“Fear mediates trophic cascades: nonconsumptive effects of predators drive aquatic ecosystem function”

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Crasso Paulo B. Breviglieri, Paulo S. Oliveira, and Gustavo Q. Romero

Terrestrial predators influence aquatic ecosystems

The great kiskadee (Pitangus sulphuratus) foraging in the restinga.
(Credit: Crasso Paulo B. Breviglieri)

Among animals, fear can change behavior in prey facing predation risk. Prey responses can be triggered by the detection of signals emitted by predators (e.g., visual, sound, or chemical cues). This phenomenon occurs in many predator-prey systems involving vertebrates (e.g., lions and gazelles), invertebrates (e.g., ants and butterflies), and both vertebrates and invertebrates (e.g., lizards and butterflies). However, regardless of the system, the behavioral responses of prey are similar, i.e., affecting their group size and patterns of activity, vigilance and foraging patterns, and often their reproductive success.

These effects can be locally confined to one ecosystem, but can also extend to neighboring ecosystems through the relationship between predators and prey with complex life cycles (i.e., organisms exhibiting aquatic and terrestrial life stages). This is precisely what is revealed in a recent study by Crasso Paulo B. Breviglieri, Paulo S. Oliveira, and Gustavo Q. Romero (Campinas State University, Brazil), appearing in The American Naturalist.

Myiarchus swainsoni (Tyrannidae) perched after catching an insect in a coastal forest. (Credit: Crasso Paulo B. Breviglieri)

In Brazilian coastal forests (“restinga”), terrestrial avian predators can influence the oviposition rate of damselflies (such as Leptagrion) in bromeliad systems. Field experiments using stuffed insectivorous birds have shown that adult damselflies can react to the visual presence of their predators and alter their oviposition behavior to avoid them. Because damselfly larvae are top predators in this aquatic system, a decrease in their abundance and biomass changes the composition and other parameters (richness, abundance, and biomass) of the bromeliad-dwelling invertebrate community. Such a change in the composition of the aquatic community accelerates the decomposition of organic matter (e.g., dead leaves), making more nutrients available for bromeliads, which grow more. These results highlight the cascading effects of apex predators across land-water boundaries, influencing ecosystem functions such as productivity, decomposition, and nutrient cycling. Read the Article