The Consequences of Herbivory: A Mixed Blessing for Jurinea mollis (Asteraceae)

Abstract

The thistle Jurinea mollis Ascherson is eaten by three types of herbivores, which the plant responds to in different ways. Multiple rosettes are produced on a single root after lepidopteran larvae eat the central part of a basal rosette, and each of these rosettes eventually produces a flower stalk. Plants with multiple stalks can produce up to three times as many seeds as those without multiple stalks. Up to 50% of flowering plants in a study site were found to have multiple stalks. Some plants lose their terminal flower heads to herbivores, probably small mammals. They respond by developing axillary flower heads, which are much less successful than terminal flower heads at producing seeds. Damage caused by moth and tephritid fly larvae to the receptacles of flower heads interrupts the development of seeds, but there is no apparent response by the plant, which may not produce any viable seed. This variety of types of herbivory, with their strikingly different consequences, serves to emphasize the importance of careful consideration of responses of plants to herbivory.