Dynamic changes in prey choice by stickleback during simultaneous encounter with large prey

Abstract

When a three‐spined stickleback Gasterosteus aculeatus encountered prey simultaneously the probability of hanging and the median pursuit time were greater than when prey were encountered sequentially. During simultaneous prey encounter fish did not choose to attack the more profitable prey but instead the nearer prey was handled first except when the difference between the two prey sizes was large. No difference was found in the level of total energetic intake by the fish regardless of prey size pairing. Fish that handled and ate the first prey of a pair in <5 s attacked the second prey with a high probability of success, demonstrating an opportunistic feeding strategy. Importantly however, the fish did not choose to maximize long term energy intake rate by eating both prey, but rather short‐term considerations over the course of feeding took precedence. With an empty stomach, the probability of a fish eating (Peat) the first prey handled was high regardless of prey size. As stomach fullness increased, the Peat the first prey handled decreased if it was the larger prey. Hence, the fish were unselective when the stomach was empty but thereafter there was a shift in preference towards the smaller prey. The decision of which prey to attack and eat appeared to be based on short‐term energy considerations and the level of stomach fullness. This study demonstrates that feeding on a short‐term scale is a crucial factor to take account of when analysing fish feeding during simultaneous prey encounter.