Fast-growing seeds and delayed rodent predatory activity in the seeding season: A combined mechanism to escape and survive rodent predation in Quercus ilex subsp. ballota L. acorns and seedlings

Abstract

Holm-oak is a sclerophyllous Mediterranean species that presents relatively fast growing, non-dormant, desiccation-sensitive seeds. We investigated the importance of this trait for decreasing acorn predation risk and increasing seedling predation tolerance in combination with delaying the maximal predatory activity of rodents within the seeding season. The study was conducted in a Mediterranean savannah-like forest ecosystem. Temporal changes in acorn availability and predation by mice were studied during the acorn fall period. In a second experiment, propagules at different stages of development (acorns, rooted but un-emerged seedlings and emerged seedlings of different heights) were exposed to rodent predation at the end of the seeding season (end of winter). The results indicated that temporal changes in acorn availability (19–0.05acornsm−2) and predation rate (0–0.11acornsday−1) were negatively correlated; the lowest predation rate occurred when the food resource was at its highest (peak acorn fall). The developmental stage reached by propagules at the end of the seeding season significantly affected their ability to escape predation: 52–16% of emerged seedlings escaped predation by mice, but only 6% of rooted, un-emerged seedlings and 2% of acorns did so. Rodent predation of seedlings mostly consisted of cotyledon consumption and its effect on seedling survival was also significantly affected by developmental stage: 70% of emerged seedlings survived predation while only 17% of rooted, un-emerged seedling did so. The acorns did not survive at all. The results reinforce the ecological significance of non-dormancy and the associated rapid seed germination and seedling development facing early recruitment in holm-oak. We suggest that, in environments subject to high rodent predatory activity, early sowing of acorns during the seeding season should be considered in order to maximize the success of forest restoration.