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The combined effect of temperature and age on development, survival, attack rate, and oviposition of the parasitoid Spalangia cameroni (Perkins) (Hymenoptera: Pteromalidae) exploiting house fly pupae was investigated by conducting... more
The combined effect of temperature and age on development, survival, attack rate, and oviposition of the parasitoid Spalangia cameroni (Perkins) (Hymenoptera: Pteromalidae) exploiting house fly pupae was investigated by conducting life-table experiments at 15, 20, 25, 30 and 35°C. Temperature had a pronounced effect on survival and development of the immature stages. Survival was highest at 25°C, where 88.5% of the parasitized host pupae resulted in adult parasitoids, and lowest at 35°C when only 3.78% emerged. Females constituted between 50% (at 20°C) and 100% (at 35°C) of the surviving immatures. Males developed faster than females, with the shortest developmental times at 30°C (18.18 d for males and 19.41 d for females). Longevity of adult females decreased with temperature from 80 d at 15°C to 18 d at 35°C. Total attack rate of female parasitoids was highest at 20°C (106 hosts per female), and life-time reproduction highest at 20°C and 25°C (about 60 offspring per female). Sex ratio was female biased (65% females). A generic model was used to estimate and predict the temperature effect on the intrinsic rate of increase (rm), the net reproduction rate (R0), and the generation time (G). The model predicted that rm peaks at 33.5°C (rm = 0.182 d(-1)), that maximum R0 is reached at 27.2°C (R0 = 50.2), and that the shortest generation time occurs at 34.5°C (G = 21.1 d). Doubling time was 4.19 d at 33°C. In the temperature range between 20°C and 30°C, S. cameroni has the potential to be an efficient control agent against nuisance flies.
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During the last decade, the study of fluctuating asymmetry (FA) in relation to different fitness aspects has become a popular issue in evolutionary biology. FA is suggested to be important as an index of selective advantage in hoth sexual... more
During the last decade, the study of fluctuating asymmetry (FA) in relation to different fitness aspects has become a popular issue in evolutionary biology. FA is suggested to be important as an index of selective advantage in hoth sexual and natural selection, Evidence for these hypotheses is obtained from field studies in which FA is found to be negatively correlated with various fitness components. In this paper, we demonstrate that the apparent significance of FA may depend on assumptions of linearity between size of a trait and FA, and between trait size and fitness. By means of numerical examples, we show that even small, and probably common, deviations from the assumed linearity can bias the statistical analyses to such an extent that it casts serious doubt on the validity of the postulated causal relationship between FA and fitness. We recommend reanalyses of existing data and emphatically suggest that the underlying statistical assumptions are critically evaluated in future studies of FA, especially concerning linear relationships between the variables.
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Research Interests: Zoology and Seasonality
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A simulation model was used to predict how temperature influences biological control of stable flies (Stomoxys calcitrans (L.)) by the pupal parasitoid Spalangia cameroni. Temperature, which was either constant or fluctuated due to... more
A simulation model was used to predict how temperature influences biological control of stable flies (Stomoxys calcitrans (L.)) by the pupal parasitoid Spalangia cameroni. Temperature, which was either constant or fluctuated due to seasonal variation and/or environmental stochasticity, was modeled as a first order autocorrelation process. The simulations showed that stable flies could tolerate a wider temperature interval than expected from their thermal performance curve (TPC). This was attributed to the fact that immature flies develop in manure, which protects them against low air temperatures. In contrast, the parasitoids were found to have a narrower thermal tolerance range than expected from their TPC. This was attributed to the temperature-dependent functional response of S. cameroni, which was a limiting factor for the parasitoid’s development and survival when host densities were low at suboptimal temperatures. The effects of seasonal variation on critical thermal limits we...
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The population fluctuations of spider mites on different soybean cultivars were studied in two experiments performed in the municipalities of São Sepé (experiment 1) and Santa Maria (experiment 2) in the state of Rio Grande do Sul,... more
The population fluctuations of spider mites on different soybean cultivars were studied in two experiments performed in the municipalities of São Sepé (experiment 1) and Santa Maria (experiment 2) in the state of Rio Grande do Sul, Brazil. The number of cultivars was 20 in São Sepé and 25 in Santa Maria, and at each location leaves were sampled from 15 plants per cultivar every week throughout the entire plant developmental cycle, amounting to 11 and 10 samplings in experiment 1 and 2, respectively. The statistical analysis revealed that mite densities varied significantly with cultivar and time. Besides, the interaction between soybean cultivars and sampling times was significant at both locations. This indicates that the populations did not vary in the same way among cultivars over time, which is attributed to differences among the cultivars with respect to their phenology and response to spider mites. Equations for describing the mite population dynamics were estimated for each c...
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The role of herbivore-induced volatile substances in prey-finding by phytoseiid mites has been repeatedly documented using an olfactometer. The objective of the present paper is to test the hypothesis that movement by Phytoseiulus... more
The role of herbivore-induced volatile substances in prey-finding by phytoseiid mites has been repeatedly documented using an olfactometer. The objective of the present paper is to test the hypothesis that movement by Phytoseiulus persimilis is affected by these volatiles even on plants. Two series of laboratory experiments were carried out. In the first series we studied searching behavior of P. persimilis females on young bean plants in which a single leaf was infested with spider mites. The effect of spider mite colony location on the walking pattern of predatory mites while on a leaf was studied in the second series of experiments. We found that P. persimilis individuals were unable to discriminate between infested and uninfested leaves when they walked up the stem of a bean plant. On the other hand, results of the second series of experiments indicate that walk was not random once a predator was on the leaf surface since it was attracted to the spider mite patch, at least over ...
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The horse chestnut leaf miner Cameraria ohridella (Lepidoptera: Gracillariidae) is an invasive pest of horse chestnut and has spread through Europe since 1985. The horse chestnut leaf blotch Guignardia aesculi (Botryosphaeriales:... more
The horse chestnut leaf miner Cameraria ohridella (Lepidoptera: Gracillariidae) is an invasive pest of horse chestnut and has spread through Europe since 1985. The horse chestnut leaf blotch Guignardia aesculi (Botryosphaeriales: Botryosphaeriaceae) is a fungal disease that also seriously damages horse chestnut trees in Europe. The interaction between the leaf miner and the fungus has not yet been sufficiently described. Therefore, the aim of the present study was to assess leaf damage inflicted to horse chestnut by both C. ohridella and G. aesculi during the vegetation season and to model their interaction. The damage to leaf area was measured monthly from May to September 2013 in České Budějovice, the Czech Republic. A simple phenomenological model describing the expected dynamics of the two species was developed. The study revealed a significant effect of sampling site and sampling period on the damage caused by both the pest and the fungus. The mathematical model indicates that ...
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Short-term effects on consumption and oviposition rates of four strains of Neoseiulus californicus (McGregor) after a diet shift were evaluated. The new feeding conditions experienced by the predators were six fixed densities of eggs or... more
Short-term effects on consumption and oviposition rates of four strains of Neoseiulus californicus (McGregor) after a diet shift were evaluated. The new feeding conditions experienced by the predators were six fixed densities of eggs or protonymphs of Tetranychus urticae Koch placed on excised strawberry leaflet discs and maintained under laboratory conditions (25 +/- 1 degrees C, 75-85% RH, 16L: 8D). The observations were made on the first and the fifth day of the experiment. The phytoseiids came from three long-term mass-reared strains fed on T. urticae, Dermatophagoidesfarinae Hughes, or Quercus spp. pollen, respectively. The fourth strain was collected directly in a strawberry field. Time since diet transfer can be added to the factors (i.e. feeding history and prey density) already known to affect the functional and numerical responses of N. californicus, both when it feeds on prey eggs and protonymphs. If consumption rates were averaged over all strains and densities, 9.04 and...
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(1) Temporal variations in the average population densities of the phytoseiid predator Phytoseiulus persimilis and its prey, the two-spotted spider mite (Tetranychus urticae), were followed during 23 weeks in three commercial... more
(1) Temporal variations in the average population densities of the phytoseiid predator
Phytoseiulus persimilis and its prey, the two-spotted spider mite (Tetranychus urticae),
were followed during 23 weeks in three commercial glasshouses. Both species showed clear oscillations attributablet o predatora nd prey interactions.
(2) Analyses of variance show that the populations become more unevenly distributed,
both vertically and horizontally, within the glasshouses as the population densities increase.
(3) The variance/mean relationship of both species is shown to obey Taylor's power law.
(4) The negative binomial and the Polya-Aeppli distributions have been fitted to the
empirical distributions. The negative binomial gives, in general, the best agreement.
(5) The parameter k of the negative binomial distribution is shown to be density
dependent. Maximum likelihood estimates of k are compared with model predicted values but the quantitative agreement is rather poor. They agree, however, reasonably well,qualitatively.
(6) Spatial coincidence between the two species is expressed by the correlation
coefficient. The predator population seems to be better distributed relative to the prey as the density of either population increases.
Phytoseiulus persimilis and its prey, the two-spotted spider mite (Tetranychus urticae),
were followed during 23 weeks in three commercial glasshouses. Both species showed clear oscillations attributablet o predatora nd prey interactions.
(2) Analyses of variance show that the populations become more unevenly distributed,
both vertically and horizontally, within the glasshouses as the population densities increase.
(3) The variance/mean relationship of both species is shown to obey Taylor's power law.
(4) The negative binomial and the Polya-Aeppli distributions have been fitted to the
empirical distributions. The negative binomial gives, in general, the best agreement.
(5) The parameter k of the negative binomial distribution is shown to be density
dependent. Maximum likelihood estimates of k are compared with model predicted values but the quantitative agreement is rather poor. They agree, however, reasonably well,qualitatively.
(6) Spatial coincidence between the two species is expressed by the correlation
coefficient. The predator population seems to be better distributed relative to the prey as the density of either population increases.
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ABSTRACT We present a general and flexible mathematical model (called SANDY) that can be used to describe many biological phenomena, including the phenology of arthropods. In this paper, we demonstrate how the model can be fitted to vital... more
ABSTRACT We present a general and flexible mathematical model (called SANDY) that can be used to describe many biological phenomena, including the phenology of arthropods. In this paper, we demonstrate how the model can be fitted to vital rates (i.e., rates associated with development, survival, hatching, and oviposition) of the two-spotted spider mite (Tetranychus urticae (Koch)) exposed to different constant temperatures ranging from 15°C to 37.5°C. SANDY was incorporated into an age-, stage- and sex-structured dynamic model, which was fitted to cohort life-tables of T. urticae conducted at five constant temperatures (15, 20, 25, 30, and 35°C). Age- and temperature-dependent vital rates for the three main stages (eggs, immatures, and adults) constituting the life-cycle of mites were adequately described by the SANDY model. The modeling approach allows for simulating the growth of a population in a variable environment.We compared the predicted net reproductive rate (R0) and intrinsic rate of natural increase (rm ) at fluctuating temperatures with empirical values obtained from life-table experiments conducted at temperatures that changed with a daily amplitude (±0, ±3, ±6, ±9, and ±12°C) around an average of 22°C. Results show that R0 decreases with increasing amplitude, while rm is more robust to variable temperatures. An advantage of SANDY is that the same simple mathematical expression can be applied to describe all the vital rates. Besides, the approach is not confined to modeling the influence of a single factor on population growth but allows for incorporating the combined effect of several limiting factors, provided that the combined effect of the factors is multiplicative.
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Short-term effects on consumption and oviposition rates of four strains of Neoseiulus californicus (McGregor) after a diet shift were evaluated. The new feeding conditions experienced by the predators were six fixed densities of eggs or... more
Short-term effects on consumption and oviposition rates of four strains of Neoseiulus californicus (McGregor) after a diet shift were evaluated. The new feeding conditions experienced by the predators were six fixed densities of eggs or protonymphs of Tetranychus urticae Koch placed on excised strawberry leaflet discs and maintained under laboratory conditions (25 +/- 1 degrees C, 75-85% RH, 16L: 8D). The observations were made on the first and the fifth day of the experiment. The phytoseiids came from three long-term mass-reared strains fed on T. urticae, Dermatophagoidesfarinae Hughes, or Quercus spp. pollen, respectively. The fourth strain was collected directly in a strawberry field. Time since diet transfer can be added to the factors (i.e. feeding history and prey density) already known to affect the functional and numerical responses of N. californicus, both when it feeds on prey eggs and protonymphs. If consumption rates were averaged over all strains and densities, 9.04 and...
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Research Interests: Evolutionary Biology, Control, Biology, Interaction, Competition, and 15 moreDISTRIBUTION, Deviance, Investment, Ant, Frequency, Clutch Size, Logistic, Hypothesis, FIT, Distribution, Factor, Logit, Dimorphism, Level, and Binomial
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... Frylestam, unpubl.). Haren er polygam og hunharen (sætteren) kan i det tidlige forår, hvor vegetation stadig er kort, ofte ses ifølge med flere hanner (ramlere). Sætteren er drægtig i 42-43 dage og kan befrugtes med næste kuld inden ...
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SUMMARY (1) A population model of the interactions between insect parasitoids and hosts in a patchy environment is proposed. It describes the searching behaviour of an individual parasitoid as being simple innate responses to host and... more
SUMMARY (1) A population model of the interactions between insect parasitoids and hosts in a patchy environment is proposed. It describes the searching behaviour of an individual parasitoid as being simple innate responses to host and parasitoid associated stimuli. However, the probability of a given response being elicited by a given stimulus is assumed to vary with an individual's current rate of oviposition. (2) The model includes the following behavioural responses of the parasitoid: (a) a functional response to the host density of a patch; (b) a response to other parasitoids encountered on a patch; (c) an aggregative response caused by the individual parasitoid being attracted more often to the favourable patches and spending more time on them than on less attractive patches; (d) a response to previously attacked hosts. (3) The model predicts the number of parasitoids and parasitized hosts to be found on the different host patches as well as the number of parasitoids in transit between the patches. (4) The model is used to simulate the dynamics of a laboratory host-parasitoid system consisting of the ichneumonid Nemeritis canescens Grav. and larvae of the moth Ephestia cautella. The simulations show that the model accounts very well for the observed adaptive behaviour of Nemeritis.
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SUMMARY (1) The model is based on a natural host-parasite system, the tortricid Epinotia tedella Cl. and its dominant parasite Pimplopterus dubius Hlmg. It is shown how field data on hatching, emergence and activity are used in the... more
SUMMARY (1) The model is based on a natural host-parasite system, the tortricid Epinotia tedella Cl. and its dominant parasite Pimplopterus dubius Hlmg. It is shown how field data on hatching, emergence and activity are used in the description of the frequency of susceptible hosts and searching parasites throughout the generations. Random search by the parasites has been adopted for the daily events, but not for the generation as a whole. (2) Moderate asynchrony, expressed as relative displacement of the temporal frequency curves for host and parasite, leads to stability, whereas the model predicts instability when the populations are synchronized and when asynchrony becomes extreme. (3) Asynchrony leads to curvilinear relationships between the calculated log (apparent area of discovery) and log (parasite density) without assuming mutual interference between parasites. It is suggested that a majority of the observed log a/log P relationships described in the literature are results of asynchrony, spatial incoincidence and aggregative behaviour, and not of any significant mutual interference. (4) To keep the model realistic, also under extreme conditions, a maximum oviposition rate of eight eggs per day per female parasite was adopted. However, the effect of asynchrony on stability did not change when this assumption was cancelled. (5) The initial densities of host and parasite proved to be of importance only in the vicinity of the limits between regions of stability and instability. (6) It is suggested that the present system, as well as other host-parasite systems, may well be described by a simple, predictive and non-explanatory model either through an apparent log a/log P relation or through an exploitation submodel using a negative binomial distribution.
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(1) A stochastic simulation model was used to analyse the effect of spatial features, such as (a) system size, (b) short and long-distance dispersal of individuals between plants, and (c) spatial coincidence between prey and predators... more
(1) A stochastic simulation model was used to analyse the effect of spatial features, such as (a) system size, (b) short and long-distance dispersal of individuals between plants, and (c) spatial coincidence between prey and predators within plants, on the population dynamics, persistence and stability of a system composed of a phytoseiid mite predator, a tetranychid mite prey and a host-plant. (2) The analyses showed that persistence increases with the number of plants in the system. A system consisting of few host-plants is very unstable, whereas larger systems can achieve overall stability for a wide range of parameter values. (3) The system exhibits cyclic stability. The amplitude of the oscillations increases with an increase in (a) the rates of dispersal of mites among plants, (b) the ratio between longand short-distance emigrations, and (c) the efficiency of the predators in finding and killing prey at low prey densities. The above factors tend to bring unstable local predatorprey oscillations into phase. Once this occurs, the system becomes regionally unstable. (4) Low mobility of the mites increases spatial asynchrony but may result in serious damage to the host-plants inflicted by the phytophagous prey. (5) Demographic stochasticity causes endogenous perturbations. Since small perturbations may lead to a completely different behaviour of the system, predictability of population dynamics in a patchy environment will be low, even if physical factors were perfectly controlled.
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Research Interests: Zoology, Biology, Japan, Medicine, Mexico, and 8 moreFemale, Animals, Male, Temperature, Oviparity, Oviposition, MEXICO, and Tetranychidae
This study presents the effects of sublethal concentrations of pesticides cypermethrin and azoxystrobin on the activity of several physiological parameters of egg-carrying Daphnia magna studied using a video-image technique. Single... more
This study presents the effects of sublethal concentrations of pesticides cypermethrin and azoxystrobin on the activity of several physiological parameters of egg-carrying Daphnia magna studied using a video-image technique. Single tethered daphnids were continuously recorded for 24 h of pesticide exposure, and the activity of the heart, the filtering limbs, the mandibles, and the focal spine were subsequently analyzed. Acute toxicity tests based on the criteria of immobilization were performed on egg-carrying D. magna, and sublethal concentrations of 0.1, 1.0, and 10 µg/L cypermethrin and 0.5, 1.0, and 2.0 mg/L azoxystrobin were established. At a concentration as low as 0.1 µg/L cypermethrin, the 5% effective concentration after 24 h of exposure (EC5,24h), the activity of the focal spine increased and the filtering limb activity decreased. The activity of the mandibles was reduced by exposure to 1.0 (EC18,24 h) and 10 µg/L (EC41,24 h) cypermethrin, whereas heart activity increased at a concentration of 10 µg/L (EC41,24 h). With regard to azoxystrobin, the activity of all response parameters except the focal spine decreased by exposure to 0.5 mg/L (EC4,24h) azoxystrobin. The focal spine was not affected by azoxystrobin. The results show that physiological mechanisms important for ingestion of food in D. magna may be impaired by low concentrations of commonly used pesticides.
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Mark-recapture techniques are used for studies of animal populations. With only three sampling occasions, both Bailey's triple-catch (BTC) and Jolly-Seber's (J-S) stochastic method can be applied. As marking and handling... more
Mark-recapture techniques are used for studies of animal populations. With only three sampling occasions, both Bailey's triple-catch (BTC) and Jolly-Seber's (J-S) stochastic method can be applied. As marking and handling of fragile organisms may harm them, and thereby affect their chances of being recaptured, handling should be minimized. This can be achieved by taking a subsample before the main sample at the second sampling occasion. Individuals in the main sample are marked and released, whereas those in the subsample are only used for identifying recaptures. Monte-Carlo simulation was used to compare the subsampling method with the ordinary mark-recapture methods. Model-generated populations were sampled with and without subsampling to provide estimates of population size, loss, and dilution rates. The estimated parameters were compared with their true values to identify biases associated with the sampling methods, using 81 different combinations of population size, dilution rate, loss rate, and sampling effort. Each combination was replicated 1,000 times. In no cases did subsampling perform more poorly than the ordinary methods. J-S was slightly more accurate than BTC to estimate the population size, but only when sampling effort was high. The relative biases associated with estimates of dilution and loss rates were substantial, but declined with increasing population size and sampling effort. Confidence limits for the population parameters generally were reliable and tended to be conservative. We therefore conclude that ordinary mark-recapture methods can be supplemented with subsampling without sacrificing accuracy. Subsampling is especially advantageous in cases where marks are difficult to observe under field conditions.
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A population of stable flies, Stomoxys calcitrans (L.), was studied on a Danish cattle farm in two successive years. Flies were captured monthly by sweep nettings and marked with fluorescent dust. Absolute population size, dilution rate,... more
A population of stable flies, Stomoxys calcitrans (L.), was studied on a Danish cattle farm in two successive years. Flies were captured monthly by sweep nettings and marked with fluorescent dust. Absolute population size, dilution rate, loss rate, and adult longevity were estimated by means of a modified version of Bailey's triple catch method. In both years, the abundance of flies peaked in July. Using a statistical model, we were able to explain 86.6% of the variation in the per capita growth rate r as a function of current temperature, precipitation, and population size. Omitting precipitation from the model, it still explained 69.3%. The model predicts that stable flies have a temperature optimum at 21.8°C, and that no development will take place when temperatures inside the stable are below 10.2°C or above 33.5°C. At the optimal temperature the intrinsic rate of natural increase is 0.070 d(-1). The per capita dilution rate increased with temperature and decreased with population size, whereas no effect of these factors on the per capita loss rate could be shown. Mean adult survival time was estimated to 6.3 d with 95% CL ranging from 4.3 to 11.1 d. The study points at the possibility of developing predictive models as tools for achieving better, and more environmentally sound, control of stable flies.
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The efficacy of the pupal parasitoid Spalangia cameroni Perkins as a biological control agent was tested against house flies Musca domestica Linnaeus and stable flies Stomoxys calcitrans (Linnaeus) in one dairy cattle and two pig... more
The efficacy of the pupal parasitoid Spalangia cameroni Perkins as a biological control agent was tested against house flies Musca domestica Linnaeus and stable flies Stomoxys calcitrans (Linnaeus) in one dairy cattle and two pig installations in Denmark. Weekly releases of S. cameroni from April through to September–October 1999 and 2000 resulted in significant suppressions of house fly populations to below nuisance level, whereas no effect on stable flies was found. Parasitism was significantly higher in the release years compared to the control years, but was below 25% averaged over the fly season for each farm. A statistical model based on a functional relationship between the innate capacity of increase of the two fly species and three explanatory variables (air temperature, fly density and parasitism) provided a fairly good fit to data with the abundances of house flies and stable flies explained mostly by temperature, but intra- and interspecific competition, and parasitism h...
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... It shows that demographic stochasticity generates sufficient endogenous 'noise' to counteract the synchronizing effect of density-dependent dispersal, provided dispersal rates are not too high and the system is not... more
... It shows that demographic stochasticity generates sufficient endogenous 'noise' to counteract the synchronizing effect of density-dependent dispersal, provided dispersal rates are not too high and the system is not too small. ... Based on the above model, the expected ...
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This study presents the effects of sublethal concentrations of pesticides cypermethrin and azoxystrobin on the activity of several physiological parameters of egg-carrying Daphnia magna studied using a video-image technique. Single... more
This study presents the effects of sublethal concentrations of pesticides cypermethrin and azoxystrobin on the activity of several physiological parameters of egg-carrying Daphnia magna studied using a video-image technique. Single tethered daphnids were continuously recorded for 24 h of pesticide exposure, and the activity of the heart, the filtering limbs, the mandibles, and the focal spine were subsequently analyzed. Acute toxicity tests based on the criteria of immobilization were performed on egg-carrying D. magna, and sublethal concentrations of 0.1, 1.0, and 10 µg/L cypermethrin and 0.5, 1.0, and 2.0 mg/L azoxystrobin were established. At a concentration as low as 0.1 µg/L cypermethrin, the 5% effective concentration after 24 h of exposure (EC5,24h), the activity of the focal spine increased and the filtering limb activity decreased. The activity of the mandibles was reduced by exposure to 1.0 (EC18,24 h) and 10 µg/L (EC41,24 h) cypermethrin, whereas heart activity increased at a concentration of 10 µg/L (EC41,24 h). With regard to azoxystrobin, the activity of all response parameters except the focal spine decreased by exposure to 0.5 mg/L (EC4,24h) azoxystrobin. The focal spine was not affected by azoxystrobin. The results show that physiological mechanisms important for ingestion of food in D. magna may be impaired by low concentrations of commonly used pesticides.
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In this paper we present a concept for using presence–absence data to recover information on the population dynamics of predator–prey systems. We use a highly complex and spatially explicit simulation model of a predator–prey mite system... more
In this paper we present a concept for using presence–absence data to recover information on the population dynamics of predator–prey systems. We use a highly complex and spatially explicit simulation model of a predator–prey mite system to generate simple presence–absence data: the number of patches with both prey and predators, with prey only, with predators only, and with neither species, along with the number of patches that change from one state to another in each time step. The average number of patches in the four states, as well as the average transition probabilities from one state to another, are then depicted in a state transition diagram, constituting the “footprints” of the underlying population dynamics. We investigate to what extent changes in the population processes modeled in the complex simulation (i.e. the predator's functional response and the dispersal rates of both species) are reflected by different footprintsThe transition probabilities can be used to f...