Effects of an insecticide on an aquatic community. (a) In the absence of an insecticide, zooplankton are abundant and they consume phytoplankton. This consumption keeps the water relatively clear and allows sunlight to reach the bottom of a wetland where periphyton grow and serve as food for tadpoles. (b) When an insecticide is added, the zooplankton populations are dramatically reduced, which allows an increase in phytoplankton. Abundant phytoplankton cause the water to turn green and prevent sunlight from reaching the periphyton at the bottom of the wetland. With less light available, the periphyton grows poorly, which limits tadpole growth. The number of individuals pictured in each group indicates the relative change in biomass.