Meeting Abstract
Organisms living at high densities may be forced to engage in conflict for access to resources such as food or shelter. When resources are limited, the outcome of agonistic interactions may have important fitness implications. We investigated the behavioral interactions of the invasive round goby (Neogobius melanostomus) in a shelter-limited environment. Round goby are benthic fish that utilize rocky shelters as reproductive sites where territorial males defend clutches of eggs. Previous work has shown that larger individuals have greater resource holding potential in dyadic interactions. In order to understand the outcome of agonistic interactions in more complex social environments, we observed same sex groups comprised of three differently sized individuals in an aquarium with limited access to shelters. We predicted that larger goby would behave aggressively towards smaller goby, and outcompete smaller goby for access to shelters. Because males defend shelters while breeding, we also predicted that male goby would compete more aggressively than females for possession of shelters. We found that the largest goby in each group behaved most aggressively towards all other individuals, and were also more often avoided by smaller conspecifics. This result was only true of the largest fish; the second largest and smallest fish were indistinguishable in terms of the counts of agonistic behaviors they performed or received in spite of comparable size differences. Overall, male goby behaved more aggressively towards same sex conspecifics than females. In spite of differences in aggressive behavior, larger goby did not spend more time inside shelters during the observation period. Our findings highlight that aspects of the social environment may limit the opportunity for individuals to establish dominance or ownership of resources.
