scholarly journals Evidence for Allee effects in an over-harvested marine gastropod: density-dependent mating and egg production

2000 ◽  
Vol 202 ◽  
pp. 297-302 ◽  
Author(s):  
AW Stoner ◽  
M Ray-Culp
Keyword(s):  
Egg Production ◽  
Allee Effects ◽  
Marine Gastropod ◽  
Density Dependent

The regulation ofOstertagia ostertagipopulations in calves: density-dependent control of fecundity

Parasitology ◽  
1987 ◽  
Vol 95 (2) ◽  
pp. 373-388 ◽  
Author(s):  
G. Smith ◽  
B. T. Grenfell ◽  
R. M. Anderson
Keyword(s):  
Worm Burden ◽  
Egg Production ◽  
Inverse Function ◽  
Single Infection ◽  
Intensity Of Infection ◽  
Density Dependent ◽  
Helminth Infections ◽  
Model Predictions ◽  
Initial Peak ◽  
Infection Experiments

SUMMARYThe decline in faecal egg counts, characteristic of calves which have been experimentally infected withOstertagia ostertagi, is analysed using a mathematical model in which parasite fecundity is assumed to be an inverse function of both the duration and intensity of infection. The model incorporates a description of the frequency distribution of mature parasites between hosts (which is less over-dispersed than is usual for many other helminth infections). The model provides a good overall description of the decline in faecal egg production observed during trickle and single infection experiments. The main discrepancy between a comparison of the model predictions and the results of the most detailed available series of trickle infection experiments occurs at the initial peak of egg production. The magnitude of this difference appears to be related to the worm burden at the peak of egg production. The possible mechanisms underlying density-dependent regulation of the fecundity ofO. ostertagiaare discussed.

Density‐dependent egg production in chub mackerel in the Kuroshio Current system

2020 ◽  
Vol 30 (1) ◽  
pp. 38-50
Author(s):  
Akinori Takasuka ◽  
Michio Yoneda ◽  
Yoshioki Oozeki
Keyword(s):  
Egg Production ◽  
Current System ◽  
Kuroshio Current ◽  
Chub Mackerel ◽  
Density Dependent ◽  
The Kuroshio

Disentangling density‐dependent effects on egg production and survival from egg to recruitment in fish

2019 ◽  
Vol 20 (5) ◽  
pp. 870-887 ◽  
Author(s):  
Akinori Takasuka ◽  
Michio Yoneda ◽  
Yoshioki Oozeki
Keyword(s):  
Egg Production ◽  
Density Dependent

scholarly journals A generic population model for the African tick Rhipicephalus appendiculatus

Parasitology ◽  
1997 ◽  
Vol 115 (3) ◽  
pp. 265-279 ◽  
Author(s):  
S. E. RANDOLPH ◽  
D. J. ROGERS
Keyword(s):  
South Africa ◽  
Population Model ◽  
Egg Production ◽  
Population Analysis ◽  
Rhipicephalus Appendiculatus ◽  
Mortality Factors ◽  
Density Dependent ◽  
Tick Abundance ◽  
Annual Range ◽  
Parameter Values

We present a simulation population model for the African tick Rhipicephalus appendiculatus, based on previous analyses of the mortality factors most closely correlated with observed population changes at 11 sites in equatorial and South Africa. The model incorporates temperature-dependent rates of egg production and development, climate-driven density-independent mortality rates, particularly during the adult-larval stage, and density-dependent regulation of both nymphs and adults. Diapause is also included for tick populations in southern Africa. The model successfully describes both the seasonality and annual range of variation in numbers of each tick stage observed at each of 4 test sites in Uganda, Burundi and South Africa. Sensitivity analysis showed that the final version of the model is robust to 4-fold variation in most parameter values (that were per force based on informed guesses), but is more sensitive to the regression coefficients determining density-dependent interstadial mortality (that were derived from analysis of field data). The model is able to predict the seasonality of ticks from a site in Kenya where a full prior population analysis was not possible because only adults and nymphs had been counted. The model is potentially applicable to other species of ticks, both tropical and temperate, to predict tick abundance and seasonality as risk factors for tick-borne diseases.

scholarly journals Recruitment dynamics of the Gulf of Riga herring stock: density-dependent and environmental effects

2010 ◽  
Vol 67 (9) ◽  
pp. 1914-1920 ◽  
Author(s):  
Tiit Raid ◽  
Georgs Kornilovs ◽  
Ain Lankov ◽  
Anne-Marin Nisumaa ◽  
Heli Shpilev ◽  
...  
Keyword(s):  
Environmental Effects ◽  
Egg Production ◽  
Age Groups ◽  
Zooplankton Community ◽  
Density Dependent ◽  
Current Period ◽  
Open Sea ◽  
Gulf Of Riga ◽  
The Baltic ◽  
Peak Abundance

Abstract Raid, T., Kornilovs, G., Lankov, A., Nisumaa, A-M., Shpilev, H., and Järvik, A. 2010. Recruitment dynamics of the Gulf of Riga herring stock: density-dependent and environmental effects. – ICES Journal of Marine Science, 67: 1914–1920. The Gulf of Riga and open-sea stocks of the Baltic herring have displayed remarkably consistent inverse recruitment and stock development patterns since the 1970s: the open-sea stocks steadily declined, whereas the Gulf stock increased rapidly in the early 1990s, reaching a peak abundance in the early 2000s and exceeding the level of the 1970s by a factor of 2–3. The increase was accompanied by a decline in the mean weight-at-age and the condition factor. The estimated decline (by 30–40%) in the average annual consumption rate per individual and changes observed in the zooplankton community suggest that density-dependent effects may have increased since the 1970s. The current period of high stock sizes is also characterized by greater recruitment variability. Historical fecundity investigations have established that the average egg production per individual has decreased in all age groups by 20–50%, along with a decrease in mean weight and condition. Yet, the effect on recruitment has been low so far, because lower fecundity has been compensated by the greater abundance and population fecundity has been maintained at the original level. Recruitment appears to be more influenced by environmental conditions than by spawning-stock biomass.

scholarly journals Modeling the effects of density dependent emigration, weak Allee effects, and matrix hostility on patch-level population persistence

2020 ◽  
Vol 17 (2) ◽  
pp. 1718-1742 ◽  
Author(s):  
James T. Cronin ◽  
◽  
Nalin Fonseka ◽  
Jerome Goddard II ◽  
Jackson Leonard ◽  
...  
Keyword(s):  
Population Persistence ◽  
Level Population ◽  
Allee Effects ◽  
Density Dependent ◽  
Effects Of Density

scholarly journals Revisiting density-dependent fecundity in schistosomes using sibship reconstruction

2021 ◽  
Vol 15 (5) ◽  
pp. e0009396
Author(s):  
M. Inês Neves ◽  
Charlotte M. Gower ◽  
Joanne P. Webster ◽  
Martin Walker
Keyword(s):  
Statistical Power ◽  
Egg Production ◽  
High Sensitivity ◽  
Monitoring And Evaluation ◽  
Statistical Modelling ◽  
Dependent Manner ◽  
Density Dependent ◽  
Helminth Infections ◽  
Modelling Assumptions ◽  
The Stability

The stability of parasite populations is regulated by density-dependent processes occurring at different stages of their life cycle. In dioecious helminth infections, density-dependent fecundity is one such regulatory process that describes the reduction in egg production by female worms in high worm burden within-host environments. In human schistosomiasis, the operation of density-dependent fecundity is equivocal and investigation is hampered by the inaccessibility of adult worms that are located intravascularly. Current understanding is almost exclusively limited to data collected from two human autopsy studies conducted over 40 years ago, with subsequent analyses having reached conflicting conclusions. Whether egg production is regulated in a density-dependent manner is key to predicting the effectiveness of interventions targeting the elimination of schistosomiasis and to the interpretation of parasitological data collected during monitoring and evaluation activities. Here, we revisit density-dependent fecundity in the two most globally important human Schistosoma spp. using a statistical modelling approach that combines molecular inference on the number of parents/adult worms in individual human hosts with parasitological egg count data from mainland Tanzania and Zanzibar. We find a non-proportional relationship between S. haematobium egg counts and inferred numbers of female worms, providing the first clear evidence of density-dependent fecundity in this schistosome species. We do not find robust evidence for density-dependent fecundity in S. mansoni because of high sensitivity to some modelling assumptions and the lower statistical power of the available data. We discuss the strengths and limitations of our model-based analytical approach and its potential for improving our understanding of density dependence in schistosomiasis and other human helminthiases earmarked for elimination.

scholarly journals When higher carrying capacities lead to faster propagation

2018 ◽  
Author(s):  
Marjorie Haond ◽  
Thibaut Morel-Journel ◽  
Eric Lombaert ◽  
Elodie Vercken ◽  
Ludovic Mailleret ◽  
...  
Keyword(s):  
Carrying Capacity ◽  
Invasion Biology ◽  
Reaction Diffusion Equations ◽  
Positive Density ◽  
Allee Effects ◽  
Demographic Stochasticity ◽  
Positive Dependence ◽  
Density Dependent ◽  
Temporal Models ◽  
Density Dependent Dispersal

AbstractThis preprint has been reviewed and recommended by Peer Community In Ecology (https://dx.doi.org/10.24072/pci.ecology.100004). Finding general patterns in the expansion of natural populations is a major challenge in ecology and invasion biology. Classical spatio-temporal models predict that the carrying capacity (K) of the environment should have no influence on the speed (v) of an expanding population. We tested the generality of this statement with reaction-diffusion equations, stochastic individual-based models, and microcosms experiments with Trichogramma chilonis wasps. We investigated the dependence between K and v under different assumptions: null model (Fisher-KPP-like assumptions), strong Allee effects, and positive density-dependent dispersal. These approaches led to similar and complementary results. Strong Allee effects, positive density-dependent dispersal and demographic stochasticity in small populations lead to a positive dependence between K and v. A positive correlation between carrying capacity and propagation speed might be more frequent than previously expected, and be the rule when individuals at the edge of a population range are not able to fully drive the expansion.

Effects of host characteristics and parasite intensity on growth and fecundity ofTrichostrongylus retortaeformisinfections in rabbits

Parasitology ◽  
2009 ◽  
Vol 136 (1) ◽  
pp. 117-123 ◽  
Author(s):  
C. CHYLINSKI ◽  
B. BOAG ◽  
M. J. STEAR ◽  
I. M. CATTADORI
Keyword(s):  
Parasite Density ◽  
Egg Production ◽  
Negative Relationship ◽  
In Utero ◽  
Major Influence ◽  
Parasitic Nematodes ◽  
Host Age ◽  
Density Dependent ◽  
Parasite Intensity ◽  
Host Characteristics

SUMMARYHost-mediated responses and parasite density-dependent processes can have a major influence on the growth and fecundity of parasitic nematodes. However, host characteristics and parasite intensity consistently change during the course of an infection and these could affect worm length and number of eggs in a non-constant way. We used a free-living population of rabbits naturally infected withTrichostronglyus retortateformisand examined how adult nematode length and the number of eggsin uterowere affected by host characteristics (i.e. age, sex, breeding status) and parasite intensity, in a seasonal environment, between 2004 and 2007. Nematode length and number of eggsin uterodecreased exponentially with host age; in contrast, parasite intensity increased, peaked in juveniles and decreased in older hosts. These patterns were consistent between rabbit cohorts. A negative relationship was observed between parasite intensity and nematode length, as well as number of eggs. Nematode length was strongly affected by nematode sex and host age, while the number of eggs was mainly influenced by nematode length. The direct influence of host-mediated effects appeared quantitatively more important than parasite density dependence in controlling length and egg production in naturally infected wild rabbits. However, their relative contribution changed during the course of the infection such that, while host immunity still influenced worm numbers, the direct effect of density-dependent interactions contributed the most at high parasite intensities.

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