Delayed density dependence and oscillatory population dynamics in overlapping-generation systems of a seed beetle Callosobruchus chinensis: matrix population model

Long-term experimental systems with overlapping generations using a seed beetle, Callosobruchus chinensis, were maintained by providing 5 g of azuki beans (Vigna angularis) in two different renewal intervals: either 7 days or 10 days. The 7-day-renewal system (system 1) showed oscillatory dynamics with a constant periodic cycle of ca. 7 weeks. More stable population dynamics were seen in the 10-day-interval system (system 2). Short-term experiments showed that survivorship of adults increased with higher adult density, and that the survival rate of adults up to the age of 7 days was much higher than up to 10 days of age. In addition, the per capita production of hatched eggs by females which had survived for 7 days increased with increasing density experienced by the females. Females aged 10 days rarely laid eggs which hatched. We constructed a matrix population model based on either 1 week for system 1 or 10 days for system 2. The model included five stages in system 1: the hatched egg, the final instar larva, the pupa, the young adult and the old adult. Four stages were incorporated in the model for system 2: the young instar larva, the pupa, the young adult, and the old adult. Logistic-difference equations were applied to formulate both overcompensatory density dependence in the hatched-egg production by adults and undercompensatory response in the larval development up to the pupa. The survivorship of young adults to the old stage and the per capita hatched-egg productivity of the old females followed a linear regression against the young adult density. Inside-bean processes were adjusted to be equivalent in the two models, irrespective of the resource renewal intervals. The model predicted that system 1 would oscillate for a long time but that system 2 would rapidly converge to the equilibrium point. Multiplicative effects of both the delayed density dependence through interstage restraint effects and the overcompensatory density dependence in hatched-egg production generated various dynamic patterns ranging from a quickly disappearing damped oscillation to stable limit cycles in system 1. The relationship between resource renewal cycles and delayed density dependence was discussed based on these simulations.     

A population model for the black tern Chlidonias niger in West-Europe

Based on empiric data of breeding success and accurate number trends in The Netherlands, a population model for the black tern was constructed. This model is based on Leslie matrices. Reproductive parameters from the four most important landscape types (river landscape, agricultural grasslands, peat marsh and heath land/moors) are used as model input. Highly accurate national population trend data were used to obtain the best (least square) estimate of overall adult and subadult survival (resp. 0.849 and 0.595). Estimating survival parameters in this way might be useful for threatened (bird) species, especially if catching and ringing is difficult or less desired from a conservation perspective. The model shows the actual importance of the river landscape as the main source for reproductive output of the Dutch black tern population. The prediction model was subsequently used to test different conservation strategies for the Dutch black tern population. Conservation strategies ranged from a null scenario (no change in conservation effort) to in- or decreasing the number of rafts in the most productive landscape (river landscape) to a scenario where breeding success is improved recently in agricultural grasslands via minimizing disturbance. For all scenarios, the model predicts a slow to rapid population increase in the Dutch black tern population after 10–20 years. Improving breeding success in agricultural grasslands habitat has the highest added value.     

Toxicity of Dinophysis spp. in relation to population density and environmental conditions on the Swedish west coast

The aim of this study in the field was to investigate whether there are differences between the outer archipelago (Gullmar Fjord) and a semi-enclosed fjord system (Koljö Fjord) in occurrences of D. acuta and D. acuminata as well as in their content of diarrheic shellfish toxin (DST) per cell. When all data pairs of cell toxicity of D. acuminata and the corresponding number of cells l⁻¹ from the two sites were tested in a regression analysis, a statistically significant negative correlation became evident and was apparent as a straight line on a log–log plot (p < 0.0001). Obviously, there was an overall inverse relationship between the population density of D. acuminata and the toxin content per cell. Plotted on a linear scale, all data-pairs of cell toxicity and cell number made up a parabolic curve. On this curve the data-pairs could be separated into three groups: (i) D. acuminata occurring in numbers of fewer than approximately 100 cells l⁻¹, and with a toxin content per cell above 5 ρg cell⁻¹; (ii) cell numbers between 100 and approximately 250 cells l⁻¹ with a cell toxin content from 5 to 2 ρg cell⁻¹; (iii) when the population became greater than 250 cells l⁻¹, the toxicity, with few exceptions, was less than 2 ρg cell⁻¹. By applying this subdivision, some clear patterns of the distribution of the differently toxic D. acuminata became evident. When comparing the cell toxicity of the two sites, it was obvious that the D. acuminata cells from all depths from the Gullmar Fjord as a mean were significantly more toxic compared to the Koljö Fjord samples. The results have demonstrated that approximately 100 high-toxicity cells in a low-density population at surface may lead to the same accumulation of DST in a mussel as the ingestion of 1500 low-toxicity cells from a high-density pycnocline population.     

Effects of population density on the sediment mixing induced by the gallery-diffusor Hediste (Nereis) diversicolor O.F. Müller, 1776

The aim of this work was to quantify the intensity of sediment mixing induced by the gallery-diffusor (functional bioturbation group) Hediste diversicolor as a function of density, using particles tracers (luminophores). In order to assess the impact of density on sediment reworking, a 1-D model was used to obtain sediment reworking coefficients such as Db (biodiffusion-like) and r (biotransport). Densities used in this experiment corresponded to population densities observed in the sampling area (Saint-Antoine Canal, Gulf of Fos, France): 144, 288, 577, 1153 indiv/m². At first, results showed that neither luminophore maximum burying depth nor the more marked tracer accumulation areas were influenced by density. Thus density did not seem to have any influence on size of galleries or complexity of structure. Then, density-dependent relations with Db (biodiffusion-like mixing) and r (biotransport) were highlighted with an observed process intensity rate twice as high at highest worm density. On the other hand, Db and r per capita coefficients were negatively influenced by density. Db and r per capita at highest density were equal to ∼ 20% of individual Db and r obtained at the lowest density. Finally, this study showed the importance of density which appears to be a key parameter in the functioning of the sedimentary ecosystem.     

A model for the temperature and density dependent reemergence of the bark beetle Ips typographus

A model is presented that describes the reemergence of parent spruce bark beetles, Ips typographus, based on breeding density and temperature conditions. Laboratory data obtained at one constant temperature provide the distribution of reemergence time and different combinations of threshold temperatures and degreedays (°D) at mean reemergence. Of these combinations, 167.71 °D above 7.5 °C gave the best correspondence between model prediction and field data obtained from densely infested standing trees. The model was in good agreement with the reemergence pattern found for two groups of infested logs under different temperature conditions when adjusted for the lower breeding density. The applicability of the model in the study of bark beetle reproductive biology and in forest management is discussed. The method used to construct the model should be useful in developing other models for poikilothermic processes.

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Résumé Ce modèle décrit la réémergence d'adultes d'I. typographus L. (Coleoptera, Scolytidae) en fonction de la densité et de la température.Les résultats obtenus en laboratoire à des températures constantes fournissent la distribution des réémergences et pour les dates de réémergence moyenne les différentes combinaisons de température de seuil et de degré de jour (°D). De toutes ces combinaisons, 167.71 °D au-dessus de 7,5 °C fournit la meilleure concordance entre les prévisions du modèle et les observations dans la nature à partir d'arbres fortement attaqués.Le modèle a montré un bon accord avec la réémergence observée dans deux groupes de branches attaquées dans différentes conditions de la température quand il a été ajusté aux faibles densités d'élevage.La discussion examine les possibilités d'application du modèle à l'étude de la biologie de la reproduction d'I. typographus et à l'aménagement forestier.La méthode utilisée pour construire le modèle pourrait être employée pour en développer d'autres chez des poikilothermes.

     

A theoretical model to predict distribution of the fabric tensor and apparent density in cancellous bone

 The adaptation of cancellous bone to mechanical forces is well recognized. Theoretical models for predicting cancellous bone architecture have been developed and have mainly focused on the distribution of trabecular mass or the apparent density. The purpose of this study was to develop a theoretical model which can simultaneously predict the distribution of trabecular orthotropy/orientation, as represented by the fabric tensor, along with apparent density. Two sets of equations were derived under the assumption that cancellous bone is a biological self-optimizing material which tends to minimize strain energy. The first set of equations provide the relationship between the fabric tensor and stress tensor, and have been verified to be consistent with Wolff’s law of trabecular architecture, that is, the principal directions of the fabric tensor coincide with the principal stress trajectories. The second set of equations yield the apparent density from the stress tensor, which was shown to be identical to those obtained based on local optimization with strain energy density of true bone tissue as the objective function. These two sets of equations, together with elasticity field equations, provide a complete mathematical formulation for the adaptation of cancellous bone. Received: 25 February 1997/Revised version: 23 September 1997     

Effect of Moniliformis moniliformis density on distribution within the definitive host population (Rattus norvegicus)

The population dynamics of Moniliformis moniliformis was studied in ‘free-ranging’ laboratory rats, Rattus norvegicus, presented with different relative density levels of M. moniliformis in cockroaches, Periplaneta americana. Changes in selected population parameters of the negative binomial distribution were evaluated as indicators of changes in aggregation. A significant increase in the degree of aggregation of parasites occurred as a result of the increase in relative density of infective stages available to the rats. This increase in aggregation was due to the increase in over-dispersion that occurred in female rats only. The degree of aggregation in females was found to be significantly higher than that in males at both treatment levels. The best indicators of the degree of aggregation were found to be the ratio of the variance to the relative density and the ratio of the log-variance to log-relative density. Changes in k were not correlated with changes in over-dispersion or the relative density.     

Novel behavioural characteristics of the superoxide dismutase 1 G93A (SOD1G93A) mouse model of amyotrophic lateral sclerosis include sex‐dependent phenotypes

Amyotrophic lateral sclerosis (ALS) involves the rapid degeneration of upper and lower motor neurons leading to weakening and paralysis of voluntary movements. Mutations in copper‐zinc superoxide dismutase 1 (SOD1) are a known genetic cause of ALS, and the SOD1 ^G93A mouse has been used extensively to investigate molecular mechanisms in ALS. In recent years, evidence suggests that ALS and frontotemporal dementia form a spectrum disorder ranging from motor to cognitive dysfunctions. Thus, we tested male and female SOD1 ^G93A mice for the first time before the onset of debilitating motor impairments in behavioural domains relevant to both ALS and frontotemporal dementia. SOD1 ^G93A males displayed reduced locomotion, exploration and increased anxiety‐like behaviours compared with control males. Intermediate‐term spatial memory was impaired in SOD1 ^G93A females, whereas long‐term spatial memory deficits as well as lower acoustic startle response, and prepulse inhibition were identified in SOD1 ^G93A mice of both sexes compared with respective controls. Interestingly, SOD1 ^G93A males exhibited an increased conditioned cue freezing response. Nosing behaviours were also elevated in both male and female SOD1 ^G93A when assessed in social paradigms. In conclusion, SOD1 ^G93A mice exhibit a variety of sex‐specific behavioural deficits beyond motor impairments supporting the notion of an ALS‐frontotemporal spectrum disorder. Thus, SOD1 ^G93A mice may represent a useful model to test the efficacy of therapeutic interventions on clinical symptoms in addition to declining motor abilities.