It is becoming increasingly clear that lake plankton communities are regulated by both predation and resources. Top predators, through effects on herbivores, can regulate phytoplankton community structure, biomass, and primary productivity (Carpenter et al. 1985; Carpenter and Kitchell 1988; Vanni and Findlay 1990). Increase in potential limiting nutrients, such as nitrogen and phosphorus, can stimulate phytoplankton production and biomass, and the ratio of limiting nutrients can influence community structure (Schindler 1977; Smith 1983). Recently, lake ecologists have realized that when attempting to explain phytoplankton dynamics, both nutrients and herbivory must be considered. Often the two interactions simultaneously influence phytoplankton, although their relative strengths may vary seasonally (e.g. Sommer et al. 1986; Vanni and Temte 1990). Furthermore, resource effects and herbivore effects may interact in complex ways to influence phytoplankton (Leibold 1980; Sterner 1990; Carpenter et al. 1991)—a case of the interactions themselves interacting (Roughgarden and Diamond 1986).