Simulated partial predation on the largest-seeded oak: Effects of seed morphology and size on early establishment

Abstract

Plant recruitment is limited by seed predation. However, seeds that are only partially consumed can still contribute to regeneration provided the embryo remains viable. Seed size and shape are important traits that influence the relative location of the embryo, as well as its survival and further development. Yet, it is unclear whether the interaction of seed size and shape affects seed tolerance to partial damage and initial seedling performance. We evaluated the effects of simulated partial damage in three different acorn shapes (flattened, triangular and typical) on early seedling establishment in the threatened Quercus insignis, the largest-seeded oak species worldwide. We also distinguished between lateral acorn damage (pericarp damage only) and cotyledon damage (1/3 of the reserves), using acorn size as a covariate. For this, we recorded the germination, emergence and performance (total height, basal diameter, specific leaf area, total leaf area, above and belowground dry biomass) of each seedling after 110 days of growth.Seed shape influenced the rate and percentage of acorn germination, seedling emergence and performance. Typical-shaped acorns germinated at higher rates and produced more seedlings with higher performance. Simulated damage increased the rate and percentages of germination and emergence, but did not affect performance (except for specific leaf area). Seed size favored performance but not germination or emergence, and no significant interaction was found between acorn shape and seed size with respect to germination, emergence or performance, depending on each damage treatment. Our results suggest that acorn size allows tolerance to partial seed predation, since low to moderate acorn damage (<1/3 of cotyledon lost) had no negative effect on germination or emergence. Larger seed size could therefore not only support seedling performance, but also help to meet the nutritional requirements of small and mid-size predators without risking the integrity or development of the embryo. Acorn shape should therefore be considered in basic and applied oak ecology since seed morphology seems to influence not only germination and emergence, but also seedling performance. These results may have important eco-evolutionary implications in the context of seed-predator interactions, since certain shapes tolerate damage better than others and may thus benefit from the selection pressures exerted by seed foragers, both predators and dispersers. In addition to acorn size, managers should consider acorn shape and its relationship to early seedling establishment, as well as the potential for using partially damaged acorns in oak forest restoration projects.