Figure 20.5 Secondary productivity. (a) In terrestrial ecosystems, an increase in primary productivity is positively correlated to an increase in secondary productivity. (b) In aquatic ecosystems, a similar relationship is found between the primary productivity of phytoplankton and the secondary productivity of the herbivorous zooplankton that consume the phytoplankton.

Data from S. McNaughton et al., Ecosystem-level patterns of primary productivity and herbivory in terrestrial habitats, Nature 341 (1989): 142–144; M. Brylinsky and K. H. Mann, An analysis of factors governing productivity in lakes and reservoirs, Limnology and Oceanography 18 (1973): 1–14.