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Collective defense by spiny lobster (Panulirus argus) against triggerfish (Balistes capriscus): effects of number of attackers and defenders

2009; Taylor & Francis; Volume: 43; Issue: 1 Linguagem: Inglês

10.1080/00288330909509978

1175-8805

Kari L. Lavalli, William F. Herrnkind,

Animal Behavior and Reproduction

Abstract Abstract Migrating queues of Caribbean spiny lobsters, Panulirus argus, suffer attacks during daylight by variable numbers of triggerfish they encounter on patch reefs. When threatened, lobsters assemble into outward facing, rosette‐like groups, remain coherent in their spacing, and defend themselves by parrying with their spinous antennae. In 90‐min field tethering trials involving predatory grey triggerfish (Balistes capriscus), solitary lobsters were subdued 44% of the time whereas grouped lobsters suffered only minor bites; triggerfish present numbered from 1 to 23. Victims of fish attack were significantly smaller than survivors in the field trials. Although attack/defense ratios did not differ between solitary and grouped lobsters, fish behaviours towards such different groups did differ with more bite attempts/bites being directed towards solitary lobsters. In a series of experiments in large seawater enclosures, we pitted 1, 3, 5, 10, or 20 free‐moving lobsters against 2 or 5 grey triggerfish, all of which had previously killed lobsters. We hypothesised that larger fish numbers would be more effective in subduing the prey independent of lobster group size, but that lobsters in larger groups would benefit by a higher per capita survival rate, as compared with smaller groups. We found that per capita mortality declined with lobster group size, but remained the same statistically whether there were two or five triggerfish. Triggerfish interference may have played a role in reducing the effect of greater numbers of attackers. Keywords: group behaviourselfish herddilution effect