The tale of the two shoals: How individual experience influences shoal behaviour

Benzaken, Zehev Schwartz (2010). The tale of the two shoals: How individual experience influences shoal behaviour M.Sc Thesis, School Of Integrative Biology, The University of Queensland.

       
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Author Benzaken, Zehev Schwartz
Thesis Title The tale of the two shoals: How individual experience influences shoal behaviour
School, Centre or Institute School Of Integrative Biology
Institution The University of Queensland
Publication date 2010-06
Thesis type M.Sc Thesis
Supervisor Dr. Kevin Warburton
Dr. Bronwen Cribb
Total pages 72
Total colour pages 4
Total black and white pages 68
Language eng
Subjects 07 Agricultural and Veterinary Sciences
Abstract/Summary This project examined how the spatial behaviour and cohesion of rainbow fish (Melanotaenia duboulayi) shoals are affected by the contrasting previous experience of individual shoal members. The main variables considered were: overall group size, the time since group members were exposed to a positive (food) or negative (threat) experience, and the proportions of shoal members having the two types of experience. The food and threat stimuli were introduced close to a habitat patch, to which fish were normally attracted. Shoals of ten or two fish were exposed to food or threat for thirty minutes. Their behaviour was then recorded in twenty- minute trials after different lengths of time had elapsed since exposure (0, 1, 24 and 48 hrs). Shoals made up of different combinations of food-exposed and threat-exposed fish were used (for ten-fish shoals: 0+10, 2+8, 5+5, 8+2 and 10+0; for two fish shoals: 0+2, 1+1, 2+0). Threat-exposed ten-fish shoals stayed away from the patch, whereas their food-exposed counterparts continued to use the patch. Such behaviour was consistent with expectations based on predator avoidance theory. However, the reaction of the threat-exposed two-fish shoals had a different reaction to the presented stimuli if compared to shoal with ten individuals. Smaller shoals continued to use the patch, possibly because of a protection trade-off where for a small group the refuge benefits of the patch outweighed the perceived risks associated with open water, or because of lower efficiencies in terms of learning and mutual reinforcement in small shoals. The effects of increasing time since exposure varied according to group composition (ratio of fish exposed to threat versus food). Thus, within the first hour after exposure, a shoal of ten threat-exposed fish moved away from the patch and began individual patch inspections, while ten food-exposed fish showed a smaller change in individual inspection frequency. After 24 hrs, all unevenly-mixed shoals had moved away from the patch, but after 48 hours shoals dominated by food-exposed individuals, but not those dominated by threat-exposed fish, were using it once more and performing more group inspections. These results showed that shoal behaviour was affected by a complex interaction between individual experience, group composition and the elapsed time since threat- or food-exposure. However, the uniform results with two-fish shoals indicated that the range of options for dynamic, risk-balancing behaviour involving factors such as memory and reprioritisation of experience was more limited when group sizes were low. Further work is proposed to investigate learning in shoaling and refuge time budgets. In summary, this project has shed some light on the poorly understood topic of how shoals perceive experiences and how memory of past experiences influences shoal behaviour.
Keyword Spatial behavior in animals
Fishes -- Behavior
Additional Notes 11, 13-15

 
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Created: Tue, 31 Aug 2010, 00:39:07 EST by Mr Zehev Benzaken on behalf of Library - Information Access Service