Researchers: Backwell, Patricia, Dr (collaborator) , Fayed, Sarah (principalInvestigator)
Brief description 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.
Lineage Maintenance and Update Frequency: notPlanned
Lineage Statement: A standard set of data was collected for each fight. For each fight the date, time, the type of floater, and winner were recorded. Additionally, all crabs were measured, and fighting phases as well as fight duration were recorded. The winner is the male that owns the territory at the end of a fight. The loser is the crab which walks away at the end of the fight. A fight was considered over when: a) the loser walked >30cm away, b) travelled past two other males territories, c) entered another burrow, or d) started another fight. Parameters: Date, ltidet (time of diurnal low tide), hightideht (high tide height of the tide which follows the diurnal low tide), rtimet (time of the fight), tsltide (number of minutes since low tide), ctype (condition, NF=natural floater, RF=removed floater, RO=removed owner, TE=owner within a plot with food added, TN=owner within a plot which is natural i.e. no food added, OB=owners burrows blocked, OUB=control-owners burrows not blocked), winner, cara (intruder carapace width - mm), chel (inturder cheliped / claw length - mm), ocara (owner carapace width - mm), ochel (owner cheliped / claw length -mm), actions observed (P=push, B=burrow, G=grapple, F=flick, D=dig, Pi=pinch, TB=true burrow fighting), dura (duration of fight - seconds), digdura (dig duration - seconds), sizediff (size difference between owner and intruder claws - mm).
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Credit
Funded by The Australian Research Council (ARC)
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Credit
Funded by The Ecological Society of Australia
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Credit
The Australian National University (ANU)
Notes
Purpose
To determine how the owner advantage persists (manifests) itself in the fiddler crab, Uca mjoebergi.
To determine which asymmetries contribute to the owner advantage by comparing 'natural' fights to fights with the asymmetry experimentally reduced or enhanced.
Data time period: 2006-09-28 to 2006-12-30
text: westlimit=130.5; southlimit=-13; eastlimit=131; northlimit=-12
text: uplimit=0; downlimit=0
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