Effects of resource holding potential and resource value on tenure at nest sites in sand gobies

Over a broad range of animal systems, male reproductive success depends on resource holding potential (RHP) and resource quality. In a field study, we randomly combined males of different sizes with nests of different sizes to investigate the relative role of resource holding potential and resource quality in determining a sand goby, Pomatoschistus minutus, male's nest tenure. Individually marked small and large males were given either small or large flowerpots for nests in isolation and were exposed to intruders after they had built nests. We found that nest tenure was longer for big males and owners of big nests. In most cases (34 of 51) the original nest owner was replaced by a bigger male. These replacements by larger males were probably due to takeovers by stronger intruders. Replacement males were larger at big nests. Our results support resource defense theory, as individuals with higher RHP and more valuable resources defended their nest for longer. On nine occasions males abandoned their nests. Owners of these nests were larger than the nest owners that were replaced. Hence, our results may provide an example of a situation in which sand goby males are able to judge the reproductive value of their current situation and act accordingly.