Evol Ecol Res 5: 131-153 (2003)     Full PDF if your library subscribes.

Movement between habitats by unequal competitors: effects of finite population size on ideal free distributions

Don M. Hugie1* and Tamara C. Grand2

11525 White Birch Terrace, #323, Fremont, CA 94536, USA and 2108 Roe Drive, Port Moody, British Columbia V3H 3M8, Canada

Author to whom all correspondence should be addressed.
e-mail: hugie@sfu.ca


Ecologists have frequently commented on the ability of Fretwell and Lucas’ (1970) ideal free distribution (IFD) theory to approximate observed animal distributions, despite frequent violations of the assumption that competitors are of equal competitive ability. In a previous paper (Hugie and Grand, 1998), we provided an explanation for this phenomenon by recognizing that animals will often move between habitats for reasons other than simply to maximize resource payoffs, given perfect information about current payoffs in all habitats. When such ‘non-IFD’ movements are incorporated into an unequal competitors IFD model, the equilibrium distribution is predicted to resemble an IFD for equal competitors. Recently, this explanation was criticized based on the results of an individual-based simulation model (Ruxton and Humphries, 1999). Here, we show that this criticism is the result of assumptions that not only differ fundamentally from those of our original model, but also are unlikely to be met in nature. We also construct our own simulation model and apply it to both an infinitely large population scenario, as assumed by our original analytical model, and a finite population scenario in the form of an individual-based model. In doing so, we confirm the validity of our original results and extend our theory to finite populations.

Keywords: habitat selection, ideal free distribution, individual-based modelling, patch switching, population size, unequal competitors.

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