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  • 1
    Electronic Resource
    Electronic Resource
    Modeling the population dynamics of annual plants with seed bank and density dependent effects (1995)
    Springer
    Acta biotheoretica 43 (1995), S. 53-65 
    Details
    ISSN: 1572-8358
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A model is proposed for the population dynamics of an annual plant (Sesbania vesicaria) with a seed bank (i.e. in which a proportion of seeds remain dormant for at least one year). A simple linear matrix model is deduced from the life cycle graph. The dominant eigenvalue of the projection matrix is estimated from demographic parameters derived from field studies. The estimated values for population growth rate (λ) indicates that the study population should be experiencing a rapid exponential increase, but this was not the case in our population. The addition of density dependent effects on seedling survivorship and adult fecundity, effects for which field studies provide evidence, considerably improves our model. Depending on the demographic parameters, the model leads to stable equilibrium, oscillations, or chaos. Study of the behaviour of this model in the parameter space shows that the existence of a seed bank allows higher among-year variation of adult fecundity, without leaving the region of demographic stability. Field data obtained over 3 years confirm this prediction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00709433
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  • 2
    Electronic Resource
    Electronic Resource
    Are tsetse fly populations close to equilibrium? (1996)
    Springer
    Acta biotheoretica 44 (1996), S. 317-333 
    Details
    ISSN: 1572-8358
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Glossina or tsetse flies, the vectors of sleeping sickness, form a unique group of insects with remarkable characteristics. They are viviparous with a slow rhythm of reproduction (one larva approximately every 10 days) determined by the regular ovulation of alternate ovaries. This unusual physiology enables the age of the females to be estimated by examining the ovaries. The resulting ovarian age structure of tsetse fly populations has been used to develop research into the demography of tsetse flies. Several authors have proposed methods of estimating population growth rates from ovarian age distribution data. However, such methods are applicable only when the growth rate (λ) is equal to 1 (i.e. the intrinsic rate of increase r is equal to 0). In fact, in this type of estimation, the adult survival rate a (or equivalently the mortality rate) cannot be dissociated from the growth rate. Other independently determined demographic parameters must be used to remove this lack of identiflability. We have built a matrix model of the dynamics of tsetse fly populations which enables the growth rate to be calculated from the pupal survival rate, the pupal period and the adult survival rate. Assuming that the age-groups of the population studied have reached a stable distribution, it is possible to calculate the probabilities for the observed sample of belonging to each of the age-groups, to construct a likelihood function and thus to obtain an estimate of the ‘apparent survival rate’ β = a/λ If the pupal survival rate and the pupal period are known, a and λ can then be calculated from β. The application of this method to data collected for over two annual cycles in a savannah habitat (Burkina-Faso) showed a high overall stability in the populations of Glossina palpalis gambiensis. Seasonal fluctuations could be easily interpreted as being the result of climatic changes between the dry and rainy seasons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00046536
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  • 3
    Electronic Resource
    Electronic Resource
    A Matrix Model to Study the Colonization by Brown Trout of a Virgin Ecosystem in the Kerguelen Islands (1998)
    Springer
    Acta biotheoretica 46 (1998), S. 253-272 
    Details
    ISSN: 1572-8358
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We present a matrix model for the study of the population dynamics of brown trout Salmo trutta L., introduced in the '60s in the virgin aquatic ecosystems of the Kerguelen Islands. This species clearly acclimatized very well: a portion of the population became migratory and spent a part of its life cycle in the sea, which allowed the rapid colonization of two rivers close to the stream of origin in the same bay (Baie Norvégienne). These migratory trout can become a smolt at 2, 3, or 4 years of age. The model takes into account age and smolt age structures and in a first step considers the fish from the Baie Norvégienne as belonging to a single population. The transition matrix looks like a 32 × 32 Leslie matrix in which some survival rates are not on the subdiagonal. They represent survival after the first sea migration and are particularly important for the dynamics of the whole population. The estimate of demographic parameters was obtained from a data base containing information collected in the field since 1970. The model was calibrated on the population size estimate and the stock structure of the migratory trout in 1979. Population size was estimated by tagging-recapture and monitoring of the migratory trout in freshwater when they returned to overwinter or reproduce. Under the hypothesis of a constant survival rate for all ages and categories of fish, it was possible to determine relationships between the annual population growth rate and survival rates at first downstream migration, for which no direct estimate was available. These constraints on the model induced paradoxical results. For instance, an increase in survival rate reduced migratory trout numbers in the first years of colonization. These data suggested that the average survival rate should be around 0.3 and not 0.5 as surmised in previous studies. However, the model systematically underestimated numbers of migratory trout during the first years of development. Thus, to improve the model it will be necessary to introduce survival rates varying with time. Another possible approach would be to consider the population as three subunits corresponding to the three colonized rivers of the Baie Norvégienne.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1001789211146
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  • 4
    Electronic Resource
    Electronic Resource
    Influence de quelques variables liées à la plante Phaseolus vulgaris sur la ponte d'Acanthoscelides obtectus dans la nature (1987)
    Springer
    Entomologia experimentalis et applicata 43 (1987), S. 105-113 
    Details
    ISSN: 1570-7458
    Keywords: Acanthoscelides obtectus ; Phaseolus vulgaris ; comportement de ponte ; distribution des pontes ; structure spatio-temporelle ; A. obtectus ; P. vulgaris ; oviposition behaviour ; eggs distribution ; spatio-temporal pattern
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Summary The influence of some of the variables associated to plants of P. vulgaris (date of maturation of the pods, height, and number of seeds in the pods) on the egg-laying of the bean weevil A. obtectus was tested. All the pods of 20 P. vulgaris plants, grown in field conditions, were regularly examined during growth time, then collected. Adult density was estimated by counting, several times a day, the number of adults observed on the pods of the 20 selected plants. Multifactorial analysis was applied to the data. The results reveal a good correlation between the number of eggs laid into the pods and the number of days when adults were observed on the same pod. Egg-laying is markedly influenced by the date of maturation of the pods. Contamination of pods by bruchids is higher in places where weeds -presumable feeding sites for the adults — are abundant. Other variables seem to be less important. A review of the data shows a strong aggregation of the oviposition on certain pods which in general mature early; but the same aggregative pattern can be observed when the females of A. obtectus can choose among several pods of the same state of maturity on the same plant. These observations disprove the existence of a ‘marking pheromon’ which would prevent repeated oviposition.
    Notes: Abstract L'influence de quelques variables liées aux plantes de Phaseolus vulgaris (date de maturation, hauteur et nombre de graines dans les gousses) sur la ponte de la bruche du haricot Acanthoscelides obtectus a été étudiée dans la nature sur 20 pieds de haricot dont toutes les gousses ont été suivies puis récoltées. Les résultats montrent une bonne corrélation entre le nombre d'oeufs émis dans une gousse et le nombre de jours avec présence d'adultes sur cette gousse. La date de maturation influence fortement la contamination des gousses. Au niveau spatial, les pieds situés dans des zones non désherbées, où peuvent s'alimenter les adultes, sont les plus contaminés. Les autres variables semblent avoir moins d'importance. On note une très forte agrégativité des pontes dans certaines gousses qui sont, en général, parmi les premières mûres, mais cette agrégativité persiste même si les femelles ont le choix, sur un même pied, entre plusieurs gousses arrivées ensemble à maturité.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00301740
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  • 5
    Electronic Resource
    Electronic Resource
    Egg dispersion in codling moth: Influence of egg extract and of its fatty acid constituents (1995)
    Springer
    Journal of chemical ecology 21 (1995), S. 2015-2026 
    Details
    ISSN: 1573-1561
    Keywords: Behavior ; Cydia pomonella ; oviposition ; pheromone ; synomone ; insect ; offspring dispersion ; fatty acids ; egg age ; Lepidoptera ; Tortricidae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Codling moth females (Cydia pomonella, Lepidoptera: Tortricidae) (CM) usually lay single eggs and have a tendency to disperse. In a first experiment we observed that single females exposed to 20 apples distribute their eggs regularly among apples, suggesting a dispersive oviposition behavior. In a dual-choice situation, isolated females avoided oviposition on areas of cardboard treated with a methylene dichloride egg extract at the dose of ca. 1.0 egg equivalent/cm2. A strong avoidance was obtained in response to a 20-fold dose, which was accompanied by a significant reduction of total oviposition. Seven major compounds found by GC analyses in the methylene dichloride extract of 2 to 3-day-old eggs were saturated or unsaturated C14-C18 straight-chain fatty acids: myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid. This was confirmed by GC-MS analysis of an extract made by ethyl ether. Smaller amounts of three methyl esters were also identified as methyl myristate, methyl palmitate, and methyl stearate. A blend of the seven fatty acids (FA) mimicked rather well the avoidance provoked by the extract, and this avoidance was confirmed by choice between treated and untreated fruits by single females. The treatment of apples with the 7FA mixture induced an aggregative distribution of the eggs among apples. We also found that the amounts of fatty acids harvested in the extract depend on the egg age. Amounts of fatty acids increased until eggs were 4 days old and then decreased before hatching. In this paper we discuss the possible role of simple molecules, such as fatty acids and their esters, as semiochemicals indicative of juvenile tissues.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02033859
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  • 6
    Electronic Resource
    Electronic Resource
    To penetrate or not to penetrate? A behavioral choice by bean beetle first-instar larvae in response toPhaseolus vulgaris seed surface quality (1994)
    Springer
    Journal of chemical ecology 20 (1994), S. 1867-1875 
    Details
    ISSN: 1573-1561
    Keywords: Coleoptera ; Bruchidae ; Acanthoscelides obtectus ; Fabacea ; seed coat ; Phaseolus vulgaris ; taste ; insect-plant relationships ; behavior
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Survival ofAcanthoscelides obtectus larvae depends on the ability of the first instar to pierce the seed coat ofPhaseolus vulgaris, which represents a critical sequence because of physical characteristics and toxicity. We have investigated the influence of seed surface quality on larval boring behavior by the usual method of surface washing with different solvents, or by removing the testa, or by coating the testa with a polymer spray. Observations were made on isolated larvae in no-choice and dual-choice bioassays. In the no-choice situation, larval penetration was reduced after seed coats were soaked with chloroform, whereas water, diethyl ether, or methanol had no significant effect. The ratio of boring attempts to successful penetrations was increased on seeds washed with chloroform. In the dual-choice situation, larvae avoided artificially coated seeds and preferred untreated seeds over those washed with chloroform or methanol. These results indicate that boring stimulants exist on the seed coat and that they are removed by chloroform and methanol or made inaccessible by artificial coating. The high mortality of first instars on seeds washed with these two solvents is attributed to a lack of chemicals necessary to initiate and sustain boring behavior, causing larval stress, possibly due to prolonged locomotory activity and starvation. Thus, seed coat quality may influence the population dynamics ofA. obtectus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02066228
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