1. On the basis of simulations at two levels of organisation (individuals and populations), we analysed the impact of altered food and temperature conditions on the Asian clam Corbicula fluminea. In particular, we addressed the role of food and temperature in explaining occasional mass mortalities. 2. A Dynamic Energy Budget Model (DEBM) was used for simulations at the individual level. We calibrated the DEBM successfully using experimental data on growth in length and mass of C. fluminea under four combinations of temperature and food. 3. The calibrated DEBM was used to simulate the annual growth in length and mass and the reproductive success under different environmental scenarios. In general, an increase in temperature and food concentration resulted in larger and heavier clams and a higher per capita rate of reproduction. However, phytoplankton densities in rivers often fluctuate strongly and densities are high only briefly. Under such conditions, our simulations suggest that the temporal interactions of temperature and food concentration are particularly important and can decisively influence annual growth. 4. With regard to occasional mass mortalities, it has been hypothesised that increased temperature might induce an unmet metabolic demand and hence starvation. To test this, we simulated the conditions observed in the Rhine in 2003, when there was a severe heat wave and a mass mortality. For this purpose, we used the calibrated DEBM and, in addition, integrated it into a Physiologically Structured Population Model (PSPM) to account for processes at the population level. 5. Based on these simulations, it seems unlikely that starvation was the main cause of the mass mortality, although not all mechanisms affecting the energy budget are fully understood. However, a prolonged negative energy budget during heat waves can increase the vulnerability of clams to direct effects of high temperatures or additional stressors and might thus be regarded as an important factor indirectly increasing mortality rates.

SUMMARYPopulation-level effects of global warming result from concurrent direct and indirect processes. They are typically described by physiologically structured population models (PSPMs). Therefore, inverse modelling offers a tool to identify parameters of individual physiological processes through population-level data analysis, e.g. the temperature dependence of growth from size-frequency data of a field population. Here, we make use of experiments under laboratory conditions, in mesocosms and field monitoring to determine the temperature dependence of growth and mortality of Gammarus pulex. We found an optimum temperature for growth of approximately 17°C and a related temperature coefficient, Q 10 , of 1.5°C -1 , irrespective of whether we classically fitted individual growth curves or applied inverse modelling based on PSPMs to laboratory data. From a comparison of underlying data sets we conclude that applying inverse modelling techniques to population-level data results in meaningful response parameters for physiological processes if additional temperature-driven effects, including within-population interaction, can be excluded or determined independently. If this is not the case, parameter estimates describe a cumulative response, e.g. comprising temperature-dependent resource dynamics. Finally, fluctuating temperatures in natural habitats increased the uncertainty in parameter values. Here, PSPM should be applied for virtual monitoring in order to determine a sampling scheme that comprises important dates to reduce parameter uncertainty. Supplementary material available online at

LowGC-type plasmids conferring resistance to sulfonamides have been frequently isolated from manure and manured soil. However, knowledge on the dynamics of plasmid-carrying populations in soil and their response to the presence of sulfonamides is scarce. Here, we investigated effects of the sulfonamide resistance conferring plasmid pHHV216 on the fitness of Acinetobacter baylyi BD413 in soil after application of manure with or without the sulfonamide antibiotic sulfadiazine (SDZ). The persistence of A. baylyi BD413 pHHV216 in competition to its plasmid-free variant was followed in soil microcosms. CFU counts showed a decrease in A. baylyi BD413 in manured soils over the experimental period of 32 days by about 0.5 log units. The proportion of the plasmid-carrying populations decreased from 50 to < 40% in the absence of SDZ, while the proportion of plasmid-carrying BD413 increased from 50 to about 65% with SDZ added. The data suggest that SDZ introduced via manure into soil was bioaccessible, providing a fitness advantage for the plasmid-carrying population of BD413 in soil, while the plasmid conferred a fitness disadvantage when selective pressure by SDZ was absent. In future, this method may be used as a tool for the assessment of bioavailability of antibiotics in soil.

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