Owner Advantage in the fiddler crab, Uca mjoebergi. Do owners win more contests than floaters because they are more motivated?

Resource owners generally win contests against intruders, a phenomenon referred to as the 'Owner Advantage' (OA). Uca mjoebergi is a typical fiddler crab that is highly sociable, territorial and lives in mixed sex colonies on intertidal mudflats. Burrows are used in territory defence, for mating, and as refuge from predators and environmental stresses. Fights are common between owners and floating males who battle for ownership of the territory and burrow.

Experiments were conducted from 28th Sept - 30 Dec 2006 at the lower reaches of Ludmilla Creek within East Point Reserve, 5km North of Darwin, NT. This experiment was designed to determine if owner advantage in the fiddler crab Uca mjoebergi is related to motivation. This was designed on the premise that at low tide owners are thought of as being more motivated than floaters in contests because they have invested in the territory. It was thought that as the tide comes in, the motivational asymmetry is likely to be reduced as both are increasingly motivated to win the contest and the territory.

The results indicate that as the tide came in owners, not floaters, were more likely to win contests, and size difference also had a significant effect on who won. The result is interesting because it is the first direct test of the role of motivation in contests, and it is a direct contradiction to established theory.