title: Community assembly in Lake Tanganyika cichlid fish: quantifying the contributions of both niche-based and neutral processes.
abstract: The cichlid family features some of the most spectacular examples of adaptive radiation. Evolutionary studies have highlighted the importance of both trophic adaptation and sexual selection in cichlid speciation. However, it is poorly understood what processes drive the composition and diversity of local cichlid species assemblages on relatively short, ecological timescales. Here, we investigate the relative importance of niche-based and neutral processes in determining the composition and diversity of cichlid communities inhabiting various environmental conditions in the littoral zone of Lake Tanganyika, Zambia. We collected data on cichlid abundance, morphometrics, and local environments. We analyzed relationships between mean trait values, community composition, and environmental variation, and used a recently developed modeling technique (STEPCAM) to estimate the contributions of niche-based and neutral processes to community assembly. Contrary to our expectations, our results show that stochastic processes, and not niche-based processes, were responsible for the majority of cichlid community assembly. We also found that the relative importance of niche-based and neutral processes was constant across environments. However, we found significant relationships between environmental variation, community trait means, and community composition. These relationships were caused by niche-based processes, as they disappeared in simulated, purely neutrally assembled communities. Importantly, these results can potentially reconcile seemingly contrasting findings in the literature about the importance of either niche-based or neutral-based processes in community assembly, as we show that significant trait relationships can already be found in nearly (but not completely) neutrally assembled communities; that is, even a small deviation from neutrality can have major effects on community patterns.
authors.affiliation: Department of Evolutionary Theory Max Planck Institute for Evolutionary Biology Plön Germany; Groningen Institute for Evolutionary Life Sciences University of Groningen Groningen The Netherlands.
authors.forename: Thijs
authors.identifier: 0000-0002-4162-1140
authors.initials: T
authors.lastname: Janzen
authors.affiliation: Groningen Institute for Evolutionary Life Sciences University of Groningen Groningen The Netherlands; Terrestrial Ecology Unit University of Ghent Ghent Belgium; Fundacion Ecomares Cali Colombia.
authors.forename: Adriana
authors.initials: A
authors.lastname: Alzate
authors.affiliation: Zoological Institute University of Basel Basel Switzerland; Department of Fish Ecology & Evolution EAWAG Centre for Ecology Kastanienbaum Switzerland.
authors.forename: Moritz
authors.initials: M
authors.lastname: Muschick
authors.affiliation: Groningen Institute for Evolutionary Life Sciences University of Groningen Groningen The Netherlands.
authors.forename: Martine E
authors.initials: ME
authors.lastname: Maan
authors.affiliation: Institute of Plant Sciences University of Bern Bern Switzerland; Biodiversity and Climate Research Centre Senckenberg Gesellschaft für Naturforschung Frankfurt Germany.
authors.forename: Fons
authors.initials: F
authors.lastname: van der Plas
authors.affiliation: Groningen Institute for Evolutionary Life Sciences University of Groningen Groningen The Netherlands.
authors.forename: Rampal S
authors.initials: RS
authors.lastname: Etienne
keywords: Lake Tanganyika; STEPwise Community Assembly Model; cichlids; trait‐based community assembly