Feind-Beute-Systeme in kybernetischer Sicht

Zusammenfassung Mit Hilfe kybernetischer Begriffe werden die Wechselwirkungen zwischen Feind und Beute beschrieben. Dabei beschränkt sich die Darstellung überwiegend auf die qualitativen Beziehungen zwischen einer Feind- und einer Beutepopulation, schließt aber Pflanzen als Beute ein.Feind- und Beutepopulation bilden durch ihre numerischen Reaktionen zusammen einen Regelkreis, in dem beide je nach Betrachtungsweise als Regelstrecke oder Regler aufgefaßt werden können. Die Gegenkopplung kommt zustande durch die begrenzte Suchfähigkeit des Feindes. Bei beiden Populationen ist die Bilanz aus (den Logarithmen) dichteunabhängiger Fruchtbarkeit und Sterblichkeit als Stör- oder Führungsgröße anzusehen. Das Zusammentreffen beider hat die Funktion eines Fühlers oder eines Stellgliedes.Beide Populationen verhalten sich etwa wie Integralglieder mit Totzeit. Damit lassen sich ihre Wechselwirkungen in diesem Regelkreis ausreichend beschreiben, und es erübrigt sich, Feinde als zeitweilig defekte Regler auzusehen.Wenn die Beuteorganismen für den Feind nicht so oft verwendbar sind, wie sie gefunden werden, so entsteht Konkurrenz um die Beute (Nahrungskonkurrenz). Ihre Intensität ist von der Feinddichte abhängig. Sie wirkt wie ein zweiter Regler negativ auf die Feindpopulation zurück. Im Regelschema (Signaflußplan) läßt sie sich durch ein zusätzliches Übertragungsglied darstellen. Zusammen mit der Beute bildet dieses einen PI-Regler für den Feind.Durch Einfügen eines weiteren Übertragungsgliedes kann der Tatsache Rechnung getragen werden, daß mit zunehmender Beutedichte meistens eine relative Aktivitätsminderung beim Feind auftritt; denn seine Vernichtungspotenz ist ja begrenzt. Dieses Übertragungsglied wirkt positiv auf die Beute zurück.Als Kombination aus zwei Integralgliedern ist das Feind-Beute-System durch die numerischen Reaktionen allein instabil. Die Konkurrenz der Feinde um die Beute kann die auftretenden Schwingungen unter Umständen dämpfen, während die relative Aktivitätsminderung durch begrenzte Vernichtungskapazität die Instabilität unterschiedlich stark begünstigt. Wenn das System in sich nicht ausreichend gedämpft ist, kann eine Dämpfung nur durch Proportionalwirkung zusätzlicher Regler eintreten.Die kybernetische Betrachtungsweise zerlegt das komplexe System in einfache Übertragungsglieder und liefert so zunächst ein Strukturmodell, welches u.a. Art und Stärke der Dichteabhängigkeit verschiedener Massenwechselfaktoren leichter erfaßbar macht. Kennzeichnet man die Wirkung der einzelnen Übertragungsglieder durch entsprechende mathematische Funktionen, so entsteht ein dynamisches Modell.Das kybernetische Modell ist grundsätzlich offen für die Zufügung weiterer Elemente.

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Cybernetical approach to enemy-prey systems

Summary The interactions between one enemy and one prey population are described by the aid of cybernetic concepts, including plants as prey.By their numerical responses the populations of enemy and prey together constitute a feedback control system (Fig.1). Both of them can be interpreted either as regulator or as controlled system. The negative feedback is made possible by limitation of the enemy's searching ability. The difference between (the logarithms of) density independent fertility and mortality of both populations can be regarded as disturbance or as command variable. The encounter of both populations has the effect of a detecting element or of an correcting element (Fig. 2).To a first approximation, both populations react like integrating elements with dead time. Their interactions in the feedback control system can be described appropriately by these means. Thus there is no need for interpreting the enemies as temporarily defective regulator.If the individual prey organisms cannot be utilized by different enemies as often as they are found, there exists a competition for prey. Its intensity depends on enemy density. In the mode of a second regulator the competition reacts negatively upon the enemy population. In the information flow diagram it can be represented by an additional element (Fig. 3). Together with the prey it composes a PI-regulator of the enemy (Fig.4).The limited feeding capacity of the enemy often causes a relative decrease of the enemy's activity with increasing prey density. This decrease can be taken into account by a further element (Fig. 5), that reacts positively upon the prey population.Considering only numerial responses the enemy-prey system is composed of two integrating elements. Consequently both densities oscillate after every change of disturbance with amplitudes that increase because of the dead time in each element. The competition for prey among enemies is probably able to damp the oscillations in certain cases. On the other hand, the relative decrease of activity caused by the limited feeding capacity favours instability. If the system is not damped sufficiently by itself quenching is possible only by the proportional effects of additional regulators.By the cybernetical approach the complex system is divided into simple components. With that cybernetics provides a model of structure which, among others, facilitates insight into kind and degree of density dependence of different factors. When the effects of the single elements are characterized by mathematical functions a dynamic model will arise.On principle the cybernetical model can be extended by adding further components.

     

Wirkungen der Exstirpation und Transplantation der Corpora allata auf den Sauerstoffverbrauch,die Eibildung und den Fettkörper vonCarausius (Dixippus) Morosus Br. et Redt.

Ohne ZusammenfassungDiss. T. H. Stuttgart 1961.     

Benthic diatom assemblages in mountain streams: community structure in relation to environmental and human pressures

The objective of this study was to determine the environmental factors that best explain the distribution and community composition of benthic diatoms in undisturbed mountain streams in the Eastern Highlands of Zimbabwe. Benthic diatoms were sampled during the dry season from 21 sampling sites established along altitudinal gradient of the study rivers. A total of 119 diatom species belonging to 38 genera and twelve families were recorded for all the 21 sites sampled. No significant differences were observed in species diversity and equitability amongst the three river systems. However, species richness, diversity and equitability decreased significantly along the longitudinal gradient of the rivers, with the highest richness, diversity and evenness being recorded in the upper reaches. Temperature, velocity, NO₃^? and Ca²⁺ levels were strongly associated with changes in diatom communities in the three rivers. Inventory of diatom communities has applications in many fields of biological research including conservation and biological monitoring of ecosystem changes.     

DETERMINING BLOOD PRESSURE IN INFANTS—Use of the Flush Technique

The flush technique that recently has come into use is probably the most satisfactory method available for measuring blood pressures in infants and is of great aid in diagnosis of diseases associated with hypertension or hypotension. The method is practical and highly accurate. Readings obtained by this technique are not influenced by the width of the cuff, are usually higher at the wrist than at the ankle, and approximate the mean rather than the systolic blood pressure.     

Die Wahrnehmung von Beute Durch die Eilarven vonAphidoletes aphidimyza [Cecidomyiidae]

Zusammenfassung Neben oder hinter einzelne schlupfreife Eier vonAphidoletes aphidimyza (Cecidomyiidae) wurden in 3 mm Entfernung Blattl?use und Ersatzobjekte auf der Unterseite von Kohlbl?ttern angebracht und die Kriechrichtungen der schlüpfenden Larven beobachtet. Seitlich festgeklebte graue Steinchen von Blattlausgr?sse führten zu einer signifikanten Bevorzugung dieser Richtung gegenüber der Gegenrichtung, doch wurden die Steinchen im Wahlversuch mit Pfirsichblattl?usen (Myzus persicae) v?llig vernachl?ssigt. Eingetrocknete Tropfen einer Honigtaul?sung von Bohnenl?usen (Aphis jabae) hatten eine st?rkere Wirkung als Steinchen. Ihre Richtung wurde auch gegenüber gleichartigen Tropfen einer Glukosel?sung signifikant bevorzugt. Dagegen erhielten festgeklebte Bohnenl?use st?rkeren Zulauf als gleich grosse Steinchen mit Honigtau. Offenbar sind die Eilarven vonA. aphidimyza in der Lage, ihre Beute auf kurze Distanz mit Hilfe des Geruchs zu lokalisieren. Der Zulauf zu geruchsfreien Steinchen weist auf eine zweite Art der Orientierung hin, die vielleicht auf optischem Wege erfolgt.

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Summary Aphids or substitute objects were attached to the lower surface of cabbage leave at a distance of 3 mm from single eggs ofA. aphidimyza. Afterwards, the newly hatched larvae were observed and the directions of their first mouvements were registered. In most experiments the larvae showed a marked preference for the direction indicated by the anterior pole of the egg. Nevertheless, the direction toward a single aphid-sized grey stone glued beside the egg was significantly preferred to the opposite direction. If the larvae, however, had the opportunity to choose between a peach aphid (Myzus persicae) and a stone, the mouvement to the latter ceased. Dried droplets of honeydew solution from bean aphids (Aphis fabae) proved to be more attractive than stones or dried droplets of glucose solution. However, glued bean aphids were more frequently approached than grey stones of equal size furnished with honeydew. Apparently the newly hatched larvae ofA. aphidimyza are able roughly to locate their prey over a short distance by means of its odour. The reaction to odorless little stones indicates that there is still another kind of orientation, perhaps by visual stimuli.

     

Genetic improvement of tree species for remediation of hazardous wastes

Summary Phytoremediation, using plants to clean up toxic wastes, is an idea that is attracting increasing attention from scientists, remediation engineers, and environmental professionals in government, industry, and universities. In situ remediation using plants has the potential to be less expensive than current technologies and to simultaneously initiate both detoxification of hazardous waste and site restoration. The perennial habit, extensive root mass, and large transpirational rates give trees advantages over other plants for use in remediation. Trees are already used for wastewater clean-up, for site stabilization, and as barriers to subsurface flow of contaminated groundwater. Clonal propagation and the genetic tools of both classical breeding and genetic engineering exist for a number of both angiosperm and gymnosperm species, opening the door to creation of tree “remediation” cultivars. Work is underway to screen tree species for their ability to tolerate, take up, translocate, sequester, and degrade organic compounds and heavy metal ions. Both an indirect approach to remediation, through enhancing rhizosphere degradation of pollutants by engineering larger root masses in trees usingAgrobacterium rhizogenes, and a direct approach to remediation, through transformation of trees with bacterial genes known to initiate the mineralization of halogenated phenolic compounds and trichloroethylene are reviewed. Presented in the Session-in-Depth Bioremediation through Biotechnological Means at the 1993 Congress on Cell and Tissue Culture, San Diego, CA, June 5–9, 1993.     

Recruitment of inflammatory cells to a tumor deposit potentiates the immunotherapeutic effects of interleukin-2

Summary Interleukin-2 (IL-2) is a potent immunotherapeutic agent in murine models of intraperitoneal, pulmonary, and hepatic tumor implantation. Because of the systemic toxicity documented at doses of IL-2 required to control tumor growth, potentiation of the effects of low dose IL-2 is an important problem in immunotherapy. To address this problem, we attempted to recruit lymphocytes into a tumor mass. Allogeneic P185 (H-2^d) tumor was mixed with MCA-105 (H-2^b) tumor and injected s. c. into C57BL/6 (H-2^b) mice. Mice were treated with 50,000 units of IL-2 twice daily from day 0 to day 6. When IL-2 alone was used to treat s. c. tumor, there was no reduction in the size of tumor implants. When allogeneic tumor was mixed with syngeneic tumor, there was a reduction in tumor size at the high dose of allogeneic tumor but not at the low dose. When allogeneic tumor was mixed with syngeneic tumor and the mice treated with IL-2, the immunotherapeutic effects of IL-2 were markedly increased. These studies show that an immune response to alloantigens, generated within tumor tissue can augment the immunotherapeutic effects of exogenous IL-2.     

Why proteins without an α-crystallin domain should not be included in the human small heat shock protein family HSPB

The presence of an α-crystallin domain documents the evolutionary relatedness of the ubiquitous family of small heat shock proteins. Sequence and three-dimensional structure provide no evidence for the presence of such a domain in HSPC034, recently proposed as the 11th member of the human HSPB family. Also, phylogenetic analyses detect no relationship between HSPC034 and the human HSPB1–10 sequences. Arguments are provided as to why inclusion in the HSPB family of proteins like HSPC034, which resemble small heat shock proteins in being heat-inducible and having chaperone-like properties and a low monomeric mass, but are evolutionarily unrelated, is misleading and confusing.     

Predator naïve minnows respond to their conspecific alarm substance but not the odour from a non-native predator

When exposed to predator cues, ostariophysan fishes exhibit short-term anti-predator behavioural responses in order to minimise predation risk. Non-native predator cues are, however, likely to elicit poor behavioural responses in native prey fishes. This study investigated whether chubbyhead barb Enteromius anoplus, a native freshwater minnow in South Africa, had the innate ability to recognise and respond to largemouth bass Micropterus salmoides, a non-native piscivore. This was experimentally evaluated by investigating behavioural responses to both the non-native predator's odour and damage-released conspecific alarm substance (CAS). Chubbyhead barbs did not exhibit any behavioural response to largemouth bass odour both before and after exposure to CAS. This suggests that the chubbyhead barbs likely lacked the innate ability to recognise the non-native largemouth bass predator kairomones. By comparison, exposure to CAS was associated with significant behavioural responses, with chubbyhead barbs shifting from free-swimming to hovering, and frequent use of refugia. This suggests that despite ineffective response to non-native largemouth bass odour, chubbyhead barbs responded to general predator attack. Overall, this study suggests the potential for non-native largemouth bass to induce negative consumptive effects on chubbyhead barbs due to their inability to identify non-native predator's odour. In addition, nonconsumptive effects are likely due to altered activities in response to predator attack.     

Stream fish assemblage and habitat structure in a tropical African river basin (Nyagui River, Zimbabwe)

Few studies have been carried out on stream ecology in southern Africa although many species are endangered. This study investigated the stream fish assemblage and their habitat associations over a period of 3 months (October 2004 to January 2005), in view of the proposal to build a dam across the Nyagui River. Twenty-four fish species were collected and were separated into groups based on preferred microhabitats. The first group, dominated by Barbus paludinosus , comprised species collected from the upstream stations with slow flow, shallow depth (pools) and fine substrate type. Species associated with riffles, which included Chiloglanis neumanni , Labeobarbus marequensis and Opsaridium zambezense , comprised the second group on the downstream. The last group comprised species preferring pools with rock substrate and slow flow such as Pharyngochromis acuticeps and Pseudocranilabrus philander . The species were consistently associated with their habitat types throughout the sampling period. This relationship may be explained by the fish's morphological adaptations. Species richness increased from nine in the upstream section to twenty in the downstream section and this was related to increasing habitat complexity downstream. The construction of the Kunzvi Dam across the Nyagui River is likely to lead to loss of rheophilic species while cichlids and introduced species may increase.