Do empty Juniperus communis seeds defend filled seeds against predation byApodemus sylvaticus?

The juniper Juniperus communis, a dominant plant in the high mountains of S E Spain, produces a high proportion of empty seeds within well-developed co nes. We tested the hypothesis that the production of empty seeds by jumper reduces seed predation by the woodmouse Apodemus sylvaticus, thereby benefi tting the plant. We performed laboratory and field experiments to determine i) woodmouse discrimination ability between filled and empty seeds, and ii woodmouse response to changes in the proportion of empty versus filled see ds and in the seed density in seed clusters. In addition, we estimated, for six juniper populations over three years, whether plants or populations sh owing a higher proportion of empty seeds suffered reduced woodmouse predati on. Experiments showed that woodmice can eventually discriminate externally between filled and empty seeds, but in most cases had to bite the seeds to identify and reject empty ones. The probability of predation for filled se eds was independent of changes in the proportion of empty versus filled see ds and in seed density per cluster. Seed predation suffered by plants in th e field was unrelated to the proportion of empty seeds per plant for all po pulations and years. The presence of empty seeds did not benefit juniper ag ainst woodmouse predation, either in terms of individual reproductive outpu t or in terms of offspring escape probability. Our study suggests that the effect of empty seeds on seed predation should be rare in plant-seed predat or interactions where predators are polyphagous and eventually able to disc riminate against empty seeds, and therefore suffer a low cost when coping w ith empty seeds.