Deciphering the role of reproductive investment, pollination success and predispersal seed predation on reproductive output in Juniperus thurifera

Background: Plant reproductive output is determined by a complex set of factors including resource availability, pollination success and pre-dispersal predation. Disentangling the relative contribution of each factor is critical to underpin the factors determining plant fitness.

Aims: To unravel the relative contributions of initial reproductive effort, pollination success and pre-dispersal seed predation to plant reproductive success in the fleshy-fruited, wind-pollinated Juniperus thurifera.

Methods: We conducted an experiment including pollen addition and pesticide application on 40 female juniper trees for 20 months. Flower production was used as a proxy for resource levels.

Results: Main fruit loss occurs in early stages of fruit development. Initial flower number affected fruit and seed set by (a) increasing the rate of fruit formation and the number of viable seeds within fruits and (b) modifying the incidence of low-mobile predators through a satiation effect. Pollination did not limit fruit set, although hand pollinated fruits had more viable seeds. Pre-dispersal seed predation by different arthropods was critical in defining final fruit set.

Conclusions: Fruit set in J. thurifera was determined by the interaction of initial reproductive effort and pre-dispersal seed predation. Pollination was not a limiting factor in this relatively dense juniper forests during a year of high flower production.