Klepoparasitism and the distribution of unequal competitors

Kleptoparasitism is an important means by which many animals obtain limited resources. The success of kleptoparasitism may be influenced by a number of factors, including competitive differences among individuals and the spatial distribution of prey and hosts. I used ideal free distribution (IFD) theory to predict the spatial distribution of kleptoparasites and their hosts between two patches differing in quality and to predict how the use of kleptoparasitism was influenced by the relative searching and fighting abilities of classes of competitors. Unlike previous IFD models incorporating kleptoparasitism, I allowed competitors to choose between attempting kleptoparasitism or searching for undefended prey. When the rates of resource inputs into the patches were high, the model predicted little use of kleptoparasitism. If competitive types were equally able to displace others from resources, then those individuals that were poorer at searching for food were more likely to kleptoparasitize. If competitive types differed in their abilities to displace others, kleptoparasites were exclusively those individuals that were best able to do so. Regardless of their competitive type, a higher proportion of individuals in the high-quality patch were kleptoparasitic, while the total density of competitors in the high-quality patch was lower than that expected based on the ratio of resource inputs. These predictions differ from previous IFD models of kleptoparasitism, suggesting that the mechanisms involved in searching for and obtaining resources can influence the spatial distribution of animals. Key words: habitat use, ideal free distribution, producer-scrounger model, searching efficiency, simulation model. [Behav Ecol 13:260–267 (2002)] Among the fundamental decisions that a foraging animalmust make are how to obtain food and where to forage