Functional ecology of aquatic phagotrophic protists - Concepts, limitations, and perspectives.
Functional ecology is a subdiscipline that aims to enable a mechanistic understanding of patterns and processes from the organismic to the ecosystem level. This paper addresses some main aspects of the process-oriented current knowledge on phagotrophic, i.e. heterotrophic and mixotrophic, protists in aquatic food webs. This is not an exhaustive review; rather, we focus on conceptual issues, in particular on the numerical and functional response of these organisms. We discuss the evolution of concepts and define parameters to evaluate predator-prey dynamics ranging from Lotka-Volterra to the Independent Response Model. Since protists have extremely versatile feeding modes, we explore if there are systematic differences related to their taxonomic affiliation and life strategies. We differentiate between intrinsic factors (nutritional history, acclimatisation) and extrinsic factors (temperature, food, turbulence) affecting feeding, growth, and survival of protist populations. We briefly consider intraspecific variability of some key parameters and constraints inherent in laboratory microcosm experiments. We then upscale the significance of phagotrophic protists in food webs to the ocean level. Finally, we discuss limitations of the mechanistic understanding of protist functional ecology resulting from principal unpredictability of nonlinear dynamics. We conclude by defining open questions and identifying perspectives for future research on functional ecology of aquatic phagotrophic protists.
University of Innsbruck, Research Institute for Limnology, Mondseestr. 9, 5310 Mondsee, Austria. Electronic address: thomas.weissse@uibk.ac.at.
Thomas
T
Weisse
University of Copenhagen, Marine Biological Section, Strandpromenaden 5, 3000 Helsingør, Denmark.
Ruth
R
Anderson
University of Cologne, Biocenter, Institute for Zoology, General Ecology, Zuelpicher Str. 47b, 50674 Cologne (Köln), Germany.
Hartmut
H
Arndt
Dept. Biologia Marina i Oceanografia, Institut de Ciències del Mar (CSIC) Passeig Marítim de la Barceloneta, 37-49, 08003 Barcelona, Spain.
Albert
A
Calbet
University of Copenhagen, Marine Biological Section, Strandpromenaden 5, 3000 Helsingør, Denmark.
Per Juel
PJ
Hansen
Institute of Integrative Biology, University of Liverpool, BioScience Building, Crown Street, Liverpool L69 7ZB, UK.
David J S
DJS
Montagnes
D059001:Aquatic Organisms / Q000502:physiology*; D005075:Biological Evolution; D056890:Eukaryota / Q000502:physiology*; D056127:Hydrobiology; D008954:Models, Biological; D012106:Research / Q000592:standards / Q000639:trends
Functional response; Independent Response Model; Mixotrophy; Nonlinear dynamics; Numerical response; Protist grazing