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Changes in demographic structure, growth and production of a population of Cerastoderma glaucum (Poiret, 1789) in an isolated brackish lagoon on the east coast of the Arcachon Basin (France) were investigated in 1976 and 1977. The early stages are present in filamentous algae or in plants (Ruppia maritima), while the 2 to 3 yr old cockles are on the bottom mud. Mortality results from bird (Laridae) predation and from dystrophic conditions which prevail in spring and summer. Migrations occur between areas with plants and unvegetated areas: Group 0 migrations are characterized by an increase in growth rate and P:B ratio of the cohorts of this group; they precede a natural recruitment or follow environmental stress. The distributions and migrations of these cockles are adaptive strategies to environmental factors in a system of brackish lagoons. 相似文献
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Although associations between myrmecophytes and their plant ants are recognized as a particularly effective form of protective
mutualism, their functioning remains incompletely understood. This field study examined the ant-plant Hirtella physophora and its obligate ant associate Allomerus decemarticulatus. We formulated two hypotheses on the highly specific nature of this association: (1) Ant presence should be correlated with
a marked reduction in the amount of herbivory on the plant foliage; (2) ant activity should be consistent with the "optimal
defense" theory predicting that the most vulnerable and valuable parts of the plant are the best defended. We validated the
first hypothesis by demonstrating that for ant-excluded plants, expanding leaves, but also newly matured ones in the long
term, suffered significantly more herbivore damage than ant-inhabited plants. We showed that A. decemarticulatus workers represent both constitutive and inducible defenses for their host, by patrolling its foliage and rapidly recruiting
nestmates to foliar wounds. On examining how these activities change according to the leaves’ developmental stage, we found
that the number of patrolling ants dramatically decreased as the leaves matured, while leaf wounds induced ant recruitment
regardless of the leaf’s age. The resulting level of these indirect defenses was roughly proportional to leaf vulnerability
and value during its development, thus validating our second hypothesis predicting optimal protection. This led us to discuss
the factors influencing ant activity on the plant’s surface. Our study emphasizes the importance of studying both the constitutive
and inducible components of indirect defense when evaluating its efficacy and optimality. 相似文献
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Laurent Goujard Pierre-Jean Roumanet Bruno Barea Yann Raoul Fabio Ziarelli Jean Le Petit Nathalie Jarroux Elisée Ferré Philippe Guégan 《Journal of Polymers and the Environment》2016,24(1):64-71
This work compares the biodegradability of polyesters produced by an esterification reaction between glycerol and oleic di-acid (D 18:1) issued from green chemical pathways, via either classical thermo-chemical methods, or an enzymatic method using the immobilized lipase of Candida antartica B (Novozym 435). An elastomeric polymer synthesized by enzymatic catalysis is more biodegradable than an elastomeric thermo-chemical polyester synthesized by a standard chemical procedure. This difference lies in percentage of the dendritic motifs, in values of the degree of substitution, and certainly in cross-links inducing an hyper-branched structure less accessible to the lipolytic enzymes in a waste treatment plant. However, when the elastomeric polymer synthesized by enzymatic catalysis is processed at high temperature as required for certain industrial applications, it presents an identical rate of biodegradation than the chemical polyester. The advantages of the thermo-chemical methods are greater speed and lower cost. Enzymatic synthesis appears be suited to producing polyesters, devoid of metallic catalysts, which must be used without processing at high temperature to keep a high biodegradability. 相似文献
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