CPM Seminar

Hierarchies of critical phenomena in marine ecologies

Frédéric Guichard

Department of Biology
McGill University

Intrinsic processes operating at local and regional spatial scales can control marine ecosystems: interactions between individual organisms (~cm) and transport of organisms (larvae) between locations (~km). I will describe a theoretical framework of large-scale coastal ecosystems where local ecological interactions (i.e. disturbance and colonization) between organisms is first described as an interacting particle system (IPS) giving rise to “robust” scale-invariance in the distribution of organisms at the landscape level (~100m). The model appears to relax the separation of time scales as a requirement for SOC found in the similar Forest-Fire Model (FFM). Landscapes ultimately become fragmented and form discrete sites along the shore coupled through dispersal of larvae. I thus present a model of regional coastal dynamics where sites are viewed as coupled oscillators. At the large-scale the model predicts a phase transition between 2 quasi-homogeneous phases controlled by the strength of interactions between species. The transition drives the system from quasi equilibrium to coherent dynamics and is marked by a critical interaction strength value leading to scale-invariant distribution of abundance along the coast. I discuss the implications of these findings for the persistence of ecological systems, and for their response to large-scale environmental changes. I conclude by indicating how model predictions can ultimately be validated using large-scale ecological datasets.