Predator-induced alarm responses in the common periwinkle, Littorina littorea: dependence on season, light conditions, and chemical labelling of predators

Chemically mediated alarm reactions of the common periwinkle, Littorina littorea (L.), were studied in laboratory experiments during two consecutive summers, and one intermediate autumn season. Responses to chemical stimuli were detected as crawl-out responses, i.e. movements of snails out of the water. Snails were exposed to extracts of injured conspecifics, extracts of the mussel Modiolus modiolus (L.), and water conditioned by the predatory crab Carcinus maenas (L.), which had been maintained on different diets. In experiments carried out during the summer, a significantly larger number of snails moved out of the water when exposed to chemical stimuli from injured conspecifics, compared to chemical stimuli from injured mussels or filtered seawater. These results suggest that chemical alarm substances are present in L. littorea. Water conditioned by crabs that had been fed L. littorea released significantly more crawl-out responses compared to water conditioned by crabs that had been kept on a fish diet. When tested in autumn, no significant differences were found in responses to the above-mentioned water samples. Crawl-out responses under different light regimes were also investigated. All series of experiments carried out in the dark evoked a higher number of responses compared to series that took place in light. These findings may indicate an adaptation of snails to night-active predators. In total, the current results suggest that a L. littorea diet may chemically “label” the predator crab with snail alarm substances, and that predator-induced responses of L. littorea are actually responses to conspecific alarm substances released from crabs that have been maintained on a L. littorea diet. The response to the alarm signal, however, appears to be dependent on season and light conditions; some ecological implications of these findings are also discussed. Received: 8 January 1999 / Accepted: 29 March 1999     

Field-scale variation in microbial activity and soil properties in relation to mineralization and sorption of pesticides in a sandy soil

Pesticides applied to agricultural soils are subject to environmental concerns because leaching to groundwater reservoirs and aquatic habitats may occur. Knowledge of field variation of pesticide-related parameters is required to evaluate the vulnerability of pesticide leaching. The mineralization and sorption of the pesticides glyphosate and metribuzin and the pesticide degradation product triazinamin in a field were measured and compared with the field-scale variation of geochemical and microbiological parameters. We focused on the soil parameters clay and organic carbon (C) content and on soil respiratory and enzymatic processes and microbial biomass. These parameters were measured in soil samples taken at two depths (Ap and Bs horizon) in 51 sampling points from a 4-ha agricultural fine sandy soil field. The results indicated that the spatial variation of the soil parameters, and in particular the content of organic C, had a major influence on the variability of the microbial parameters and on sorption and pesticide mineralization in the soil. For glyphosate, with a co-metabolic pathway for degradation, the mineralization was increased in soils with high microbial activity. The spatial variability, expressed as the CV, was about five times higher in the Bs horizon than in the Ap horizon, and the local-scale variation within 100 m(2) areas were two to three times lower than the field-scale variation within the entire field of about 4 ha.     

Energy intensities and the impact of high energy prices on producing and consuming sectors in Malaysia

The increase in oil prices has put pressure on the global economy. Even economies that have a high degree of self-sufficiency concerning oil products are experiencing rising production costs and price increases for households energy use. Therefore, changes in energy policies are under consideration for countries highly dependent on imported energy as well as countries with a high degree of self-sufficiency. Examination of dependence on cheap energy sources for economic growth in different economic sectors is becoming more important as countries are trying to promote activities that are less energy intense. Among the policy changes under consideration, the adjustment of domestic energy subsidies is of particular interest. The effect of high energy prices on a fast growing economy, such as in Malaysia, is considerable, as the country will shift from being a net exporter of energy to a net importer in less than 10 years. Malaysia until recently has experienced increasing overall energy intensity and the growth up to 2,000 was quite high, especially for electricity intensity. A continued rise in energy intensity will be quite problematic in this new high oil price regime. This paper investigates the impact of rising energy prices on production costs for the different sectors of the Malaysian economy. Input–output (I–O) calculations demonstrate that the impact on the exporting component of the manufacturing sectors is less than for the average production. Therefore the production cost increase caused by, for example, an adjustment in electricity prices of 25% will result in less than 1/2% increase. As the competing countries in world markets are experiencing the same rise in energy costs, including electricity based on fossil fuels, there is no vital argument for not allowing domestic energy prices to adjust to the international price changes.