Temporal prey distribution affects the competitive ability of parasitized sticklebacks

Parasitized animals are often reported to have a reduced competitive abilit y in experimental studies designed to examine foraging success under a spec ific type of competitive interaction; however, since animals compete under a range of competition regimes in natural situations, and because success i s likely to require different foraging skills under each, it is unclear whe ther infected animals should be equally poor competitors under all competit ive scenarios. We studied the foraging success of three-spined sticklebacks , Gasterosteus aculeatus, infected with plerocercoids of a cestode, Schisto cephalus solidus, in competition with uninfected conspecifics. When pairs o f differentially infected sticklebacks were presented with sequentially int roduced items, the numbers of available prey taken by infected and uninfect ed competitors did not differ significantly, although nonparasitized fish w ere more successful at taking items over which there was direct competition . In contrast, when prey items were presented simultaneously in a locally d ense patch, nonparasitized fish ingested significantly more of the availabl e food than their infected counterparts: an apparent consequence of their g reater ability to take items in rapid succession. Our results show that the type of competition conditions generated as a result of specific prey dist ribution patterns plays a role in determining the relative foraging success of parasitized sticklebacks, and suggest that this may have consequences f or the distribution of different infection classes in natural, heterogeneou s environments. (C) 1998 The Association for the Study of Animal Behaviour.