Who wins in the battle for space? The importance of priority, behavioural history and size

Abstract

The pulsed nature of new individuals entering into existing communities means that prior residents can greatly influence the establishment and persistence of later-arriving individuals. The unique set of interactions experienced by an individual can also affect how it behaves and its likelihood of winning future encounters. In the present study, we used field experiments to investigate the circumstances under which residency (resident or intruder), behavioural history (prior dominance or subordinance) and body size determined the direction and strength of intraspecific interactions. We paired recently metamorphosed individuals of a coral reef damselfish, Pomacentrus amboinensis, with different suites of these traits to observe how each behaved in a competitive interaction. Our results show the importance of priority and size advantages, and suggest that prior behavioural history has the least influence on the outcome of future confrontations. Prior history was only important when combatants were of similar size, with previously subordinate residents losing against similarly sized previously dominant intruders. Aggression affected space use on a habitat patch and was itself affected by the relative size difference between combatants. Aggressive residents were larger than their competitors, occupied higher areas of the patch and chased intruders to lower areas of the patch and further away from the patch. Space use was not affected by behavioural history. These results demonstrate the importance of priority effects in structuring fish communities, and how an individual's physical and behavioural characteristics interact to predict community dynamics. This has important implications for predicting fish community structure under certain environmental or ecological scenarios.