Intraspecific food competition in fishes

Intraspecific food competition exerts powerful selective forces on all animals; successful foragers thrive relative to weaker conspecifics. Understanding competition is therefore fundamental both to ecological insight and to conservation efforts. Fish are adaptable and tractable experimental organisms, offering excellent model systems for studies on competition, and they lend themselves to two approaches: (i) studies of short-term competition, which quantify the components of behavioural interactions; (ii) studies of long-term interactions, in which the indeterminate nature of fish growth makes it possible to measure rates directly and correlate them with competitive success. The nature and the intensity of competition vary according to resource characteristics and distributions in time and space, the ecological context, and the relative competitive abilities of the foragers. Second-order effects, such as winner and loser consequences, add to the complexity and frustrated early attempts to develop realistic models of intraspecific competition. Recently, however, considerable advances have been made in both laboratory and field studies on fishes adding to our understanding of these interacting effects. At the same time, the application of individual-based modelling offers the prospect of progress towards greater realism and accuracy in predicting competitive outcomes. This review draws together a wide and disparate literature on intraspecific competition in fishes to facilitate the work of both empiricists and theoreticians towards these important goals. In the short term, competing individuals may adopt different behavioural strategies and feeding patterns or establish dominance hierarchies and feeding territories. In the longer term, competition can drive character displacement and the formation of species pairs and fish provide some of the most compelling examples of these processes in evolutionary biology. The challenge for the future is to further develop our understanding of the relationship between the competitive environment and the responses of fishes, particularly with closer co-operation between empiricists and theoreticians, and to apply this knowledge to aquaculture and to better management of exploited fish stocks.