Predator Size Structure Fails to Alter Nonconsumptive Effects in Streams

Area of Science:

• Ecology
• Aquatic Ecology
• Predator-Prey Dynamics

Background:

• Predator population size structure influences ecosystem dynamics through top-down effects.
• The role of predator size variation in nonconsumptive effects remains understudied.

Purpose of the Study:

• To investigate the impact of predator size structure and feeding ability on benthic invertebrate communities.
• To determine whether predator biomass or size structure is more critical for nonconsumptive effects.

Main Methods:

• Field enclosures were used in a headwater stream to manipulate stonefly (Acroneuria abnormis) predator size structure and feeding ability.
• Prey community responses, including abundance and emigration, were measured.
• Effects were compared across different predator size structures with equivalent biomass.

Main Results:

• Stonefly predators reduced total prey abundance by approximately 30%, irrespective of feeding ability, highlighting significant nonconsumptive effects.
• This reduction in prey abundance was consistent across different predator size structures.
• Predator biomass appeared to be a stronger determinant of nonconsumptive effects than predator size structure.

Conclusions:

• Stonefly predators exert community-scale nonconsumptive effects on benthic invertebrates.
• Predator biomass, rather than size structure, may be the primary factor influencing the strength of these nonconsumptive effects in aquatic ecosystems.