The interplay between resources, body size and neighbours in competition over nesting opportunities in sand gobies

In many species, both the distribution and quality of nesting resources can influence the intensity and outcome of competitive interactions and, ultimately, reproductive success. We carried out a series of field-based experiments on the sand goby, Pomatoschistus minutus , a fish species with a resource defence mating system, to investigate how resource aggregation and quality affect ownership of nesting resources. We found that when male gobies had access to an abundance of nesting resources, nest occupancy was lower when there was a neighbouring nest close by, irrespective of resource size (i.e. quality). However, under lower resource availability of a subsequent experiment, this pattern was no longer apparent. Nest owner phenotype was important, with larger males consistently more likely to claim large nesting resources than smaller males. In contrast, the body condition of nesting males was not significantly linked to nesting resource size, the presence of a neighbour, neighbour size or the size of the neighbour's resource. Together, our findings highlight a complex interplay between resource distribution, resource quality and outcomes of competitive interactions. • Resource availability and quality are often studied separately, yet they can interact. • In sand gobies, resource distribution, quality and social context were relevant. • Overall, resource value outweighed competitor proximity in nest acquisition. • Risk of competition also mattered when more nesting resources were available. • Hence, males fine-tuned their resource-holding strategy to resource availability.