Maximum Reproductive Rate Research Articles

DEBBIES Dataset to study Life Histories across Ectotherms

Demographic models are used to explore how life history traits structure life history strategies across species. This study presents the DEBBIES dataset that contains estimates of eight life history traits (length at birth, puberty and maximum length, maximum reproduction rate, fraction energy allocated to respiration versus reproduction, von Bertalanffy growth rate, mortality rates) for 185 ectotherm species. The dataset can be used to parameterise dynamic energy budget integral projection models (DEB-IPMs) to calculate key demographic quantities like population growth rate and demographic resilience, but also link to conservation status or biogeographical characteristics. Our technical validation shows a satisfactory agreement between observed and predicted longevity, generation time, age at maturity across all species. Compared to existing datasets, DEBBIES accommodates (i) easy cross-taxonomical comparisons, (ii) many data-deficient species, and (iii) population forecasts to novel conditions because DEB-IPMs include a mechanistic description of the trade-off between growth and reproduction. This dataset has the potential for biologists to unlock general predictions on ectotherm population responses from only a few key life history traits.

Life history of the two predacious mites species, Amblyseius swirskii, and Neoseiulus cucumeris (Acari: Phytoseiidae), as biological control agents of the date palm mite, Oligonychus afrasiaticus (Acari: Tetranychidae).

The date palm mite, Oligonychus afrasiaticus (McGregor) (Acari: Tetranychidae), is a serious pest of dates in the Middle East and North Africa, inflicting severe economic damage if not controlled early. As predaceous mites are known to be potential biocontrol agents against several pests, so predation capacity, life table, reproduction, and survival of Amblyseius swirskii Athias-Henriot and Neoseiulus cucumeris (Oudemans) (Acari: Phytoseiidae), collected from date palm farms in Qassim Saudi Arabia, were studied under laboratory conditions (25 °C, 30 °C, 35 °C and 50 ± 5% RH) against all motile stages of O. afrasiaticus. For both predators, mean developmental time, oviposition period, and longevity were inversely related to temperature from 25 to 35 °C. Various parameters were studied for A. swirskii and N. cucumeris at 25 °C, 30 °C and 35 °C, i.e. the female developmental time, 9.37, 7.29, 5.56, and 10.67, 8.38, 6.45 d; oviposition period, 19.77, 16.18, 13.94 and 15.90, 13.84, 10.64 d; longevity, 29.39, 24.79, 20.64 and 25.42, 21.94, 17.39 d; fecundity, 31.91, 37.10, 42.16 and 21.75, 26.84, 30.56 eggs per female, respectively. The maximum daily predation rate for both the predators was recorded at 35 °C during the oviposition period. The total predation of A. swirskii and N. cucumeris female was 370.86, 387.54, 405.83, 232.14, 263.32, 248.85 preys at 25 °C, 30 °C and 35 °C respectively. The maximum reproduction rate of A. swirskii and N. cucumeris (3.02, 2.87 eggs/♀/day) was recorded at 35 °C while the minimum (2.00, 1.36 eggs/♀/day) was recorded at 25 °C. The life table parameters were estimated as net reproductive rate (Ro) 21.68, 25.94, 29.52 and 18.95, 20.25, 22.78; the mean generation time (T) 24.92, 21.82, 18.24 and 26.30, 23.60, 20.56 d; the intrinsic rate of increase (rm) 0.181, 0.232, 0.248 and 0.170, 0.185, 0.196; the finite rate of increase (λ) 1.365, 1.551, 1.706 and 1.126, 1.324, 1.428 for A. swirskii and N. cucumeris at 25 °C, 30 °C and 35 °C respectively. The results of this study suggested that the two phytoseiid species are promising biological control agents of O. afrasiaticus at a wide range of temperatures.

Epidemiological Characteristics of COVID-19 in Chungju City from 2021 July to 2021 December

Objectives: This study aimed to investigate the epidemiological characteristics of COVID-19 in Chungju City from July to December 2021.Methods: The authors processed and analyzed the epidemiological analysis report written by researcher. The estimated reproduction rate was analyzed using web-based software that calculates time-varying reproduction numbers. The results were analyzed through univariate multiple regression analysis, with a maximum significance level set at 0.05.Results: During the study period, a total of 1,188 patients were identified, with 7.9% of them progressing to a severe status. The maximum reproduction rate recorded was 3.48. Factors associated with the transition to a severe status included the presence of symptoms at the time of diagnosis, lack of vaccination, and belonging to the age group over 40.Conclusion: Based on the findings of this study, it can be strongly supported that the measures implemented in Chungju City, such as social distancing, vaccination, and preemptive diagnostic tests, were appropriate. Furthermore, it demonstrates that Chungju City effectively managed the impact of COVID-19. Korean Medicine Doctors made significant contributions to the epidemiological investigations of COVID-19. To comprehensively manage infectious diseases, it is crucial to provide administrative and legal support and encourage active research to expand the role of Korean Medicine Doctors in this area.

<i>In vitro</i> Study of Biological Properties of SARS-CoV-2 Coronavirus Strains Related to Various Genetic Variants

The aim of the research was to study reproduction features of SARS-CoV-2 coronavirus strains of various genetic lines on Vero and Vero E6 cell culture.Materials and methods. The SARS-CoV-2 virus strains related to the variants of concern (VOC) circulating in the territory of the Russian Federation were used in the research. The strains of the SARS-CoV-2 virus were deposited in the State Collection of Pathogens of Viral Infections and Rickettsioses at the FBIS SSC VB “Vector” of the Rospotrebnadzor. The experiments were carried out on Vero and Vero E6 cell cultures. The dynamics of infectious virus accumulation was determined by titration of culture fluid samples 24, 48, 72, 96 hours after infection (MOI – from 1 to 0,00001 CPE50/cell). Plaque formation was studied on Vero E6 cell culture under 0.2 % agar coating. Image analysis and plaque size calculation were performed using GIMP (GNU Image Manipulation Program).Results and discussion. The study describes the dynamics of accumulation of infectious virus in the culture fluid depending upon multiplicity of infection for the strains of SARS-CoV-2 virus belonging to different genetic lines. Differences in the morphology of plaques on the monolayer of Vero E6 cell culture under agar coating are shown. SARS-CoV-2 virus strains related to Alfa and Delta VOC demonstrate maximum reproduction rate among the studied strains (infectious titer is higher than 7 lg TCID50/100µl). Omicron VOC forms small plaques under agar coating and at a low multiplicity of infection has a low reproduction rate. Thus, SARS-CoV-2 virus strains belonging to different genetic lines have significant differences in the rate of reproduction on Vero and Vero E6 cell culture.

Temperature based phenology model for predicting establishment and survival of Spodoptera litura (Fab.) on groundnut during climate change scenario in India

Studies were conducted to develop temperature-based phenology model for Spodoptera litura on groundnut, at both constant and fluctuating temperatures and to predict the possibility of pest risk in future climate change scenarios of India using ‘stochastic simulation tool’ in Insect Life Cycle Modelling (ILCYM) software ,which is based on rate summation and cohort up-dating approach. Phenology model predicted temperatures between 25oC and 30oC as the favourable range for S. litura development, survival and reproduction. The intrinsic rate of increase (rm), and finite rate of increase (») increased with increase in temperature from 15oC to 30oC and decreased with increase in temperature. Intrinsic rate of increase (rm), varied from 0.05 females/female/day at 15oC to 0.17 females/female/day at 30oC. S. litura population attained a maximum net reproductive rate ‘Ro’ (334.09 females/female/generation) and total fecundity (1041.88 individuals/ female/generation) at 27°C temperature. Simulated life table parameters were used to determine indices such as the establishment risk index (ERI), the generation index (GI), and activity index (AI) by using the ‘Population distribution and risk mapping’ module of software during present and future climatic scenarios and significant increase in AI and ERI with higher GI at future (2050) climatic conditions compared to current (2000) climatic conditions indicating the strong suitability for establishment and survival of S.litura in India.

Evaluation of the combined effect of elevated temperature and cadmium toxicity on Daphnia magna using a simplified DEBtox model

Thermal discharge and heatwaves under climate change may increase water temperature. In this study, the individual and combined effect of elevated temperature and cadmium (Cd) toxicity on somatic growth and reproduction of Daphnia magna was evaluated using a simplified dynamic energy budget model (DEBtox). The model predicted that the maximum body length (Lm) would be shorter (3.705 mm) at an elevated temperature of 25 °C than at 20 °C (3.974 mm), whereas the maximum reproduction rate (R˙m) would be higher at 25 °C (5.735) than at 20 °C (5.591). The somatic growth and reproduction of D. magna were significantly (p < 0.05) reduced with increasing Cd concentrations, and the reduction was greater at 25 than at 20 °C. Potentiation of Cd toxicity by elevated temperature was correctly simulated by assuming four toxicological modes of action influencing assimilation, somatic maintenance and growth, and reproduction. Overall, the population growth rate of D. magna was expected to decrease linearly with increasing Cd concentrations, and the decrease was expected to be higher at 25 than at 20 °C. These findings suggest a significant ecological risk of toxic metals at elevated temperature, with a mechanistic interpretation of the potentiation effect using a DEBtox modeling approach.

Effect of Citrullus amarus accessions on the population dynamics of Meloidogyne incognita and M. javanica and watermelon yield

The aims of this study were to determine i) the effect of grafted watermelon cv. Sugar Baby onto C. amarus accessions BGV0005164 and BGV0005167 on M. incognita and M. javanica population growth estimated by means of the values of maximum reproduction rate, maximum nematode density and equilibrium density in pot experiments; ii) the effect of increasing nematode densities on plant productivity in pot experiments; and iii) the effect of repeated cultivation of watermelon cv. Sugar Baby grafted onto both C. amarus accessions and onto C. lanatus ‘Robusta’ during two seasons in a plastic greenhouse on M. incognita reproduction, disease severity, crop yield and selection for nematode virulence. In pot experiments, the values of maximum reproduction rate, maximum nematode density and equilibrium density of M. incognita were 37 %, 72 % and 68 % lower in watermelon grafted onto BGV0005164 than in ungrafted, and 28 %, 76 % and 77 % lower when grafted onto BGV0005167. Regarding M. javanica, the values of maximum reproduction rate, maximum nematode density and equilibrium density in watermelon grafted onto BGV0005164 were 88 %, 65 % and 14 % lower than in ungrafted, and 80 %, 76 % and 33 % lower when grafted onto BGV0005167. Dry shoot weight of ungrafted and grafted watermelon inoculated with a range of nematode densities between 0 and 1200 s-stage juveniles per 100 cm3 of soil was not affected, irrespective of the nematode isolate. In the plastic greenhouse experiment, M. incognita reproduced less in grafted than in ungrafted watermelon. Disease severity was higher in ungrafted than in grafted watermelon. The level of resistance of both C. amarus accessions was not affected after two-year cultivation, but it decreased from moderately resistant in 2017 to slightly resistant in rootstock ‘Robusta’. Watermelon grafted yielded between 2.9 and 5.6 kg more per plant than the ungrafted in 2017, and between 2.0 and 2.7 kg more per plant in 2018. In conclusion, C. amarus accessions BGV0005164 and BGV0005167 performed as poorer hosts to M. incognita and M. javanica. Watermelon grafted onto these C. amarus accessions improved fruit yield when they were cultivated in nematode infested soils without affecting its level of resistance to M. incognita after two consecutive crops.

Effect of temperature and humidity on development, reproduction, and predation rate of Amblyseius swirskii (Phytoseiidae) fed on Phyllocoptruta oleivora (Eriophyidae) and Eutetranychus orientalis (Tetranychidae)

ABSTRACT The developmental, survival, predation rates, and reproduction of Amblyseius swirskii (Phytoseiidae), as affected by feeding on the motile stages of Phyllocoptruta oleivora (Eriophyidae) and nymphs of Eutetranychus orientalis (Tetranychidae), were studied in the laboratory at six constant temperatures and relative humidities: 9°C and 70% RH; 16°C and 65% RH; 23°C and 60% RH; 30°C and 55% RH, 37°C and 50% RH and 40°C and 45% RH. The maximum daily consumption rate was recorded at 30°C and occurred during the oviposition period, when the females consumed an average of 169.40 specimens of P. oleivora and 24.58 of E. orientalis. The maximum reproduction rate (4.20, and 3.84 eggs/♀/day, on P. oleivora and E. orientalis, respectively) was recorded at 30°C and 50% RH, while the minimum one (1.20 and 0.86 eggs/♀/day, on P. oleivora and E. orientalis, respectively) was observed at 16°C and 65% RH. It is demonstrated in the life-table parameters that when the predatory mite A. swirskii is fed on P. oleivora, the highest reproduction rates (rm = 0.144, 0.195, 0.280, and 0.181 females/female/day) are obtained, while feeding on E. orientalis gave the lowest reproduction rates (rm = 0.121, 0.172, 0.204, and 0.141) at 16°C and 65% RH, 23°C and 60% RH, 30°C and 55% RH, and 37°C and 50% RH, respectively. The results suggest that A. swirskii is a promising control agent for P. oleivora and E. orientalis on orange trees.

Decadal changes in the productivity of New England fish populations

The Northwest Atlantic continental shelf is a large ecosystem undergoing rapid environmental changes, which are expected to modify the productivity of natural marine resources. Current management of most fished species assumes stationary production relationships or time-invariant recruitment rates. With linear state-space models, we examined the evidence of dynamic productivity for 25 stocks of the Northeast US shelf. We expanded the suite of options available within the state-space approach to produce robust estimates. Fifteen of the stocks exhibited time-varying productivity or changes in their maximum reproductive rate. Few productivity time series are related across the whole region, though adjacent stocks of the same species exhibited similar trends. Some links to region-wide environmental variables were observed. We demonstrate that fish recruitment can often be better predicted over a short-term horizon by accounting for dynamic productivity, which could be valuable for fisheries management. Improving predictions by incorporating environmental covariates or covariance among the stocks must be considered case by case and with caution, as their relationships may change over time.

Trait-based predictions and responses from laboratory mite populations to harvesting in stochastic environments.

Predictions on population responses to perturbations are often derived from trait‐based approaches like integral projection models (IPMs), but are rarely tested. IPMs are constructed from functions that describe survival, growth and reproduction in relation to the traits of individuals and their environment. Although these functions comprise biologically non‐informative statistical coefficients within standard IPMs, model parameters of the recently developed dynamic energy budget IPM (DEB‐IPM) are life‐history traits like “length at maturation” and “maximum reproduction rate”. Testing predictions from mechanistic IPMs against empirical observations can therefore provide functional insights into the links between individual life history, the environment and population dynamics.Here, we compared the population dynamics of the bulb mite (Rhizoglyphus robini) predicted by a DEB‐IPM with those observed in an experiment where populations experienced daily food rations that were either positively correlated over time (red noise), negatively (blue noise) or uncorrelated (white noise). We also selectively harvested large adults in half of these populations. The model failed to generate detailed predictions of population structure as juvenile numbers were overestimated; likely because juvenile–adult interference competition was underestimated. The model performed well at the population level as, for both harvested and unharvested populations, simulations matched the observed, long‐term stochastic growth rate λs.We next generalised the model to investigate how stochastic change affects mite λs, which correlated well with the frequency f of experiencing periods of good environment, but, due to the relationship between f and noise colour ρ, did not correlate well with shifts in ρ. The sensitivity of λs to perturbations in life‐history parameters depended on the type of stochastic change, as well as population growth.Our findings show that responses to differential mortality depend on individual life‐history traits, environmental characteristics and population growth. As long‐term climate change causes ever greater environmental fluctuations, trait‐based approaches will be increasingly important in predicting population responses to change. We therefore conclude by illustrating what questions can be examined with mechanistic trait‐based models like the DEB‐IPM, the answers to which will advance our knowledge of the functional links between individual traits, the environment and population dynamics.

Effect of temperature on rice white backed plant hopper Sogatella furcifera

Influence of variable temperature combinations viz. 32 & 22°C, 32 & 24°C, 32 & 26°C, 35 & 22°C, 35 & 24°C and 35 & 26°C (maximum & minimum) maintained for 12: 12 hours, on developmental and reproductive physiology of the white backed plant hopper, Sogatella furcifera (Horvath), a serious sucking insect pest of rice in Punjab was studied. The survival of nymphs caged on rice variety PR 121 maintained at combination of 32 & 24°C was observed to be significantly higher (95%) than those at 35 & 22°C and 32 & 22°C (90 and 88%, respectively) while it was minimum at 35 & 26°C (61%). The period of nymphal development was maximum (17.7 days) at combination of 32 & 22°C and minimum (9.78 days) at 35 & 26°C. Growth index, a measure of suitability of temperature for growth and development was observed to be maximum at combination of 35 & 24°C (7.57). Maximum reproductive rate (198) was observed at combination of 35 & 24°C as against 99.33 at 32 & 22°C and 129.0 at 32 & 24°C. These results suggest that an increase in mean maximum and minimum temperature might potentially enhance the numbers and generations of the S. furcifera that will add to its increased menace.

Gaussian process framework for temporal dependence and discrepancy functions in Ricker-type population growth models

Density dependent population growth functions are of central importance to population dynamics modelling because they describe the theoretical rate of recruitment of new individuals to a natural population. Traditionally, these functions are described with a fixed functional form with temporally constant parameters and without species interactions. The Ricker stock-recruitment model is one such function that is commonly used in fisheries stock assessment. In recent years, there has been increasing interest in semiparametric and temporally varying population growth models. The former are related to the general statistical approach of using semiparametric discrepancy functions, such as Gaussian processes (GP), to model deviations around the expected parametric function. In the latter, the reproductive rate, which is a key parameter describing the population growth rate, is assumed to vary in time. In this work, we introduce how these existing Ricker population growth models can be formulated under the same statistical approach of hierarchical GP models. We also show how the time invariant semiparametric approach can be extended and combined with the time varying reproductive rate using a GP model. Then we extend these models to the multispecies setting by incorporating cross-covariances among species with a continuous time covariance structure using the linear model of coregionalization. As a case study, we examine the productivity of three Pacific salmon populations. We compare the alternative Ricker population growth functions using model posterior probabilities and leave-one-out cross validation predictive densities. Our results show substantial temporal variation in maximum reproductive rates and reveal temporal dependence among the species, which have direct management implications. However, our results do not support inclusion of semiparametric discrepancy function and they suggest that the semiparametric discrepancy functions may lead to challenges in parameter identifiability more generally.

Exploiting rRNA operon copy number to investigate bacterial reproductive strategies.

SummaryThe potential for rapid reproduction is a hallmark of microbial life, but microbes in nature must also survive and compete when growth is constrained by resource availability. Successful reproduction requires different strategies when resources are scarce compared to when they are abundant1,2, but a systematic framework for predicting these reproductive strategies in bacteria has not been available. Here we show that the number of ribosomal RNA operons (rrn) in bacterial genomes predicts two important components of reproduction – growth rate and growth efficiency – which are favored under contrasting regimes of resource availability3,4. We find that the maximum reproductive rate of bacteria doubles with a doubling of rrn copy number, while the efficiency of carbon use is inversely related to maximal growth rate and rrn copy number. We also identify a feasible explanation for these patterns: the rate and yield of protein synthesis mirror the overall pattern in maximum growth rate and growth efficiency. Furthermore, comparative analysis of genomes from 1,167 bacterial species reveals that rrn copy number predicts traits associated with resource availability, including chemotaxis and genome streamlining. Genome-wide patterns of orthologous gene content covary with rrn copy number, suggesting convergent evolution in response to resource availability. Our findings indicate that basic cellular processes adapt in contrasting ways to long-term differences in resource availability. They also establish a basis for predicting changes in bacterial community composition in response to resource perturbations using rrn copy number measurements5 or inferences6,7.

Comparison of growth parameters of the predator, Chrysoperla nipponensis-B (Neuroptera: Chrysopidae) reared on a diet of eggs of Corcyra cephalonica (Lepidoptera: Pyralidae) and an artificial diet containing ginger

The growth parameters of the green lacewing, Chrysoperla nipponensis-B (Okamoto), were studied under laboratory conditions. The highest mortality was recorded in the immature stages (instars 1st, 2nd, 3rd and pupae) of C. nipponensis fed on the eggs of Corcyra cephalonica (37.26%). The sex ratios (proportion of female to male) when reared on the eggs of C. cephalonica and an artificial diet with ginger were 0.93 : 1.00 and 0.87 : 1.00, respectively. The maximum life spans of females reared on the eggs of C. cephalonica and an artificial diet with ginger were 63 and 64 days, respectively. The females reared on the eggs of C. cephalonica produced the highest number of eggs (10.4) on the fifth day of oviposition, whereas on the artificial diet with ginger it was 9.26 on the eighth day of oviposition. The net reproductive rate (Ro) and maximum gross reproductive rate (GRR) of C. nipponensis fed on the eggs of C. cephalonica were 69.50 and 223.10 females per female per generation, respectively, whereas for the artificial diet with ginger they were 117.24 and 236.89 females per female per generation, respectively. Mean generation time (T) was 37.06 and 48.16 for the eggs of C. cephalonica and artificial diet with ginger, respectively. The intrinsic rate of natural increase (r) was 0.11 and 0.09 females per female per day for the eggs of C. cephalonica and artificial diet with ginger, respectively. The finite rate of increase (λ) was 1.12 and 1.11 females per female per day for the eggs of C. cephalonica and artificial diet with ginger, respectively. The population doubling time (DT) was 6.05 days on the diet of eggs of C. cephalonica and 7.00 on the artificial diet with ginger.

Evidence and implications of higher-order scaling in the environmental variation of animal population growth

Environmental stochasticity is an important concept in population dynamics, providing a quantitative model of the extrinsic fluctuations driving population abundances. It is typically formulated as a stochastic perturbation to the maximum reproductive rate, leading to a population variance that scales quadratically with abundance. However, environmental fluctuations may also drive changes in the strength of density dependence. Very few studies have examined the consequences of this alternative model formulation while even fewer have tested which model better describes fluctuations in animal populations. Here we use data from the Global Population Dynamics Database to determine the statistical support for this alternative environmental variance model in 165 animal populations and test whether these models can capture known population-environment interactions in two well-studied ungulates. Our results suggest that variation in the density dependence is common and leads to a higher-order scaling of the population variance. This scaling will often stabilize populations although dynamics may also be destabilized under certain conditions. We conclude that higher-order environmental variation is a potentially ubiquitous and consequential property of animal populations. Our results suggest that extinction risk estimates may often be overestimated when not properly taking into account how environmental fluctuations affect population parameters.

Damage functions and thermal requirements of Meloidogyne javanica and Meloidogyne incognita on watermelon

ABSTRACTThe relationship between the initial (Pi) and final (Pf) population densities of Meloidogyne javanica and yield of watermelon, Citrullus lanatus, cv. Sugar Baby were determined in pot and field experiments. In the pots, the maximum reproduction rate of the nematode was 14, and the equilibrium density was 49 400 eggs/100 cm3 of soil. Yield data represented as fresh top weight fitted the Seinhorst damage function (P &lt; 0.001, R2 = 0.7), and the minimum relative yield (m) was 0.65 at Pi ≥ 3200 eggs/100 cm3 of soil and the tolerance limit (T) 74 eggs/100 cm3. In the field experiments (2011 and 2012), the maximum reproduction rate was 73 and 70, and the equilibrium density 32 and 35 second‐stage juveniles (J2)/100 cm3 soil. Yield data represented as fruit weight fitted the Seinhorst damage function in 2011 (P &lt; 0.001, R2 = 0.92) and the m‐ and T‐values were 0.63 and 20 J2/100 cm3 of soil, respectively. Meloidogyne incognita and M. javanica needed similar length of time for development to egg‐laying females and life cycle completion at 24.4°C.

Refining Reproductive Parameters for Modelling Sustainability and Extinction in Hunted Primate Populations in the Amazon

Primates are frequently hunted in Amazonia. Assessing the sustainability of hunting is essential to conservation planning. The most-used sustainability model, the ‘Production Model’, and more recent spatial models, rely on basic reproductive parameters for accuracy. These parameters are often crudely estimated. To date, parameters used for the Amazon’s most-hunted primate, the woolly monkey (Lagothrix spp.), come from captive populations in the 1960s, when captive births were rare. Furthermore, woolly monkeys have since been split into five species. We provide reproductive parameters calculated by examining the reproductive organs of female Poeppig’s woolly monkeys (Lagothrix poeppigii), collected by hunters as part of their normal subsistence activity. Production was 0.48–0.54 young per female per year, and an interbirth interval of 22.3 to 25.2 months, similar to parameters from captive populations. However, breeding was seasonal, which imposes limits on the maximum reproductive rate attainable. We recommend the use of spatial models over the Production Model, since they are less sensitive to error in estimated reproductive rates. Further refinements to reproductive parameters are needed for most primate taxa. Methods like ours verify the suitability of captive reproductive rates for sustainability analysis and population modelling for populations under differing conditions of hunting pressure and seasonality. Without such research, population modelling is based largely on guesswork.

Productivity dynamics of Atlantic cod

Productivity is a central determinant of population dynamics with consequences for population viability, resilience to exploitation, and extinction. In fish, the strength of a cohort is typically established during early life stages. Traditional approaches to measuring productivity do not allow for interannual variation in the maximum reproductive rate, a parameter governing population productivity. Allowing such process variation provides the ability to track dynamic changes instead of assuming a static productivity regime. Here we develop and evaluate a multivariate stock–recruitment state-space model to simultaneously estimate time-varying stock productivity and synchronicity of dynamics across populations. We apply the method to North Atlantic cod (Gadus morhua) populations, showing that the productivity of early life stages has varied markedly over time, with many populations at historically low productivity. Trends in productivity were similar in some adjacent populations but less regionally coherent than previously thought, particularly in the Northwest Atlantic. Latitudinal variation in the Northeast Atlantic suggests a differential response to environmental change. We conclude that time-varying productivity provides a useful framework that integrates across many dimensions of environmental change affecting early life history dynamics.

A semiparametric Bayesian approach to estimating maximum reproductive rates at low population sizes

The maximum annual reproductive rate (i.e., the slope at the origin in a stock-recruitment relationship) is one of the most important biological reference points in fisheries; it sets the upper limit to sustainable fishing mortality. Estimating the maximum reproductive rate by fitting parametric models to stock-recruitment data may not be a robust approach because two statistically indistinguishable models can generate radically different estimates. To mitigate this issue, we developed a flexible, semiparametric Bayesian approach based on a conditional Gaussian process prior specifically designed to estimate the maximum annual reproductive rate, and applied it to analyze simulated stock-recruitment data sets. Compared with results based on other Gaussian process priors, we found that the conditional Gaussian process prior provided superior results: the accuracy and precision of estimates were enhanced without increasing model complexity. Moreover, compared with parametric alternatives, performance of the conditional Gaussian process prior was comparable to that of the data-generating model and always better than the wrong model.

Effects of a bioassay-derived ivermectin lowest observed effect concentration on life-cycle traits of the nematode Caenorhabditis elegans

The pharmaceutical ivermectin is used to treat parasitic infections, such as those caused by nematodes. While several studies have demonstrated the severe effects of ivermectin on non-target organisms, little is known about the drug's impact on free-living nematodes. In the present work, a full life-cycle experiment was conducted to estimate how an ivermectin lowest observed effect concentration derived from a Caenorhabditis elegans bioassay (endpoint reproduction) might translate into effects at the population level of this free-living nematode. The results showed that fecundity decreased to levels similar to those determined in the bioassay after a time of corresponding duration (18.6 % inhibition compared to the control), but the impact then rather weakened until the end of the experiment, at which point the net reproductive rate (R(0)) was still, but not significantly, reduced by 12.4 %. Moreover, the average lifespan, length of the reproductive period, maximum daily reproduction rate, and intrinsic rate of increase (r(m)) were significantly reduced by 30.0, 25.9, 11.2, and 3.5 %, respectively. The experiment revealed that a 4-day bioassay is protective enough for C. elegans with respect to ivermectin's effects on fecundity. However, the pronounced effects of a low drug concentration on survival, a highly elastic trait, may better account for the observed population-level response, i.e., a decrease of r(m), than the effects on fecundity. These results emphasize that full life-cycle experiments are valuable for assessment of pollutants, because the effects on several life-cycle traits can be simultaneously measured and integrated into an ecologically relevant parameter, the population growth rate, that reflects a population's response to a specific pollutant.