Many biologists now recognize that environmental variance can exert important effects on patterns and processes in nature that are independent of average conditions. Jensen’s inequality is a mathematical proof that is seldom mentioned in the ecological literature but which provides a powerful tool for predicting some direct effects of environmental variance in biological systems. Qualitative predictions can be derived from the form of the relevant response functions (accelerating versus decelerating). Knowledge of the frequency distribution (especially the variance) of the driving variables allows quantitative estimates of the effects. Jensen’s inequality has relevance in every field of biology that includes nonlinear processes.

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Jensen's inequality predicts effects of environmental variation.

Medicinal chemistry and pharmacology of genus Tripterygium (Celastraceae).

Steviol glycosides are a group of highly sweet diterpene glycosides discovered in only a few plant species, most notably the Paraguayan shrub Stevia rebaudiana. During the past few decades, the nutritional and pharmacological benefits of these secondary metabolites have become increasingly apparent. While these properties are now widely recognized, many aspects related to their in vivo biochemistry and metabolism and their relationship to the overall plant physiology of S. rebaudiana are not yet understood. Furthermore, the large size of the steviol glycoside pool commonly found within S. rebaudiana leaves implies a significant metabolic investment and poses questions regarding the benefits S. rebaudiana might gain from their accumulation. The current review intends to thoroughly discuss the available knowledge on these issues.

Steviol glycosides: chemical diversity, metabolism, and function.

Previous explanations for the evolution of induced resistance of plants to herbivory emphasized arguments based on saving costs when allocations to defense were not needed; these models met with limited empirical support. We offer a novel explanation based on induced resistance providing increased variability in defense. As long as maximal levels of defense are constrained, variability will increase the effectiveness of a given level of investment in defense. We show that variability can decrease herbivore performance if herbivore performance is a concave function of the level of resistance. In particular, if herbivores can choose among different plants and plant tissues, then variability created by induced resistance may benefit plants under attack and hence may be favored by selection. The key assumptions of this model are broadly supported by empirical data from many plant-herbivore systems.

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The benefits of induced defenses against herbivores

Chapter 5 – Terpenoids

Kaurenoic and trachylobanoic acids from sunflower inhibited larval development in several Lepidoptera species. The tricyclic resin acids were also effective in curtailing growth ofPectinophora gossypiella and either reduction to carbinol or esterification of the carboxyl group lowered activity. Partial reversal of growth inhibition in the presence of relatively large amounts of cholesterol suggests an interaction with the insects' hormonal system.

C. A. Elliger

Papers

Diterpene acids as larval growth inhibitors