A chemical polymorphism in a multitrophic setting: thyme monoterpene composition and food web structure

Area of Science:

• Ecology
• Plant Science
• Chemical Ecology

Background:

• Plant chemical variation can influence ecological interactions.
• Thyme (Thymus vulgaris L.) exhibits diverse monoterpene profiles (chemotypes).
• Interactions with competitors and herbivores are crucial for plant success.

Purpose of the Study:

• To investigate how thyme chemotype affects interactions with competitors, herbivores, and predators.
• To determine the impact of aphid herbivory and grass competition on thyme growth and reproduction.
• To understand the interplay between chemical defenses, predation, and competition in shaping plant communities.

Main Methods:

• A factorial experiment using four thyme chemotypes, two caging treatments (to manipulate predator access), and competition with Bromus madritensis grass.
• Quantification of aphid population dynamics and effects on thyme size and flowering.
• Assessment of competitive effects of Bromus madritensis on thyme.

Main Results:

• Caging reduced arthropod predator numbers, leading to a fourfold increase in thyme-feeding aphids (Aphis serpylli Koch).
• Aphids and Bromus competition negatively impacted thyme size and flowering.
• The combined effects of aphids and competition were less than additive.
• Differential thyme flowering was linked to chemotype-specific aphid interactions.

Conclusions:

• Aphids exert differential selection pressures on thyme chemotypes.
• Bromus madritensis competition modulates the negative impact of aphids on thyme.
• Plant chemical defenses play a role in mediating herbivore interactions and plant performance.