Competition, conflict and cooperation : social interactions within and between species
Creators: name: Booksmythe, Isobel Jessica Judith
Publisher: name: The Australian National University
Year: 2012
Subjects: subject: QL776.B66 2012
subject: Animal communication
subject: Fiddler crabs Behavior

description: This thesis addresses several aspects of cooperation and conflict in social interactions. Male fiddler crabs use their enlarged claw as a weapon in territorial interactions. Clawless males are severely disadvantaged in fighting. Chapter 2 investigates whether clawless males use their resemblance to females to avoid male aggression during burrow acquisition and defence. Clawless and intact males differed in burrow acquisition methods and fighting behaviour, but were equally successful at acquiring and retaining burrows. Although treated as female by courting males, clawless males did not mimic female behaviour, but altered their territorial strategies to avoid conflicts. Chapter 3 examines the 'dear enemy' effect, where residents are more aggressive towards strangers than neighbours. The greater threat posed by strangers explains why residents are differentially aggressive, but not how they distinguish neighbours from strangers. I manipulated the residency status of fiddler crab neighbours to determine whether familiarity facilitates reduced aggression. Fights between neighbours were less escalated than fights between residents and both familiar and unfamiliar 'strangers', suggesting that residents use behavioural cues to determine the threat posed by an intruder. Cooperative territory defence is expected when helping a neighbour is less costly than establishing new boundaries with the usurper of a neighbouring territory. In fiddler crabs cooperation depends on the relative sizes of participants - large residents help smaller neighbours repel intermediate-sized intruders. Chapter 4 tests whether familiarity or the relative size of the smaller neighbour affect the likelihood that a resident helps, by replacing neighbours and simulating intrusions onto their territories. The likelihood of helping familiar and unfamiliar neighbours of the same size did not differ, but decreased when the replacement neighbour differed in size from the original neighbour. This suggests that residents do not recognise their neighbours individually, but use size as a cue to neighbour identity. Chapter 5 demonstrates that cooperative defence occurs between heterospecific neighbours. Residents were equally likely to help a smaller conspecific or heterospecific neighbour during simulated intrusions by intermediate-sized conspecifics. Helping was significantly less likely when the intruder was heterospecific. Chapter 6 investigates the effect of simultaneous vs. sequential mate encounter on male mate discrimination between conspecific and heterospecific females. Under sequential encounter, males were equally likely to court conspecific and heterospecific females. However, when simultaneously viewing a conspecific and a heterospecific female, males courted and attempted to mate conspecifics more often, indicating that males can discriminate between conspecific and heterospecific females and prefer conspecifics when given a choice. Chapter 7 explores the effects of social context on male reproductive success, testing whether the mate choice of male mosquitofish depends on the size of competitors, and quantifying the effect of competitor size on male mating success. In two-choice trials, males preferred large over small males. However, when females were present males associated equally with large and small males. The mating success of competing males increased with male size, and with decreasing competitor size. The benefits of associating with small competitors in a mating context appear to be balanced by other benefits of associating with larger males.