Plant species coexistence, impact of resource and enemies

Local biodiversity has many drivers in natural communities. Spatial and temporal variability in species interactions drive mechanisms of species coexistence (Chesson 2000), but their relation to environmental drivers beyond the pairwise level remains unknown (Levine et al. 2017). We need to improve our understanding of the impacts of global changes drivers on species interactions, to uncover the link between biodiversity and ecosystem functioning. In this thesis, we explored the cascading effects of plant species interactions on the coexistence and functioning of their community. We focused on the impacts of plant growth strategies, resources and natural enemies on competition networks, niche and fitness differences, and ecosystem multifunctionality. Our study involved quantifying competition networks among 18 plant species varying in growth strategies, examining how nitrogen enrichment and reduced foliar pathogens influenced intra and interspecific interactions, as well as their intrinsic growth rates. We then established a new experiment using these results, explicitly assembling communities forming a gradient of coexistence mechanisms, in order to disentangle the effect of niche differences and indirect interactions on ecosystem multifunctionality. Overall, our findings indicate that most species interactions were competitive, with intraspecific competition surpassing interspecific competition, leading to high niche and fitness differentiation and communities far from neutrality. Despite the dominance of competitive interactions, communities exhibited mean values outside, yet close to the coexistence area, suggesting that factors of environmental variation contribute significantly to long-term diversity maintenance. Notably, communities predicted to stably coexist demonstrated higher levels of multifunctionality, suggesting the ecosystem-level importance of species coexistence.

dissertation

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