Long-term memory for food patches and its implications for the ideal free distribution in sticklebacks

Population foraging in a patchy environment can lead to an ideal free distribution of competitors among the patches. If patch profitabilities do not change too quickly, individuals may remember patches in which they had been successful and use their memory when they have to deal with new competitors. I investigated whether three-spined sticklebacks (Gasterosteus aculeatus) expect to find food in a patch in which they had foraged between 1 and 14 d ago. Long-term memory for a patch in which the fish had formerly been fed existed for at least 8 d. In another experiment I tested whether sticklebacks use their long-term memory in population foraging. A group of four sticklebacks, each of which had been fed singly in one of two patches, was offered food in both patches simultaneously 3 d later. The four fish achieved an ideal free distribution, with those that had fed in the left patch preferring the left patch and those that had fed in the right patch preferring the right patch, although all fish sampled both patches frequently. The preference for the former patch in the ideal free distribution was similar when there had been a pause of 6 d between feeding and test. Implications of long-term memory for competitive foraging are discussed