Precopulatory mate guarding in the hermit crab Pagurus middendorfii (Brandt) (Decapoda : Paguridae): effects of population parameters on male guarding duration

The effects of sex ratio, competitor size, and the encounter rate with fema les on the duration of male precopulatory guarding were tested in the hermi t crab Pagurus middendorffii (Brandt, 1851) to examine how guarding duratio n varies in relation to social factors. Size and owner advantages in male-m ale contest competition were also examined. Larger and owner males were str onger competitors than smaller and challenger males, respectively. Males gu arded females earlier and, consequently, longer when the sex ratio was more male biased, when size differences between competitor sizes were small, an d when encounter rates were low, which are consistent with theoretical pred ictions. However, contrary to these predictions, small males did not guard earlier than large males when size differences were large. These results su ggest that males might assess not only the operational sex ratio based on t he encounter rate with females but also their competitive ability relative to other males and the possibility of successful guarding. (C) 1999 Elsevie r Science B.V. All rights reserved.