Ecological fish production in Long Pond,a lakeshore lagoon on Long Point,Lake Erie

Synopsis Long Pond, a recently formed 2.4 ha lagoon on Long Point, Lake Erie (Canada), was treated with piscicide and found to contain 47,768 fishes of 22 species. Nine dominant species (Notropis heterolepis, Pimephales notatus, Notemigonus crysoleucas, Lepomis gibbosus, L. macrochirus, Perca flavescens, Cyprinus carpio, Micropeterus salmoides and Carassius auratus) comprised 91% and 97% of total numbers and standing crop respectively. Age, growth and production were determined giving a total fish production estimate (corrected for all species) of 87.5 kg ha^–1 y^–1 for this lagoon. Dominant species were deemed either invaders (Cyprinus carpio, Carassius auratus), which had entered the lagoon to spawn and been trapped, or residents. The invaders comprised 82% of the 277.8 kg ha^–1 total standing crop. Their successful spawning and subsequent escape of the young from the lagoon would have resulted in some 615 kg y^–1 of fish production outside the lagoon. Resident stocks were dominated by young fishes, a characteristic of exploitation or early colonization. This may have been due to the recent formation and subsequent expansion of the lagoon or high annual mortality due to extreme physical conditions but was most likely the result of excessive predation by Micropterus salmoides. Relationship between biomass and production show that the chance inclusion of the invaders produces an immediate shift from a characteristically early to a characteristically late phase of ecological development.     

A model management systems approach to manufacturing systems design

Manufacturing systems design involves the solution of a complex series of interrelated problems. This complexity will increase in the future as manufacturing practices change to meet increased global competition. Research within manufacturing systems design has mainly been focused on finding improved models for solving particular problems, or extending existing modeling techniques. This has resulted in numerous modeling tools being available to support manufacturing systems design. However, little research work has been carried out into consolidating the existing theories and models. As a result, a large body of this work has not been applied in industry. Model management has evolved as a research area which investigates methods for storing, modifying, and manipulating models. This article describes a prototype model management system for manufacturing systems design. The objective here is not to develop “another” decision support system for manufacturing design, but to illustrate, through the development of a prototype system, a number of key ideas of how concepts from the area of model management systems can be used to support manufacturing systems design. The prototype model management system utilizes the structured modeling framework and uses an extended version of the structured modeling language. An important aspect of the prototype model management system is the incorporation of the model development task, thus allowing the system to be easily updated and adapted. The prototype system was evaluated using a range of queueing network models for manufacturing systems design.     

Differences in the Activation of the Mitochondrial Permeability Transition Among Brain Regions in the Rat Correlate with Selective Vulnerability

Mitochondria from different regions of the brain were prepared, and the activation of the mitochondrial permeability transition (MPT) by calcium was investigated by monitoring the associated mitochondrial swelling. In general, the properties of the MPT in brain mitochondria were found to be qualitatively similar to those observed in liver and heart mitochondria. Thus, swelling was inhibited by adenine nucleotides (AdNs) and low pH (<7.0), whereas thiol reagents and alkalosis facilitated swelling. Cyclosporin A and its nonimmunosuppressive analogue N-methyl-Val-4-cyclosporin A (PKF 220-384) both inhibited swelling and prevented the translocation of cyclophilin D from the matrix to the membranes of cortical mitochondria. However, the calcium sensitivity of the MPT differed in mitochondria from three brain regions (hippocampus > cortex > cerebellum) and is correlated with the susceptibility of these regions to ischemic damage. Depleting mitochondria of AdNs by treatment with pyrophosphate ions sensitized the MPT to [Ca2+] and abolished regional differences, implying regional differences in mitochondrial AdN content. This was confirmed by measurements showing significant differences in AdN content among regions (cerebellum > cortex > hippocampus). Our data add to recent evidence that the MPT may be involved in neuronal death.     

Chemo-tactile predator avoidance responses of the common Antarctic limpet Nacella concinna

The Antarctic limpet, Nacella concinna, has the ability to escape predation by the predatory sea star, Neosmilaster georgianus. When the sea star comes into contact with the limpet, the limpet undergoes characteristic behaviors that include extension of its pallial tentacles, raising its shell in a mushroom-like fashion, rotation, and flight. These behaviors were not observed until the sea star physically contacted the limpets and were not induced by the omnivorous sea star, Odontaster validus, which occupies the same habitats as Ne. georgianus. Crude hydrophilic extracts from Ne. georgianus, but not from O. validus, induced the escape behaviors, indicating that this response is chemical as well as tactile. These putative escape behaviors displayed by Na. concinna may contribute to avoidance of predation by Ne. georgianus.