The guide effect influence on the gregariousness of juvenile Caribbean spiny lobsters

Many animals are gregarious and potentially benefit from the presence of conspecifics. We examined both den finding and den sharing by vulnerable juvenile Caribbean spiny lobsters, Panulirus argus, and compared three functional explanations of why lobsters might benefit from being gregarious. Lobsters sharing dens did not have higher survival than those in dens by themselves, suggesting that cooperative group defence may not be important at this life history stage. Lobsters in areas of high conspecific density did not have higher survival than those in areas of low density, suggesting that the dilution effect may not be important either. Den sharing provided no additional benefit beyond that provided by the shelter. However, lobsters were able to find shelter significantly faster when conspecific residents were already present in a den. This 'guide effect' benefits the shelter-seeking individual by reducing the time of exposure and associated predation risk. Habitat or risk assessment based solely on the presence of conspecifics may be a critical first step in the evolution of more complex social behaviours. (C) 2001 The Association for the Study of Animal Behaviour.