2,862 research outputs found
Tolerance to air exposure of the New Zealand mudsnail Potamopyrgus antipodarum (Hydrobiidae, Mollusca) as a prerequisite to survival in overland translocations
Spreading throughout a new ecosystem is the last step of an exotic species to become invasive. In the case of invasive aquatic molluscs, tolerance to air exposure is one of the main mechanisms allowing overland translocation and spreading. The mudsnail Potamopyrgus antipodarum (Hydrobiidae, Mollusca) is native to New Zealand but it has spread worldwide, invading ecosystems in Europe, Australia, America and Asia. The aim of our study is to assess mudsnail tolerance to air exposure, which may contribute to the successful overland translocation of this species. We conducted a laboratory experiment with four levels of air exposure (9, 18, 24 and 36 hours in a controlled climatic chamber). Snails were placed for 60 seconds in a laboratory paper filter to remove surface snail water. Then they were placed back in empty vessels during the four periods of air exposure, except the control group, which was immediately returned to water. At the end of each period of air exposure all vessels were filled with water and the cumulative mortality was monitored after 24, 96, 168 and 264 hours of rehydration. The calculated Lethal Times (i.e. the time of air exposure (in hours) necessary to cause the death of 50% (LT50) or 99% (LT99) of the population) and their 95% confidence limits at 24, 96, 168 and 264 hours were 28.1 (25.2–31.9), 26.9 (24.2–30.1), 25.9 (23.4–28.9) and 25.9 (23.4–28.9) hours, respectively for LT50, and 49.6 (42.7–63.3), 45.6 (39.9–56.5), 43.2 (38.0–53.0) and 43.2 (38.0–53.0) hours, respectively for LT99. Therefore an air exposure time over 43 hours caused the death of all studied individuals during all monitoring periods. Extending the monitoring period beyond 24 hours did not significantly change lethal times. Therefore, we recommend exposing fishing tools or boats at open air during at least 53 hours as a low cost measure to control mudsnail spread in early stages of invasion
Information systems models in higher education
This paper intends to contribute to a better understanding of the process through which information resource, information technology, and organisation actors can contribute to the performance and quality of higher education institutions. Conceptual models will be presented and discussed
Puesta en marcha de la gestión de calidad en las pymes
La gestión de calidad es un enfoque de gestión que se está difundiendo con
gran velocidad, sin embargo, aparte de algunas ideas generales, a las empresas de
pequeña o mediana dimensión no llega información suficiente para de un modo
claro y sencillo intentar su puesta en marcha. De este modo, se convierte en necesario
el facilitar un esquema general no excluyeme de los pasos que estas organizaciones
pequeñas deberían afrontar y algunos de los problemas subyacentes, lo que se
hace en la ponencia mediante una propuesta que describe un modelo en el que se
expresan los distintos elementos, su conexión y el contenido de los mismo
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