Collective Response from Individual Behavior in Groups and Ecosystems

Publishable summary: 

Ecosystems are currently endangered by new global environmental changes about which we have virtually no past records and poor prior knowledge. A crucial case is that of tropical rainforests, which are exposed to multiple unprecedented changes in their environment. The rise in atmospheric CO2, which is stimulating photosynthesis, is coming along with increased temperatures and increased frequency of extreme climate events, a typical example being the droughts related to El Niño. The potential impact and feedback generated by such conditions are the subject of a heated debate. Some global vegetation models simulate a severe dieback of the Amazon forest in the coming century, while other models predict a more resilient ecosystem. The major challenge in understanding and modelling climate change responses of a complex hyperdiverse system, like the tropical rainforest, is to upscale the response of individuals (trees) to the ecosystem level. This exact same challenge occurs at different scales in a multitude of biological systems characterized by distributed interactions. Among such systems, animal groups displaying decentralized collective behaviour, as bird flocks and insect swarms, have attracted huge scientific attention in the last ten years. The common challenge that all ecosystem modellers have, namely scaling up from individual to system, is taken in this project as an opportunity for innovation. We aim at developing theoretical and numerical tools able to analyze the empirical data and predict how biological ecosystems respond and adjust to external perturbations. This is a complex multiscale task. Ecosystems are large heterogeneous aggregates of interacting individuals belonging to different species and different taxa, so that a global analysis is a daunting endeavour. Ecosystems, however, are organized into smaller scale homogeneous collective groups of single species individuals, which interact with other groups and which respond collectively to environmental stimuli. Biodiversity stems from the interplay, and sometimes through the conflict, between different collective units, each one working at the homogeneous level, but interacting with each other. An integrated approach to the study of ecosystems' response and robustness therefore needs to analyze how the single species homogeneous group-level behaviour scales up to the multispecies heterogeneous ecosystem level phenomenology. This will be the objective of the project.

We will study how the response and robustness of ecosystems in the face of global changes and threats generates from the lower level of homogeneous group response. By using both an empirical and modeling approach we will focus on the key concepts of criticality, tipping points and across system information transfer, aiming at developing a predictive understanding about ecosystems response to environmental changes.