Spatial and temporal patterns of trophic control across marine ecosystems
The relative strength and importance of consumer versus resource control within and across marine ecosystems has been intensively investigated using empirical, experimental, and theoretical approaches for over a century. This research has led to numerous interesting discoveries, yet a unified explanation for spatial and temporal differences in trophic control and the factors influencing these patterns at macro-ecological scales remain elusive. Here, we synthesize published field studies to quantitatively examine these patterns within and across marine ecosystems. The reported relationship (Pearson correlation; r) between time-series of predators and prey were used as an index of consumer (-r) or resource (+r) control of ecosystem structure.
Our analysis includes 150 correlations between trophically dependent species ranging from phytoplankton to whales extracted from 50 studies published since 1950. Multivariate spatial regression analysis was used to quantitatively test the effect of several biotic and abiotic factors influencing trophic control within and across ecosystems. Consumer control was observed to attenuate through the food chain, with strong consumer control exerted at higher trophic levels and resource control exerted at the plankton level. Spatial variability in trophic control of marine ecosystems is best explained by gradients in upper ocean temperature and species richness. Systems where temperature or species richness were higher tended to exhibit strong resource control, possibly due to increased complementarity. Phytoplankton cell size, primary production, and ecosystem omnivory were also positively related to trophic control. We conclude that temperature and species richness are leading correlates of spatial variability in the trophic state of marine ecosystems with important implications for ecosystem stability and recovery following anthropogenic or environmental perturbations.