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. The series of experiments was run to assess which asymmetries between owner-floater contribute to the owner advantage.
The studies reveal that in Uca mjoebergi the OA is >90%. Floaters were found not to be poorer fighters, performing just as well as owners of the same size in standardised treatments. This meant that asymmetries other than fighting ability were contributing to the substantial OA. Mechanical advantage was found to be highly significant providing advantage to owners during fights. At low tide owners are more motivated than intruders based on their investment in territory. As the tide rolls in it was expected that floaters-owners experience motivational symmetry, however this was found not to reduce owner fighting success. In fact, when motivation was heightened to symmetric, owners won more contests. The effects of high quality territories on contests and owner motivation were weak. Although owners in high quality territories won more contests this was not a significant difference. The results also indicate there was a trend for owner fighting success to increase with an increase in the investment in neighbour relations.