0.2 larvae/animal) on heifers was more influenced by rainfall and exhibited two population peaks during the year. 1/2 Holstein heifers harbored significantly more H. irritans and D. hominis than 1/4 Holstein heifers. The results are discussed considering the most appropriate periods to apply ectoparasiticides and the genetic make-up of the animals.

The Population of a Trout Stream and the Survival of Released Fish

1958 ◽  
Vol 9 (3) ◽  
pp. 319 ◽  
Author(s):  
AG Nicholls
Keyword(s):  
Salmo Trutta ◽  
Age Groups ◽  
River System ◽  
Fish Population ◽  
Curvilinear Relationship ◽  
Growth And Survival ◽  
Younger Age ◽  
Brown Trout Salmo Trutta ◽  
Preceding Season ◽  
The Mean

The fish population of a river system was studied by electro-fishing in 25 places, after which 1000 marked yearling brown trout, Salmo trutta L., were released at each of 10 sites. In a re-examination 8 to 9 months after the release it was estimated that about 10 per cent. of these were surviving; the survival after 18 months was estimated to be below 5 per cent., and the survival to takable size, at about 3 years of age, at 2 per cent. At no site were the younger age groups of the natural population truly represented in either season, but the numbers of older fish in the second season were greater than those of the corresponding year classes in the preceding season, showing that the streams receive recruitment of younger fish from other sources. Some evidence is produced to show that "nursery" streams provide the source of recruitment. The average annual mortality for fish of 2 and 3 years of age is estimated at from 70 to 80 per cent. for the system. It is estimated that there were about 45,000 takable fish in this river system at the beginning of each season. It is shown that the mean lengths of trout decrease with increasing density of population, and that there is a curvilinear relationship between population density and total weight of all fish per acre. The standing crop of trout at different sites ranged from 1 to 182 lb/acre over the two seasons. The condition factor showed a decrease with increasing age of the fish, and the released fish had a lower factor than resident fish of the same age at all sites. In general there was a relationship between the depth of water and the length of the fish, sections over 14 in. deep having greater populations of larger fish. A study of the ability of each section of stream to carry fish, based on the lengths and condition factors of the fish, the number and weight of the population per acre, and the ability of each section to absorb additions to the population, shows that where populations were low, conditions were Iess favourable to the growth and survival of fish.

scholarly journals 23. Ambulance Sphygmomanometer Accuracy: Can It Affect Triage to the Trauma Center?

1996 ◽  
Vol 11 (S2) ◽  
pp. S33-S33
Author(s):  
Charles E. Cady ◽  
Ronald G. Pirrallo ◽  
Clarence E. Grim
Keyword(s):  
Blood Pressure ◽  
Systolic Blood Pressure ◽  
Blunt Trauma ◽  
Frequency Distribution ◽  
Trauma Center ◽  
Trauma Patients ◽  
Cross Sectional ◽  
Industry Standards ◽  
Study Population ◽  
The Mean

Objectives: To determine the accuracy of sphygmomanometers (SPHYGs) from a metropolitan EMS system and quantitate the mis-triage of adult blunt trauma patients based on erroneous systolic blood pressure (SBP) readings.Methods-A: A cross-sectional, convenient sample of 150 SPHYGs was checked for accuracy using industry standards. Mean high and low deviations were calculated at 90 mmHg.Methods-B: Retrospectively, a frequency distribution of the initial SBPs of all blunt trauma patients, age ≥21, seen in 1994 was plotted to characterize our study population. The numbers of patients potentially over- or under-triaged were identified when their reported SBP was corrected for using the mean high and low deviation plus 2 SDs.Results-A: Overall, 25.3% of the SPHYGs were inaccurate. At 90 mmHg, 28.0% (42/150) were inaccurate with 16.7% (7/42) high by 4.6±1.5 mmHg and 81.0% (34/42) low by 6.2±4.2 mmHg; one was inoperable.Results-B: 1,005 adult blunt trauma patients were evaluated; 61 were eliminated: 35 had initial SBPs of 0 mmHg and 26 had no SBP recorded (n = 944). The mean initial SBP was 138 ±30mmHg, and 3.8% (36/944) of the patients had SBPs <90 mmHg. Potentially, 2.0% (19/944) of the patients were undertriaged (initial erroneously high SBP reading 90–98 mmHg) and 2.5% (24/944) over-triaged (initial erroneously low SBP reading 74–90 mmHg).

scholarly journals Stability of Asteroidal Motion in the Hecuba Gap

1974 ◽  
Vol 62 ◽  
pp. 77-79 ◽  
Author(s):  
H. Scholl ◽  
R. Giffen
Keyword(s):  
Frequency Distribution ◽  
Mean Motion ◽  
The Mean ◽  
Hecuba Gap ◽  
Asteroidal Motion

There exist gaps in the frequency distribution of the osculating mean motions of the asteroids. In these gaps, the mean motions of the asteroids are commensurable to Jupiter's mean motion.

scholarly journals Ultrastructural Differences Between Thymic and Lymph Node Small Lymphocytes of Mice: Nucleolar Size and Cytoplasmic Volume

Blood ◽  
1967 ◽  
Vol 30 (3) ◽  
pp. 288-300 ◽  
Author(s):  
H. J. HEINIGER ◽  
H. RIEDWYL ◽  
H. GIGER ◽  
B. SORDAT ◽  
H. COTTIER
Keyword(s):  
Lymph Node ◽  
Lymph Nodes ◽  
Frequency Distribution ◽  
Cross Section ◽  
Rna Turnover ◽  
Size Frequency Distribution ◽  
Particle Size Analyzer ◽  
Nucleolar Volume ◽  
The Mean ◽  
Uniform Population

Abstract Ultrastructural differences between small lymphocytes of the thymic cortex and those located in the cortical zone of lymph nodes of mice were examined by electron microscopy and cytometric methods. The particle size analyzer TGZ 3 (Zeiss) was used to measure the size-frequency distribution of nucleolar cross-section diameters, and the resulting data were computed mathematically and statistically to determine the corresponding mean volumina. It could be shown that thymic, as compared to lymph node cortical small lymphocytes, (1) have a smaller mean nucleolar volume (0.11µ3 versus 0.46µ3); (2) represent a more uniform population with regard to the frequency distribution of the nucleolar cross section diameters; and (3) are of smaller size due to less cytoplasm, while the mean nuclear volume does not differ significantly from that of small lymphocytes located in the cortex of lymph nodes. These findings are discussed in relation to qualitative ultrastructural peculiarities and probable differences in the magnitude of RNA turnover as estimated by the use of tritiated cytidine. The possible significance of cytometrically defined populations of small lymphocytes with regard to sensitized and nonsensitized cells is considered.

Fish population size, and not density, as the determining factor of parasite infection: a case study

Parasitology ◽  
2004 ◽  
Vol 128 (3) ◽  
pp. 305-313 ◽  
Author(s):  
A. M. BAGGE ◽  
R. POULIN ◽  
E. T. VALTONEN
Keyword(s):  
Species Richness ◽  
Population Density ◽  
Population Size ◽  
Fish Population ◽  
Host Population ◽  
Fish Length ◽  
Total Fish ◽  
Infection Parameters ◽  
The Mean

The diversity and abundance of parasites vary widely among populations of the same host species. These infection parameters are, to some extent, determined by characteristics of the host population or of its habitat. Recent studies have supported predictions derived from epidemiological models regarding the influence of host population density: parasite abundance and parasite species richness are expected to increase with increasing host population density, at least for directly transmitted parasites. Here, we test this prediction using a natural system in which populations of the crucian carp, Carassius carassius (L.), occur alone, with no other fish species, in a series of 9 isolated ponds in Finland. The ectoparasite communities in these fish populations consist of only 4 species of monogeneans (Dactylogyrus formosus, D. wegeneri, D. intermedius and Gyrodactylus carassii); the total and relative abundance of these 4 species varies among ponds, with one or two of the species missing from certain ponds. Across ponds, only one factor, total fish population size, explained a significant portion of the variance in both the mean number of monogenean species per fish and the mean total abundance of monogenean individual per fish. In contrast, fish population density did not influence either monogenean abundance or species richness, and neither did any of the other variables investigated (mean fish length per pond, number of fish examined per pond, distance to the nearest lake, and several water quality measures). In our system, proximity among fish individuals (i.e. host population density) may not be relevant to the proliferation of monogeneans; instead, the overall availability of host individuals in the host population appeared to be the main constraint limiting parasite population growth.

The dynamics of infection of Tribolium confusum by Hymenolepis diminuta: the influence of exposure time and host density

Parasitology ◽  
1982 ◽  
Vol 84 (1) ◽  
pp. 157-166 ◽  
Author(s):  
Anne Keymer
Keyword(s):  
Exposure Time ◽  
Parasite Burden ◽  
Host Density ◽  
Faecal Pellet ◽  
Experimental Results ◽  
Hymenolepis Diminuta ◽  
Parasite Transmission ◽  
Experimental Conditions ◽  
Instantaneous Rate ◽  
The Mean

SUMMARYSurvival of Hymenolepis diminuta eggs (as measured by their infectivity to the intermediate host) was found to be age-dependent with an expected value of 11 days when the eggs were retained within the faecal pellet at 10 °C. The expected life-span of eggs under experimental conditions (i.e. extracted from faecal material and placed on filter paper at 30 °C) was estimated as 33 min. The mean parasite burden of populations of Tribolium exposed to known densities of H. diminuta eggs was found to rise to a plateau with increasing exposure time. The experimental results provided a method of estimating the instantaneous rate of parasite transmission: a value of 0·0004/egg/min/host/13 cm2 was obtained. The mean parasite burden of populations of T. confusum exposed to known densities of H. diminuta eggs was found to decrease exponentially with increasing host density. A second estimate of the instantaneous rate of parasite transmission of 0·004/egg/min/host/13 cm2 was obtained from the experimental results. No differences in susceptibility to infection between 2-week-old male and female beetles were found. A marked decrease, however, was apparent with increasing beetle age up to 14 weeks post-eclosion.

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