Spiny lobsters (Palinuridae) commonly share crevice shelters with
conspecifics, a behaviour usually hypothesized to benefit mutually cooperative
defenders through reduced predation risk. The group-defence hypothesis
predicts a suite of distinct corollary life history traits and ecological
correlates including more frequent co-denning than solitary denning,
especially where predators or den competitors are numerous and when the
lobsters are small, moulting or otherwise vulnerable. Two alternative
co-denning hypotheses, the dilution effect (a type of selfish herding) and the
guide effect (attraction to a denned conspecific), have different and
distinctive sets of predictions. To test among these hypotheses, the
den-sharing patterns of newly emerged postalgal juveniles of
Panulirus argus and associated ecological conditions in
the Florida Bay (USA) nursery habitat were examined. Only half of the
juveniles shared dens, and rarely was den sharing in an area greater than that
expected by chance. Den-sharing frequency was most highly correlated with
conspecific density and scarcity of local dens. The lack of correlation
between den sharing and lobster size, moult condition, shelter type and
predator density failed to support either the group-defence or the
dilution-effect hypothesis. Instead, the data better support the guide-effect
hypothesis.
Substratum type and conspecific density as drivers of mussel patch formation
