Male-Male Competition for Nest Sites in the Sand Goby, Pomatoschistus minutus

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Abstract
Nest size and amount of eggs in sand goby nests show a positive correlation. Nest size explained 40 to 51% of the variation in egg mass size. This relationship remained the same for most of the breeding season. Sand goby males were allowed to choose between large and small artificial nest sites in the field. When the distance between alternative sites was 10 cm, males showed a clear preference for larger nest sites. However, when the distance between alternatives was increased to 50 cm males occupied sites randomly in relation to the size of the site. In the case where alternative sites were 50 cm apart, both sites in a pair were frequently occupied, whereas when they were 10 cm apart both very rarely were occupied. In a square of 10*6 artificial nest sites of three different size categories, larger males were occupying larger nests three weeks after the beginning of the experiment. However, two weeks earlier there was no relationship between male size and nest size category. The most likely explanation for the observed pattern is that large males gradually displace smaller males from large nests. It is concluded that nest size is an important factor determining a male''s potential fitness and that sand goby males show the adaptive behavior of preferring larger nest sites. Males complete for nest sites which are in short supply. This competition will lead to intra-sexual selection for larger male size.