title: Network of Interactions Between Ciliates and Phytoplankton During Spring.
abstract: The annually recurrent spring phytoplankton blooms in freshwater lakes initiate pronounced successions of planktonic ciliate species. Although there is considerable knowledge on the taxonomic diversity of these ciliates, their species-specific interactions with other microorganisms are still not well understood. Here we present the succession patterns of 20 morphotypes of ciliates during spring in Lake Zurich, Switzerland, and we relate their abundances to phytoplankton genera, flagellates, heterotrophic bacteria, and abiotic parameters. Interspecific relationships were analyzed by contemporaneous correlations and time-lagged co-occurrence and visualized as association networks. The contemporaneous network pointed to the pivotal role of distinct ciliate species (e.g., Balanion planctonicum, Rimostrombidium humile) as primary consumers of cryptomonads, revealed a clear overclustering of mixotrophic/omnivorous species, and highlighted the role of Halteria/Pelagohalteria as important bacterivores. By contrast, time-lagged statistical approaches (like local similarity analyses, LSA) proved to be inadequate for the evaluation of high-frequency sampling data. LSA led to a conspicuous inflation of significant associations, making it difficult to establish ecologically plausible interactions between ciliates and other microorganisms. Nevertheless, if adequate statistical procedures are selected, association networks can be powerful tools to formulate testable hypotheses about the autecology of only recently described ciliate species.
authors.affiliation: Limnological Station, Institute of Plant Biology and Microbiology, University of Zurich Kilchberg, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Posch
authors.affiliation: Limnological Station, Institute of Plant Biology and Microbiology, University of Zurich Kilchberg, Switzerland.
authors.forename: Bettina
authors.initials: B
authors.lastname: Eugster
authors.affiliation: Department Aquatic Ecology, Swiss Federal Institute of Aquatic Science and Technology Dübendorf, Switzerland.
authors.forename: Francesco
authors.initials: F
authors.lastname: Pomati
authors.affiliation: Limnological Station, Institute of Plant Biology and Microbiology, University of Zurich Kilchberg, Switzerland.
authors.forename: Jakob
authors.initials: J
authors.lastname: Pernthaler
authors.affiliation: Limnological Station, Institute of Plant Biology and Microbiology, University of Zurich Kilchberg, Switzerland.
authors.forename: Gianna
authors.initials: G
authors.lastname: Pitsch
authors.affiliation: Limnological Station, Institute of Plant Biology and Microbiology, University of Zurich Kilchberg, Switzerland ; Microbial Ecology Group, Consiglio Nazionale Delle Ricerche- Istituto per lo studio degli ecosistemi Verbania Pallanza, Italy.
authors.forename: Ester M
authors.initials: EM
authors.lastname: Eckert
keywords: ciliate morphotypes; ciliophora; local similarity analysis; network analysis; phytoplankton spring bloom