Herbivore Population Differences Rival Geographic and Biophysical Variation in Structuring Ecosystem Function.

Area of Science:

• Ecology
• Ecosystem Science
• Zoology

Background:

• Geographic variation in ecosystem function is traditionally linked to abiotic factors like climate and soil.
• Biotic interactions, such as herbivory, also vary geographically and can influence ecosystem processes.
• Previous research often overlooks the role of consumer diversity in shaping ecosystem functions.

Purpose of the Study:

• To investigate how population-level functional differences in a widespread arthropod herbivore mediate geographic variation in ecosystem function.
• To quantify the direct and indirect effects of herbivory on plant biomass, soil carbon, and nitrogen cycling.
• To compare the influence of herbivore functional variation against historical conditions and climate in driving ecosystem processes.

Main Methods:

• A replicated three-year field experiment was conducted.
• Structural equation modeling was employed to analyze causal relationships.
• Population-level functional differences in a key arthropod herbivore were assessed.

Main Results:

• Herbivores had significant direct effects on plant biomass, soil carbon, and nitrogen mineralization, often exceeding abiotic influences.
• Functionally distinct herbivore populations exhibited divergent impacts on nutrient cycling and plant diversity.
• Geographic variation in herbivore populations introduced novel pathways affecting ecosystem function.

Conclusions:

• Consumer-driven feedbacks, specifically from functionally diverse herbivore populations, are critical regulators of ecosystem function.
• Ecosystem models need to incorporate biotic interactions and consumer diversity, moving beyond solely abiotic constraints.
• Understanding population-level variation in herbivores is essential for predicting and managing ecosystem responses to environmental change.