Departamento de Silvopascicultura, ETSI, Montes, Universidad Politécnica de Madrid, Ciudad Universitaria, Madrid, Spain.
PLoS One. 2013 Jun 11;8(6):e65573. doi: 10.1371/journal.pone.0065573. Print 2013.
Seed masting and production of empty seeds have often been considered independently as different strategies to reduce seed predation by animals. Here, we integrate both phenomena within the whole assemblage of seed predators (both pre and post-dispersal) and in two contrasting microsites (open vs. sheltered) to improve our understanding of the factors controlling seed predation in a wind-dispersed tree (Ulmus laevis). In years with larger crop sizes more avian seed predators were attracted with an increase in the proportion of full seeds predated on the ground. However, for abundant crops, the presence of empty seeds decreased the proportion of full seeds predated. Empty seeds remained for a very long period in the tree, making location of full seeds more difficult for pre-dispersal predators and expanding the overall seed drop period at a very low cost (in dry biomass and allocation of C, N and P). Parthenocarpy (non-fertilized seeds) was the main cause of seed emptiness whereas seed abortion was produced in low quantity. These aborted seeds fell prematurely and, thus, could not work as deceptive seeds. A proportion of 50% empty seeds significantly reduced ground seed predation by 26%. However, a high rate of parthenocarpy (beyond 50% empty seeds) did not significantly reduce seed predation in comparison to 50% empty seeds. We also found a high variability and unpredictability in the production of empty seeds, both at tree and population level, making predator deception more effective. Open areas were especially important to facilitate seed survival since rodents (the main post-dispersal predators) consumed seeds mostly under shrub cover. In elm trees parthenocarpy is a common event that might work as an adaptive strategy to reduce seed predation. Masting per se did not apparently reduce the overall proportion of seeds predated in this wind-dispersed tree, but kept great numbers of seeds unconsumed.
结实大小年和秕粒产生通常被认为是动物减少种子捕食的两种不同策略。在这里，我们将这两种现象整合到整个种子捕食者集合（包括预分散和后分散）中，并在两个对比的微生境（开阔和遮蔽）中进行研究，以提高我们对风传播树木（榆树）中控制种子捕食的因素的理解。在结实大年，吸引了更多的鸟类种子捕食者，被地面捕食的完整种子比例增加。然而，对于丰富的作物，秕粒的存在降低了被地面捕食的完整种子的比例。秕粒在树上停留的时间非常长，这使得预分散捕食者更难找到完整的种子，并以非常低的成本（在干生物量和 C、N 和 P 的分配方面）扩大了整个种子脱落期。孤雌生殖（未受精的种子）是秕粒产生的主要原因，而败育种子的产生数量较少。这些败育种子过早脱落，因此不能作为欺骗性种子。50%的秕粒比例显著降低了地面种子捕食率 26%。然而，与 50%的秕粒相比，超过 50%的秕粒并不能显著降低种子捕食率。我们还发现，无论是在树木还是种群水平上，秕粒的产生都具有很高的变异性和不可预测性，这使得捕食者的欺骗更加有效。开阔区域对于促进种子的存活尤为重要，因为啮齿动物（主要的后分散捕食者）主要在灌木下消耗种子。在榆树中，孤雌生殖是一种常见的现象，可能是一种减少种子捕食的适应性策略。结实大小年本身并没有明显减少这种风传播树木中被捕食的种子的总体比例，但保持了大量未被消耗的种子。
