Figure 18.19 Indirect effects between communities. (a) A food web of species from the aquatic and terrestrial communities includes fish that consume larval dragonflies, adult dragonflies that consume pollinators, and pollinators that pollinate plants. Solid lines represent direct effects. Dashed lines with a minus sign represent a negative indirect effect and dashed lines with a plus sign represent a positive indirect effect. (b) Researchers found that ponds without fish had higher dragonfly populations, which reduced the numbers of pollinators available to visit flowering plants on the surrounding shoreline. Error bars are standard errors.
Data from T. M. Knight et al., Trophic cascades across ecosystems, Nature 237 (2005): 880–883.