The aim of this research program is to examine the response of animal populations to environmental variability at different spatial scales. We attempt to determine how individuals respond to the spatial heterogeneity of their environment, and what are the consequences of this response for the dynamics of subdivided populations. Specifically, we consider an ecological system involving biotic interactions at three levels: seabirds, their tick _Ixodes uriae_, and the microparasite _Borrelia burgdorferi_ sensu lato (Lyme disease agent). Colonies of seabirds represent discrete entities, within and among which parasites can circulate. Our previous work on this system in the norwegian arctic has enable us to show that (1) host dispersal can be affected by local conditions, (2) seabird tick populations are specialised among different host species, namely between sympatric kittiwakes _Rissa tridactyla_ and puffins _Fratercula arctica_, (3) in the kittiwake, females transmit antibodies against _Borrelia burgdorferi_ when their chicks have a high probability to be exposed to the tick vector. We propose to combine different approaches, incorporating field surveys and experiments and population genetic studies (of hosts and parasites), in order to better understand the role of local interactions and dispersal in the dynamics of such a system. The research program implies collaborations with researchers from other french groups, as well as with Canadian (Queen’s University) and Norwegian colleagues (from NINA and the University of Tromsø).