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Introductions of fish into lakes can be viewed as whole system experiments, which can be used to study the principles of community assembly and factors determining the outcome of species invasions. Freshwater fish species have been translocated by humans for centuries in Sweden, and this activity has been documented by national and regional authorities starting at the end of the 19th century. Based on this documentation and additional interviews with local fishermen, we have compiled a data set that includes 1157 intentional introductions of 26 freshwater fish species into 821 Swedish lakes. The data include both successful and failed introductions; where a successful introduction means that the introduced fish species was present in the lake for ≥20 yr or that reproduction was observed earlier than that. The oldest introduction is from 1658 and the latest from 2002. Additionally, the data set includes species composition, water temperature sum, maximum water temperature, lake area, elevation, longitude, and latitude for all lakes. These data have been used to test hypotheses about biotic resistance and invasion success in three papers. We found the presence or absence of specific species predicted invasion success better than the species richness of the lakes. We also found that species with high invasion success tend to make a large contribution to biotic resistance, which will make communities more resistant in the future as they are invaded by additional species.

Introductions of fish into lakes can be viewed as whole system experiments, which can be used to study the principles of community assembly and factors determining the outcome of species invasions. Freshwater fish species have been translocated by humans for centuries in Sweden and this activity has been documented by national and regional authorities starting at the end of the 19th century. Based on this documentation and additional interviews with local fishermen we have compiled a dataset that includes 1158 introductions of 26 freshwater fish species into 821 Swedish lakes. The data includes both successful and failed introductions; where a successful introduction means that the introduced fish species was present in the lake for ≥20 years or that reproduction was observed earlier than that. The oldest introduction is from 1658 and the latest from 2002. Additionally, the dataset includes species composition, temperature sum, maximum temperature, lake area, elevation, longitude and latitude for all lakes. This data has been used to test hypotheses about biotic resistance and invasion success in three papers. We found the presence or absence of specific species predicted invasion success better than the species richness of the lakes. We also found that species with high invasion success tend to make a large contribution to biotic resistance, which will make communities more resistant in the future as they are invaded by additional species.

Intraspecific competition has been shown to favor diet specialization among individuals. However, the question whether the competition takes the form of interference or exploitative in driving diet specialization has never been investigated. We investigated individual diet specialization in the isopod Saduria entomon, in relation to forager and resource biomasses in a system that exhibits predator–prey fluctuations in density. We found that individual diet specialization was only affected by the biomass of their preferred prey (Monoporeia affinis) and not by Saduria biomass; diet specialization was higher when Monoporeia biomass was low compared to when there were high Monoporeia biomass. Population diet breadth increased at low Monoporeia biomass whereas individual diet breadths were marginally affected by Monoporeia biomass. Overall, this led to the increase in diet specialization at low Monoporeia biomass. This study shows that predator–prey dynamics might influence diet specialization in the predator and that resource biomass, not forager biomass might be important for individual diet specialization.