Temporal prey distribution affects the competitive ability of parasitized sticklebacks

Parasitized animals are often reported to have a reduced competitive ability in experimental studies designed to examine foraging success under a specific type of competitive interaction; however, since animals compete under a range of competition regimes in natural situations, and because success is likely to require different foraging skills under each, it is unclear whether infected animals should be equally poor competitors under all competitive scenarios. We studied the foraging success of three-spined sticklebacks, Gasterosteus aculeatus, infected with plerocercoids of a cestode, Schistocephalus solidus, in competition with uninfected conspecifics. When pairs of differentially infected sticklebacks were presented with sequentially introduced items, the numbers of available prey taken by infected and uninfected competitors did not differ significantly, although nonparasitized fish were more successful at taking items over which there was direct competition. In contrast, when prey items were presented simultaneously in a locally dense patch, nonparasitized fish ingested significantly more of the available food than their infected counterparts: an apparent consequence of their greater ability to take items in rapid succession. Our results show that the type of competition conditions generated as a result of specific prey distribution patterns plays a role in determining the relative foraging success of parasitized sticklebacks, and suggest that this may have consequences for the distribution of different infection classes in natural, heterogeneous environments. (c) 1998 The Association for the Study of Animal Behaviour.