The patch distributed producer–scrounger game

Abstract

Grouping in animals is ubiquitous and thought to provide group members antipredatory advantages and foraging efficiency. However, parasitic foraging strategy often emerges in a group. The optimal parasitic policy has given rise to the producer-scrounger (PS) game model, in which producers search for food patches, and scroungers parasitize the discovered patches. The N-persons PS game model constructed by Vickery et al. (1991. Producers, scroungers, and group foraging. American Naturalist 137, 847-863) predicts the evolutionarily stable strategy (ESS) of frequency of producers (q;) that depends on the advantage of producers and the number of foragers in a group. However, the model assumes that the number of discovered patches in one time unit never exceeds one. In reality, multiple patches could be found in one time unit. In the present study, we relax this assumption and assumed that the number of discovered patches depends on the producers' variable encounter rate with patches (lambda). We show that q; strongly depends on lambda within a feasible range, although it still depends on the advantage of producer and the number of foragers in a group. The basic idea of PS game is the same as the information sharing (parasitism), because scroungers are also thought to parasitize informations of locations of food patches. Horn (1968) indicated the role of information-parasitism in animal aggregation (Horn, H.S., 1968. The adaptive significance of colonial nesting in the Brewer's blackbird (euphagus cyanocephalus). Ecology 49, 682-646). Our modified PS game model shows the same prediction as the Horn's graphical animal aggregation model; the proportion of scroungers will increase or animals should adopt colonial foraging when resource is spatiotemporally clumped, but scroungers will decrease or animals should adopt territorial foraging if the resource is evenly distributed.

Role of social interactions in dynamic patterns of resource patches and forager aggregation

“…One subset of such models examines so-called producer-scrounger systems wherein one species (the scrounger) exploits another (the producer). Most such investigations fail to account for spatially explicit interactions (16,22,25), which have been the focus of our paper.…”

“…Recent studies suggest that the amount of food obtained by producers vs. scroungers (the finders' share), can depend strongly on patch structure and distances between individuals (1,15,16). This idea motivated our second major thrust, to explore the relative benefits of the two social foraging strategies in the model.…”

“…Although explored in vast literature, KS has yet to be applied to the situation of dual social behavior here described, but see the individual-based model for gradient climbers and their highly social followers (14). Further, how organisms shape and are in turn affected by the spatial distribution of their resources is still an emerging area of research, addressed in this paper.In group foraging studies, resource distribution, patch size and structure, and distance between foragers were shown to influence the "finders' share" (food obtained by producers vs. scroungers) (1,15,16), which motivated us to ask which strategy confers an advantage under various conditions. To do so, we ask how limited resource distribution, patch size, and movement/search parameters contribute to relative success, quantified by a ratio of net food consumed by foragers vs. exploiters.…”

“…In group foraging studies, resource distribution, patch size and structure, and distance between foragers were shown to influence the "finders' share" (food obtained by producers vs. scroungers) (1,15,16), which motivated us to ask which strategy confers an advantage under various conditions. To do so, we ask how limited resource distribution, patch size, and movement/search parameters contribute to relative success, quantified by a ratio of net food consumed by foragers vs. exploiters.…”

Spatial population dynamics in a producer-scrounger model

“…When scrounging occurs within a species, it can 1592 CHRIS COSNER AND ANDREW L. NEVAI result from asymmetric competition between individuals belonging to dominance hierarchies [8,35], it can occur when the benefit of joining a discovery elsewhere outweighs the cost of moving there [10,49], and the success of scrounging can depend on an individual's ability to adapt its strategy in response to those of its peers [9] or in response to variable environmental conditions [46]. Game-theoretic techniques have been particularly successful in elucidating the roles of aggression and retaliation on patterns of evolutionarily stable strategies (ESSs) [13,14,15,16,17,40].…”