Overcompensation in Response to Mammalian Herbivory: The Advantage of Being Eaten

Abstract

Plants of scarlet gilia, Ipomopsis aggregata, are exposed to high levels of mammalian herbivory (by mule deer, Odocoileus hemionus, and elk, Cervus elaphus) early in the season, before flowering. During this period of our study, up to 56% of all individuals experienced a 95% reduction in aboveground biomass. Browsed plants rapidly responded by producing new inflorescences and flowering within 3 wk. Unbrowsed plants produced only single inflorescences, whereas browsed plants produced multiple inflorescences. Field observations and experimental manipulations showed that plants with multiple inflorescences produced significantly greater numbers of flowers and fruits than unbrowsed individuals. Because there were no differences between browsed and unbrowsed individuals in the number of seeds produced per fruit, seed weight, subsequent germination success, and survival, browsed plants enjoyed a 2.4-fold increase in relative fitness. Consequently, there is an immediate reproductive advantage to being eaten. Under the natural field conditions of this study, mammalian herbivores played a beneficial role in the survival and reproductive success of scarlet gilia.