Abstract
AbstractSupply and demand affect the values of goods exchanged in cooperative trades. Studies of humans and other species typically describe the standard scenario that an increase in demand leads to a higher price. Here, we challenge the generality of that logic with empirical data and a theoretical model. In our study system, "client" fishes visit cleaner wrasse (Labroides dimidiatus) to have ectoparasites removed, but cleaners prefer client mucus, which constitutes "cheating." We removed 31 of 65 preselected cleaners from a large isolated reef patch. We compared cleaner-client interactions at the reef and a control reef before removal and 4 weeks after removal. Cleaner fish from the experimental treatment site interacted more frequently with large clients (typically visitors with access to alternative cleaning stations), but we did not observe any changes in service quality measures. A game-theoretic analysis revealed that interaction duration and service quality might increase, decrease, or remain unchanged depending on the precise relationships between key parameters, such as the marginal benefits of cheating as a function of satiation or the likelihood of clients responding to cheating as a function of market conditions. The analyses show that the principle of diminishing return may affect exchanges in ways not predicted by supply-to-demand ratios.
Highlights
The values of goods exchanged in human economic markets follow the rules of supply and demand (Smith 1776), wherein goods in high demand become more expensive
A game-theoretic analysis revealed that interaction duration and service quality might increase, decrease or remain unchanged depending on the precise relationships between key parameters, such as the marginal benefits of cheating as a function of satiation or the likelihood of clients responding to cheating as a function of market conditions
How supply and demand predict payoff distribution among cooperating individuals in human markets has been successfully applied to other species within the framework of “biological market theory” (Noë et al 1991; Noë and Hammerstein 1994)
Summary
The values of goods exchanged in human economic markets follow the rules of supply and demand (Smith 1776), wherein goods in high demand become more expensive. Mathematical models of biological market theory typically predicted that an increase in the demand for a given service or commodity would cause an increase in the price through partner choice (Noë and Hammerstein 1995; Schwartz and Hoeksema 1998; Johnstone and Bshary 2008; Mazancourt and Schwartz 2010; Akcay et al 2012; for partial exceptions see Wyatt et al 2014). While these models invariably explore evolutionary time scales, evidence from short-term empirical studies conforms to the demand-price relationship. Examples range from interspecific mutualisms involving mycorrhiza and plant interactions (Kiers et al 2011), fig trees and their pollinators (Herre and West 1997), and lycaenid larvae and ants (Leimar and Axén 1993), to intraspecific interactions in meerkats (Kutsukake and Clutton-Brock 2010), hyenas (Smith et al 2007), Mediterranean wrasse (Hellmann et al 2020) and paper wasps (Grinsted and Field 2017), as well as in mating markets (Metz et al 2007; Noë 2017) and primate grooming markets (Barrett and Henzi 2001; Fruteau et al 2009)
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