Kees de Koning

Avoidance of macrophytes and additional notes on avoidance of the shore by ‘Acanthodiaptomus denticornis’ (Wierzejski, 1887) from Lake Pavin (Auvergne, France)

Summary1.Literature on the horizontal distribution patterns from the littoral zone into the open water of fresh-water zooplankton is reviewed. The results of experiments on the avoidance of macrophytes and of the shore are presented.2.In the lightAcanthodiaptomus avoidedMyriophyllum andPotamogeton as well as plastic plants in aquaria. The repelling effect of the macrophytes was stronger than that of the plastic plants. In the dark the avoidance reaction was absent, showing that both living and plastic plants exert a repellent ‘shading effect’ onAcanthodiaptomus, and supporting that macrophytes militate against zooplankton due to the secretion of repelling substances that is coupled with photosynthesis.3.When a shore was gently slopingAcanthodiaptomus avoided the shore where trees (at a distance of 20 m of the waterside) were present; this reaction did not occur where, about 100 m further, meadows bordered the lake.4.Adults were far more abundant in the littoral zone during the night as compared with day-time. This phenomenon was less distinct in the copepodites and absent in the nauplii.

A DISTINCT TEMPORAl. SEPARATION OF MAXIMUM BACTERIAL NUMBERS AND PHYTOPLANKTON BIOMASS IN THE OPEN-WATER ZONE OF LAKE MAARSSEVEEN I: RESULTS AND LITERATURE REVIEW

SummaryStarting in March there was an increase in bacterial number until a maximum was reached at the end of April; from then there was a decrease in number until the end of summer. The biomass of the phytoplankton followed an opposite curve,viz. a maximum in February, a minimum at the end of April and several pulses in summer. Two hypothetical models are described to explain this phenomenon. (a) Competition for phosphate between phytoplankton and bacteria (with subsequent grazing by herbivorous zooplankton on bacteria), and (b) excretion by bacteria of compounds that inhibit phytoplankton growth.

Qualitative Reasoning in Tutoring Interactions

In various research projects, qualitative models are claimed to be beneficial for teaching systems. Thus far, little experimental research has been undertaken to investigate the usefulness of these models in actual teaching situations. In this paper, we present an experimental study that examines to what extent existing qualitative reasoning representations and techniques are sufficient for modelling the interaction between a student an a teacher when discussing the (qualitative) behaviour of physical devices. The main results are that the knowledge representations as used in qualitative reasoning are largely adequate, whereas the reasoning techniques need adaptation for teaching.

Modeling the Influence of Non-Changing Quantities

In qualitative modelling, information is lost by abstracting from quantitative formulae. We show that when the behaviour of two similar systems is compared, non-changing quantities from these formulae can have a significant influence on the qualitative prediction. We propose the addition of a new ontological primitive for representing these influences in qualitative models, and provide a calculus for exploiting this primitive in the reasoning process. Augmentation with the new primitive enhances the power of the qualitative simulator, resulting in a more appropriate prediction of behaviour, and also improves the explanation capacities of the model. The latter feature is of major importance for tutoring systems using qualitative reasoning.