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Species exist in complex biotic environments, engaging in a variety of antagonistic and cooperative interactions. While these interactions are generally recognized to be context-dependent, varying in outcome in the presence of other interactions, studies tend to focus on each interaction in isolation. One of the main classes of species interaction is mutualism, in which partner species gain a net benefit from their interaction. However, mutualisms are beset by a variety of species that can reduce or even eliminate the benefits of mutualism through exploitation of and competition for the resources and services offered by mutualists. These exploiter species potentially threaten the ecological stability of mutualisms and may alter selection on mutualistic traits. Thus, understanding the ecology and evolution of mutualisms requires consideration of interactions with exploiter species. In this dissertation, I investigated the effects of exploiter species on mutualisms between plants and pollinators using a combination of eco-evolutionary modeling, optimization theory, and behavioral studies. Using two adaptive dynamics models of coevolution in exploited pollinating seed parasite mutualisms, I found that exploiters reduce mutualist densities and select for more parasitic mutualists. Nevertheless, the models demonstrate that intraspecific competition for host resources and host defense of those resources restrict the ecological conditions that lead to extinction of the mutualism, as well as the chances of evolution to extinction. Thus, exploiters are unlikely to be the threat to mutualisms that has been assumed previously. On the other hand, in another type of exploitation, exploitative predators may pose a greater threat to investment in mutualism than has been presumed. Through both optimal foraging theory and behavioral experiments on bumble bees, I found that the risk from ambush predators can change pollinator floral preferences when predators preferentially use high-quality flowers to locate their prey. This research suggests that predators of mutualists may have important top-down effects and that further research is needed to investigate the effects of exploitative predators on selection on mutualist traits.

The emergence of the eukaryotic cell was one of the key events that paved the path to the vast variety of complex life visible all around us. A pivotal event in the process of eukaryogenesis was an endosymbiosis of two prokaryotic cells which in time resulted in the mitochondria. Phagocytosis, which is the process in which  larger cells envelope and digest smaller cells is one of the feasible explanations for how one cell came to be within another. It is common in eukaryotes, however, no contemporary examples of prokaryotes practicing phagocytosis exist. But phagocytosis had to evolve at some point, so how did it happen? This thesis gives an attempt to determine what conditions facilitate the evolution of phagocytosis. In this endeavour, we constructed chemostatic models for two different population structures where secondary consumers are subject to an invasion by a mutant with predatory capabilities. The different population structures are denoted as "competition" and "cross-feeding". By using random parameter sampling we show that the predator has a higher likelihood to invade in the cross-feeding environment. We also showed using adaptive dynamics that a mutant that is able to invade and replace its predecessor favours evolving towards a higher predation strategy in the cross-feeding case whereas in competition  such behaviour is less clear and a more balanced strategy seems preferable.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19220号 / 理博第4112号 / 新制||理||1592(附属図書館) / 32219 / 京都大学大学院理学研究科生物科学専攻 / (主査)教授 山内 淳, 教授 石田 厚, 教授 田村 実 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

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It is well known that in contrast to the Prisoner's Dilemma, the snowdrift game can lead to a stable coexistence of cooperators and cheaters. Recent theoretical evidence on the snowdrift game suggests that gradual evolution for individuals choosing to contribute in continuous degrees can result in the social diversification to a 100% contribution and 0% contribution through so-called evolutionary branching. Until now, however, game-theoretical studies have shed little light on the evolutionary dynamics and consequences of the loss of diversity in strategy. Here, we analyze continuous snowdrift games with quadratic payoff functions in dimorphic populations. Subsequently, conditions are clarified under which gradual evolution can lead a population consisting of those with 100% contribution and those with 0% contribution to merge into one species with an intermediate contribution level. The key finding is that the continuous snowdrift game is more likely to lead to assimilation of different cooperation levels rather than maintenance of diversity. Importantly, this implies that allowing the gradual evolution of cooperative behavior can facilitate social inequity aversion in joint ventures that otherwise could cause conflicts that are based on commonly accepted notions of fairness. (authors' abstract)

I present a simple model of an evolutionary financial market with heterogeneous agents, based on the concept of adaptive belief systems introduced by Brock and Hommes (1997a). Agents choose between different forecast rules based on past performance, resulting in an evolutionary dynamics across predictor choice coupled to the equilibrium dynamics. The model generates endogenous price fluctuations with similar statistical properties as those observed in real return data, such as fat tails and volatility clustering. These similarities are demonstrated for data from the British, German, and Austrian stock market. (author's abstract) / Series: Working Papers SFB "Adaptive Information Systems and Modelling in Economics and Management Science"

京都大学 / 0048 / 新制・課程博士 / 博士(情報学) / 甲第21914号 / 情博第697号 / 新制||情||120(附属図書館) / 京都大学大学院情報学研究科先端数理科学専攻 / (主査)教授 木上 淳, 教授 磯 祐介, 准教授 藤原 宏志 / 学位規則第4条第1項該当 / Doctor of Informatics / Kyoto University / DFAM

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Understanding mechanisms regulating the assembly of ecological communities is a major goal of community ecology. I combined experimental and theoretical approaches to investigate the influences of various ecological factors on the assembly of protist communities. My research included three experimental studies and one theoretical study. Two experimental studies used freshwater heterotrophic ciliated protists as model organisms to examine how species dispersal across local communities and functional and phylogenetic diversity of the species pool influence historical contingency of the assembled communities, respectively. The results of the first experiment showed that the differences in species colonization history led to alternative community states that substantially differed in species composition and abundances, regardless of the level of species dispersal. The results of the second experiment showed that historical contingency, measured by beta diversity and the strength of inhibitive priority effects decreased as phylogenetic and functional diversity of the species pool increased. In the third experimental study, I used the same model system and observed positive relationships between phylogenetic diversity and temporal stability of community biomass. These positive relationships are likely due to the reduced competition among species and increased asynchronous species responses to environmental changes under higher phylogenetic diversity. The theoretical study explored how phytoplankton and zooplankton coevolution drives species diversity patterns along productivity gradients in a mathematical model system. I explored the conditions for evolutionary divergence in phytoplankton and zooplankton and the consequent productivity-diversity relationships (PDR) using the theory of adaptive dynamics and numerical simulations. The results of numerical simulations showed that the coevolutionary dynamics of phytoplankton and zooplankton can generate transient unimodal or positive PDRs, and positive PDRs when the systems reach steady states. The findings of my research suggest an important role of traits and species ecological difference in understanding causes and consequences of biodiversity in community ecology.