Combined effects of deer, mice and insect seed predation on the reproductive success of a Mediterranean shrub

Abstract

The sum of fruit and seed predation by multiple species may strongly affect plant reproduction and population dynamics. We evaluated the combined effects of ungulates, seed-eating rodents and insect pre-dispersal seed predators on the reproductive success of the Mediterranean gum cistus shrub (Cistus ladanifer), over two consecutive years within a long-term ungulate-exclusion experiment. We compared fruiting success in shrubs exposed and protected from ungulates by examining fruit abortion and fruit production. We also investigated the effect of insect predation on seed production (i.e. proportion of depredated fruit and seed loss) and measured fruit weight, seed number per fruit, and seed weight of unpredated fruits. Ungulate browsing directly removed 42.3% of the plant reproductive structures, early in the reproductive season and insect predation reduced mature seeds by over 40%. Results also emphasize the additive effects of ungulate browsing on pre-dispersal insect predation and fruit abortion which increased by 74.7% and 60.9%, respectively. Rodents, which only occurred in ungulate-excluded plots, had a limited and later effect on seed production with 6% of mature fruit loss. Fruit weight, seed weight and number were higher in shrubs protected from ungulates. Our study indicated that seed predation by mice was irrelevant, but ungulate and invertebrate seed predation interacted to strongly limit the reproductive success of C ladanifer, potentially affecting plant population dynamics in the long-term.