Establishment success in young cladoceran communities: An experimental test

Abstract

We tested the relative importance of regional and local factors in determining zooplankton community composition in an enclosure experiment. In this experiment, we assessed establishment success of immigrant cladoceran zooplankton species in young communities in the first and second year of existence in five newly created pools. In both years, we created four treatments, representing a gradient of strength in biotic interactions with the resident communities, to explore differences in establishment success of immigrant species. In general, species diversity increased when immigrant species were added, suggesting dispersal limitation. However, this increase was lower in the second than in the first year, indicating a declining effect of regional factors during the course of community assembly. No significant difference in establishment success between the experimental treatments could be detected in the first year. In the second year, immigrant species were more often present in the treatment without resident species than in the treatments with resident species, at least during the first weeks. Our results demonstrate that species sorting and biotic interactions, mainly competition among zooplankton species and predation by Chaoborus, become important in determining the zooplankton community composition early in community assembly.