Neighbor palatability generates associational effects by altering herbivore foraging behavior

Area of Science:

• Ecology
• Plant-herbivore interactions
• Community ecology

Background:

• Herbivory on plants is influenced by neighboring species.
• Mechanisms driving these "associational effects" are not fully understood.
• Neighbor identity can alter herbivore pressure on focal plants.

Purpose of the Study:

• Investigate mechanisms behind associational effects on herbivory.
• Evaluate the role of plant neighborhood density and frequency.
• Examine the influence of historical land use on plant-herbivore interactions.

Main Methods:

• Factorial field experiment across 14 sites (80,000 hectares).
• Manipulated neighborhood plant density and frequency.
• Nested experiment within habitats with and without past agricultural land use.
• Conducted behavioral assays to support field findings.

Main Results:

• Palatable Solidago nemoralis experienced reduced herbivory (associational resistance) when rare, due to decreased grasshopper foraging.
• Less palatable S. odora experienced increased herbivory (associational susceptibility) in even-frequency neighborhoods, but only in historically agricultural sites.
• Grasshopper foraging behavior was key in generating observed associational effects.

Conclusions:

• Associational effects are contingent on relative plant palatability and past land use.
• Neighborhood-level foraging decisions significantly influence herbivory.
• Larger-scale environmental context, shaped by land-use legacies, can modify neighborhood interactions.