Specialization and Resource Trade: Biological Markets as a Model of Mutualisms

Abstract

Most ecological theory suggests that the conditions that would give rise to the evolution of mutualisms are rare. In contrast, empirical evidence suggests that mutualisms are common. Thus, there appears to be a need for additional theory to describe conditions under which mutualisms may evolve. Furthermore, there is a need for theory to predict the conditions under which we expect interactions to remain mutualistic once established. We adopt a biological market approach to present a model for the evolution of resource exchange mutualisms, using the relationship between plants and mycorrhizal fungi as an example. We apply the economic theory of relative advantage to investigate the conditions under which species ought to specialize and trade. A simple economic analogy demonstrates that, in a two-resource model, a species that is relatively efficient at acquiring one resource would benefit from specialization on acquisition of that resource accompanied by trade for the other resource. The theory of relative advantage extends this prediction to show that specialization and trade confer an advantage even for species that are relatively poor resource competitors for both resources. Under the assumptions of our model, we show that two species ought to specialize in the acquisition of one resource and trade for a second resource as long as each species perceives different relative acquisition costs for the two resources. We also describe the conditions under which changing resource availabilities will benefit, or harm, both partners in a mutualism. We predict conditions conducive to mutualisms to occur when the costs of resource exchange are low, the opportunity to ensure fair trade is high, or the cost of tolerating cheaters is low. Market models such as ours may help to explain the conditionality often observed in mutualisms.

Inter-group cooperation in humans and other animals

“…Groups that are more efficient at acquiring one type of resource may specialize on that resource, leading to group-level division of labour: this 'comparative advantage' principle explains both the economics of international trade and resource exchange between species [20]. When the scale at which resources vary and specialization occurs is large, an entire nation could be considered to act as a 'group'.…”

Egalitarian despots: hierarchy steepness, reciprocity and the grooming-trade model in wild chimpanzees, Pan troglodytes

“…Multiple studies have proffered BMT as an explanation for the trade of commodities in social animals, such as the exchange of services in primates (e.g. Barrett, Gaynor, & Henzi, 2002; Barrett & Henzi, 2006; Barrett, Henzi, Weingrill, Lycett, & Hill, 1999; Fruteau, Voelkl, van Damme, & Noë, 2009; Gumert, 2007; Koyama, Caws, & Aureli, 2012; Norscia, Antonacci, & Palagi, 2009), between cleaner fishes and their clients (Bshary, 2001; Bshary & Grutter, 2002; Bshary & Noë, 2003; Bshary & Schäffer, 2002), the exchange of protection for nectar between ants and aphids (Fischer, Hoffmann, & Völkl, 2001; Leimar & Axén, 1993), the nutrient exchange between plants and fungi in mycorrhiza (Hoeksema & Schwartz, 2001; Schwartz & Hoeksema, 1998) and in the trading of grooming for mating between male and female wood mice ( Apodemus sylvaticus : Stopka & Macdonald, 1999). …”

Green Roof Ecosystems

“…AM fungi have long been known to aid plants in drought tolerance (Auge 2001). Mycorrhizal fungi also increase the volume of soil that a plant has access to for nutrient foraging, which would be beneficial on roofs that have minimal fertilizer inputs (Schwartz and Hoeksema 1998).…”

“…Mycorrhizal functioning can exist along a continuum from mutualism to parasitism, and in disturbed ecosystems, the reversal of mutualisms to more parasitic relationships has been observed (Kiers et al 2010). However, it is also possible that the abiotic stresses experienced on green roofs may result in greater symbiont reliance due to poor environmental quality (Schwartz and Hoeksema 1998).…”