Conspecific density modulates the effect of predation on dispersal rates
- 394 Downloads
Dispersal decisions underlie the spatial dynamics of metacommunities. Prey individuals may disperse to reduce the risk of either predation or starvation, and both of these risks may depend on conspecific density. Surprisingly, there is little theory examining how dispersal rates should change in response to the combined effects of predation and changes in conspecific density. We develop such a model and show that, under certain conditions, predators may induce dispersal at low prey densities but not high prey densities. We then experimentally manipulate the density of the ciliate Paramecium aurelia and the perceived presence of its predator, the flatworm Stenostomum virginiamum, in a two-patch metacommunity to parameterise the model. Paramecium dispersed in response to Stenostomum at low densities, but they reduced their dispersal in response to predation risk at high predator densities. By applying our model to the empirical data, we show that this switch in dispersal strategy, linked to increases in prey density, occurred because predators increased the difficulty or risk of dispersal. Together, the model and experiment reveal that the effects of predators on dispersal are contingent on prey density. Previous studies have sometimes reported an increase in dispersal rate when predation risk is elevated, and other times a decrease in dispersal rate. Our demonstration of a switch point, with predation risk increasing dispersal at low prey densities but reducing dispersal above a threshold of prey density, may reconcile the diversity of prey dispersal behaviours reported in these previous investigations and observed in nature.
KeywordsTrophic interactions Non-consumptive effects Dispersal Meta-community Protozoa
We would like to thank Owen Petchey, Jeff Shima, Frederic Barraquand and the members of the Srivastava lab group for their insightful comments during the development of this project. This work was funded by an NSERC E.W.R. Steacie Memorial Fellowship awarded to D.S.S. All applicable institutional and/or national guidelines for the care and use of animals were followed.
Conflict of interest
The authors have no conflicts of interest to declare.
- Anholt BR, Werner EE (1995) Interaction between food availability and predation mortality mediated by adaptive behavior. Ecology 76:2230–2234Google Scholar
- Barraquand F, Murrell DJ (2012) Intense or spatially heterogeneous predation can select against prey dispersal. PLoS One 7:e28924Google Scholar
- Dehn MM (1990) Vigilance for predators—detection and dilution effects. Behav Ecol Sociobiol 26:337–342Google Scholar
- Hammill E, Beckerman AP (2010) Reciprocity in predator–prey interactions: exposure to defended prey and predation risk affects intermediate predator life history and morphology. Oecologia 163:193–202Google Scholar
- Hauzy C, Hulot FD, Gins A, Loreau M (2007) Intra- and interspecific density-dependent dispersal in an aquatic prey–predator system. J Anim Ecol 76:552–558Google Scholar
- Holyoak M, Lawler SP (1996) Persistence of an extinction-prone predator–prey interaction through metapopulation dynamics. Ecology 77:1867–1879Google Scholar
- Huffaker CB (1958) Experimental studies on predation: dispersion factors and predator–prey oscillations. Hilgardia 27:343–383Google Scholar
- Kunert G, Weisser WW (2003) The interplay between density- and trait-mediated effects in predator–prey interactions: a case study in aphid wing polymorphism. Oecologia 135:304–312Google Scholar
- Kusch J, Kuhlmann HW (1994) Cost of Stenostomum-induced morphological defense in the ciliate Euplotes octocarinatus. Arch Hydrobiol 130:257–267Google Scholar
- R Development Core Team (2011) R: a language and environment for statistical computing. R Foundation for Statistical Computing, ViennaGoogle Scholar
- Relyea RA, Werner EE (2000) Morphological plasticity in four larval anurans distributed along an environmental gradient. Copeia 2000:178–190Google Scholar
- Rohani P, Ruxton GD (1999) Dispersal-induced instabilities in host–parasitoid metapopulations. Theor Popul Biol 55:23–36Google Scholar
- Ryan MR, Killen SS, Gregory RS, Snelgrove PVR (2012) Predators and distance between habitat patches modify gap crossing behaviour of juvenile Atlantic cod (Gadus morhua, L. 1758). J Exp Mar Biol Ecol 422:81–87Google Scholar
- Savill NJ, Hogeweg P (1999) Competition and dispersal in predator–prey waves. Theor Popul Biol 56:243–263Google Scholar
- Schoeppner NM, Relyea RA (2008) Detecting small environmental differences: risk–response curves for predator-induced behavior and morphology. Oecologia 154:743–754Google Scholar
- Weisser W (2001) The effects of predation on dispersal. In: Clobert J, Danchin E, Dhondt A, Nichols J (eds) Causes, consequences and mechanisms of dispersal at the individual, population and community level. Oxford University Press, New York, pp 180–188Google Scholar