Fig. 1.

A conceptual model demonstrating connectivity and feedbacks between systems. Circles represent ecosystems, areas or populations, whereas the thickness of the arrows indicates different levels of influence. Enlarged circles represent systems affecting other systems by, e.g. increased population size and/or high degree of mutual influence. (1) One-sided effects: a simple donor and recipient scenario without feedbacks. (2) Mutual effects, control mechanisms operating at both sites: a steady-state system with mutual feedbacks between systems. (3) Mutual effects, control at one site: a feedback system where the original donor system (lower panel) is impacted by e.g. increased productivity or population size (e.g. by climate change or fertilization). (4) Mutual effects at both sites: a non-equilibrium feedback situation where increased productivity or population in both systems pose a mutual stimulation. In the case of the goose-Arctic lake system, the lower panel may represent overwintering grounds in central Europe, while the upper panel represents breeding grounds in the high Arctic