The effects of quality of shelters and prior residence on Marmorkrebs (marbled crayfish)

Many animals fight over a limited valuable resource. In Marmorkrebs (marbled crayfish), large animals usually defeated small opponents but they were frequently beaten by small opponents who were shelter owners. A prior residence effect of marbled crayfish was analyzed quantitatively. More than 2 hr of residency in a shelter was sufficient for small owners to defeat large intruders. Small animals that stayed in a shelter for 24 hr still tended to win following removal of the shelter 10 min before pairing with large intruders, but 2 hr residents were occasionally beaten by large intruders without the support of shelters during pairings. The prior residence effect thus developed depending on the time of residency. To clarify whether the strength of the prior residence effect was affected by the quality of a shelter, large and small owners with different combinations of two high and low quality of shelters were paired. When both large and small owners possessed a high quality shelter, the frequency of agonistic bouts was reduced. Even if agonistic bouts occurred, the win frequency of small owners was almost equal to that of large owners. Thus, the residence effect on small owners was sufficiently strong to overcome the physical disadvantage of small animals to large opponents. By contrast, small owners of low quality shelters were frequently beaten by large owners with the shelters of same or better quality. We conclude that the outcomes of fighting over the resource shelter are highly dependent on both the perception of shelter quality and body size differences.