Rythmes nutritionnels et organisation trophique d'une population de crustacés pélagiques (Euphausiacea)

The nature of the food (animal, plant or mixed) and the fullness of the stomachs at different times of the day have been studied through dissection of 18620 specimens representative of almost all the euphausiid species of the Central and Western Tropical Pacific Ocean. Animal food predominates in 22 of the 28 species studied, while 12 can be considered as omnivorous; only 4 are mainly phytophagous. The trophic level of a given species is more or less the same in different zones, but scarcity of phytoplankton in oligotrophic tropical regions results in an increase of the trophic level of herbivorous and omnivorous species. There is no correlation between trophic level and vertical distribution of a species. Each species follows a clearly defined feeding rhythm, usually characteristic for each genus: nutrition most active by night in Euphausia, continuous in Thysanopoda, restricted to light hours in Stylocheiron, mainly from noon to midnight in Nematoscelis and Nematobrachion. As a rule, it is obvious that the smaller the daily vertical migration, the more pronounced the feeding rhythm: the range of fluctuations in fullness of stomachs over 24 h is weak or non-existent in migrating species, maximum in non-migrating ones. Nevertheless, daily vertical migration does not appear to be “advantageous” from the point of view of trophic efficiency: assuming that the stomachal transit is the same for all species (a speculative proposition), it is shown that the ratio “total biomass of species: food consumed during 24 h”, i.e., “biomass permanently available for the upper link: biomass eaten daily at the expense of the lower link” is 4 times higher in non-migrating than in migrating species. It is thus considered that daily vertical migration is an expensive manner to transfer energy from link to link, and therefore fulfills other functions, amongst which diffusion throughout the whole water column of the biomass produced in the upper levels is probably one of the most important.     

Système planctonique et pollution urbaine: un aspect des populations zooplanctoniques

Zooplankton populations of a marine area exposed to pollution from the sewage outfall of Marseille-Cortiou have been studied in relation to their horizontal distribution related to distance from the outfall. Samples were collected by various means, and confirmed preliminary results which had indicated that some species tend to cluster in a facies characteristic of a polluted environment. The zone in immediate proximity to the outfall is the most turbid zone; it is extremely poor in fauna but not azoic. Outside this zone and up to 500 m distance from the sewage outlet into the sea, the most euryoecious species (e.g. Acartia clausi, Oithona nana, Euterpina acutifrons, and Oikopleuridae) are frequently present. An intermediate zone then occurs, in which, together with the species mentioned above, other species quite tolerant to pollution (e.g. Clausocalanus spp., Centropages typicus, Paracalanus spp., Candacia armata and some Corycaeidae and Oncaeidae) are well represented. Outside this zone, the zooplanktonic populations show a better defined and more stable structure. Paracalanus spp. are still very abundant, together with Fritillaridae, and fish eggs and larvae. Beneath the turbid surface zone, the impact of pollution seems less marked, and an homogenous zooplankton assemblage is found whose composition is identical to that of species inhabiting unpolluted areas.

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avec la participation du Groupe EPOPEM (Equipe de Pollution Pélagique de Marseille)     

Estimation in situ d'une population d'Oikopleura longicauda (Appendicularia) à l'aide de deux filets de maille différente

A population of Oikopleura longicauda was sampled daily for 10 days, a period longer than their life cycle, using two nets of different mesh size (53 and 200 m). Analysis of variance revealed that the number of specimens collected by the two nets was not significantly different for individuals larger than 300 m in trunk length. A grand mean regression plotted for log of length versus log of number of specimens indicated that the number of small-sized O. longicauda (<300 m), which are not quantitatively sampled by nets, can be estimated from the collections by use of a coefficient of correction.     

Etude préliminaire des effets de la pollution globale sur le peuplement planctonique des ports Nord de Marseille

A preliminary study of hydrological and biological parameters has been undertaken on surface waters of the Northern Harbour of Marseilles, France. The present work is part of a broader research scheme relating to secondary zooplankton production in an environment half closed off from the sea. It represents a primary contribution to the exploration of halfclosed or closed marine spaces which come under the influence of pollution and eutrophic factors. The complexity of the harbour milieu is discussed, and the basic problems defined. The harbour waters are characterized by high concentrations of seston; this parameter enables a delimitation dividing polluted waters from the Marseilles Gulf waters to be determined. Other hydrological parameters, although of more complex nature, may also help, in some cases, in characterizing harbour waters. High temperory concentrations of characteristic holoplankton species, which seem to find here their preferred biotope, divide the harbour milieu from the open waters of the Gulf, as do other meroplanktonic or semi-benthic species. Finally, the half-closed milieu studied here provides, for particular periods and under conditions still to be specified, a eutrophic milieu which promotes intensive growth of zooplankton and phytoplankton.     

Estimating population dynamics without population data

We develop a biologically correct cost system for production systems facing invasive pests that allows the estimation of population dynamics without a priori knowledge of their true values. We apply that model to a data set for olive producers in Crete and derive from it predictions about the underlying population dynamics. Those dynamics are compared to information on population dynamics obtained from pest sampling with extremely favorable results.     

Evolution d'une population de copépodes dans le système des courants équatoriaux de l'Océan Pacifique. Zoogéographie, écologie et diversité spécifique

During the cruise “Alizé” along the Equator in the Pacific Ocean from 86° 20 W to 151° 01 E (Fig.1), 33 night tows were made with a 1 m plankton net, in the 0 to 200 m layer. The samplings show, 3 types of copepod distribution (Figs. 2 to 5); the main type presents the well-documented decrease from east to west. The different distributions seem controlled by: suface phytoplankton abundance in the case of Eucalanus sublenuis temperature and the thermocline in Euchaeta media and Pleuromamma quadrungulata; type and availability of prey in Euchaeta marina; upwelling and the Peru current in Eucalanus elongatus hyalinus and Rhincalanus nasutus. The 3 warm-water species Rhincalanus cornutus, Eucalanus attenuata and Eucalanus subcrassus are more abundant in the western part of the Pacific Ocean, where temperature is higher. The 2 cosmopolitan species Pleuromamma xiphias and P. abdominalis do not show any clear relationship with the biotope. Probably the presence of some species in the upper water layer in the zone of intense divergence and upwelling emphasizes the westward decrease. It has been possible to define 4 zones by phytoplankton distribution, currents, vertical circulation, and the physical and chemical properties of the biotope; these zones agree with the zonation of the copepods in accordance with the results of a rank test. Within these limits, the 4 indices of specific diversity I=-Σ pi log₂ pi and the equitibility have been calculated. The diversity variations account for the ecosystem evolution after Margalef's theory. The lower specific diversity in the oriental zone is related to the well developed divergence, the high rates of nutrients, the intense phytoplankton production, the instability in time and the southern water inflow; in this zone, the ecosystem is in an early stage of succession with a percentage of herbivores such as Eucalanus subtenuis (45%) present. The diversity index confirms the changes introduced by the trade winds along the Equator, mainly in the eastern part of the Pacific Ocean.     

Estimating population abundance using counts from an auxiliary population

Environmental and Ecological Statistics - We develop a new method for estimating population abundance for notoriously difficult to count populations. This is made possible using an easy to count...     

Robust population management under uncertainty for structured population models.

Structured population models are increasingly used in decision making, but typically have many entries that are unknown or highly uncertain. We present an approach for the systematic analysis of the effect of uncertainties on long-term population growth or decay. Many decisions for threatened and endangered species are made with poor or no information. We can still make decisions under these circumstances in a manner that is highly defensible, even without making assumptions about the distribution of uncertainty, or limiting ourselves to discussions of single, infinitesimally small changes in the parameters. Suppose that the model (determined by the data) for the population in question predicts long-term growth. Our goal is to determine how uncertain the data can be before the model loses this property. Some uncertainties will maintain long-term growth, and some will lead to long-term decay. The uncertainties are typically structured, and can be described by several parameters. We show how to determine which parameters maintain long-term growth. We illustrate the advantages of the method by applying it to a Peregrine Falcon population. The U.S. Fish and Wildlife Service recently decided to allow minimal harvesting of Peregrine Falcons after their recent removal from the Endangered Species List. Based on published demographic rates, we find that an asymptotic growth rate lambda > 1 is guaranteed with 5% harvest rate up to 3% error in adult survival if no two-year-olds breed, and up to 11% error if all two-year-olds breed. If a population growth rate of 3% or greater is desired, the acceptable error in adult survival decreases to between 1% and 6% depending of the proportion of two-year-olds that breed. These results clearly show the interactions between uncertainties in different parameters, and suggest that a harvest decision at this stage may be premature without solid data on adult survival and the frequency of breeding by young adults.     

Extinction-effective population index: incorporating life-history variations in population viability analysis

Viability status of populations is a commonly used measure for decision-making in the management of populations. One of the challenges faced by managers is the need to consistently allocate management effort among populations. This allocation should in part be based on comparison of extinction risks among populations. Unfortunately, common criteria that use minimum viable population size or count-based population viability analysis (PVA) often do not provide results that are comparable among populations, primarily because they lack consistency in determining population size measures and threshold levels of population size (e.g., minimum viable population size and quasi-extinction threshold). Here I introduce a new index called the "extinction-effective population index," which accounts for differential effects of demographic stochasticity among organisms with different life-history strategies and among individuals in different life stages. This index is expected to become a new way of determining minimum viable population size criteria and also complement the count-based PVA. The index accounts for the difference in life-history strategies of organisms, which are modeled using matrix population models. The extinction-effective population index, sensitivity, and elasticity are demonstrated in three species of Pacific salmonids. The interpretation of the index is also provided by comparing them with existing demographic indices. Finally, a measure of life-history-specific effect of demographic stochasticity is derived.     

An architectural model of spring wheat: Evaluation of the effects of population density and shading on model parameterization and performance

ADELwheat is an architectural model that describes development of wheat in 3D. This paper analyzes the robustness of the parameterization of ADELwheat for spring wheat cultivars in relation to plant population density and shading. The model was evaluated using data from two spring wheat experiments with three plant population densities and two light regimes. Model validation was done at two levels of aggregation: (a) by comparing parameterization functions used as well as parameter values to the data (leaf and tiller appearance, leaf number, blade dimensions, sheath length, internode length) and (b) by comparing ground cover (GC) and leaf area index (LAI) of simulated virtual wheat plots with GC and LAI calculated from data. A sensitivity analysis was performed by modulating parameters defining leaf blade dimensions and leaf or tiller appearance rate.In contrast to population density, shading generally increased phyllochron and delayed tiller appearance. Both at the level of the organ and at the level of the canopy the model performed satisfactorily. Parameterization functions in the model that had been established previously applied to independent data for different conditions; GC and LAI were simulated adequately at three population densities. Sensitivity analysis revealed that calibration of phyllochron and blade area needs to be accurate to prevent disproportional deviations in output.The robustness of the model parameterization and the simulation performance confirmed that the model is a complete architectural model for aboveground development of spring wheat. It can be used in studies that require simulation of spring wheat structure, such as studies on plant–insect interaction, remote sensing, and light interception.     

Removal process estimation of population size for a population with a known sex ratio

A removal model for estimating population size which uses the known population sex ratio is studied. A maximum likelihood estimate and an optimal martingale estimate of the population size are proposed. Their standard errors and large sample properties are obtained. Simulation studies are reported, and the performance of the proposed estimators are compared with the standard maximum likelihood estimator which ignores the sex ratio information. An example on a capture study of deer mice is given.     

Setting population targets for mammals using body mass as a predictor of population persistence

Conservation planning and biodiversity assessments need quantitative targets to optimize planning options and assess the adequacy of current species protection. However, targets aiming at persistence require population‐specific data, which limit their use in favor of fixed and nonspecific targets, likely leading to unequal distribution of conservation efforts among species. We devised a method to derive equitable population targets; that is, quantitative targets of population size that ensure equal probabilities of persistence across a set of species and that can be easily inferred from species‐specific traits. In our method, we used models of population dynamics across a range of life‐history traits related to species’ body mass to estimate minimum viable population targets. We applied our method to a range of body masses of mammals, from 2 g to 3825 kg. The minimum viable population targets decreased asymptotically with increasing body mass and were on the same order of magnitude as minimum viable population estimates from species‐ and context‐specific studies. Our approach provides a compromise between pragmatic, nonspecific population targets and detailed context‐specific estimates of population viability for which only limited data are available. It enables a first estimation of species‐specific population targets based on a readily available trait and thus allows setting equitable targets for population persistence in large‐scale and multispecies conservation assessments and planning.     

Réponse d'une communauté de diatomées de glace à un gradient de salinité (baie d'Hudson)

Sea ice offers a physical support to the growth of microalgae (epontic community). Almost all the studies on ice microflora in the Arctic and the Antarctic have been performed in waters of high salinities, and they generally reported a very high standing crop. From February through May 1978, 15 stations were sampled in the southeastern part of Hudson Bay (Manitounuk Sound), Quebec, Canada. The peculiar physical condition of the water bodies establishes a salinity gradient in the underlying waters from the mouth of the Great Whale River to the upper reaches of Manitounuk Sound, leading to a parallel gradient in the ice dynamics. The main goal of this study was to examine the effect of these gradients on the biomass and the taxonomic composition of the epontic community. Thus, there are two distinct gradients in the ice, one ruled by the surface-water salinity gradient controlling the ice thickness and the settlement efficiency, which triggers the biomass of the epontic community (higher standing crop in the upper reaches of Manitounuk Sound). In addition, the ice salinity gradient influences the taxonomic composition (lower number of microalgae taxa toward the mouth of the Great Whale River). Salinity of the underlying surface waters, following discriminant analyses of species-based clusters of observations, emerges as a major environmental variable controlling the distribution and abundance of species. In addition to adequate light intensity and nutrient supply, salinity of the underlying waters is therefore another limiting factor to the settlement and growth of an ice microflora. This factor is of great potential significance in coastal and esturine glacial waters.     

Spatial scaling of avian population dynamics: population abundance, growth rate, and variability

Synchrony in population fluctuations has been identified as an important component of population dynamics. In a previous study, we determined that local-scale (<15-km) spatial synchrony of bird populations in New England was correlated with synchronous fluctuations in lepidopteran larvae abundance and with the North Atlantic Oscillation. Here we address five questions that extend the scope of our earlier study using North American Breeding Bird Survey data. First, do bird populations in eastern North America exhibit spatial synchrony in abundances at scales beyond those we have documented previously? Second, does spatial synchrony depend on what population metric is analyzed (e.g., abundance, growth rate, or variability)? Third, is there geographic concordance in where species exhibit synchrony? Fourth, for those species that exhibit significant geographic concordance, are there landscape and habitat variables that contribute to the observed patterns? Fifth, is spatial synchrony affected by a species' life history traits? Significant spatial synchrony was common and its magnitude was dependent on the population metric analyzed. Twenty-four of 29 species examined exhibited significant synchrony in population abundance: mean local autocorrelation (rho)= 0.15; mean spatial extent (mean distance where rho=0) = 420.7 km. Five of the 29 species exhibited significant synchrony in annual population growth rate (mean local autocorrelation = 0.06, mean distance = 457.8 km). Ten of the 29 species exhibited significant synchrony in population abundance variability (mean local autocorrelation = 0.49, mean distance = 413.8 km). Analyses of landscape structure indicated that habitat variables were infrequent contributors to spatial synchrony. Likewise, we detected no effects of life history traits on synchrony in population abundance or growth rate. However, short-distance migrants exhibited more spatially extensive synchrony in population variability than either year-round residents or long-distance migrants. The dissimilarity of the spatial extent of synchrony across species suggests that most populations are not regulated at similar spatial scales. The spatial scale of the population synchrony patterns we describe is likely larger than the actual scale of population regulation, and in turn, the scale of population regulation is undoubtedly larger than the scale of individual ecological requirements.     

Ungulate population dynamics and optimization models

Optimal harvesting strategies for an ungulate population are estimated using stochastic dynamic programming. Data on the Llano Basin white-tailed deer (Odocoileus virginianus) population were used to construct a 2-variable population dynamics model. The model provided the basis for estimating optimal harvesting strategies as a feedback function of the current values of the state variables (prefawning older deer and juveniles). Optimal harvest strategies were insensitive to assumptions about the probability distributions of the stochastic variable (rainfall). The response of the population components to harvesting and the returns obtained from applying optimal strategies were explored through simulation. Mean annual harvest is about 15% of the population. Simplified harvesting strategies based on age-ratios as well as a simplified version based on optimal strategies—but assuming persisting equilibrium juvenile deer density—were compared to optimal strategies through examining values of information. Simplified harvesting strategies lead to a lower harvest over a 50-year simulation period.     

Uncertainty analysis of transient population dynamics

Two types of demographic analyses, perturbation analysis and uncertainty analysis, can be conducted to gain insights about matrix population models and guide population management. Perturbation analysis studies how the perturbation of demographic parameters (survival, growth, and reproduction parameters) may affect the population projection, while uncertainty analysis evaluates how much uncertainty there is in population dynamic predictions and where the uncertainty comes from. Previously, both perturbation analysis and uncertainty analysis were conducted on the long-term population growth rate. However, the population may not reach its equilibrium state, especially when there is management by harvesting or hunting. Recently, there has been an increased interest in short-term transient dynamics, which can differ from asymptotic long-term dynamics. There are currently techniques to conduct perturbation analyses of short-term transient dynamics, but no techniques have been proposed for uncertainty analysis of such dynamics. In this study, we introduced an uncertainty analysis technique, the general Fourier Amplitude Sensitivity Test (FAST), to study uncertainties in transient population dynamics. The general FAST is able to identify the amount of uncertainty in transient dynamics and contributions by different demographic parameters. We applied the general FAST to a mountain goat (Oreamnos americanus) matrix population model to give a clear illustration of how uncertainty analysis can be conducted for transient dynamics arising from matrix population models.     

Evaluation of spawning frequency in a Mediterranean sardine population (<Emphasis Type="Italic">Sardina pilchardus sardina</Emphasis>)

The postovulatory follicle method was used to assess the frequency of spawning of sardine (Sardina pilchardus sardina) in the Central Aegean Sea (eastern Mediterranean) in November–December 1999 and 2000. A field-based aging key for postovulatory follicles (POFs) was developed, and preliminary evidence is presented of a temperature influence on the degeneration of POFs. Bias in the fraction of day-0 spawners (females that had, were, or would spawn the night of sampling) with respect to sampling time was identified and attributed to spawning behavior. An appraisal of consistency in spawners' fractions and sex ratio, based on four sets of sequential trawl hauls, showed a considerably high small-scale variability, which suggested that spawning schools are structures limited in space and/or ephemeral in time. Sampling gear, i.e. commercial purse seines and research pelagic trawls, did not differ significantly with respect to spawners' fractions. The fractions of day-1 and day-2 females were the same during both years, and their combination resulted in more precise, composite estimates of spawning frequency. In both years, the Mediterranean sardine spawned every 11–12 days. The incidence of spawning increased significantly with fish size. When compared to all estimates available for other sardine genera, species and subspecies, the spawning frequency of the Mediterranean sardine was lower; this was attributed to the synergetic effect of oligotrophy and smaller body sizes in the Mediterranean.     

The optimum population and an affluent society

The population optimum is formulated such that income-related shifts are permitted in rates of substitution between arguments in the welfare function. Under plausible assumptions, when income, the number of people, open space, leisure, and pollution are explicitly included in the welfare function, and even though the income elasticity of added children is positive, families will tend to have fewer children as incomes rise, while enjoying more open space and reduced levels of pollution. A shift toward leisure tends to have the partial effect of increasing the optimum. The model predicts that consumption will become increasingly extra-market as incomes rise.     

Optimal control of Atlantic population Canada geese

Management of Canada geese (Branta canadensis) can be a balance between providing sustained harvest opportunity while not allowing populations to become overabundant and cause damage. In this paper, we focus on the Atlantic population of Canada geese and use stochastic dynamic programming to determine the optimal harvest strategy over a range of plausible models for population dynamics. There is evidence to suggest that the population exhibits significant age structure, and it is possible to reconstruct age structure from surveys. Consequently the harvest strategy is a function of the age composition, as well as the abundance, of the population. The objective is to maximize harvest while maintaining the number of breeding adults in the population between specified upper and lower limits. In addition, the total harvest capacity is limited and there is uncertainty about the strength of density-dependence. We find that under a density-independent model, harvest is maximized by maintaining the breeding population at the highest acceptable abundance. However if harvest capacity is limited, then the optimal long-term breeding population size is lower than the highest acceptable level, to reduce the risk of the population growing to an unacceptably large size. Under the proposed density-dependent model, harvest is maximized by maintaining the breeding population at an intermediate level between the bounds on acceptable population size; limits to harvest capacity have little effect on the optimal long-term population size. It is clear that the strength of density-dependence and constraints on harvest significantly affect the optimal harvest strategy for this population. Model discrimination might be achieved in the long term, while continuing to meet management goals, by adopting an adaptive management strategy.     

Lyapunov stability for an age-structured population model

This is a short notice on the McKendrick equation that I actually learned from Yu.M. Svirezhev in the 1990s. This McKendrick equation modelling the evolution in time of an age-structured population has received attention recently from mathematicians. The initial and boundary conditions for the McKendrick equation imposed by the population model are not the standard side conditions one sees in PDE theory for an evolution equation. In the simplest case, the problem reduces to a well-known model in demography, the Lotka integral equation.