Parent record: Owner advantage in the fiddler crab, Uca mjoebergi: Investigating why owners win more contests?

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. \n\nExperiments 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. \n\nThe 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.

资源所有者通常会在与入侵者的争斗中获胜，这一现象被称为“所有者优势（Owner Advantage, OA）”。乔氏招潮蟹（Uca mjoebergi）是一类典型的招潮蟹，具有高度群居性、领地意识强，栖息于潮间带泥滩的混合性别种群中。洞穴被用于领地防御、交配活动，同时也是躲避捕食者与环境胁迫的庇护所。领地所有者与游荡雄蟹之间的争斗十分常见，二者会为争夺领地与洞穴的所有权展开较量。

本实验于2006年9月28日至12月30日期间，在北领地（Northern Territory, NT）达尔文以北5公里处的东点保护区（East Point Reserve）内的拉德米勒溪（Ludmilla Creek）下游河段开展。本系列实验旨在探究所有者与游荡雄蟹之间存在的哪些不对称性，促成了所有者优势现象的出现。

研究结果显示，乔氏招潮蟹的所有者优势占比超过90%。研究发现，游荡雄蟹的格斗能力并不逊色于领地所有者：在标准化实验处理中，二者体型相当时的格斗表现并无显著差异。这表明，除格斗能力之外的其他不对称性，是促成显著所有者优势的关键因素。研究发现，格斗中的机械优势对领地所有者具有极为显著的增益效果。在退潮时段，领地所有者基于其对领地的投入，比入侵者更具格斗动机。随着涨潮，学界曾预期游荡雄蟹与领地所有者的格斗动机会趋于对称，但实验结果显示这并未降低领地所有者的格斗胜率。事实上，当二者格斗动机被调整至对称状态时，领地所有者仍能赢得更多争斗。高质量领地对争斗结果与领地所有者格斗动机的影响较弱。尽管栖息于高质量领地的领地所有者能赢得更多争斗，但该差异并未达到统计学显著性水平。研究结果还显示，领地所有者的格斗胜率随其对邻里关系投入的增加而呈现上升趋势。