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Buchberger, Felicitas; Stockenreiter, Maria (2018): Unsuccessful invaders structure a natural freshwater phytoplankton community. In: Ecosphere, Vol. 9, No. 3, e02158
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Abstract

Species invasion dynamics are a core topic in ecology and the effects of species invasions on ecosystems are well described. However, the knowledge about the mechanisms during the invasion process itself is limited. Many interactions between invaders and resident species occur during the invasion process. These interactions influence individual species abundance and subsequently community composition. Even though invaders are often unsuccessful, the very short interactions with the resident species can influence species abundances and therefore community composition. The prominent effects of unsuccessful invaders on community composition were already predicted in a theoretical model. To empirically test the effect of such unsuccessful invaders on a resident phytoplankton community, we conducted a mesocosm experiment in a mesotrophic freshwater pond. Six freshwater algae belonging to three taxonomic groups (chlorophyta, cyanobacteria, and bacillariophyta) were added as potential invader species to the natural phytoplankton community of the pond (as single species or as combination of two species of the same taxonomic group). After nine days, the invasion success and the impact on the natural phytoplankton community were estimated. Results show that although all invaders were unsuccessful, they had lasting effects on the resident community. In all communities exposed to invasion, biodiversity (H') was maintained. In contrast, in control communities, the diversity at the end of the experiment was lower compared to the initial community. Furthermore, communities exposed to invasion were less similar to control communities without invasion than to the other invaded communities. Differences were found in taxonomic group composition as well as in species composition. Additionally, we found evidence for synergistic effects between the combined added species. Our results give clear evidence of strong transient effects of unsuccessful invaders on freshwater phytoplankton community composition.