Background: The preference of a predator for a certain type of prey affects the fitness of species in nature, the optimal foraging theory predicted that prey density may change the predator’s selection preferences, furthermore, predation on prey may be frequency-dependent. However, there are few studies demonstrate that how such frequency-dependent selection influences predator-prey dynamics, especially in plants.
Methods: We tested the frequency-dependent preying on Quercus wutaishanica seedlings by rodents and seedlings' survival and growth in different habitats. We transplanted seedlings with five frequency of large and small seed (FLSD) (9:1, 7:3, 5:5, 3:7, 1:9) in the forest gap and under the canopy in a warm temperate forest in the Liupan Mountains, northwest, Ningxia, China.
Results: (1) Rodents prefer the cotyledon of seedlings established from large seeds with more nutrients in the early stage of transplanting. Nonetheless, we found the net effect of rodent predation to be positively frequency-dependent, and this predation effect should function as a species coexistence promoting mechanism. (2) The seedling cotyledon retention rate has the maximum fitness when the FLSD was almost the same, which can provide energy for the growth of seedlings of different phenotypes and ensure their survival as much as possible. (3) Only the cotyledons were preyed on, the apical buds were bitted off, and the whole seedling was uprooted, which mostly occurred under the forest canopy, but the survival rates of cotyledon-predated seedling, apical bud-predated seedling, and intact seedling in the forest gap were higher than those under the canopy, indicating rodents prefer to active or prey under the hidden forest canopy, but the forest gap can provide suitable light for seedling growth and survival. (4) If only cotyledons were preyed on, the growth of Q. wutaishanica seedling would not be affected. Although it is not fatal to bite off the seedling apical bud, the growth is still hindered.
Conclusion: These results of this experiment enrich the theory of "frequency dependence", and provide new insights into the coexistence between rodents and seedlings established different seed phenotypes. Furthermore, it also better reveals the ecological characteristics of deciduous Quercus regeneration.