Risk of grazing and flower number in a perennial plant

Costs of reproduction may be due to exhaustion of resources or due to increased risk of predation during reproduction. In animals both types of costs have been examined frequently whereas in plants most studies have focused on costs mediated by resource depletion. Here I present an examination of the effects of flower number on vertebrate grazing, seed predation and fruit-set in a perennial plant, Lathyrus vernus. Fruit number increased with flower number but so did also the risk of damage. Seed predation intensity was not affected by flower number. Modelling the total effect of fruit set and grazing showed that fruit number always increased with increasing flower number but that the returns on the addition of flowers to the inflorescence were much larger in small than in large inflorescences. Moreover, negative effects of grazing on future growth and reproduction further diminished the returns on additional flowers. This study is the first to quantitatively report on selection pressures on flower number of vertebrate grazing damage. It is suggested that current and long-term effects of damage may have important implications for our conclusions regarding plant reproductive investment strategies.