|Competition and co-existence with particular reference to gadoid fish species|
Jones, R. (1978). Competition and co-existence with particular reference to gadoid fish species. Rapp. et Proc.-Verb. Cons. Int. Explor. Mer 172: 292-300
In: Rapports et Procès-Verbaux des Réunions du Conseil Permanent International pour l'Exploration de la Mer. Conseil Permanent International pour l'Exploration de la Mer: Copenhague. ISSN 0074-4336, more
Competition; Gadidae Rafinesque, 1810 [WoRMS]; Marine
An investigation with reference to some gadoid species has led to the view that wherever two gadoid species appear to be eating the same kind of food, detailed analysis shows that direct 'competition' appears to be avoided in one way or another. In general, either different prey species are eaten, or different sizes of individual prey species are taken, or similar prey species of similar sizes are taken but at different times or places. It is suggested that these differences are primarily due to mutually exclusive behaviour patterns, and this has led to a view of the 'ecological niche' in terms of mutually exclusive behaviour patterns. The basic assumption is that predators and their prey have evolved patterns of distribution and behaviour respectively, such that no two predators go about exploiting their food in exactly the same way. In particular, it is suggested that there are certain behaviour patterns which are mutually exclusive. For example, a predator may have a high attack speed at the expense of having to ignore objects that cannot be identified positively as food. Alternatively, it could have a very slow approach speed at the possible risk of losing the more active prey species. Other possibilities are that predators could hunt for their food or lie in wait for it. In the case of pelagic predators, they could look up or look down. The important suggestion, however, is that there are a number of alternatives which are mutually exclusive and that the efficiency that comes from specialization has led to different patterns of feeding behaviour. As a consequence, it is suggested that different predators take different kinds of food in different proportions without there being any question of 'food selection' as an act of deliberate 'choice'. The situation is one in which two predators are feeding on two kinds of food. Each predator has a choice of feeding strategies. At high food densitia there could be a considerable overlap of diet. However, at high predator densities, food densities should be reduced, and the 'competition' that might otherwise have arisen should be correspondingly reduced.