Empty seeds reduce seed predation by birds in Juniperus osteosperma

Utah juniper (Juniperus osteosperma) is one of many plant species that prod uce large numbers of fruits containing parthenocarpic or otherwise empty or inviable seeds. We tested the hypothesis that production of empty fruits i n this species results in reduced levels of predation on fertile seeds. In a population in west-central Utah, we estimated the proportion of fruits wi th filled seeds in trees suffering high levels of fruit destruction by the seed-eating bird Parus inornatus and in neighbouring trees similar in crown and fruit-crop size but suffering negligible predation. We found that the heavily attacked trees had higher proportions of hired seeds. Thus, juniper may benefit from producing fruits that contain no offspring. This is the f irst study to demonstrate that empty seeds may reduce predation by vertebra te seed eaters and the first to demonstrate discrimination based on seed fi lling at the level of whole plants.