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New insights from niche theory on plant adaptation and ecosystem functioning

Abstract : As living organisms, plants present a dual relationship with their biotic and abiotic environment. The environment selects plant strategies that can establish, and selected strategies in turn impact and shape the environment as they spread. When fueled by variation ,this environmental feedback loop drives evolution, community assembly and ecosystem development, and eventually determines the emergent properties of ecosystems.Theoretical ecology approaches have long recognized this duality, as it is at the core of contemporary niche theory through the concepts of requirement and impact niche. Similarly, game-theoretical approaches such as adaptive dynamics have emphasized the role played by the environmental feedback loop in driving eco-evolutionary dynamics. However, niche theory could benefit from a more individualistic, selection based perspective, while adaptive dynamics could benefit from niche theory’s duality and graphical approach.In my dissertation, I unify these theoretical perspectives and apply them to various ecological situations in an attempt to understand how the reciprocal interaction between plants and their environment determines plant adaptive traits and emergent ecosystem functions.First, I introduce a general and rigorous mathematical framework to contemporary niche theory and the associated graphical approach. By extending these ideas to a continuum of interacting strategies using geometrical envelopes, I show how contemporary niche theory enables the study of both eco-evolutionary dynamics and community assembly through species sorting. I show how these two perspectives only differ by the range of invaders considered, from infinitesimally similar mutants to any strategy from the species pool. My results also emphasize the fact that selection only acts on the requirement niche, evolution of the impact niche being just an indirect consequence of the former.Second, I use this approach to study the evolution of plant defenses against herbivores along a nutrient gradient, by considering the joint evolution of resource acquisition, tolerance and resistance to herbivores. I show that trophic transfers lead to the selection of very competitive, undefended strategies in nutrient-poor environments, while defended strategies -- either resistant, tolerant or the coexistence of both -- always dominate in nutrient-rich environments. My results highlight the central, and often underestimated, role played by plant-environment feedbacks in shaping plant defense patterns.Third, I extend contemporary niche theory to facilitation originating from positive environmental feedback loops. I use these new tools to show how colonization of a bare substrate by a community of nitrogen-fixing plants coupled with nutrient recycling can lead to facilitative succession. Contrarily to previous competition-based succession models, I point out that facilitative succession leads to autogenic ecosystem development, relatively ordered trajectories and late succession bistability between the vegetated ecosystem and the bare substrate. By showing how facilitative succession can turn into competition-based succession along an increasing nitrogen gradient, I derive a new resource-ratio theory of succession.Overall, these new theoretical developments demonstrate that niche theory can be adapted to study a broad range of ecological situations, from facilitation to eco-evolutionary dynamics and community assembly. Within this framework, my envelope-based approach provides a powerful tool to scale from the individual level to the ecosystem level, lumping selection-driven species turnover into plastic ecosystem properties. This, is turn, helps describing the emergence at the ecosystem scale of regulation feedback loops that drive ecosystem dynamics and functioning, as exemplified by my results along increasing resource gradients showing a transition from facilitation- to competition-based succession or the emergence of trophic dead-ends.
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https://tel.archives-ouvertes.fr/tel-01841340
Contributor : Montpellier Supagro <>
Submitted on : Friday, July 27, 2018 - 5:35:36 PM
Last modification on : Wednesday, October 14, 2020 - 3:41:59 AM
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  • HAL Id : tel-01841340, version 2

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Thomas Koffel. New insights from niche theory on plant adaptation and ecosystem functioning. Ecosystems. Montpellier SupAgro, 2017. English. ⟨NNT : 2017NSAM0024⟩. ⟨tel-01841340v2⟩

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