Insect Behavior Determines Plant Distribution in Alpine Habitat

Specialist leaf-mining fly Scaptomyza nigrita is a major herbivore of its host plant Cardamine cordifolia. Host plants are found along a gradient from sun-exposed bog to deep spruce shade habitat where herbivory decreases as shade increases. Prior studies have failed to support the hypothesis that plant quality determines plant distribution. A series of outdoor cage experiments utilizing a factorial design tested whether herbivore choice may instead drive plant distribution. It was found that adult female S. nigrita exhibited a significant preference for feeding and ovipositing on C. cordifolia leaves exposed to light, regardless of habitat origin of plant, leaf width, or presence of prior herbivore damage. This study does not support the phytocentric explanation that host plant distribution is determined by herbivore preference for plants based on their quality. My findings instead support the hypothesis that herbivores drive plant distributions into the shade by creating enemy-free space for host plants through their preference for light