Fig. 1: Conceptual food web diagrams for a size-structured ecosystem or an ecosystem with diverse omnivores and variable predator:prey size ratios.

Conceptual food web diagrams for a size-structured ecosystem with fixed predator:prey size ratios (a, b) or diverse omnivores with highly variable predator:prey size ratios (c, d) in a large-phytoplankton-dominated system (a, c) or a small-phytoplankton-dominated system (b, d). The color of circles is proportional to the production (primary or secondary) of a functional group. The trophic amplification hypothesis is based on conventional size-structured ecosystem models (a, b). Thus, shifts toward small phytoplankton in a future climate (represented by moving from a to b) lead to food chain elongation through the insertion of additional protistan trophic levels. In contrast, the compensatory foodweb dynamic suggests that bottom–up processes driving a shift from large (c) to small (d) phytoplankton would be accompanied by a shift of metazoan communities toward filter feeders with large predator:prey ratios (e.g., salps). This conceptualization of the foodweb involves high functional diversity amongst consumer trophic levels and substantial intraguild predation. These processes could stabilize ecosystem functions in response to climate change disruptions of nutrient supply.