Pre- and postdispersal seed predation by rodents: balance of food and safety

Seed presentation and availability for seed predators change during every plant reproductive cycle. We know very little about how those changes impinge on both the ability of seed predators to impact plant populations and the foraging costs associated with seed consumption. Therefore, we conducted several field experiments to evaluate whether wood mice Apodemus sylvaticus balance food and safety while foraging on Helleborus foetidus seeds during both the pre- and early postdispersal phases of the plant reproductive cycle. Both food and safety were key determinants of mouse foraging on H. foetidus seeds, though their roles were not consistent along the plant reproductive cycle. Thus, augmenting ambient food reduced fruit removal by mice during the predispersal phase. During the postdispersal phase, seeds in sheltered microsites experienced higher removal rates than those located in nonsheltered microsites; however, no effect of food augmentation was detected. This apparent reversed role of food and safety on decision making by mice seemed closely linked to both the dramatic changes in accessibility and presentation of H. foetidus seeds and the coupled changing foraging costs faced by mice at different phases of the plant reproductive cycle. For instance, because the cost of foraging for predispersal seeds was higher than for postdispersal seeds, the effect of food augmentation on foraging by wood mice was greater during the predispersal phase. Thus, our study illustrates the need of considering differences between pre- and postdispersal seed predation in the study of granivore rodents and their impact on plant populations. Copyright 2005.