Density-dependent movement and the consequences of the Allee effect in the model organism Tetrahymena.
Movement and dispersal are critical processes for almost all organisms in natural populations. Understanding their causes and consequences is therefore of high interest. While both theoretical and empirical work suggest that dispersal, more exactly emigration, is plastic and may be a function of local population density, the functional relationship between the underlying movement strategies and population density has received less attention. We here present evidence for the shape of this reaction norm and are able to differentiate between three possible cues: the relative number of individuals, the presence of metabolites (chemical cues) and resource availability. We performed microcosm experiments with the ciliate model organism Tetrahymena in order to understand the plasticity of movement strategies with respect to local density while controlling for possible confounding effects mediated by the availability of different cues. In addition, we investigated how an Allee effect can influence movement and dispersal plasticity. Our findings suggest that movement strategies in Tetrahymena are plastic and density-dependent. The observed movement reaction norm was U-shaped. This may be due to an Allee effect which led to negative density dependence at low population densities and generally positive density dependence at high population densities due to local competition. This possibly adaptive density-dependent movement strategy was likely mediated by chemical cues. Our experimental work in highly controlled conditions indicates that both environmental cues as well as inherent population dynamics must be considered to understand movement and dispersal.
Department of Aquatic Ecology, Eawag: Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, CH-8600, Dübendorf, Switzerland.
Emanuel A
EA
Fronhofer
Department of Environmental Systems Science, ETH Zürich, CH-8092, Zürich, Switzerland.
Tabea
T
Kropf
Department of Aquatic Ecology, Eawag: Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, CH-8600, Dübendorf, Switzerland.|Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, CH-8057, Zürich, Switzerland.
Florian
F
Altermatt
D063147:Animal Distribution; D000818:Animals; D003463:Cues; D008124:Locomotion; D008954:Models, Biological; D011156:Population Density; D013768:Tetrahymena / Q000502:physiology*
Allee effect; Tetrahymena; chemical cue; density‐dependent dispersal; density‐dependent movement; emigration; metapopulation; microcosm; movement