Instantaneous Population Growth Rate Research Articles

Are there useful life history indicators of stock recovery rate in gadoids?

Age at maturity is one of the key variables determining the maximum rate of population growth and so may be a good indicator of stock recovery potential. Spawner age composition may also affect the probability of high recruitment and so could be relevant to stock recovery. This study examined the relation between early survival, age at maturity, and the demographic composition of spawners in many cod and haddock stocks. Reported measures of fecundity and maturity were used to estimate total egg production for comparison with numbers at age 1 and age at 50% maturity. The instantaneous rate of population growth (r) was estimated for cohorts from life history tables during periods when spawning biomass was depleted (e.g. <Bpa) using reproductive and mortality data for stocks. Age-specific survival was found to be far more important than reproductive rate in determining population growth rate. Stocks that experienced low and more variable survival matured early and had a high relative fecundity. Hence, while early maturing stocks have the potential for high population growth following favourable recruitment events, they would not be expected to recover any faster than late maturing stocks because of the generally low early survival rate that they experience. Measures of spawner age diversity and mean age were found to be positively correlated with offspring survivorship in a few cod stocks. However, in general, it appears difficult to infer recovery potential from life history characteristics, which may be expected, given that regional variation in reproductive success will ultimately be expected to shape local reproductive schedules.

Evaluation of non-conventional insecticides for the control of Aphis gossypii Glover (Hemiptera: Aphididae) in beans

The lethal concentration (CL) is used to estimate the toxicity of pesticides in arthropods; however, CL is an incomplete measure of the effects of these products on populations, since it only examines toxicity as a function of mortality. It is known that individuals which survive the exposure to pesticides may suffer sublethal effects. This work studied, under laboratory conditions the lethal and sublethal effects of lime sulphur, Azadirachta indica (Bioneem®) and Allium sativum- Capsicum chinense (Alisin®) on the population growth of A. gossypii and the phytotoxic effect of these insecticides on bean plants. Lethal effects were estimated through tests of acute toxicity to obtain dosage-response curves and their respective lethal concentrations and sublethal effects by estimating the instantaneous population growth rate (ri). The lethal and sublethal concentrations of lime sulfur against were 1.22 and 0.25% of the product, respectively, for the Bioneem® were 1.22 and 0.71% of the product, respectively, and the Alisin® 2.18 and 0,94% of the product, indicating that it could be used to control this phytophagous insect. There were no severe symptoms of phytotoxicity detected on sprayed plants. The management of A. gossypii in beans can be made with lime sulphur, Bioneem® and Alisin®.

Resistance of Cowpea Genotypes to Zabrotes subfasciatus (Boheman, 1833) (Coleoptera: Chrysomelidae: Bruchinae)

Cowpea (Vigna unguiculata (L.) Walp.) when stored is mainly attacked by bruchid Coleopterans. The control of these pests is done primarily through chemicals, however, with problems related to the selection of resistant insects, alternative forms of control are searched. Seeking an alternative control, the objective this work was to evaluate the resistance of cowpea genotypes to the attack of Z. subfasciatus. In the first selection of genotypes were evaluated 35 cowpea genotypes, being observed the variables: number of eggs, number of insects emerged and weight loss (%). In this first selection of cowpea were selected 10 genotypes. In the second selection of genotypes, the 10 most resistant from the first selection were used, but with eight repetitions per genotype, besides evaluating the egg viability (%) and instantaneous rate of population growth. The cowpea genotypes showed significant differences for resistance to attack by Z. subfasciatus. The most resistant to Z. subfasciatus were BRS Tracuateua, 31 MNC03-720C-20, 26 MNC00-553D-8-1-2-2 and 37 MNC05-832B-234-5.

Susceptibility and physiological responses of Jatropha curcas accessions to broad mite infestation

The broad mite Polyphagotarsonemus latus is a key pest of physic nut (Jatropha curcas L.). The purpose of this study was to identify physic nut accessions that are less susceptible to P. latus, in support of the breeding program of J. curcas. We first evaluated population growth rate and injury symptoms of P. latus on different J. curcas accessions and then carried out physiological analyses on P. latus-infested and uninfested accessions. From the germplasm bank of the Federal University of Viçosa, 15 physic nut accessions with high seed oil content, with different genetic background, were tested. The following traits were evaluated: instantaneous population growth rate of P. latus (r i ), injury symptoms, relative leaf water content, specific leaf area, gas exchange, photosynthetic pigments, nitrogen and biomass of the aerial part. Significant differences were observed for P. latus population growth rate and injury symptoms among accessions. A positive correlation between P. latus growth rate and injury was found. The UFVJC72 accession stood out as the more resistant, considering P. latus growth rate and injury symptoms, compared with most accessions. Physiological responses did not vary among accessions, but did between infested and uninfested plants. In P. latus-infested plants, net photosynthesis was on average 50.5 % lower than in uninfested plants, whereas stomatal conductance and transpiration decreased by 46.2 and 51.6 %, respectively.

Resistência de genótipos de feijão-caupi ao ataque de Callosobruchus maculatus (Fabr., 1775) (Coleoptera: Chrysomelidae: Bruchinae)

O objetivo deste trabalho foi avaliar a resistência de quatro genótipos de feijão-caupi (Vigna unguiculata) ao caruncho Callosobruchus maculatus (Fabr., 1775). Os genótipos utilizados foram BR 17-Gurguéia, BRS Rouxinol, TE96-290-12G e BRS Guariba. Foram realizados testes com e sem chance de escolha, em delineamento experimental inteiramente casualizado, totalizando 4 tratamentos cada um com 5 repetições, avaliando-se número de ovos, número de insetos emergidos, viabilidade de ovos (%) e taxa instantânea de crescimento populacional. Nos testes com e sem chance de escolha, o genótipo TE96-290-12G mostrou-se como o mais resistente. BRS Rouxinol foi o genótipo mais suscetível.

Effects of botanical insecticides on the instantaneous population growth rate of Aphis gossypii Glover (Hemiptera: Aphididae) in cotton

Botanical insecticides have been studied aiming the alternative pest control. The present study investigated the effects of these insecticides on the instantaneous population growth rate (ri) of Aphis gossypii. Botanical insecticides were tested in the following concentrations: Compostonat®, Rotenat-CE® and Neempro (0, 0.50, 0.75, 1.00, 1.25, 1.50 and 1.75%); Natuneem® and Neemseto® (0, 0.25, 0.50, 0.75 and 1.00%) and essential oils of Foeniculum vulgare Mill., Cymbopogom winterianus (L.), Chenopodium ambrosioides L. and Piper aduncum L (0, 0.0125, 0.025, 0.0375 and 0.05%). Cotton leaf discs, CNPA 8H cultivar with 5 cm in diameter were immersed for 30 seconds in products broth and dried for 30 minutes. Eight replicates per concentration were used and each disc was infested with five apterous adult females of A. gossypii uniform in size and confined for 10 days. Compostonat®, Rotenat® and Neempro provided negative ri decreasing A. gossypii population. Natuneem® and Neemseto® and the essential oil of F. vulgare showed positive ri increasing the population. The coefficients of determination (R2) of regression lines ranged from 0.46 to 0.85. The essential oils of C. winterianus, C. ambrosioides and P. aduncum were not statistically significant precluding the establishment of regression lines.

Contrasting effects of climate on grey heron, malleefowl and barn owl populations

Context The population dynamics of many wildlife species are associated with fluctuations in climate. Food and abundance may also influence wildlife dynamics. Aims The present paper aims to evaluate the relative effects of climate on the annual instantaneous population growth rate (r) of the following three bird species: grey heron and barn owl in parts of Britain and malleefowl in a part of Australia. Methods A priori hypotheses of mechanistic effects of climate are derived and evaluated using information theoretic and regression analyses and published data for the three bird species. Climate was measured as the winter North Atlantic Oscillation (NAO) for herons and owls, and rainfall and also the Southern Oscillation Index (SOI) for malleefowl. Key results Population dynamics of grey heron were positively related to the winter NAO, and of malleefowl were positively related to annual rainfall and related in a non-linear manner to SOI. By contrast, population dynamics of barn owl were very weakly related to climate. The best models for the grey heron differed between time periods but always included an effect of the NAO. Conclusions The annual population growth rate of grey heron, malleefowl and barn owl show contrasting relationships with climate, from stronger (heron and malleefowl) to weaker (barn owl). The results were broadly consistent with reported patterns but differed in some details. Interpretation of the effects of climate on the basis of analyses rather than visual assessment is encouraged. Implications Effects of climate differ among species, so effects of future climate change may also differ.

Environmental and fishing limitations to the rebuilding of the northern Gulf of St. Lawrence cod stock (Gadus morhua)

Time series of life history traits determining the reproductive potential and productivity of Atlantic cod ( Gadus morhua ) in the northern Gulf of St. Lawrence (nGSL) were obtained for the period covering the collapse and failure of the stock to recover. Decreasing trends in these traits were observed under unfavourable oceanographic conditions, with lowest values reached in the early 1990s. These changes had a negative impact on reproductive rate and instantaneous rate (r) of population growth. Estimates of r used as a proxy of stock productivity were negative when the stock collapsed, indicating that the biomass would have decreased even without fishing. Population abundance projections for the recent period suggest a potential increase in population size of 7.3% per year, with a doubling time of 10.5 years in the absence of exploitation and a near 0% rate with current fishing mortality, indicating that present harvesting does not allow any rebuilding of the stock. Given the similarities in environmental conditions and key life history traits, the situation in the nGSL might reflect the state of many northwest Atlantic cod stocks.

Population growth of Cathartus quadricollis (Guerin- Meneville) (Coleoptera: Silvanidae) in products stored at different temperatures

This study aims to assess the influence of temperature and food type on the instantaneous population growth rate of Cathartus quadricollis (Guerin-Meneville). ri was evaluated at 20, 25, 30 and 35°C in association with broken maize, wheat, sorghum and rice, maize flour and wheat bran. The optimum development temperature was also estimated for each food. The instantaneous growth rate of C. quadricollis was influenced by temperature and food type. ri values were low at the 20°C in all food types and increased at 25°C. There was a slight reduction at 30°C, but there was no insect development at 35°C, except for maize flour, with low ri (instantaneous population growth rate) values. Optimum temperature for C. quadricollis growth ranged from 26.26 to 27.14°C for the most suitable foods (broken maize, wheat and sorghum and maize flour). Under favorable conditions of food and temperature, C. quadricollis showed high population growth values in relation to other stored-product pests, indicating that this species has reproductive potential to become an important stored-product pest. Key words: Reproductive parameters, environmental conditions, food type.

Stock–Recruitment Dynamics and the Maximum Population Growth Rate of the Barndoor Skate on Georges Bank

AbstractIn 1998, the barndoor skateDipturus laeviswas reported to have been locally extirpated in parts of its northern range and to be potentially on the brink of extinction. Managers were faced with assessing the species with virtually no information other than a limited number of individuals observed in annual groundfish surveys. Since that time, a number of the primary life history parameters have been estimated, but the population dynamics of the species remain largely unexplored. In this study, we use information from the National Marine Fisheries Service (NMFS) annual groundfish surveys to investigate two critical components of barndoor skate population dynamics: the relationship of recruitment to spawner abundance and the maximum population growth rate. A strong stock–recruitment relationship was found in the fall survey data, suggesting that recruitment is closely tied to spawner abundance. The Ricker and Beverton–Holt stock–recruit models were fitted to the survey data, and estimates of the slope at the origin was generated. These parameters provided an estimate of the maximum annual reproductive rate, which was then converted to an estimate of the instantaneous maximum population growth rate of 0.37–0.38 per year. A second analysis was also conducted using a Leslie matrix and data from the NMFS survey. Observed rates of population change were used to estimate early life history parameters and incorporate density dependence into the density‐independent framework of a Leslie matrix demographic model. From this method, the instantaneous maximum population growth for the barndoor skate was estimated to be 0.36–0.48 per year. Our results suggest that the species is more resilient to fishing pressure than previously believed and is capable of growing at an instantaneous rate in excess of 35% at low population sizes.

Organophosphate resistance in the maize weevil Sitophilus zeamais: Magnitude and behavior

Development of insecticide resistance is a serious worldwide challenge for pest management of stored-product insects, as recognized since the FAO Global Survey of the mid-1970s. In this study, we carried out a survey of physiological and behavioral resistance to two organophosphate insecticides (chlorpyrifos-methyl and fenitrothion) in 14 populations of Sitophilus zeamais Motsch. (Coleoptera: Curculionidae) from Brazil and one from Paraguay and investigated if differences in population growth, body size, and respiration rate were associated with the resistance. Concentration-mortality bioassays were carried out and behavioral resistance was studied by recording the walking behavior on filter-paper half-treated with insecticide and determining the distance walked, walking velocity, resting time, and time spent on the treated side of the arena. The instantaneous rate of population growth ( r i ) was determined, and so were maize consumption, insect body mass, and insect respiration rate. Only low levels of resistance were detected to chlorpyrifos-methyl (≤6.1-fold) and fenitrothion (≤7.7-fold). The walking behavior on treated surfaces varied among the populations, but no repellence was detected and no significant correlation was observed between the level of organophosphate resistance and the mobility parameters assessed. Population growth and respiration rate were similar among the populations although there were differences in food consumption and insect body mass. The results of this study indicate that the levels of organophosphate resistance in Brazilian populations of maize weevil are low and not associated with fitness costs. No evidence of behavioral avoidance to organophosphates was observed.

Ozone as a management alternative against phosphine-resistant insect pests of stored products

This study was carried out to assess ozone toxicity to 16 populations of Tribolium castaneum (Herbst), 11 populations of Rhyzopertha dominica (F.) and nine populations of Oryzaephilus surinamensis (L.) collected from six regions of Brazil. These populations were also used to test if there is cross-resistance to ozone and phosphine. The relationship between susceptibility to ozone and respiration rate, and associated fitness costs were also evaluated. The instantaneous population growth rate ( r i ), CO 2 production and mean insect body mass of each population were measured. Ozone toxicity was determined using time-response bioassays at the dosage rate of 150 ppm ozone in a continuous flow of 2 L min −1. All of the populations were susceptible to ozone and there was no cross-resistance to ozone and phosphine. The populations of each species differed in respiration rate and body mass, but there was no significant association between respiration rate or body mass and susceptibility to ozone, as was also the case for the instantaneous rate of population increase ( r i ). As none of the populations showed resistance to ozone, regardless of their susceptibility to phosphine, ozone is a potential alternative for phosphine resistance management in the insect species evaluated in this study.

Using Demographic Models to Determine Intrinsic Rate of Increase and Sustainable Fishing for Elasmobranchs: Pitfalls, Advances, and Applications

AbstractLeslie matrices and life tables are demographic models commonly used to evaluate the ability of specific elasmobranch life history strategies to sustain given levels and patterns of fishing pressure. These models are generally density independent and provide an instantaneous rate of population growth for a specified set of life history traits that correspond to a specific population size. Many investigators are using these models to compute rates of population growth that they claim are estimates of the maximum population growth rate (rintrinsic); they then use these estimates to compute purported estimates of maximum sustainable fishing mortality. However, neither a Leslie matrix nor a life table can be used to estimate rintrinsic without additional information, except in the special case where a severely depleted population is modeled. Only in a severely depleted population will competition for resources be at a minimum and both density‐dependent compensation and the rate of population growth be at a maximum (i.e., at rintrinsic). The fundamental problem is to determine the life history parameters that would occur if the population were extremely depleted because extensive observations on extremely depleted populations are rare. In the absence of such data, rintrinsic can only be estimated from these types of density‐independent models by extrapolating observed population growth rates toward zero population size. We illustrate the problems in, and describe methods for, estimating rintrinsic and present information on two species of elasmobranch: barndoor skate Dipturus laevis and lemon shark Negaprion brevirostris

Climate, food, density and wildlife population growth rate

1. The aim of this study was to derive and evaluate a priori models of the relationship between annual instantaneous population growth rate (r) and climate. These were derived from the numerical response of annual r and food, and the effect of climate on a parameter in the numerical response. The goodness of fit of a range of such deductive models to data on annual r of Soay sheep and red deer were evaluated using information-theoretic (AICc-based) analyses. 2. The analysis for sheep annual r showed negative effects of abundance and negative effects of the interaction of abundance and climate, measured as March rainfall (and winter NAO) in the best fitting models. The analysis for deer annual r showed a negative effect of deer abundance and a positive effect of climate measured as March rainfall (but a negative effect of winter NAO), but no interaction of abundance and climate in the best fitting models. 3. There was most support in the analysis of sheep dynamics for the ratio numerical response and the assumption that parameter J (equilibrium food per animal) was influenced by climate. In the analysis of deer dynamics there was most support for the numerical responses assuming effects of food and density (Ivlev and density, food and density, and additive responses) and slightly less support for the ratio numerical response. The evaluation of such models would be aided by the collection of and incorporation of food data into the analyses.

Lethal and sub-lethal selectivity of fenbutatin oxide and sulfur to the predator Iphiseiodes zuluagai (Acari: Phytoseiidae) and its prey, Oligonychus ilicis (Acari: Tetranychidae), in Brazilian coffee plantations

Lethal concentration (LC) has been widely used to estimate pesticide toxicity. However, it does not consider the sub-lethal effects. Therefore we included the instantaneous rate of increase in association with LC to estimate population-level effects of the acaricides fenbutatin oxide and sulfur on the predator Iphiseiodes zuluagai and its prey, the phytophagous southern red mite, Oligonychus ilicis. The predator was 32.84x and 17.20x more tolerant to fenbutatin oxide and sulfur, respectively, than its prey, based on LC50 estimates obtained from acute concentration-mortality bioassays. The instantaneous rate of population growth in both mite species decreased with increasing acaricide concentration. Both acaricides provided effective control of O. ilicis at their recommended concentrations, but sulfur drastically compromised the predator populations quickly leading them to extinction due to the low reproductive potential of this species compared with its prey.

Life-history responses of Daphnia pulicaria to diets containing freshwater diatoms: Effects of nutritional quality versus polyunsaturated aldehydes

Like marine diatoms, some freshwater diatoms produce α, β, γ, δ-polyunsaturated aldehydes (PUA) when damaged. Some of these oxylipins are suspected of impairing egg viability in marine copepods. To determine whether these compounds also play a role in influencing the trophic interactions in freshwater environments, we measured growth and reproduction of the cladoceran Daphnia pulicaria in response to diets composed of seven diatoms differing in PUA production. The juvenile growth rate of Daphnia varied with the diatom species, but was not related to oxylipin production. Egg hatching success was nearly 100% in all clutches for all diets, except with a diet of the decadienal producing Fragilaria sp., where it decreased dramatically in clutches 5–7. In vitro tests of egg hatching in the presence of PUA showed a dose-dependent inhibition for decadienal. Population parameters (i.e., life-time fecundity and instantaneous rate of population growth) were not affected by PUA, as the contribution of late clutches to them was negligible. Consequently, the wound-activated production of PUA by diatoms cannot be regarded as a defensive mechanism against Daphnia population recruitment.

Effect of interaction between density dependence and toxicant exposure on population growth rate of the potworm Enchytraeus doerjesi

Laboratory cultures of the potworm Enchytreaus doerjesi were exposed to zinc-contaminated soil at nominal concentrations 0, 75, 150, 300, or 600 mg Zn/kg dry weight for four weeks (one generation) at five different initial densities (5, 10, 20, 40, or 80 individuals per 20 g soil). The final culture numbers and the instantaneous population growth rate, r(i) were used as measures of culture response to both factors. In all treatments, the number of individuals increased during the experiment; thus, all the cultures exhibited positive r(i) values. The population growth rates decreased significantly with increasing Zn concentration and were also affected by the initial density. However, the latter effect was nonlinear and the initial density of 20 individuals resulted in the highest r(i) values throughout the whole range of Zn concentrations tested, while the lowest population growth rates were recorded for the highest initial density. Significant interaction between zinc toxicity and population size was found for the two lowest initial densities, where synergistic effects were noted. No effect of density on zinc toxicity was found at initial densities of 20 to 80 individuals, most probably because the animals were fed ad libitum and thus were not food limited.

Optimal Intraguild Foraging and Population Stability

This article explores effects of adaptive intraguild predation on species coexistence and community structure in three species' food webs. Two Lotka–Volterra models that assume a trade-off between competition and predation strength are considered in detail. The first model does not explicitly model resource dynamics and is considered with both nonadaptive and adaptive intraguild predation; in the latter case predators choose their diet in order to maximize their instantaneous population growth rate. The second model includes resource population dynamics. Effects of adaptive intraguild predation on the community structure along a gradient in environment productivity are analyzed and compared with some experimental results of protist food webs. Conditions under which intraguild predation is adaptive are discussed for both models. It is proved that if intraguild predators are perfect optimizers then intraguild predation should decrease with increasing environmental productivity and adaptive intraguild predation is a stabilizing factor provided environmental productivity is high enough.

Effect of starvation time on the prey capture behaviour, functional response and population growth of Asplanchna sieboldi (Rotifera)

1. We examined the effect of different periods of prior starvation(from 30 min to 16 h) on the prey capture behaviour, and functional and numerical responses of the predatory rotifer Asplanchna sieboldi using the rotifer Brachionus calyciflorus as prey.2. Feeding activity (i.e. encounter, attack, capture and ingestion) by Asplanchna increased significantly with increasing prey densities from 2 to 16 mL−−1 and with increasing prior starvation periods from 0.5 to 8 h.3. Asplanchna sieboldi showed a type II functional response at all the prior starvation periods tested. The asymptotic prey density was highest after 8 h of starvation.4. The instantaneous population growth rate of A. sieboldi ranged from 0.089 ± 0.044 (when starved for 8 h in every 24 h and at a prey density of 2 individuals mL−−1 for the other 16 h) to 1.015 ± 0.142 in the control (no starvation and at a prey density of 16 individuals mL−−1). The effect of starvation time on the numerical response was evident only at the higher prey density.

A Maximum Likelihood Methodology for Estimating Length-at-Maturity with Application to Pacific Cod (Gadus macrocephalus) Population Dynamics

A maximum likelihood methodology for the analysis of maturity-at-length data is presented, and illustrated with data for female Pacific cod (Gadus macrocephalus) from Hecate Strait, British Columbia. Our approach explicitly accounts for the binomial nature of maturity data. Estimated maturity–length relationships show substantial differences for females sampled from different grounds within Hecate Strait, as well as large between-year differences in the maturity–length relationships for individual grounds. However, the maturity–length characteristics for a single ground are stable thoughout the spawning season, and we argue that the observed temporal variability is unlikely to be a sampling artefact. Assuming constant somatic growth rates, these differences correspond to shifts of slightly more than 1 yr in the median age-at-maturity; this shift implies that the instantaneous population growth rate rm, for Pacific cod can increase by up to 0.25 yr−1 in years when maturation occurs at smaller body size. This corresponds to an increase of over 50% in the sustainable fishing mortality rate, independent of other factors. Our results suggest that more attention should be focussed on assessing the reproductive dynamics of adult fish.