A FIELD-STUDY OF INTRASPECIFIC COMPETITION FOR FOOD IN HERMIT-CRABS (PAGURUS-BERNHARDUS)

A tethered, frame-mounted video camera deployed on the sea-bed was use d to observe the competitive interactions that occurred between hermit crabs, Pagurus bernhardus, that were attracted to food patches (dead dragonets, Callionymus lyra) of differing size. Hermit crab numbers on the small food patch ceased increasing c. 20 min after the camera arr ived on the sea-bed, whilst numbers on the large patch increased throu ghout the experiment. The number of observed aggressive interactions i ncreased with increasing hermit crab density, but was generally highes t on the small patch. The probability of a hermit crab being able to f eed increased with size for each of three size-groups on the small pat ch, whereas on the large patch, both large and medium-sized hermit cra bs were equally likely to feed. Small and medium-sized hermit crabs ha d a higher probability of being able to feed on the large patch than t he small patch. As the density of hermit crabs around a patch increase d, the proportion of small individuals actively feeding decreased. The size-frequency distribution of hermit crabs on the large patch was si gnificantly different from that on the small patch, with the latter be ing skewed towards larger individuals. These results suggest that the intensity of competition increases both with increasing numbers of her mit crabs and decreasing size of food resource. Large hermit crabs wer e more successful at feeding than smaller crabs when competition was m ore intense. (C) 1997 Academic Press Limited.