Fluctuations in ecological systems

Environments are expected to become more variable and unpredictable in response to climate change and escalating human disturbances. Although variability is often seen as detrimental for species and assemblages, there is increasing evidence that stochasticity can promote species performance and adaptation in changing environments. Understanding how species and ecosystems respond and adapt to increasing environmental variation is therefore a great challenge to anticipate and manage biodiversity responses to climate change. This thesis explores the ecological effects of environmental fluctuations at different levels of biological organization, through a combination of modeling and experimental approaches. The importance of disturbance legacies under constant and fluctuating conditions to promote adaptation to present and future environments has been assessed through a field experiment. This experiment tested hypotheses on the effects of varying the frequency, amplitude, and intensity of climate and anthropic disturbances (sediment accretion, eutrophication) on biodiversity and ecosystem functioning. Functional traits approaches have been used in combination with experiments to elucidate how species traits can filter environmental variability to promote adaptation in fluctuating environments. Experimental model systems included rocky shore assemblages of algae, invertebrates, and intertidal biofilms. Biofilms provide a tractable system owing to their microscopic size and short life cycles, which enabled assessing ecological responses over several generations within the period of the PhD. Rocky intertidal macroalgal forests dominated by fucoid canopies in (Cystoseira sensu lato) have been used to explore the role of small-scale spatial heterogeneity in generating large-scale patterns. This work helped to uncover thermal mosaics, how they are modulated by habitat-forming species, and the cascading effects on associated assemblages. A meta-analysis has been conducted to evaluate the prevalence of positive and negative effects of environmental fluctuations across species and ecosystems. This project clarifies the multifaceted nature of environmental stochasticity and provides a roadmap to disentangle the effects of different types of environmental fluctuations on biodiversity and ecosystem functioning. Furthermore, the project improves our understanding of how organisms filter environmental fluctuations to increase their resilience to climate change and to direct anthropogenic perturbations.