Assembling the jigsaw puzzle of biodiversity–ecosystem stability relationships

Abstract

Biodiversity loss and climate change threaten the long-term stability of ecosystem functioning and the ecosystem services upon which human societies depend. Understanding how biodiversity stabilizes ecosystem functioning has therefore become one of the central challenges in ecology. Although it is widely recognized that biodiversity enhances ecosystem functioning, its effects on ecosystem stability remain incompletely understood due to differences in methodological approaches and the multifaceted nature of both biodiversity and stability. A first objective of this thesis is to evaluate how methodological choices influence the characterization of biodiversity–stability relationships. In Chapter 2, I examine how different measures of species abundance (cover versus biomass) affect estimates of biodiversity and stability. I demonstrate a convex relationship between cover and biomass and show that, while species-level estimates are relatively robust to choice of abundance measures, community-level stability estimates differ substantially depending on whether cover or biomass is used. These findings show that cover and biomass cannot always be used interchangeably, providing practical guidance for selecting abundance measures. In Chapter 3, I further show that the direction and strength of biodiversity–stability relationships depend strongly on the specific diversity and stability metrics applied. Stronger negative biodiversity–stability relationships emerge when using abundance-weighted stability metrics and cumulative richness, highlighting the importance of dominant species and long-term species turnover. Together, these findings demonstrate that methodological choices can substantially influence inferred biodiversity–stability relationships. A second objective of this thesis is to delve into the multifaceted nature of biodiversity and ecosystem stability. In Chapter 4, I investigate how plant functional traits influence species stability and species asynchrony. Species’ mean trait values along the fast–slow spectrum emerge as strong predictors of species stability, with slowgrowing species exhibiting greater temporal stability. In contrast, the effects of trait dissimilarity depend strongly on ecological context. In monocultures, trait dissimilarity is associated with greater synchrony driven by shared environmental responses, whereas in species-rich communities species interactions become increasingly important in generating asynchrony. These findings reveal that the drivers of species asynchrony shift with increasing biodiversity. In Chapter 5, I experimentally test how biodiversity influences ecosystem stability under drought, focusing on resistance and recovery. I found that biodiversity stabilizes ecosystem productivity primarily through increased resistance to drought rather than greater recovery. Communities containing a greater representation of slow-growing species and higher functional diversity exhibit greater drought resistance and consequently higher temporal stability. Biodiversity thus buffers ecosystems against climatic extremes primarily through trait-mediated drought resistance, highlighting the importance of functional composition in determining ecosystem responses to environmental stress. This thesis shows that biodiversity stabilizes ecosystems through multiple interacting mechanisms linking species-level processes to community-level ecosystem stability. Ecosystem stability depends not only on species richness, but also on functional composition, species interactions, and compensatory dynamics among species. Communities containing slow-growing, stress-tolerant species and diverse ecological strategies appear better able to maintain stable functioning under climatic extremes. By integrating methodological, functional, and ecological perspectives, this thesis provides a unified framework for understanding how biodiversity stabilizes ecosystem functioning under global environmental change.