The coevolution of cooperation and structure in biological markets [electronic resource]
Keywords: Biology.

This dissertation centers on the theme of the coevolution of cooperation and structure in biological markets. Analogous to the market economy of human societies, a typical biological market consists of two types of individuals, where one or both types of individuals are mobile so that they can not only change their individual behavior within given partnerships but also actively choose partners to interact with. However, partner choice is constrained by the dynamic supply and demand in a biological market. Therefore, ecological dynamics provide feedback to the evolutionary process. I integrate behavioral, ecological and evolutionary dynamics to explore two common types of biological markets: intraspecific interactions in breeding systems (Chapter 1) and interspecific interactions in plant-pollinator mutualisms (Chapter 2 and 3). Chapter 1 focuses on the coevolution of intraspecific pairwise cooperation and pair-bonding in a population with a symmetric sex ratio. The fitness payoff of pairwise cooperation, such as biparental care, often depends on the pair-matching structure of a population, and the latter often emerges as a collective outcome of individual pair bonding traits, which are also under selection. Here we develop an analytical model and individual-based simulations to study the coevolution of long-term pair bonds and cooperation in parental care, where partners play a Snowdrift game in each breeding season. We illustrate that long-term pair bonds may coevolve with cooperation when bonding cost is below a threshold. As long-term pair bonds lead to assortative interactions through pair-matching dynamics, they may promote the prevalence of cooperation. In addition to the payoff matrix of a single game, the evolutionarily stable equilibrium also depends on bonding cost and accidental divorce rate, and it is determined by a form of balancing selection because the benefit from pair-bond maintenance diminishes as the frequency of cooperators increases. Our findings highlight the importance of ecological factors affecting social bonding cost and stability in understanding the coevolution of social behaviour and social structures, which may lead to the diversity of biological social systems. In Chapter 2, we shift our attention to cooperative interactions between two species with dynamic population densities. Mutualism between plants and animals, such as in pollination and seed dispersal, is a fundamental mechanism facilitating the productivity and biodiversity of ecosystems, and it is often considered as an analog of a free-market economy. The coevolution of plant reward and animal choosiness, however, involves an apparent paradox due to incomplete information and limited mutation rates: Plant rewards evolve only when animals are choosy, but choosy animals purge the heritable variations of plants, which then favors less choosy animals. We use a two-species mathematical model to illustrate how non-heritable phenotypic variances of plants may facilitate the coevolution of rewards and choosiness and solve the paradox with low mutation rates. We simultaneously track the ecological and evolutionary dynamics and show that the population ratio links the two processes and tunes the stable eco-evolutionary equilibrium. Numerical simulations confirm the analytic prediction with varying mutation rates (heritable variance). The efficiency of a biological market is generally suboptimal due to the information constraint and individual competition. In the last chapter, we explore the question how adaptive foraging behaviors, e.g., flower constancy, of individual pollinators, which are sensitive to floral density and diversity, may shape the structure and stability of co-flowering plant communities. We construct a mathematical model integrating pollinator adaptive foraging behavior and plant population dynamics, and use numerical analyses to study the ecological consequences for the plant community. The result is significantly different from that of a model in which pollinators are either strict generalists or specialists. In general, pollinators with adaptive foraging behavior enhance the stability of plant species coexistence compared to strict generalists, but less effectively than strict specialists. This suggests that individual adaptive behavior in mutualistic interactions can have a very different impact on community structure from that in predator-prey interactions. This could be an important complementary mechanism to adaptive foraging at the species level. In addition, the adaptive behavior of pollinators may cause a sharp regime shift between the sink and source states for invading plant species. This novel result is relevant to the conservation of native plant communities as well as the management of invasive plant species.