Figure 1.

Conceptual model depicting a trophic cascade, where predators indirectly facilitate primary producers (dashed line) by controlling herbivore populations (a), across spatial scales in three different scenarios (b–d). (b) Interactions between trophic levels are scale invariant (i.e. in fractal-like systems); they do not depend upon, or interact, across scales. (c) Interactions between trophic levels are scale-dependent; they change in intensity (black arrows) and/or direction (red arrows) across spatial scales. For example, predators control over grazers acts at larger scales, while grazer control over primary producers acts at smaller scales. (d) CSIs; TIs are not only scale-dependent but interact across scales. For example, effects of predators at one scale may influence (strengthen or weaken) TIs at another scale.