Lethal and nonlethal predator effects on an herbivore guild mediated by system productivity

Area of Science:

• Ecology
• Community Ecology
• Food Web Dynamics

Background:

• Indirect ecological effects influence community properties through species interactions.
• Traditionally, indirect effects were viewed via density changes, but trait-mediated responses are increasingly recognized as significant.
• Understanding transmission mechanisms of density- and trait-mediated effects is crucial for predicting ecological interactions.

Purpose of the Study:

• To investigate the mechanisms and consequences of density- and trait-mediated indirect effects of a predator on herbivores and their resources.
• To explore how system productivity influences the transmission of these indirect effects.
• To determine if trait- and density-mediated effects transmit independently in food webs.

Main Methods:

• Examined lethal (density-mediated) and nonlethal (trait-mediated) effects of a larval odonate predator.
• Studied interactions with a guild of four herbivore species (anuran larvae, snails) and their resources.
• Manipulated system productivity to assess environmental context effects.

Main Results:

• Trait-mediated effects were often stronger than density-mediated effects on herbivores and resource communities.
• Many indirect effects were contingent on system productivity.
• Evidence suggests trait- and density-mediated effects can transmit independently, especially with spatial prey responses.
• Prey growth responses to predator traits varied predictably with time and indirect food web effects.

Conclusions:

• Trait-mediated indirect effects play a substantial role in trophic cascades and keystone predator interactions.
• The mechanisms of trait-mediated effects can be integrated into ecological theory.
• Ecological indirect effects are complex, involving both density and trait changes, and are context-dependent.