Genetic diversity increases insect herbivory on oak saplings

Area of Science:

• Ecology
• Evolutionary Biology
• Forest Science

Background:

• Ecosystem functions are often linked to species richness, but the role of genetic diversity within species is less understood.
• The diversity-resistance relationship, particularly concerning insect herbivory and plant genetic diversity, requires further investigation.

Purpose of the Study:

• To determine if genetic diversity in oak (Quercus robur) populations influences damage by insect herbivores.
• To differentiate between complementarity and selection effects in the context of plant genetic diversity and herbivory.

Main Methods:

• A manipulative field experiment using synthetic communities of one to four oak half-sib families.
• Quantification of genetic diversity through genotyping oak saplings.
• Assessment of damage by ectophagous and endophagous herbivores across a gradient of genetic diversity.

Main Results:

• Damage from ectophagous herbivores increased with oak genetic diversity, primarily due to complementarity effects.
• Polyphagous herbivores benefited from diverse oak assemblages, likely through enhanced host location and diet mixing.
• Endophagous herbivore abundance was poorly predicted by genetic diversity, correlating instead with individual sapling apparency.

Conclusions:

• Plant genetic diversity can enhance foraging for generalist herbivores but may not deter specialist herbivores.
• The impact of genetic diversity on herbivory may vary with tree ontogeny and herbivore adaptation.
• Further long-term studies are needed to understand the evolving relationship between tree genetic diversity and herbivory.