Modelling confinement experiments in community ecology: Differential mobility among competitors

Field experiments in which mobile organisms are confined inside enclosures have been widely used in many areas of marine, freshwater and terrestrial ecology in the past three decades. Some ecologists believe that at least some and possibly most, of the interpretation of this work may be subject to dispute because of potential artefacts associated with the confinement itself. Simulations suggested that moderate or even severe artefacts may arise from using enclosures that are ‘too small’, which could produce inferential nonsense in some circumstances (Mac Nally, 1997). Here, the influence of differential mobility is explicitly considered in a simulated environment, with organisms confined in enclosures of a variety of sizes. Some simulations involve single populations, while others pit together competitors differing only in mobility. Three foraging strategies based on simple movement principles are simulated. Results indicate that the relationships between resource consumption and mobility will depend upon foraging strategy, often in unexpected ways compared with the implications of spatial averaging. Outcomes of interactions among pairs of populations having the same foraging strategy but with different mobilities also are complex, indicating that the results of confinement experiments may involve non-intuitive interactions between mobility and foraging method. There needs to be a refocusing on basic biology of organisms used in confinement experiments (e.g. movement distributions) and, particularly, constructing defensible statements on why the selected scales were used.